Routing Protocols
Companion Guide
Cisco Networking Academy

Cisco Press
800 East 96th Street Indianapolis, Indiana 46240 USA

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Routing Protocols Companion Guide

Routing Protocols Companion Guide
Cisco Networking Academy
Copyright© 2014 Cisco Systems, Inc. Published by: Cisco Press 800 East 96th Street Indianapolis, IN 46240 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America First Printing February 2014 Library of Congress Control Number: 2013957291 ISBN-13: 978-1-58713-323-7 ISBN-10: 1-58713-323-7

Publisher Paul Boger Associate Publisher Dave Dusthimer Business Operation Manager, Cisco Press Jan Cornelssen Executive Editor Mary Beth Ray Managing Editor Sandra Schroeder Development Editor Ellie C. Bru Project Editor Mandie Frank Copy Editor Bill McManus Technical Editor Bruce Brumley Editorial Assistant Vanessa Evans Designer Mark Shirar Composition Tricia Bronkella Indexer Brad Herriman Proofreader Debbie Williams

Warning and Disclaimer
This book is designed to provide information about the Cisco Networking Academy Routing Protocols course. Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied. The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it. The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc.

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Trademark Acknowledgements
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Routing Protocols Companion Guide

About the Contributing Authors
Rick Graziani teaches computer science and computer networking courses at Cabrillo College in Aptos, California. Prior to teaching, Rick worked in the information technology field for Santa Cruz Operation, Tandem Computers, and Lockheed Missiles and Space Corporation. He holds an M.A. in Computer Science and Systems Theory from California State University Monterey Bay. Rick is also a member of the Curriculum Development team for the Cisco Networking Academy since 1999. Rick has authored multiple books for Cisco Press and multiple online courses for the Cisco Networking Academy. Rick is the author of the Cisco Press book IPv6 Fundamentals and has presented on IPv6 at several Cisco Academy conferences. When Rick is not working, he is most likely surfing at one of his favorite Santa Cruz surf breaks. Bob Vachon is a professor in the Computer Systems Technology program at Cambrian College in Sudbury, Ontario, Canada, where he teaches networking infrastructure courses. He has more than 30 years of work and teaching experience in the computer networking and information technology field. Since 2001, Bob has collaborated as team lead, lead author, and subject matter expert on various CCNA, CCNA-S, and CCNP projects for Cisco and the Cisco Networking Academy. He also co-authored Accessing the WAN, CCNA Exploration Companion Guide and authored CCNA Security (640-554) Portable Command Guide. In his downtime, Bob enjoys playing the guitar, shooting darts or pool, and either working in his gardens or white-water canoe tripping.

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Contents at a Glance
Introduction Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Appendix A xxiv 1

Routing Concepts Static Routing 73

Routing Dynamically EIGRP 239

155

EIGRP Advanced Configurations and Troubleshooting Single-Area OSPF 393 461

333

Adjust and Troubleshoot Single-Area OSPF Multiarea OSPF 527 565 653

Access Control Lists

IOS Images and Licensing

Answers to the “Check Your Understanding” Questions Glossary Index 709

693

723

3) Configure an IPv4 Loopback Interface (1.Contents Introduction xxiv Chapter 1 Routing Concepts Objectives Key Terms 1 1 1 Introduction (1.3) Console Access (1.1.6) Connect to a Network (1.1.1) 22 24 25 28 29 Configure an IPv4 Router Interface (1.2.1.2.2.4) Device LEDs (1.1.1.2) Configure an IPv6 Router Interface (1.1) Send a Packet (1.3) 4 Routers Interconnect Networks (1.1.2.2) Enable IP on a Host (1.1.1.1.0.1) Default Gateways (1.6) Enable IP on a Switch (1.1.1.1.1.1.1) Why Routing? (1.1.4) Routers Choose Best Paths (1.2.1.2.2) 39 .3.1) 3 4 Initial Configuration of a Router (1.3.3) Configure Basic Router Settings (1.4.4.2.1.1.3) Command History Feature (1.2) Filter Show Command Output (1.1.1) 29 31 34 Verify Connectivity of Directly Connected Networks (1.1.4.2) 12 7 9 9 Packet Forwarding Mechanisms (1.4.1.1.1.1.1.2) 38 36 38 Router Switching Function (1.3.1.4) Verify IPv6 Interface Settings (1.7) Basic Settings on a Router (1.1) Characteristics of a Network (1.1.1.5) 18 19 20 22 13 15 14 16 Document Network Addressing (1.4) Routing Decisions (1.1.4) Verify Interface Settings (1.5) Connect Devices (1.1.2) 5 6 Routers Are Computers (1.2.3.1.1.2.1.

4.5) 64 Summary (1.3.5) Routing Decisions (1.3.4.3.1) 74 .3.2.3.4) Practice 67 66 51 Class Activities Labs 67 67 Packet Tracer Activities 67 Check Your Understanding Questions 68 Chapter 2 Static Routing Objectives Key Terms 73 73 73 Introduction (2.2.1) 47 Routing Table Sources (1.1) 61 IPv4 Routing Protocols (1.0.3.3) 63 IPv6 Routing Protocols (1.1.2) 51 Directly Connected Interfaces (1.2) 62 IPv4 Dynamic Routing Examples (1.3.1) Best Path (1.1.3.2) 48 Remote Network Routing Entries (1.2.2.3) 52 Directly Connected IPv6 Example (1.3.3) Packet Routing (1.1.3.2.1.3.3) 49 Directly Connected Routes (1.4.2) 40 41 42 43 Reach the Destination (1.1) 47 The Routing Table (1.1.2) 44 45 Load Balancing (1.3) 56 Static Routes (1.4.4) Path Determination (1.4) 53 Statically Learned Routes (1.3) Router Operation (1.3.3.2.2) 57 Static IPv6 Route Examples (1.2.2) Directly Connected Examples (1.1.3.3) 59 Dynamic Routing Protocols (1.2.3.3.3.3.2.2.1) 56 Static Route Examples (1.2.1) 51 Directly Connected Route Table Entries (1.2.4.4) 46 Analyze the Routing Table (1.1.3) 47 43 Administrative Distance (1.2.3.2.3.vii Forward to the Next Hop (1.2.2.3.4) 61 Dynamic Routing (1.3.4) 64 IPv6 Dynamic Routing Examples (1.

1) 75 Reach Remote Networks (2.3.4) 106 Default Static IPv6 Route (2.4) Floating Static Route (2.3.3.6) 91 Configure IPv4 Default Routes (2.1) 109 Classful Network Addressing (2.2) 84 Configure a Next-Hop Static Route (2.3.4.5) 89 Verify a Static Route (2.2.3.1) 106 Configure a Default Static IPv6 Route (2.1.viii Routing Protocols Companion Guide Static Routing Implementation (2.2.2.2.1.1.3.6) 105 Configure IPv6 Default Routes (2.1) 109 Classful Subnet Masks (2.2) 115 .3) Summary Static Route (2.2.1) 82 Next-Hop Options (2.1.3) 85 Configure a Directly Connected Static Route (2.3) 112 Classful Addressing Waste (2.2.2.2.1) Standard Static Route (2.3.3.1) 82 ip route Command (2.4) 113 CIDR (2.2) 110 Classful Routing Protocol Example (2.2.2.2.3) 94 Configure IPv6 Static Routes (2.2) 82 Configure IPv4 Static Routes (2.3.2.3) 109 Classful Addressing (2.2.3) 108 Review of CIDR and VLSM (2.2.3) 100 Configure a Directly Connected Static IPv6 Route (2.1.1.2) Default Static Route (2.2.4.2.1.1.3.2.1.2) 75 76 77 78 When to Use Static Routes (2.5) 104 Verify IPv6 Static Routes (2.1.1.1.1.2.2.2.2) 114 Classless Inter-Domain Routing (2.3.1.3) Static Route Applications (2.2.2) 94 Verify a Default Static Route (2.1) 93 Configure a Default Static Route (2.4.1) 96 Next-Hop Options (2.1.2) 107 Verify a Default Static Route (2.3.2.2.2.1.3.1.4) 102 Configure a Fully Specified Static IPv6 Route (2.3) 96 The ipv6 route Command (2.5) 79 79 80 81 Configure Static and Default Routes (2.1) 114 Classless Inter-Domain Routing (2.1) Why Use Static Routing? (2.3.2.1.2.2.2.2) 97 Configure a Next-Hop Static IPv6 Route (2.1.1.2.4) 87 Configure a Fully Specified Static Route (2.2.2.2) 93 Default Static Route (2.2.1.

4.3.4.3) 117 Classless Routing Protocol Example (2.6) Practice 151 150 Class Activities Labs 152 151 Packet Tracer Activities 152 Check Your Understanding Questions 152 Chapter 3 Routing Dynamically Objectives Key Terms 155 155 155 Introduction (3.3.5.4) 128 Configure IPv4 Summary Routes (2.3.1) 133 Summarize IPv6 Network Addresses (2.1) 143 Static Routes and Packet Forwarding (2.4.4) 118 VLSM (2.3.3.ix Static Routing CIDR Example (2.2) 147 Summary (2.2) 140 Test the Floating Static Route (2.5) 142 Packet Processing with Static Routes (2.4.3) 141 Troubleshoot Static and Default Route Issues (2.1) 138 Configure a Floating Static Route (2.3.1.2.4) 123 VLSM Example (2.5.3.3.1.3) 130 Configure IPv6 Summary Routes (2.1.1) 128 Route Summarization (2.1) 128 Calculate a Summary Route (2.1) 119 Variable-Length Subnet Masking (2.4.4.1) 143 Troubleshoot IPv4 Static and Default Route Configuration (2.5) 125 Configure Summary and Floating Static Routes (2.3.2) 129 Summary Static Route Example (2.2.3) 138 Floating Static Routes (2.3) 122 Subnetting Subnets (2.5.1.3) 137 Configure Floating Static Routes (2.2) 121 VLSM in Action (2.2) 134 Configure an IPv6 Summary Address (2.3.1) 144 Solve a Connectivity Problem (2.4.3.4.3.1) 133 Calculate IPv6 Network Addresses (2.3) 119 Fixed-Length Subnet Masking (2.2.2.3.1) 157 .2.2.3.1.0.4.4.3.5.2) 144 Troubleshooting a Missing Route (2.2.3.4.5.4.

1.3.4.1.1.1.2.1.2.1.1.3) Dynamic Routing Scorecard (3.3.3.4.1.3.2.4.1.2) 181 183 182 183 184 Types of Distance Vector Routing Protocols (3.8) Distance Vector Dynamic Routing (3.2) Configuring the RIP Protocol (3.7) 180 181 Distance Vector Technologies (3.2.1.1.2.1) 186 Advertising Networks (3.4) 190 Disabling Auto Summarization (3.1) 161 162 163 164 Static Routing Scorecard (3.2.5) Classless Routing Protocols (3.1.1.3.4.1.x Routing Protocols Companion Guide Dynamic Routing Protocols (3.3.1.1.3) Dynamic versus Static Routing (3.1.6) Routing Protocol Metrics (3.3) 189 Enabling RIPv2 (3.1.4.5) 192 .3.2) Routing Information Protocol (3.4) 168 170 171 Classifying Routing Protocols (3.2.1.4) 163 Routing Protocol Operating Fundamentals (3.1.1) 186 Router RIP Configuration Mode (3.1) Distance Vector Algorithm (3.1.1) Cold Start (3.5) Types of Routing Protocols (3.2) Using Dynamic Routing Protocols (3.2) 165 166 Network Discovery (3.2) 188 Examining Default RIP Settings (3.1.2) 161 158 159 160 Using Static Routing (3.1.2.2) 174 175 177 179 Routing Protocol Characteristics (3.4) Achieving Convergence (3.1.2) 172 Distance Vector Routing Protocols (3.1) RIP and RIPng Routing (3.1.3) 173 Link-State Routing Protocols (3.3) Dynamic Routing Protocol Operation (3.3.3) 186 Enhanced Interior Gateway Routing Protocol (3.1.4) Classful Routing Protocols (3.1) 158 The Evolution of Dynamic Routing Protocols (3.1.2.2.3) 165 Exchanging the Routing Information (3.4.2) The Role of Dynamic Routing Protocols (3.1.1.1.1.3.4.3.1) Purpose of Dynamic Routing Protocols (3.4.1) 171 IGP and EGP Routing Protocols (3.2.1.3.1.

1) 219 Ultimate Route (3.2) 196 Advertising IPv6 Networks (3.3) 218 Dynamically Learned IPv4 Routes (3.1.2.3.1.4.4.5.6) 232 .2.2.5.4.3) 213 Why Use Link-State Protocols? (3.5.1.4.5.4.1) 200 Dijkstra’s Algorithm (3.2.1) 200 Shortest Path First Protocols (3.4.4) 200 Link-State Routing Protocol Operation (3.2) 201 SPF Example (3.1.5.2.2.2.4.7) 211 Adding OSPF Routes to the Routing Table (3.4.5.7) 195 Configuring the RIPng Protocol (3.4.5) 209 Building the Link-State Database (3.3) 230 Summary (3.6) 210 Building the SPF Tree (3.3.5.8) 212 Why Use Link-State Routing Protocols? (3.3.5) 222 The IPv4 Route Lookup Process (3.1.2) 203 Link-State Routing Process (3.4.5.1) 227 Directly Connected Entries (3.4) 208 Flooding the LSP (3.3.5.2.2.5.3) 202 Link-State Updates (3.1) 215 Routing Table Entries (3.4.2.3) 224 Route Lookup Process (3.4) 227 IPv6 Routing Table Entries (3.2) 219 Routing Table Terms (3.xi Configuring Passive Interfaces (3.4.1) 213 Link-State Protocols Support Multiple Areas (3.5.2) 220 Level 1 Route (3.3) 220 Level 1 Parent Route (3.6) 193 Propagating a Default Route (3.4.3.1) 215 Directly Connected Entries (3.4.3) 214 The Routing Table (3.5.4.2) 214 Protocols that Use Link-State (3.3.3.1) 196 Examining the RIPng Configuration (3.5.5.1) 203 Link and Link-State (3.1.3.3.2) 204 Say Hello (3.2) 217 Remote Network Entries (3.2.2.5.1.4.5.1) 224 Best Route = Longest Match (3.2.2) 226 Analyze an IPv6 Routing Table (3.3) 207 Building the Link-State Packet (3.1.5) 215 Parts of an IPv4 Route Entry (3.2) 198 Link-State Dynamic Routing (3.4.2.5.4.4.4.4) 221 Level 2 Child Route (3.2.3.2) 228 Remote IPv6 Network Entries (3.

2) 245 EIGRP Packet Types (4.2) 272 Verifying EIGRP: Examine the IPv4 Routing Table (4.1.1.2) 270 Verifying EIGRP: Examining Neighbors (4.1.2.4) 261 Configuring the EIGRP Router ID (4.1.2.2) 252 Configuring EIGRP for IPv4 (4.1.0.1.1.2.2) 247 EIGRP Update and Acknowledgment Packets (4.2) 255 Configuring EIGRP with IPv4 (4.1.1) 245 EIGRP Hello Packets (4.2.3) 251 Encapsulating EIGRP Messages (4.2.1.2.2) 257 The Router EIGRP Command (4.1.7) 266 Passive Interface (4.1) Basic Features of EIGRP (4.4) 249 EIGRP Messages (4.1.1) 255 EIGRP Network Topology (4.2) 242 Reliable Transport Protocol (4.2.1) Characteristics of EIGRP (4.1.1.2.1.4) 244 Types of EIGRP Packets (4.1.1.2.2.1) 255 Autonomous System Numbers (4.2.3) 273 .6) 264 The Network Command and Wildcard Mask (4.2.1.1) 241 Protocol-Dependent Modules (4.2.1.1.2.2.2.1.1.1) 240 Features of EIGRP (4.1.3.1.2.1) 251 EIGRP Packet Header and TLV (4.xii Routing Protocols Companion Guide Practice 233 Class Activities Lab 233 233 Packet Tracer Activities 234 Check Your Understanding Questions 234 Chapter 4 EIGRP 239 239 239 240 240 Objectives Key Terms Introduction (4.3) 248 EIGRP Query and Reply Packets (4.1.2.8) 268 Verifying EIGRP with IPv4 (4.1) 270 Verifying EIGRP: show ip protocols Command (4.2.3) 259 EIGRP Router ID (4.3) 243 Authentication (4.5) 262 The Network Command (4.2.1.3.

3) 284 Delay Metric (4.7) 300 DUAL and Convergence (4.6) 288 DUAL and the Topology Table (4.1.3.3) 290 DUAL Concepts (4.4) 286 Calculating the EIGRP Metric (4.4.4.3.4.3.3.3.4.4.4.3) 316 ipv6 eigrp Interface Command (4.2.3.2.3.2.1) 308 Comparing EIGRP for IPv4 and IPv6 (4. Feasibility Condition.3.2) 283 Bandwidth Metric (4.3) 277 EIGRP Initial Route Discover (4.3) 311 Configuring EIGRP for IPv6 (4.1.1.3.1) 308 EIGRP for IPv6 (4.3.5) 326 .5) 297 Topology Table: No Feasible Successor (4.2) 312 EIGRP for IPv6 Network Topology (4.2.2.2) 278 EIGRP Convergence (4.2) 304 DUAL: No Feasible Successor (4.1) 291 Introduction to DUAL (4.3.xiii Operation of EIGRP (4.3.2. and Reported Distance (4.3) 319 Verifying EIGRP for IPv6: Examining Neighbors (4.2) 310 IPv6 Link-local Addresses (4.2.1.3) 306 Configuring EIGRP for IPv6 (4.3.3.3.3.4.3) 293 Feasible Successors.4) 308 EIGRP for IPv4 vs.1) 312 Configuring IPv6 Link-local Addresses (4. IPv6 (4.4.3.1) 319 Verifying EIGRP for IPv6: show ip protocols Command (4.3) 280 Metrics (4.4.1) 302 DUAL: Feasible Successor (4.3.3.2.3.4.3.1.3.3.4) 295 Topology Table: show ip eigrp topology Command (4.4.3.2) 291 Successor and Feasible Distance (4.3.3.2) 314 Configuring the EIGRP for IPv6 Routing Process (4.3.2) 321 Verifying EIGRP for IPv6: Examine the IPv6 Routing Table (4.4.4) 302 DUAL Finite State Machine (FSM) (4.3.4.3.4) 318 Verifying EIGRP for IPv6 (4.4.5) 287 Calculating the EIGRP Metric: Example (4.3) 322 Summary (4.2) 280 EIGRP Composite Metric (4.4.3.1) 277 EIGRP Topology Table (4.1) 277 EIGRP Neighbor Adjacency (4.3.4.1) 281 Examining Interface Values (4.2.2.1.

1.5.2) 365 EIGRP Authentication Example (5.2.2.3) 366 Verify Authentication (5.1.1.1.4) 357 EIGRP Bandwidth Utilization (5.8) 345 Manual Summarization (5.1) 364 Configuring EIGRP with MD5 Authentication (5.1.4) 351 Default Route Propagation (5.3) 351 EIGRP for IPv6: Manual Summary Routes (5.1.1.1.1.1.1.2) 359 Load Balancing IPv4 (5.1.0.3) 361 Load Balancing IPv6 (5. 5.1.3) 353 Propagating a Default Static Route (5.1.2.2.5) 342 Verifying Auto-Summary: Routing Table (5.1.1.1.1) 335 Network Topology (5.1.4.1.1.1.5) 364 Routing Protocol Authentication Overview (5.2.4) 369 Troubleshoot EIGRP (5.1.1.1) 335 EIGRP Auto-summarization (5.5.1.1.4) 363 Secure EIGRP (5.7.3) 338 Verifying Auto-Summary: show ip protocols (5.1.2) 349 Verifying Manual Summary Routes (5.5.5.3.2) 347 Manual Summary Routes (5.4.1) Components (5.1) 353 Verifying the Propagated Default Route (5.2) 372 370 .1.1.2) 355 EIGRP for IPv6: Default Route (5.xiv Routing Protocols Companion Guide Practice 327 Class Activities Labs 328 328 Packet Tracer Activities 328 Check Your Understanding Questions 328 Chapter 5 EIGRP Advanced Configurations and Troubleshooting Objectives Key Terms 333 333 334 334 333 Introduction (5.1.4.3.2) 337 Configuring EIGRP Auto-summarization (5.1.4.1) 370 Basic EIGRP Troubleshooting Commands (5.1.1.1.2.1) Advanced EIGRP Configurations (5.1.1) Auto-summarization (5.1) 357 Hello and Hold Timers (5.3) 355 Fine-tuning EIGRP Interfaces (5.1) 347 Configuring EIGRP Manual Summary Routes (5.4) 340 Verifying Auto-Summary: Topology Table (5.1.3.1.6) 343 Summary Route (5.2) 370 Components of Troubleshooting EIGRP (5.1.1.2.1.

2.2.1.4) OSPF Messages (6.1.1.1.5) Encapsulating OSPF Messages (6.2) 380 Auto-summarization (5.5) OSPF Operation (6.1) 378 Missing Network Statement (5.2.1.2) Synchronizing OSPF Databases (6.3.1) 394 394 Characteristics of OSPF (6.1.2.2) .3.1.3.1.xv Troubleshoot EIGRP Neighbor Issues (5.3) 376 Troubleshooting EIGRP Routing Table Issues (5.1.1) Features of OSPF (6.2.2.2.2) 375 EIGRP Interfaces (5.3.2.2) 394 395 396 398 399 402 Components of OSPF (6.2.3) Practice 388 386 378 Class Activities Labs 388 388 Packet Tracer Activities 388 Check Your Understanding Questions 389 Chapter 6 Single-Area OSPF Objectives Key Terms 393 393 393 Introduction (6.1.1) 414 415 Router OSPF Configuration Mode (6.2) 374 Layer 3 Connectivity (5.3) Link-State Operation (6.2.3) 403 404 405 406 Hello Packet Intervals (6.2.1) Evolution of OSPF (6.1.1.2) Hello Packet (6.1.3) 408 Establish Neighbor Adjacencies (6.2.4) Link-State Updates (6.2.3) 406 402 OSPF Operational States (6.4) Configuring Single-Area OSPFv2 (6.2.1) 374 EIGRP Parameters (5.3) Passive Interface (5.2) 401 Single-Area and Multiarea OSPF (6.2.1.3.1.1.1) Types of OSPF Packets (6.1.2.1.2.1.3.1.1.3) 382 Summary (5.1.2.2) 414 407 411 OSPF Network Topology (6.3.1.1) OSPF DR and BDR (6.0.1.

3.3.4) 430 Adjusting the Interface Bandwidths (6.2.3.3.1) Link-Local Addresses (6.2.3.2.1.4.1) Wildcard Mask (6.3.2.3.1.2) 426 423 Adjusting the Reference Bandwidth (6.2.2.3) Default Interface Bandwidths (6.2.1) 435 Verify OSPF Protocol Settings (6.2) 443 442 443 445 446 449 450 OSPFv3 Network Topology (6.3.2.2) 420 Enabling OSPF on Interfaces (6.1) 425 OSPF Accumulates Costs (6.2.2.2.1.3) Modifying an OSPFv3 Router ID (6.2.4) 420 421 422 The network Command (6.3.3) 451 Configuring the OSPFv3 Router ID (6.4) Verify OSPFv3 Neighbors (6.2.3) 420 Configuring Passive Interfaces (6.2.3.2.2.1.1) 439 440 441 Similarities Between OSPFv2 and OSPFv3 (6.4) Configuring OSPFv3 (6.2.3.3.5) Enabling OSPFv3 on Interfaces (6.2.2.6) Verify OSPF (6.5) OSPF Cost (6.2.1.2) 444 Assigning Link-Local Addresses (6.2.2.6) Verify OSPFv3 (6.3) Link-Local Addresses (6.2.2.5) 418 Using a Loopback Interface as the Router ID (6.3.3) 425 OSPF Metric = Cost (6.1) 451 452 Verify OSPFv3 Protocol Settings (6.2) Differences Between OSPFv2 and OSPFv3 (6.4) Configure Single-Area OSPFv3 (6.3.2.2.6) Configure Single-Area OSPFv2 (6.4.3) 439 438 OSPFv3 (6.xvi Routing Protocols Companion Guide Router IDs (6.5) Manually Setting the OSPF Cost (6.3) 437 Verify OSPF Interface Settings (6.3.3.3.4) Modifying a Router ID (6.2.3) 415 417 419 Configuring an OSPF Router ID (6.4.2) 436 Verify OSPF Process Information (6.3.3.4) 435 427 433 434 Verify OSPF Neighbors (6.2.3.1.2.1.3.1.2) .3.2.4.2.2.2) Passive Interface (6.2.

2.1.1.2) .3.3.1.1.1) 462 465 467 469 472 474 Challenges in Multiaccess Networks (7.4) 489 485 486 488 Routers Are Targets (7.4.0.1.2) 481 Propagating a Default Static Route in OSPFv3 (7.3) 489 492 495 Secure Routing Updates (7.1.1.3) 485 480 482 484 OSPF Hello and Dead Intervals (7.1.9) Default Route Propagation (7.3) Secure OSPF (7.1) Advanced Single-Area OSPF Configurations (7.1.1.1.4) Practice 456 455 453 453 Verify the IPv6 Routing Table (6.2.1) MD5 Authentication (7.xvii Verify OSPFv3 Interfaces (6.3.1.1.1.1.1.2.3) Summary (6.3) Verifying the Propagated IPv6 Default Route (7.5) DR/BDR Election Process (7.1.2) 480 Default DR/BDR Election Process (7.1.4) Verifying DR/BDR Adjacencies (7.1.4) Fine-tuning OSPF Interfaces (7.1.1.7) The OSPF Priority (7.1.1) Modifying OSPFv2 Intervals (7.3.1.1.1.8) 477 Changing the OSPF Priority (7.3) Verifying DR/BDR Roles (7.2) Modifying OSPFv3 Intervals (7.3.3.2) OSPF Designated Router (7.1.1.1.2.6) 475 478 Propagating a Default Static Route in OSPFv2 (7.1.4.4.3.1.4) Class Activities Labs 456 456 Packet Tracer Activities 456 Check Your Understanding Questions 457 Chapter 7 Adjust and Troubleshoot Single-Area OSPF Objectives Key Terms 461 461 462 461 Introduction (7.1.1) 462 OSPF Network Types (7.1.1) Verifying the Propagated Default Route (7.

3) Components of Troubleshooting OSPF (7.2.2.1) Multiarea OSPF (8.2.1) 508 505 508 Troubleshoot Single-Area OSPFv2 Routing Issues (7.4.2) .3.2) 501 502 496 497 499 501 Troubleshooting Single-Area OSPF Implementations (7.4) OSPF MD5 Authentication Example (7.1.1.5) Verifying OSPF MD5 Authentication (7.2) Troubleshoot Single-Area OSPFv3 Routing Issues (7.1.2) Troubleshooting OSPF Routing Table Issues (7.1.2.2.2.1.2.2.2) Summary (7.3) Types of OSPF Routers (8.1.2.6) 534 535 536 536 537 538 Multiarea OSPF LSA Operation (8.1.2.2) OSPF Troubleshooting Commands (7.2.2.1.2.4) Troubleshooting Neighbor Issues (7.1.2.1.1.1.1.1) 528 528 Multiarea OSPF Operation (8.1) Troubleshooting OSPFv3 (7.3) OSPF LSA Type 3 (8.6) OSPF States (7.1.1.1.1.1) OSPF LSA Type 1 (8.0.2) 528 529 530 532 534 OSPF Two-Layer Area Hierarchy (8.3) Practice 523 521 514 517 Class Activities Labs 523 523 Packet Tracer Activities 523 Check Your Understanding Questions 524 Chapter 8 Multiarea OSPF Objectives Key Terms 527 527 527 Introduction (8.1.2.4) OSPF LSA Type 4 (8.1.2.2.1) Single-Area OSPF (8.4.5) OSPF LSA Type 5 (8.1.2) OSPF LSA Type 2 (8.1.xviii Routing Protocols Companion Guide Configuring OSPF MD5 Authentication (7.4.3.1.4) OSPF LSA Types (8.3) 511 514 OSPFv3 Troubleshooting Commands (7.

2) 575 Types of Cisco IPv4 ACLs (9.1.3.3.2) 576 .2.2.1) 575 Numbering and Naming ACLs (9.1.1.1) 545 Configuring Multiarea OSPFv3 (8.3.1.1.1.1.2.1.1) 552 550 Verify General Multiarea OSPF Settings (8.1.3.2.1.1) 567 What Is an ACL? (9.1) Configuring Multiarea OSPF (8.1.1.1.2) Interarea Route Summarization (8.2.2.3.1.3) Practice 562 560 556 Class Activities Labs 562 562 Packet Tracer Activities 562 Check Your Understanding Questions 562 Chapter 9 Access Control Lists Objectives Key Terms 565 565 565 Introduction (9.4) Verify Multiarea OSPFv3 (8.2.3) 554 555 553 Verify the Multiarea OSPF LSDB (8.2.1) OSPF Route Calculation (8.3) 572 Packet Filtering Example (9.3) Calculating the Summary Route (8.2.1) 567 A TCP Conversation (9.5) Summary (8.1) 566 567 Purpose of ACLs (9.1.1) IP ACL Operation (9.1.1.2) 541 539 540 541 542 544 546 Implementing Multiarea OSPF (8.1.2) Configuring Multiarea OSPF (8.4) 573 ACL Operation (9.2.2.2.1.3.2.2.2.4) 548 550 Configuring Interarea Route Summarization (8.5) 574 Standard Versus Extended IPv4 ACLs (9.xix OSPF Routing Table and Types of Routes (8.3) Interarea and External Route Summarization (8.1.2) OSPF Route Summarization (8.2.1.3) 539 OSPF Routing Table Entries (8.2.2) Verify the OSPF Routes (8.2.2) 568 Packet Filtering (9.2.3.5) Verifying Multiarea OSPF (8.2.0.

4) 582 Examples Wildcard Mask Keywords (9.3) 614 Structure of an Extended IPv4 ACL (9.1.2) 615 .5.1.3.1.2.4.2) 588 Extended ACL Placement (9.4) 595 Applying Standard ACLs to Interfaces: Permit a Specific Subnet (9.1.1) 611 Verifying a Standard ACL Used to Secure a VTY Port (9.2) 604 Editing Standard Named ACLs (9.2.2) 603 Editing Standard Numbered ACLs: Using a Text Editor (9.2.5) 596 Applying Standard ACLs to Interfaces: Deny a Specific Host (9.1.2.2) 592 Configuring a Standard ACL (9.2) 591 Configure Standard IPv4 ACLs (9.xx Routing Protocols Companion Guide Wildcard Masks in ACLs (9.1.1.2.5) 584 Guidelines for ACL Creation (9.1.2.1.3.1) 614 Extended ACLs: Testing Packets (9.1) 585 ACL Best Practices (9.1.2.4) 606 ACL Statistics (9.1.1.2.3.3.5.4.7) 600 Commenting ACLs (9.3) 589 Standard IPv4 ACLs (9.2.1.1) 587 Standard ACL Placement (9.2) 612 Extended IPv4 ACLs (9.3) 577 Introducing ACL Wildcard Masking (9.3.1.2) 579 Calculating the Wildcard Mask (9.3) 611 Configuring a Standard ACL to Secure a VTY Port (9.2.3) 581 Wildcard Mask Keywords (9.6) 598 Creating Named Standard ACLs (9.2.5.2.2.2.2.3.1) 591 Entering Criteria Statements (9.1.1) 614 Extended ACLs: Testing Ports and Services (9.2.2.4) 584 General Guidelines for Creating ACLs (9.1.1.1.1) 603 Editing Standard Numbered ACLs: Using the Sequence Number (9.1) 577 Wildcard Mask Examples (9.5) 587 Where to Place ACLs (9.3) 605 Verifying ACLs (9.2.1.6) 608 Securing VTY Ports with a Standard IPv4 ACL (9.3) 593 Internal Logic (9.2.1.3.3.1) 591 Standard ACL Logic (9.2.2.2) 586 Guidelines for ACL Placement (9.2.1.1.2.5) 607 Standard ACL Sequence Numbers (9.1.3.2.3.2.8) 601 Modifying IPv4 ACLs (9.

3.2) 637 Configuring IPv6 Topology (9.5) 643 Summary (9.2.Example 2 (9.xxi Configure Extended IPv4 ACLs (9.4) 625 Processing Packets with ACLs (9.2.1.Example 5 (9.2) 639 Applying an IPv6 ACL to an Interface (9.4.0.4) 629 Common ACL Errors (9.2) 629 Troubleshooting Common ACL Errors .1) 635 Comparing IPv4 and IPv6 ACLs (9.1) 625 Inbound and Outbound ACL Logic (9.5.4) 632 Troubleshooting Common ACL Errors .5.2.1.2.2) 616 Configuring Extended ACLs (9.3.2.1) 629 Troubleshooting Common ACL Errors .Example 3 (9.1) 625 ACL Logic Operations (9.5.4.1.3) 632 Troubleshooting Common ACL Errors .2.2.4.6) Practice 648 646 Class Activities 648 Labs 648 Packet Tracer Activities 648 Check Your Understanding Questions 649 Chapter 10 IOS Images and Licensing Objectives Key Terms 653 653 654 653 Introduction (10.4) 642 Verifying IPv6 ACLs (9.1) 637 Syntax for Configuring IPv6 ACLs (9.4.5) 633 IPv6 ACLs (9.1.4) 621 Verifying Extended ACLs (9.1.3.2.5.5.4.2.1) .4.3) 620 Creating Named Extended ACLs (9.2) 636 Configuring IPv6 ACLs (9.2) 627 Standard ACL Decision Process (9.5.4.2.2.5.Example 1 (9.1.1.Example 4 (9.3) 641 IPv6 ACL Examples (9.4.3.2.5) 635 IPv6 ACL Creation (9.2.2.4.4.3) 628 Extended ACL Decision Process (9.4.2.5.2.3.5) 622 Editing Extended ACLs (9.5.3.1) 635 Type of IPv6 ACLs (9.6) 623 Troubleshoot ACLs (9.2) 630 Troubleshooting Common ACL Errors .3.1) 616 Applying Extended ACLs to Interfaces (9.2) 618 Filtering Traffic with Extended ACLs (9.

1.1) 672 Licensing Process (10.2.4) 670 IOS Licensing (10.1.4) 658 Cisco IOS 15.1.1.1.1.7) 662 IOS Image Filenames (10.1.0 M and T Trains (10.2.1) 672 Licensing Overview (10.2.1.2.2.2) 667 TFTP Servers as a Backup Location (10.1.1.1) 655 Cisco IOS 12.3) 682 Uninstall the License (10.1.2) 680 Back Up the License (10.2.2) 678 License Verification (10.3) 657 Cisco IOS 12.2) 667 Copying a Cisco IOS Image (10.1.2.1.5) 677 License Verification and Management (10.2.1) 654 Naming Conventions (10.2.1.4 Mainline and T Trains (10.2.8) 663 Managing Cisco IOS Images (10.1) 678 Activate an Evaluation Right-To-Use License (10.2.1.2.2) 674 Step 1.2.xxii Routing Protocols Companion Guide Managing IOS System Files (10.3) 669 Boot System (10.1.2.1. Obtain a License (10.6) 661 IOS 15 System Image Packaging (10.1.2) 672 Software Licensing (10.2.1.4 System Image Packaging (10.2. Install the License (10.3) Practice 688 685 Class Activities 688 688 Packet Tracer Activities 688 Check Your Understanding Questions Appendix A Answers to the “Check Your Understanding” Questions Glossary 709 Index 723 693 . Purchase the Software Package or Feature to Install (10.1.2) 655 Cisco IOS 12.1.1.5) 659 Cisco IOS 15 Train Numbering (10.3) 675 Step 2.1.1.4) 675 Step 3.2.1) 667 Creating Cisco IOS Image Backup (10.2.4 Mainline and T Numbering (10.4) 682 Summary (10.1.1.1) 654 Cisco IOS Software Release Families and Trains (10.1.2.

■ ■ ■ ■ ■ . In actual configuration examples and output (not general command syntax). mutually exclusive elements. Vertical bars (|) separate alternative. boldface indicates commands that are manually input by the user (such as a show command).xxiii Icons Used in This Book IP Phone Phone Cisco CallManager 100BaseT Hub Wireless Router Route/Switch Processor Cisco ASA 5500 Printer Cisco 5500 Family Access Point Router Workgroup Switch PC Laptop Modem Network Cloud Headquarters Branch Office File/ Application Server Hub Line: Ethernet Command Syntax Conventions The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. Square brackets ([ ]) indicate an optional element. The Command Reference describes these conventions as follows: ■ Boldface indicates commands and keywords that are entered literally as shown. Braces ({ }) indicate a required choice. Italic indicates arguments for which you supply actual values. Braces within brackets ([{ }]) indicate a required choice within an optional element.

while providing opportunities for you to gain the skills and hands-on experience needed to design. and devices as the online curriculum. As a textbook. the objectives reference the core concepts covered in the chapter. and maintain networks in small. Topic Coverage The following features give you a thorough overview of the topics covered in each chapter so that you can make constructive use of your study time: ■ Objectives: Listed at the beginning of each chapter. The curriculum emphasizes real-world practical application. readability. terms. The content of this text provides the foundation for additional Cisco Academy courses. as well as the course. Cisco Networking Academy is a comprehensive program that delivers information technology skills to students around the world. install.to medium-sized businesses. Who Should Read This Book The book. The objectives match the objectives . and preparation for the CCENT and CCNA Routing and Switching certifications. and practice of the course material to facilitate your full understanding of the course material. technologies. is designed as an introduction to routing protocols for those pursuing careers as network professionals as well as those who need only an introduction to routing protocols for professional growth. operate. protocols. this book provides a ready reference to explain the same networking concepts. and activities and provides some alternate explanations and examples as compared with the course. as well as enterprise and service provider environments. starting with the most fundamental concepts and progressing to a comprehensive understanding of routing protocols. This book emphasizes key topics. You can use the online curriculum as directed by your instructor and then use this Companion Guide’s study tools to help solidify your understanding of all the topics. Topics are presented concisely. Book Features The educational features of this book focus on supporting topic coverage.xxiv Routing Protocols Companion Guide Introduction Routing Protocols Companion Guide is the official supplemental textbook for the Cisco Network Academy CCNA Routing Protocols course.

the icon helps you easily refer to this feature as you skim through the book. the question format in the Companion Guide encourages you to think about finding the answers as you read the chapter. the text lists the steps as a how-to list. When you are studying. and important safety issues. The key terms are listed in the order in which they are explained in the chapter. Appendix A. It provides a synopsis of the chapter and serves as a study aid. timesaving methods. Glossary: This book contains an all-new Glossary with approximately 175 terms. You will find the following features valuable and effective in reinforcing the instruction that you receive: ■ Check Your Understanding Questions and answer key: Updated review questions are presented at the end of each chapter as a self-assessment tool. . and Packet Tracer Activities to refer back to for study time. ■ Practice Practice makes perfect. however. Chapter summaries: Each chapter includes a summary of the chapter’s key concepts. Class Activities. ■ ■ ■ Readability The following features have been updated to assist your understanding of the networking vocabulary: ■ Key terms: Each chapter begins with a list of key terms. How To ■ “How-to” feature: When this book covers a set of steps that you need to perform for certain tasks. “Answers to the ‘Check Your Understanding’ Questions.xxv stated in the corresponding chapters of the online curriculum. and see the term used in context. This new Companion Guide offers you ample opportunities to put what you learn into practice. The Glossary defines all the key terms. This handy reference allows you to find a term. along with a pagenumber reference from inside the chapter for each key term. These questions match the style of questions that you see in the online course. Notes: These are short sidebars that point out interesting facts. flip to the page where the term appears.” provides an answer key to all the questions and includes an explanation of each answer. “Practice” section: The end of each chapter includes a full list of all the Labs.

1.xxvi Routing Protocols Companion Guide ■ Packet Tracer Activity Video ■ Labs and activities: Throughout each chapter. The Packet Tracer Activities PKA files are found in the online course. In addition. perform a lab. Practice and Study Guides Additional Study Guide exercises. Lab Manual The supplementary book Routing Protocols Lab Manual. the end of each chapter includes a “Practice” section that collects a list of all the labs and activities to provide practice with the topics introduced in that chapter.3). or review a topic. you will see.2. Each Practice and Study Guide coordinates with the recommended curriculum sequence—the CCENT book follows the course outlines for Introduction to Networks and Routing and Switching Essentials. Page references to online course: After each heading. contains all the labs and class activities from the course. and scenarios are available in the new CCENT Practice and Study Guide (978-158713-345-9) and CCNA Routing and Switching Practice and Study Guide (978-158713-344-2) books by Allan Johnson. by Cisco Press (ISBN 9781-58713-322-0). practice an activity. and the CCNA book follows the course outlines for Scaling Networks and Connecting Networks. activities. This number refers to the page number in the online course so that you can easily jump to that spot online to view a video. The labs and class activities are available in the companion Routing Protocols Lab Manual (ISBN 978-1-58713-322-0). you will be directed back to the online course to take advantage of the activities created to reinforce concepts. (1. for example. .

The activity files are available in the course. and dynamic routing protocols. “Static Routing”: Introduces the use of static routes and the role they play in modern networks. Chapter 2. The process of packet forwarding is also reviewed. RIP and RIPng routing protocols are introduced as a foundation for understanding other routing protocols discussed in this book. “Routing Dynamically”: Examines the purpose of dynamic routing protocols and compares their use to static routing. Floating static routes and summary routes are also discussed. and configuration of IPv4 and IPv6 static routes using next-hop IP addresses and exit interfaces. one appendix. ■ ■ . This chapter serves as an introduction to terms and concepts that are examined more fully in later chapters. “Routing Concepts”: Introduces initial router configuration. you can use Packet Tracer with the listed file to perform a task suggested in this book. along with the IP routing table.xxvii Packet Tracer Activity About Packet Tracer Software and Activities Interspersed throughout the chapters you’ll find many activities to work with the Cisco Packet Tracer tool. Packet Tracer allows you to create networks. and a glossary of key terms: ■ Chapter 1. Ask your instructor for access to Packet Tracer. visualize how packets flow in the network. static routing. This chapter describes the advantages. The chapter includes a review of VLSM and CIDR. directly connected networks. including the path determination and switching functions. When you see this icon. uses. Distance vector and link-state routing protocols are discussed. and use basic testing tools to determine whether the network would work. Packet Tracer software is available only through the Cisco Networking Academy website. Chapter 3. How This Book Is Organized This book corresponds closely to the Cisco Networking Academy Routing Protocols course and is divided into 10 chapters.

“Adjust and Troubleshoot Single-Area OSPF”: Focuses on advanced features of OSPF. EIGRP authentication of routing updates. This chapter describes the basic features and operations of EIGRP. Multiarea OSPF link-state advertisements are discussed along with implementing multiarea OSPF. ■ ■ ■ ■ ■ . The configuration and verification of IPv4 standard named and extended ACLs (both named and numbered) are discussed. Chapter 6. Chapter 7. “Access Control Lists”: Examines how access control lists (ACLs) are used to filter traffic in IPv4 and IPv6 networks. Chapter 5. The components of troubleshooting EIGRP are discussed along with neighbor and routing table issues. EIGRP is a Ciscoproprietary. EIGRP packet formats. OSPF messages. modifying OSPF interface settings to improve network performance. The use of wildcard masks for IPv4 ACLs is discussed along with the guidelines for creating ACLs and the placement of ACLs. This chapter includes the basic configuration and verification of EIGRP for IPv4 and EIGRP for IPv6. propagating a default route with an OSPF routing domain. “Multiarea OSPF”: Examines the purpose and advantages of multiarea OSPF. “Single-Area OSPF”: Introduces the link-state routing protocol OSPF. Single-area OSPF operations are discussed. and how DUAL determines best path and loop-free back up paths. Chapter 8. This chapter includes the configuration and verification of multiarea OSPFv2 and OSPFv3. The configuration and verification of IPv6 ACLs are also examined. and how the composite metric is calculated by EIGRP. The use of ACLs to limit debug output and secure VTY access is demonstrated. including how routers achieve convergence in an OSPF network. The OSPF DR/BDR election process is discussed along with OSPF link-state advertisements. advanced distance vector routing protocol. neighbor adjacencies. This chapter includes the configuration and verification of single-area OSPFv2 (OSPF for IPv4) and OSPFv3 (OSPF for IPv6). manual summarization. This chapter includes troubleshooting OSPF missing route entries for OSPFv2 and OSPFv3. and configuring OSPF authentication. Chapter 9.xxviii Routing Protocols Companion Guide ■ Chapter 4. and fine-tuning EIGRP interfaces. “EIGRP”: Introduces the routing protocol EIGRP. the OSPF metric of cost. “EIGRP Advanced Configurations and Troubleshooting”: This chapter includes the configuration and verification of advanced EIGRP features such as automatic summarization. and the use of the OSPF router ID. default route propagation. The concepts and operations of DUAL (Diffusing Update Algorithm) are discussed.

4 and IOS 15. “Answers to the ‘Check Your Understanding’ Questions”: Lists the answers to the “Check Your Understanding” review questions that are included at the end of each chapter. Glossary: Provides you with definitions for all the key terms identified in each chapter.xxix ■ Chapter 10. Appendix A. The IOS 15 licensing process is discussed along with how to install an IOS 15 software image license. “IOS Images and Licensing”: Explains the IOS image and naming conventions for IOS 12. ■ ■ .

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CHAPTER 1

Routing Concepts

Objectives
Upon completion of this chapter, you will be able to answer the following questions:
Q

What are the primary functions and features of a router? How do you connect devices for a small routed network? Can you configure basic settings on a router to route between two directly connected networks? How can you verify connectivity between two networks that are directly connected to a router?

Q

Q

How do routers encapsulate and de-encapsulate packets when switching packets between directly connected interfaces? How do routers determine the best path? How do routers build a routing table of directly connected networks? How do routers build a routing table using static routes? How do routers build a routing table using a dynamic routing protocol?

Q Q

Q

Q

Q

Q

Key Terms
This chapter uses the following key terms. You can find the definitions in the Glossary. default gateway page 3 physical topology logical topology availability scalability reliability page 4 page 4 fast switching page 10 page 11

Cisco Express Forwarding (CEF) IP address subnet mask page 14 page 14 page 16 page 16

page 5 page 5 page 5 page 6

topology diagram addressing table

Random Access Memory (RAM) Read-Only Memory (ROM)

statically assigned IP address

page 16 page 16

page 6

dynamically assigned IP address console cable page 19

Non-Volatile Random Access Memory (NVRAM) page 6 Flash page 6

terminal emulation software

page 19 page 20

switched virtual interface (SVI)

process switching page 9

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Routing Protocols Companion Guide

High-Speed WAN Interface Card (HWIC) page 24 loopback interface page 28 page 43

best path

page 44 page 45 page 45

equal cost load balancing

unequal cost load balancing administrative distance routing table page 47

directly connected network remote network page 43

page 46

Gateway of Last Resort metric page 44

page 43

Chapter 1: Routing Concepts 3

Introduction (1.0.1.1)
Networks allow people to communicate, collaborate, and interact in many ways. Networks are used to access web pages, talk using IP telephones, participate in video conferences, compete in interactive gaming, shop using the Internet, complete online coursework, and more. At the core of the network is the router. A router connects one network to another network. The router is responsible for the delivery of packets across different networks. The destination of the IP packet might be a web server in another country or an email server on the local-area network. The router uses its routing table to determine the best path to use to forward a packet. It is the responsibility of the routers to deliver those packets in a timely manner. The effectiveness of internetwork communications depends, to a large degree, on the ability of routers to forward packets in the most efficient way possible. When a host sends a packet to a device on a different IP network, the packet is forwarded to the default gateway because a host device cannot communicate directly with devices outside of the local network. The default gateway is the destination that routes traffic from the local network to devices on remote networks. It is often used to connect a local network to the Internet. This chapter will also answer the question, “What does a router do with a packet received from one network and destined for another network?” Details of the routing table will be examined, including connected, static, and dynamic routes. Because the router can route packets between networks, devices on different networks can communicate. This chapter will introduce the router, its role in the networks, its main hardware and software components, and the routing process.
Class Activity 1.0.1.2: Do We Really Need a Map?

This modeling activity asks you to research travel directions from source to destination. Its purpose is to compare those types of directions to network routing directions. Scenario Using the Internet and Google Maps, located at http://maps.google.com, find a route between the capital city of your country and some other distant town or between two places within your own city. Pay close attention to the driving or walking directions Google Maps suggests. Notice that in many cases, Google Maps suggests more than one route between the two locations you chose. It also allows you to put additional constraints on the route, such as avoiding highways or tolls.

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Routing Protocols Companion Guide

Copy at least two route instructions supplied by Google Maps for this activity. Place your copies into a word processing document and save it for use with the next step. Open the .pdf accompanying this modeling activity and complete it with a fellow student. Discuss the reflection questions listed on the .pdf and record your answers. Be prepared to present your answers to the class.

Initial Configuration of a Router (1.1)
A router is essentially a special-purpose computer with an internetwork operating system optimized for the purpose of routing and securing networks. This section will examine the functions of a router and how a router determines the best path. It will also review the command-line interface (CLI) commands required to configure the base settings of a router.

Characteristics of a Network (1.1.1.1)
Networks have had a significant impact on our lives. They have changed the way we live, work, and play. Networks allow us to communicate, collaborate, and interact in ways we never did before. We use the network in a variety of ways, including web applications, IP telephony, video conferencing, interactive gaming, electronic commerce, education, and more. There are many terms, key structures, and performance-related characteristics that are referred to when discussing networks. These include:
Q

Topology: There are physical and logical topologies. The physical topology is the arrangement of the cables, network devices, and end systems. It describes how the network devices are actually interconnected with wires and cables. The logical topology is the path over which the data is transferred in a network. It describes how the network devices appear connected to network users. Speed: Speed is a measure of the data rate in bits per second (b/s) of a given link in the network. Cost: Cost indicates the general expense for purchasing of network components, and installation and maintenance of the network. Security: Security indicates how protected the network is, including the information that is transmitted over the network. The subject of security is important,

Q

Q

Q

Chapter 1: Routing Concepts 5

and techniques and practices are constantly evolving. Consider security whenever actions are taken that affect the network.
Q

Availability: Availability is a measure of the probability that the network is available for use when it is required. Scalability: Scalability indicates how easily the network can accommodate more users and data transmission requirements. If a network design is optimized to only meet current requirements, it can be very difficult and expensive to meet new needs when the network grows. Reliability: Reliability indicates the dependability of the components that make up the network, such as the routers, switches, PCs, and servers. Reliability is often measured as a probability of failure or as the mean time between failures (MTBF).

Q

Q

These characteristics and attributes provide a means to compare different networking solutions.
Note While the term “speed” is commonly used when referring to the network bandwidth, it is not technically accurate. The actual speed that the bits are transmitted does not vary over the same medium. The difference in bandwidth is due to the number of bits transmitted per second, not how fast they travel over wire or wireless medium.

Why Routing? (1.1.1.2)
How does clicking a link in a web browser return the desired information in mere seconds? Although there are many devices and technologies collaboratively working together to enable this, the primary device is the router. Stated simply, a router connects one network to another network. Communication between networks would not be possible without a router determining the best path to the destination and forwarding traffic to the next router along that path. The router is responsible for the routing of traffic between networks.
Video 1.1.1.2: Routers Route Packets
Video

Go to the online course and play the animation of a packet being sent through a Cisco 1841 router from sender to receiver. When a packet arrives on a router interface, the router uses its routing table to determine how to reach the destination network. The destination of the IP packet might be a web server in another country or an email server on the local-area network. It is

ROM. routing functions. ROM is firmware and referred to as non-volatile because it does not lose its contents when power is turned off. the running configuration file. It requires a CPU and memory to temporarily and permanently store data to execute operating system instructions. various tables (i. Flash: Provides permanent storage for the IOS and other system-related files. computers. Routers store data using: Q Random Access Memory (RAM): Provides temporary storage for various applications and processes. The IOS is copied from flash into RAM during the bootup process. Note Cisco devices use the Cisco Internetwork Operating System (IOS) as the system software. and buffers for packet processing.e. basic diagnostic software. Flash is nonvolatile and does not lose its contents when power is turned off. Q Q Q Table 1-1 provides a summary of the types of router memory. on the ability of routers to forward packets in the most efficient way possible. and a limited IOS in case the router cannot load the full featured IOS. The effectiveness of internetwork communications depends. including the running IOS. such as system initialization. RAM is referred to as volatile because it loses its contents when power is turned off.e.3) Most network capable devices (i.. IP routing table. to a large degree. Ethernet ARP table). Routers Are Computers (1. NVRAM is non-volatile and does not lose its contents when power is turned off. their volatility.. and switching functions.1. hard drive) A router is essentially a specialized computer. NVRAM. and smartphones) require the following components to operate: Q Q Q Central processing unit (CPU) Operating system (OS) Memory and storage (RAM.1. Non-Volatile Random Access Memory (NVRAM): Provides permanent storage for the startup configuration file (startup-config). and examples of what is stored in each. tablets. . Read-Only Memory (ROM): Provides permanent storage for bootup instructions. Flash.6 Routing Protocols Companion Guide the responsibility of routers to deliver those packets efficiently.

Instead. Figure 1-1 Back Panel of a 1941 ISRG2 Routers Interconnect Networks (1. Figure 1-1 displays the back panel of a Cisco 1941 ISRG2 and identifies those special ports and interfaces. regardless of whether the server accessed is on their own network or on . routers have specialized ports and network interface cards to interconnect devices to other networks.4) Most users are unaware of the presence of numerous routers on their own network or on the Internet. a router does not have video adapters or sound card adapters.1. send emails. Users expect to be able to access web pages.1.Chapter 1: Routing Concepts 7 Table 1-1 Memory RAM Router Memory Volatile/Non-Volatile Volatile Stores Q Q Q Q Running IOS Running configuration file IP routing and ARP tables Packet buffer Bootup instructions Basic diagnostic software Limited IOS Startup configuration file IOS file Other system files ROM Non-volatile Q Q Q NVRAM Flash Non-volatile Non-volatile Q Q Q Unlike a computer. and download music.

The interface that the router uses to forward the packet may be the final destination. Networking professionals know that it is the router that is responsible for forwarding packets from network to network. which means that it has multiple interfaces that each belong to a different IP network. For example. or it may be a network connected to another router that is used to reach the destination network. a WAN connection is commonly used to connect a LAN to the Internet service provider (ISP) network. In this topology. R1 and R2 are responsible for receiving the packet on one network and forwarding the packet out another network toward the destination network.1.4: Routers Connect Video Go to the online course and play the animation of a packet being sent through two Cisco routers. printers. it determines which interface to use to forward the packet to the destination. Each network that a router connects to typically requires a separate interface. A router connects multiple networks. Video 1.1. Even the Home Office requires a router. When a router receives an IP packet on one interface. the router located at the Home Office is a specialized device that performs multiple services for the home network. These interfaces are used to connect a combination of both local-area networks (LANs) and wide-area networks (WANs). WANs are used to connect networks over a large geographical area.8 Routing Protocols Companion Guide another network. Figure 1-2 Sample Routed Topology . Notice that each site in Figure 1-2 requires the use of a router to interconnect to other sites. LANs are commonly Ethernet networks that contain devices. from the original source to the final destination. and servers. such as PCs.

Frame Relay. The data link encapsulation depends on the type of interface on the router and the type of medium to which it connects.5: How the Router Works Video Go to the online course and play the animation of a packet being sent through two routers from sender to receiver. When a packet arrives on an interface. This process-switching mechanism is very slow and . Bluetooth). even if the destination is the same for a stream of packets.1. Video 1.Chapter 1: Routing Concepts 9 Routers Choose Best Paths (1. When a match is found. Note Routers use static routes and dynamic routing protocols to learn about remote networks and build their routing tables.11. Packet Forwarding Mechanisms (1. and wireless (802.1. and to forward the packet out of an interface that uses a different type of data link frame.1. and the packet is forwarded toward its destination. where the CPU matches the destination address with an entry in its routing table.5) The primary functions of a router are to: Q Q Determine the best path to send packets Forward packets toward their destination The router uses its routing table to determine the best path to use to forward a packet. it is forwarded to the control plane. DSL. The routing table also includes the interface to be used to forward packets for each known network.1. PPP. The different data link technologies that a router can connect to include Ethernet. and then determines the exit interface and forwards the packet. the router encapsulates the packet into the data link frame of the outgoing or exit interface. When the router receives a packet. it examines the destination address of the packet and uses the routing table to search for the best path to that network. cable. but must forward the packet out of an interface configured with the Point-to-Point Protocol (PPP). a router may receive a packet on an Ethernet interface.1. For example.1.6) Routers support three packet-forwarding mechanisms: Q Process switching: An older packet-forwarding mechanism still available for Cisco routers. It is important to understand that the router does this for every packet. It is possible for a router to receive a packet that is encapsulated in one type of data link frame.

the next-hop information in the cache is re-used without CPU intervention. Figure 1-3 Q Process Switching Fast switching: This is a common packet-forwarding mechanism which uses a fast-switching cache to store next-hop information. it is process-switched and forwarded to the exit interface. Figure 1-3 illustrates how packets are process-switched. where the CPU searches for a match in the fast-switching cache. If it is not there. The flow information for the packet is also stored in the fast-switching cache. it is forwarded to the control plane. Figure 1-4 Fast Switching . If another packet going to the same destination arrives on an interface.10 Routing Protocols Companion Guide rarely implemented in modern networks. When a packet arrives on an interface. Figure 1-4 illustrates how packets are fast-switched.

including the interface and Layer 2 information. As shown in Figure 1-3. Contrast this with fast switching. Cisco Express Forwarding is the fastest forwarding mechanism and the preferred choice on Cisco routers. when a network has converged. with process switching. each packet must be processed by the CPU individually. after the network has converged. Figure 1-5 illustrates how packets are forwarded using CEF. The FIB contains pre-computed reverse lookups and next-hop information for routes. The next four packets are quickly processed based on the information in the fast-switching cache. the FIB and adjacency tables contain all the information a router would have to consider when forwarding a packet. . the table entries are not packet-triggered like fast switching but change-triggered such as when something changes in the network topology. All five packets are quickly processed in the data plane. However. Assume a traffic flow consisting of five packets all going to the same destination.Chapter 1: Routing Concepts 11 Q Cisco Express Forwarding (CEF): CEF is the most recent and preferred Cisco IOS packet-forwarding mechanism. CEF builds a Forwarding Information Base (FIB) and an adjacency table. notice how only the first packet of a flow is processswitched and added to the fast-switching cache. Therefore. as shown in Figure 1-4. Finally. in Figure 1-5. With fast switching. CEF builds the FIB and adjacency tables. Like fast switching. Figure 1-5 Cisco Express Forwarding Figures 1-3 to 1-5 illustrate the differences between the three packet-forwarding mechanisms.

Fast switching solves a problem by doing math long hand one time and remembering the answer for subsequent identical problems. You will connect to the edge router of the new location to determine the devices and networks attached.1. . You asked for a topology map of the new location. However. Lab 1. Packet Tracer Activity Packet Tracer Activity 1. even if it is the identical problem. you have username and password information for the new branch’s networking devices and you know the web address for the new branch’s server.1. you will use various show commands to gather the necessary information to finish documenting the IP addressing scheme and create a diagram of the topology.1. and default gateways.1.9: Mapping the Internet In this lab.2) In this section. subnet masks.1.1. This section will also introduce how to configure the initial settings of a switch.8: Using Traceroute to Discover the Network The company you work for has acquired a new branch location. Therefore.7: Identify Router Components Go to the online course to perform this practice activity. you will verify connectivity and use the tracert command to determine the path to the location. Q Q Interactive Graphic Activity 1.1. but apparently one does not exist.12 Routing Protocols Companion Guide A common analogy used to describe the three packet-forwarding mechanisms is as follows: Q Process switching solves a problem by doing math long hand. As a part of this process. you will complete the following objectives: Q Q Part 1: Determine Network Connectivity to a Destination Host Part 2: Trace a Route to a Remote Server Using Tracert Connect Devices (1. you will see how accessing a network involves connecting hosts and infrastructure devices with IP addresses. CEF solves every possible problem ahead of time in a spreadsheet.

e. Figure 1-6 Sample LAN and WAN Connections Home Office devices can connect as follows: Q Q Laptops and tablets connect wirelessly to a home router. Refer to the sample reference topology in Figure 1-6. The home router connects to the service provider cable modem using an Ethernet cable.1.1) Network devices and end users typically connect to a network using a wired Ethernet or wireless connection. Laptops and smartphones connect wirelessly to wireless access points (WAPs). Q Q The Branch site devices connect as follows: Q Corporate resources (i. Q Q Q .Chapter 1: Routing Concepts 13 Connect to a Network (1.. The cable modem connects to the Internet service provider (ISP) network.2. A network printer connects using an Ethernet cable to the switch port on the home router. The LANs in the figure serve as an example of how users and network devices could connect to networks. Desktop PCs and voice over IP (VoIP) phones connect to Layer 2 switches using Ethernet cables. The WAPs connect to switches using Ethernet cables. file servers and printers) connect to Layer 2 switches using Ethernet cables.

Layer 3 multilayer switches connect to an Ethernet interface on the edge router using Ethernet cables. because a host device cannot communicate directly with devices outside of the local network. Layer 2 switches connect redundantly to multilayer Layer 3 switches using Ethernet fiber-optic cables (orange connections). hosts are connected either directly or indirectly (via WAPs) to the network infrastructure using a Layer 2 switch. Q Q The Central site devices connect as follows: Q Desktop PCs and VoIP phones connect to Layer 2 switches using Ethernet cables. . then the packet is forwarded to the default gateway. The default gateway is the destination that routes traffic from the local network to devices on remote networks. The edge router connects to a WAN service provider (SP).1. Q Q Q Q Q In the Branch and Central LANs. The edge router also connects to an ISP for backup purposes. An edge router is a device that sits at the edge or boundary of a network and routes between that network and another. The edge router connects to a WAN SP. When a host sends a packet to a device on a different IP network. Default Gateways (1. The corporate website server is connected using an Ethernet cable to the edge router interface. devices must be configured with IP address information to identify the appropriate: Q Q Q IP address: Identifies a unique host on a local network Subnet mask: Identifies with which network subnet the host can communicate Default gateway: Identifies the router to send a packet to when the destination is not on the same local network subnet When a host sends a packet to a device that is on the same IP network.2. The edge router also connects to an ISP for backup purposes. such as between a LAN and a WAN. the packet is simply forwarded out of the host interface to the destination device.14 Routing Protocols Companion Guide Q Layer 2 switches connect to an Ethernet interface on the edge router using Ethernet cables. It is often used to connect a local network to the Internet.2) To enable network access.

document the network.Chapter 1: Routing Concepts 15 The default gateway is usually the address of the interface on the router connected to the local network. and determines the best path to reach those destinations. The packet protocol data unit (PDU) in Figure 1-7 identifies the source and destination IP and MAC addresses. therefore. For example. Document Network Addressing (1.3) When designing a new network or mapping an existing network. Figure 1-7 Note Getting the Pieces to the Correct Network A router is also usually configured with its own default gateway.1.16. the documentation should identify: Q Q Q Q Device names Interfaces used in the design IP addresses and subnet masks Default gateway addresses .1.2. it would discover that the Web Server is not on the local network and it.99. This is sometimes known as the Gateway of Last Resort. if PC1 sends a packet to the Web Server located at 172. The router maintains routing table entries of all connected networks as well as entries of remote networks. At a minimum. must send the packet to the Media Access Control (MAC) address of its default gateway.

168.1.0 255. Q Figures 1-9 and 1-10 provide static and dynamic IPv4 address configuration examples. Often created using software. IPv4 addresses.0 Default Gateway N/A N/A N/A N/A 192. The DNS server IP address can also be configured.1 192.3. Dynamically Assigned IP Address: IP address information is provided by a server using the Dynamic Host Configuration Protocol (DHCP). and default gateway for end devices.0 255.1 192.0 255.16 Routing Protocols Companion Guide This information is captured by creating two useful network documents: Q Topology diagram: Provides a visual reference that indicates the physical connectivity and logical Layer 3 addressing.255.168. subnet mask.1. and default gateway.255.255. Figure 1-8 Table 1-2 Device R1 Documenting Network Addressing Addressing Table Interface Fa0/0 S0/0/0 IP Address 192. Addressing table: A table that captures device names.168. interfaces.2 192.255.0 255.2. The DHCP server provides a valid IP address.255.168.1 192. and default gateway addresses.1. subnet masks. Q Figure 1-8 displays the sample topology diagram.255.3. such as Microsoft Visio.10 192.1 R2 Fa0/0 S0/0/0 PC1 PC2 N/A N/A Enable IP on a Host (1.255. A host can get a: Q Statically Assigned IP Address: The host is manually assigned the correct IP address.168. Other information may be provided by the server.255.1.255.168.2. .255.255.168.1 192. subnet mask.0 255.3.255.2.10 Subnet Mask 255.168.4) A host can be assigned its IP address information in one of two ways. while Table 1-2 provides a sample addressing table for the topology.

most host devices acquire their IPv4 address information by accessing a DHCP server. However. They can also be used in smaller networks with few hosts. In large enterprises. DHCP services can be provided by a Cisco Catalyst switch or a Cisco ISR. dedicated DHCP servers providing services to many LANs are implemented. . In a smaller branch or small office setting.Chapter 1: Routing Concepts 17 Figure 1-9 Statically Assigning an IP Address Figure 1-10 Dynamically Assigning an IP Address Statically assigned addresses are commonly used to identify specific network resources. such as network servers and printers.

Cisco ISRs use various LED indicators to provide status information. Consult the device-specific documentation for an accurate description of the LEDs. The LEDs of the Cisco 1941 router shown in Figure 1-11 are explained in Table 1-3. If the link light is not on. Each device has a unique set of LEDs. try a different network cable.1.2. network infrastructure devices commonly use multiple LED indicators to provide a quick status view.18 Routing Protocols Companion Guide Device LEDs (1. Note The actual function of the LEDs varies between computer manufacturers. The LEDs on the router help the network administrator conduct some basic troubleshooting. Most network interfaces have one or two LED link indicators next to the interface. For example.5) Host computers connect to a wired network using a network interface and RJ-45 Ethernet cable. If one or both ends are not lit. Typically. These LEDs are generally lit green when the switch is functioning normally and lit amber when there is a malfunction. then there may be a problem with either the network cable or the network itself. a green LED means a good connection while a blinking green LED indicates network activity. The switch port where the connection terminates would also have an LED indicator lit. a Cisco Catalyst 2960 switch has several status LEDs to help monitor system activity and performance. Figure 1-11 Cisco 1941 LEDs . Similarly.

PuTTY. Console access requires: Q Q Console cable: RJ-45-to-DB-9 console cable Terminal emulation software: Tera Term. the RJ-45 port becomes inactive. as well as an operating system device driver. a USB Type-A to USB Type-B (mini-B USB) is required. A special USB-to-RS-232 compatible serial port adapter is required when using the USB port.cisco. . If the host does not have a serial port.2.6) In a production environment. the USB port can be used to establish a console connection.1. Most computers and notebooks no longer include built-in serial ports. HyperTerminal The cable is connected between the serial port of the host and the console port on the device. or if remote access fails. the RJ-45 port becomes active.Chapter 1: Routing Concepts 19 Table 1-3 # 1 Port Description of the Cisco 1941 LEDs LED S (Speed) Color 1 blink + pause 2 blink + pause 3 blink + pause L (Link) Green Off Description Port operating at 10 Mb/s Port operating at 100 Mb/s Port operating at 1000 Mb/s Link is active Link is inactive Port is active Port is inactive Port is active Port is inactive GE0/0 and GE0/1 2 Console EN Green Off 3 USB EN Green Off Console Access (1. only one console port can be active at a time. To establish connectivity. The Cisco ISR G2 supports a USB serial console connection. Although these routers have two console ports. When the USB cable is removed from the USB port. infrastructure devices are commonly accessed remotely using Secure Shell (SSH) or HyperText Transfer Protocol Secure (HTTPS). Console access is really only required when initially configuring a device. When a cable is plugged into the USB console port. This device driver is available from http://www. com.

Instead.7) Network infrastructure devices require IP addresses to enable remote management. the IP address information is configured on a virtual interface called a switched virtual interface (SVI). while Figure 1-12 displays the various ports and cables required. A switch does not have a dedicated interface to which an IP address can be assigned.1. Using the device IP address.2.com USB Type-B (Mini-B USB) Figure 1-12 Ports and Cables Enable IP on a Switch (1. or HTTPS. Table 1-4 Port on Computer Serial Port Console Connection Requirements Cable Required RJ-45 to DB-9 Console Cable USB to RS-232 compatible serial port adapter Q Port on ISR Terminal Emulation Adapter may require a software driver RJ-45 Console Port Tera Term PuTTY USB Type-A RJ-45 to DB-9 Console Cable Port USB Type-A to USB Type-B (Mini-B USB) Q A device driver is required and available from Cisco. the network administrator can remotely connect to the device using Telnet. HTTP. SSH. .20 Routing Protocols Companion Guide Table 1-4 summarizes the console connection requirements.

168. Name the device. not any hosts connected to the switch. Packets generated by the switch and destined for an address other than its management network segment will be forwarded to this address. . Packets generated by the switch and destined for an address outside of the 192. the address is that of the G0/0 interface of R1. Figure 1-13 Configuring the SVI of S1 S1(config)# interface vlan 1 S1(config-if)# ip address 192.0/24 network segment will be forwarded to this address.Chapter 1: Routing Concepts 21 How To The steps to configure the basic settings on a switch are as follows: Step 1.10.168. Enable the SVI. Activity 1.10. Step 2. Configure the default gateway for the switch. For example.10.2 255.7: Configure the Management SVI on S2 Interactive Graphic Go to the online course to use the Syntax Checker in the second graphic to configure the S2 Layer 2 switch.2/24 and a default gateway of the router located at 192.1.1. Step 4. This makes the switch accessible for network management.1 S1(config)# In the example.0 S1(config-if)# no shutdown %LINK-5-CHANGED: Interface Vlan1.10. changed state to up S1(config-if)# exit S1(config)# S1(config)# ip default-gateway 192.255.168. Step 3. Configure the SVI. In the example.168.168. the switch SVI is configured and enabled with the IP address 192. the following commands would configure the management VLAN interface and default gateway of switch S1 shown in Figure 1-13.2.1. This default gateway is used by the switch only for the packets it generates.255.

22 Routing Protocols Companion Guide Interactive Graphic Activity 1. and many of the same commands. Basic Settings on a Router (1.1. . the following commands would configure the basic settings for router R1 shown in Figure 1-14.3. You will need to use a variety of commands to gather the required information.3) The basic addressing and configuration of Cisco devices was covered in either the Introduction to Networks or Network Basics course. Although optional. Specifically. the following steps should be executed: How To Step 1. Save the configuration. Step 3. This changes the router prompt and helps distinguish the device from others. Name the device. and Telnet access. secure the privileged EXEC.8: Document an Addressing Scheme Go to the online course to perform this practice activity. They support a similar modal operating system.2. However. In addition. Step 2.2. For example. Configure Basic Router Settings (1. and encrypt passwords to their highest level. Configure a banner. Secure management access. user EXEC. Step 4. similar command structures.9: Documenting the Network Your job is to document the addressing scheme and connections used in the Central portion of the network. Packet Tracer Activity Packet Tracer Activity 1.1. this is a recommended step to provide legal notice to anyone attempting to access the device.1.1. both devices have similar initial configuration steps.1) Cisco routers and Cisco switches have many similarities. When initially configuring a Cisco switch or router. we will spend some time reviewing these topics as well as preparing you for the hands-on lab experience in this course.

3.1: Configure Basic Settings on R2 Go to the online course to use the Syntax Checker in the fifth graphic to configure basic settings on R2. Router(config)# hostname R1 R1(config)# R1(config)# enable secret class R1(config)# R1(config)# line console 0 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# line vty 0 4 R1(config-line)# password cisco R1(config-line)# login R1(config-line)# exit R1(config)# R1(config)# service password-encryption R1(config)# R1(config)# banner motd $ Authorized Access Only! $ R1(config)# end R1# R1# copy running-config startup-config Destination filename [startup-config]? Building configuration.Chapter 1: Routing Concepts 23 Figure 1-14 Configuring the Basic Settings of R1 End with CNTL/Z.. . [OK] R1# Interactive Graphic Activity 1. Router# configure terminal Enter configuration commands.1. one per line..

Q Optionally. Layer 2 switches support LANs and. configured with an address and a subnet mask: Use the ip address ip-address subnet-mask interface configuration command. Step 3. Enable the interface. If the interface connects to an ISP or service carrier. it must be activated using the no shutdown command.) The interface must also be connected to another device (a hub. This is only necessary on the DCE device in our lab environment and does not apply to Ethernet interfaces. including serial. To enable an interface. additional parameters may be required.3. the serial interface connecting to the serial cable end labeled DCE must be configured with the clock rate command. an interface must be: Q If using IPv4. the interface could also be configured with a short description. it is helpful to enter the third-party connection and contact information. Routers support LANs and WANs and can interconnect different types of networks. Note Accidentally using the clock rate command on a DTE interface generates a “%Error: This command applies only to DCE interface” message. in the lab environment. Add a description. LAN and WAN interfaces are not activated (shutdown). To be available. DSL.2) One distinguishing feature between switches and routers is the type of interfaces supported by each. a description can be helpful in troubleshooting by providing information about the type of network to which the interface is connected. For example. a switch. Configure the IPv4 address. and cable interfaces. For example.1. . they support many types of interfaces.24 Routing Protocols Companion Guide Configure an IPv4 Router Interface (1. The description text is limited to 240 characters. Step 4. therefore. It is good practice to configure a description on each interface. or another router) for the physical layer to be active. (This is similar to powering on the interface. Depending on the type of interface. therefore. On production networks. Activated: By default. How To The steps to configure an IPv4 interface on a router are: Step 1. G2 ISRs have one or two integrated Gigabit Ethernet interfaces and High-Speed WAN Interface Card (HWIC) slots to accommodate other types of network interfaces. it is a necessary component for documenting a network. Step 2. Although optional. Configure a clock rate on Serial interfaces. For example. have multiple FastEthernet or Gigabit Ethernet ports.

Most IPv6 configuration and verification commands in the Cisco IOS are very similar to their IPv4 counterparts.1.2: Configure the R2 Interfaces Go to the online course to use the Syntax Checker in the fourth graphic to configure the R2 interfaces.Chapter 1: Routing Concepts 25 For example. .3.168.11.255. Activated: The interface must be activated using the no shutdown command.200.255.1 255. An IPv6 interface must be: Q Configured with IPv6 address and subnet mask: Use the ipv6 address ipv6address/prefix-length [link-local | eui-64] interface configuration command.1.3) Configuring an IPv6 interface is similar to configuring an interface for IPv4.0 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# R1(config)# interface serial 0/0/0 R1(config-if)# description Link to R2 R1(config-if)# ip address 209.255. In many cases.165.255. Configure an IPv6 Router Interface (1.1 255. the only difference uses ipv6 in place of ip in commands.3. Q Note An interface can generate its own IPv6 link-local address without having a global unicast address by using the ipv6 enable interface configuration command.10.255.252 R1(config-if)# clock rate 128000 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# Interactive Graphic Activity 1.0 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# R1(config)# interface gigabitethernet 0/1 R1(config-if)# description Link to LAN 2 R1(config-if)# ip address 192.225 255.255. the following commands would configure the three directly connected interfaces of router R1 shown in Figure 1-14 (in the previous section): R1(config)# interface gigabitethernet 0/0 R1(config-if)# description Link to LAN 1 R1(config-if)# ip address 192.168.

R1 must be configured to support the following IPv6 global network addresses: Q Q Q 2001:0DB8:ACAD:0001:/64 (2001:DB8:ACAD:1::/64) 2001:0DB8:ACAD:0002:/64 (2001:DB8:ACAD:2::/64) 2001:0DB8:ACAD:0003:/64 (2001:DB8:ACAD:3::/64) . Recall. IPv6 interfaces will typically have more than one IPv6 address. IPv6 also supports the ability for an interface to have multiple IPv6 global unicast addresses from the same subnet. ipv6 address ipv6-address/prefix-length eui-64: Configures a global unicast IPv6 address with an interface identifier (ID) in the low-order 64 bits of the IPv6 address using the EUI-64 process. Q Q How To The steps to configure an IPv6 interface on a router are: Step 1. it is a necessary component for documenting a network. Configure a clock rate on Serial interfaces. Configure the IPv6 global unicast address. Configure a link-local unicast address which automatically assigns a linklocal IPv6 address and overrides any previously assigned address. Add a description. This is only necessary on the DCE device in our lab environment and does not apply to Ethernet interfaces. Step 3. Step 4. ipv6 address ipv6-address/prefix-length link-local: Configures a static linklocal address on the interface that is used instead of the link-local address that is automatically configured when the global unicast IPv6 address is assigned to the interface or enabled using the ipv6 enable interface command. Step 5.26 Routing Protocols Companion Guide Unlike IPv4. Step 2. an IPv6 device must have an IPv6 link-local address but will most likely also have an IPv6 global unicast address. At a minimum. the ipv6 enable interface command is used to automatically create an IPv6 link-local address whether or not an IPv6 global unicast address has been assigned. Configuring a global unicast address automatically creates a link-local IPv6 address. The following commands can be used to statically create a global unicast or link-local IPv6 address: Q ipv6 address ipv6-address/prefix-length: Creates a global unicast IPv6 address as specified. In the example topology shown in Figure 1-15. Although optional. Enable the interface.

the following commands would configure the IPv6 global unicast addresses of the three directly connected interfaces of the R1 router shown in Figure 1-15: R1# configure terminal R1(config)# interface gigabitethernet 0/0 R1(config-if)# description Link to LAN 1 R1(config-if)# ipv6 address 2001:db8:acad:1::1/64 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# . Alternatively. a PC connected to the IPv6 network can get its IPv6 address statically assigned.Chapter 1: Routing Concepts 27 Figure 1-15 IPv6 Topology When the router is configured using the ipv6 unicast-routing global configuration command. the router begins sending ICMPv6 Router Advertisement messages out the interface. This enables a PC connected to the interface to automatically configure an IPv6 address and to set a default gateway without needing the services of a DHCPv6 server. as shown in Figure 1-16. Notice that the default gateway address configured for PC1 is the IPv6 global unicast address of the R1 Gigabit Ethernet 0/0 interface. Figure 1-16 Statically Assign an IPv6 Address to PC1 For example.

Configure the IP address. it is a necessary component for documenting a network.3. such as the Open Shortest Path First (OSPF) routing process. For example.4) Another common configuration of Cisco IOS routers is enabling a loopback interface. How To The steps to configure a loopback interface on a router are: Step 1. it can be used for testing purposes. It is not assigned to a physical port and can therefore never be connected to any other device. By enabling a loopback interface. . Although optional. Create the loopback interface using the interface loopback number global configuration command. the router will use the always available loopback interface address for identification. The loopback interface is a logical interface internal to the router. as long as the router is functioning. Add a description. Additionally.1. by emulating networks behind the router. the IPv4 address assigned to the loopback interface can be significant to processes on the router that use an interface IPv4 address for identification purposes. It is considered a software interface that is automatically placed in an “up/up” state.3. Step 3. such as testing internal routing processes.28 Routing Protocols Companion Guide R1(config)# interface gigabitethernet 0/1 R1(config-if)# description Link to LAN 2 R1(config-if)# ipv6 address 2001:db8:acad:2::1/64 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# R1(config)# interface serial 0/0/0 R1(config-if)# description Link to R2 R1(config-if)# ipv6 address 2001:db8:acad:3::1/64 R1(config-if)# clock rate 128000 R1(config-if)# no shutdown R1(config-if)# Interactive Graphic Activity 1. Configure an IPv4 Loopback Interface (1. Step 2. rather than an IP address assigned to a physical port that may go down.3: Configure the R2 Interfaces Go to the online course to use the Syntax Checker in the sixth graphic to configure the IPv6 global unicast addresses on the R2 router. The loopback interface is useful in testing and managing a Cisco IOS device because it ensures that at least one interface will always be available.1.

This is an important step and should be done before any other configurations are added to the router.0. In previous IOS versions.255. .0. Verify Interface Settings (1.1.5: Configuring IPv4 and IPv6 Interfaces Packet Tracer Activity Routers R1 and R2 each have two LANs. The IPv4 address for each loopback interface must be unique and unused by any other interface.0 R1(config-if)# exit R1(config)# A loopback interface is always enabled and therefore does not require a no shutdown command.1.1 255.4.3.1. Packet Tracer Activity 1.255. the following commands configure a loopback interface of the R1 router shown in Figure 1-14 (shown earlier in the chapter): R1# configure terminal R1(config)# interface loopback 0 R1(config-if)# ip address 10.4) The first task to undertake once the basic settings and interfaces are configured is to verify and validate the configured settings. active interfaces should appear in the routing table with two related entries identified by the code 'C' (Connected) or 'L' (Local). The following three commands are especially useful to quickly identify an interface status: Q show ip interface brief: Displays a summary for all interfaces. In Cisco IOS 15. Multiple loopback interfaces can be enabled on a router. Your task is to configure the appropriate addressing on each device and verify connectivity between the LANs. only a single entry with the code 'C' will appear. Q Q Figure 1-17 displays the output of the show ip interface brief command. show running-config interface interface-id: Displays the commands configured on the specified interface. show ip route: Displays the contents of the IPv4 routing table stored in RAM. Verify Connectivity of Directly Connected Networks (1.1) There are several show commands that can be used to verify the operation and configuration of an interface. including the IPv4 address of the interface and current operational status.Chapter 1: Routing Concepts 29 For example.

1 graphic number 1. Figure 1-18 displays the output of the show ip route command. Note In Figure 1-17. The Embedded-Service-Engine0/0 interface is outside the scope of this course.1. Figure 1-18 Verify the IPv4 Routing Table .30 Routing Protocols Companion Guide Figure 1-17 Display Interface Summaries The output reveals that the LAN interfaces and the WAN link are all activated and operational as indicated by the Status of “up” and Protocol of “up.” A different output would indicate a problem with either the configuration or the cabling.4. the Embedded-Service-Engine0/0 interface is displayed because Cisco ISRs G2 have dual-core CPUs on the motherboard. Note The entire output of the show ip interface brief command in Figure 1-17 can be viewed in the online course on page 1.

4.Chapter 1: Routing Concepts 31 Note The entire output of the show ip route command in Figure 1-18 can be viewed in the online course on page 1.1. It is used to allow the router to process packets destined to that IP.1: Verify Router Interfaces Go to the online course to use the Syntax Checker in the fourth and fifth graphics to verify the interfaces of the R2 router.2) The commands to verify the IPv6 interface configuration are similar to the commands used for IPv4.4.4. Figure 1-19 Verify an Interface Configuration The following two commands are used to gather more detailed interface information: Q show interfaces: Displays interface information and packet flow count for all interfaces on the device show ip interface: Displays the IPv4-related information for all interfaces on a router Q Interactive Graphic Activity 1. Notice the three directly connected network entries and the three local host route interface entries. The output displays the current commands configured on the specified interface. and a /128 mask for IPv6. It also has a /32 mask for IPv4. Verify IPv6 Interface Settings (1.1. The local host route is for routes on the router owning the IP address. . Figure 1-19 displays the output of the show running-config interface command. A local host route has an administrative distance of 0.1.1 graphic number 2.

1. The show ipv6 interface gigabitethernet 0/0 command output shown in Figure 1-21 displays the interface status and all of the IPv6 addresses belonging to the interface. The “up/up” output on the same line as the interface name indicates the Layer 1/ Layer 2 interface state. An IPv6 network interface is required to have a link-local address. The other address.2 graphic number 1. Along with the link-local address and global unicast address. but not necessarily a global unicast address. . A link-local address is automatically added to an interface whenever a global unicast address is assigned. This is the same as the Status and Protocol columns in the equivalent IPv4 command. One address is the IPv6 global unicast address that was manually entered.32 Routing Protocols Companion Guide The show ipv6 interface brief command in Figure 1-20 displays a summary for each of the interfaces. the output includes the multicast addresses assigned to the interface. beginning with prefix FF02. which begins with FE80. Figure 1-20 Note Verify the R1 IPv6 Interface Status The entire output of the show ipv6 interface brief command in Figure 1-20 can be viewed in the online course on page 1.4. The output displays two configured IPv6 addresses per interface. is the link-local unicast address for the interface.

1.Chapter 1: Routing Concepts 33 Figure 1-21 Note Verify the IPv6 Configuration on R1 G0/0 The entire output of the show ipv6 interface command in Figure 1-21 can be viewed in the online course on page 1. not IPv4 networks. Within the routing table. The show ipv6 route command will only display IPv6 networks. The local route has a /128 prefix. Figure 1-22 Note Verify the R1 IPv6 Routing Table The entire output of the show ipv6 route command in Figure 1-22 can be viewed in the online course on page 1. as indicated with an ‘L’ next to the route entry.2 graphic number 2. When the router interface is configured with a global unicast address and is in the “up/up” state. The IPv6 global unicast address configured on the interface is also installed in the routing table as a local route. a ‘C’ next to a route indicates that this is a directly connected network. The show ipv6 route command shown in Figure 1-22 can be used to verify that IPv6 networks and specific IPv6 interface addresses have been installed in the IPv6 routing table. Local routes are used by the routing table to efficiently process packets with the interface address of the router as the destination. .4.1.2 graphic number 3. the IPv6 prefix and prefix length is added to the IPv6 routing table as a connected route.4.

To enable the filtering command. Figure 1-23 Verify Connectivity on R1 Other useful IPv6 verification commands include: Q Q show interface show ipv6 routers Filter Show Command Output (1. the ping command is used to verify Layer 3 connectivity between R1 and PC1. At the end of the paused output.3) Commands that generate multiple screens of output are. . the --More-. A value of 0 (zero) prevents the router from pausing between screens of output. Filtering commands can be used to display specific sections of output. enter a pipe (|) character after the show command and then enter a filtering parameter and a filtering expression. starting with the line that matches the filtering expression Note Output filters can be used in combination with any show command. Use the terminal length number command to specify the number of lines to be displayed.4. Another very useful feature that improves the user experience in the command-line interface (CLI) is the filtering of show output. paused after 24 lines.text displays. As shown in Figure 1-23. The filtering parameters that can be configured after the pipe include: Q Q Q Q section: Shows entire section that starts with the filtering expression include: Includes all output lines that match the filtering expression exclude: Excludes all output lines that match the filtering expression begin: Shows all the output lines from a certain point. by default.1. Pressing Enter displays the next line and pressing the spacebar displays the next set of lines.34 Routing Protocols Companion Guide The ping command for IPv6 is identical to the command used with IPv4 except that an IPv6 address is used.

The example in Figure 1-26 uses the pipe character and the exclude keyword. Figure 1-26 Filter show Commands to Exclude Rows of Output .Chapter 1: Routing Concepts 35 Figures 1-24 through 1-27 provide examples of the various output filters.1. Figure 1-24 Filter show Commands by Section The example in Figure 1-25 uses the pipe character and the include keyword. The example in Figure 1-24 uses the pipe character and the section keyword. Figure 1-25 Note Filter show Commands by Common Keyword The entire output of the show ip interface brief command in Figure 1-25 can be viewed in the online course on page 1.3 graphic number 2.4.

Command History Feature (1. .4.3: Filter Command Output Go to the online course to use the Syntax Checker in the fifth graphic to practice how to filter command output on the R1 router. Figure 1-27 Filter show Commands Beginning from a Keyword Interactive Graphic Activity 1. It is also practical to increase the number of command lines that the history buffer records during the current terminal session only. Repeat the key sequence to recall successively more recent commands. Use the show history privileged EXEC command to display the contents of the buffer. The command output begins with the most recent command. Repeat the key sequence to recall successively older commands. command history is enabled and the system captures the last 10 command lines in its history buffer.1.36 Routing Protocols Companion Guide Note The entire output of the show ip interface brief command in Figure 1-26 can be viewed in the online course on page 1.1. press Ctrl+N or the Down Arrow key. By default. because it temporarily stores the list of executed commands to be recalled. To recall commands in the history buffer.3 graphic number 3.4) The command history feature is useful.4. Use the terminal history size user EXEC command to increase or decrease the size of the buffer. The example in Figure 1-27 uses the pipe character and the begin keyword. press Ctrl+P or the Up Arrow key.4. To return to more recent commands in the history buffer.1.

1. you will configure a router with basic settings including IP addressing.165.200.4. Packet Tracer Activity Packet Tracer Activity 1. you will complete the following objectives: Q Q Q Q Part 1: Set Up the Topology and Initialize Devices Part 2 Configure Devices and Verify Connectivity Part 3: Display Router Information Part 4: Configure IPv6 and Verify Connectivity . You will also configure a switch for remote management and configure the PCs.1. the following displays a sample of the terminal history size and show history commands: R1# terminal history size 200 R1# R1# show history show ip interface brief show interface g0/0 show ip interface g0/1 show ip route show ip route 209.4: Adjusting the Command History Go to the online course to use the Syntax Checker in the second graphic to adjust and list the command history output on the R1 router.6: Configuring Basic Router Settings with IOS CLI In this lab.4.4.224 show running-config interface s0/0/0 terminal history size 200 show history R1# Interactive Graphic Activity 1.Chapter 1: Routing Concepts 37 For example. After you have successfully verified connectivity.1. you will use show commands to gather information about the network. Lab 1.5: Configuring and Verifying a Small Network In this activity.

1.38 Routing Protocols Companion Guide Lab 1. What does a router do with a packet received from one network and destined for another network? The router performs the following three major steps: Step 1. Note In this context. After the router has determined the exit interface using the path determination function.4. you will complete the following objectives: Q Q Q Q Q Q Part 1: Set Up the Topology and Initialize Devices Part 2: Configure Devices and Verify Connectivity Part 3: Configure Router to Allow CCP Access Part 4: (Optional) Install and Set Up CCP on PC-A Part 5: Configure R1 Settings Using CCP Part 6: Use CCP Utilities Routing Decisions (1. . Examines the destination IP address of the IP packet to find the best path in the routing table. De-encapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer. the router must encapsulate the packet into the data link frame of the outgoing interface. which is the process used by a router to accept a packet on one interface and forward it out of another interface. Step 2.1) A primary function of a router is to forward packets toward their destination. a router also operates at Layers 1 and 2. Router Switching Function (1. This is accomplished by using a switching function.7: Configuring Basic Router Settings with CCP In this lab. A key responsibility of the switching function is to encapsulate packets in the appropriate data link frame type for the outgoing data link. However.2.2) The key to understanding the role of a router in the network is to understand that a router is a Layer 3 device responsible for forwarding packets.1. the term “switching” literally means moving packets from source to destination and should not be confused with the function of a Layer 2 switch.

Chapter 1: Routing Concepts 39 Step 3. PC1 must determine if the destination IPv4 address is on the same network. Next. PC1 is sending a packet to PC2.2) In the animation in the online course.2. Video 1.1. PC1 . PC1 determines its own subnet by doing an AND operation on its own IPv4 address and subnet mask. As a packet travels from the source device to the final destination device. It is very likely that the packet is encapsulated in a different type of Layer 2 frame than the one in which it was received.168.1. it encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface. devices have Layer 3 IPv4 addresses and Ethernet interfaces have Layer 2 data link addresses.10 and an example MAC address of 0A-10. and then processed to be forwarded out of a serial interface as a Point-to-Point Protocol (PPP) encapsulated frame. For example. an Ethernet encapsulated frame might be received by the router on a FastEthernet interface. For example.2: PC1 Sends a Packet to PC2 Video Go to the online course and play the animation of a packet being sent from PC1 to PC2. PC1 is configured with IPv4 address 192.2. However. This produces the network address that PC1 belongs to. Figure 1-28 Encapsulating and De-Encapsulating Packets Send a Packet (1. the Layer 3 IP addresses do not change.1. As shown in Figure 1-28. If the router finds a path to the destination. the Layer 2 data link addresses change at every hop as the packet is deencapsulated and re-encapsulated in a new frame by each router.

168. 4.3) The following processes take place when R1 receives the Ethernet frame from PC1: 1.168.168.4.4. PC1 can then forward the packet to the MAC address of the default gateway. If the destination network address is on a different network. PC1 sends an ARP request. If the MAC address is not in the cache. PC1 refers to its ARP cache for the MAC address of the device with that destination IPv4 address. A similar process is used for IPv6 packets. IPv6-to-MAC address mappings are kept in a table similar to the ARP cache. then PC1 generates an ARP request to acquire the address to complete the packet and send it to the destination. 3.1. Instead of the ARP process. Router R1 sends back an ARP reply. Forward to the Next Hop (1. IPv6 address resolution uses ICMPv6 Neighbor Solicitation and Neighbor Advertisement messages.0/24 network. R1 searches the routing table for a network address that would include the destination IPv4 address of the packet as a host address within that network. therefore. This means that the IPv4 packet is encapsulated in a new Ethernet frame with the destination MAC address of the IPv4 address of the next-hop router. FastEthernet 0/0. copies the frame into its buffer. R1 de-encapsulates the Ethernet frame. R1 examines the destination MAC address. called the neighbor cache. then PC1 does not use the default gateway.0/24 network has a next-hop IPv4 address of 192.40 Routing Protocols Companion Guide does this same AND operation using the packet destination IPv4 address and the PC1 subnet mask. R1 consults its routing table to route this packet. PC1 checks its ARP table for the IPv4 address of the default gateway and its associated MAC address. The destination IPv4 address of the packet is 192.10. which means that the Ethernet frame contains an IPv4 packet in the data portion of the frame. .4. If an ARP entry does not exist in the ARP table for the default gateway. which is a host IPv4 address on that network. then PC1 forwards the packet to its default gateway. the routing table has a route for the 192.2. the Fa0/0 interface of router R1. In this example. 2.2 and an exit interface of FastEthernet 0/1. Instead. which matches the MAC address of the receiving interface. Because the destination IPv4 address of the packet does not match any of the directly connected networks of R1. To determine the MAC address of the default gateway. The route that R1 finds to the 192. R1. R1 identifies the Ethernet Type field as 0x800. If the destination network address is the same network as PC1.168.2.

R1 looks up the next-hop IPv4 address of 192. which matches the MAC address of the receiving interface. FastEthernet 0/0. 2. R1 would send an ARP request out of its FastEthernet 0/1 interface and R2 would send back an ARP reply.4.0/24 network.Chapter 1: Routing Concepts 41 Because the exit interface is on an Ethernet network. The IPv4 packet is now encapsulated into a new Ethernet frame and forwarded out the FastEthernet 0/1 interface of R1.168. R1 must resolve the next-hop IPv4 address with a destination MAC address using ARP: 1.2. R2 searches the routing table for the destination IPv4 address of the packet using the same process R1 used.168. R2 de-encapsulates the Ethernet frame. R1 would then update its ARP cache with an entry for 192.2 and the associated MAC address. The animation in the online course illustrates how R1 forwards the packet to R2. Because the destination IPv4 address of the packet does not match any of the interface addresses of R2.2. R2 does not have to resolve the nexthop IPv4 address with a destination MAC address. R2 identifies the Ethernet Type field as 0x800.1. copies the frame into its buffer.4) The following processes take place when R2 receives the frame on its Fa0/0 interface: 1.2 and an exit interface of Serial 0/0/0.2 in its ARP cache. with a nexthop IPv4 address of 192. R2.168. therefore. The routing table of R2 has a route to the 192.2. Video 1. If the entry is not in the ARP cache.3: R1 Forwards the Packet to R2 Video Go to the online course and play the animation of a packet being sent through three routers from sender to receiver.1. 3. 4. R2 examines the destination MAC address. Because the exit interface is not an Ethernet network.3.2. . 5. The IPv4 packet is now encapsulated into a new data link frame and sent out the Serial 0/0/0 exit interface. 2. R2 consults its routing table to route this packet. which means that the Ethernet frame contains an IPv4 packet in the data portion of the frame. Packet Routing (1. 6.168.

Because the exit interface is a directly connected Ethernet network.168. The IPv4 packet is encapsulated into a new Ethernet data link frame and sent out the FastEthernet 0/0 interface of R3. Video 1. This means that the packet can be sent directly to the destination device and does not need to be sent to another router.1. When PC2 receives the frame. The routing table has a route to a directly connected network on R3. R3 must resolve the destination IPv4 address of the packet with a destination MAC address: 1. 5. therefore. copies the rest of the frame into its buffer. R3 searches the routing table for the destination IPv4 address of the packet.). which matches the MAC address of the receiving interface.42 Routing Protocols Companion Guide When the interface is a point-to-point (P2P) serial connection. 3. etc. Because there are no MAC addresses on serial interfaces. If the entry is not in the ARP cache. The animation in the online course illustrates how R2 forwards the packet to R3. PC2 sends back an ARP reply with its MAC address. its Ethernet network interface card (NIC). R3 searches for the destination IPv4 address of the packet in its Address Resolution Protocol (ARP) cache. PC2 de-encapsulates the Ethernet frame and passes the IPv4 packet to the IPv4 process of its operating system. R3 then updates its ARP cache with an entry for 192. R3 sends an ARP request out of its FastEthernet 0/0 interface.1. PC2 identifies the Ethernet Type field as 0x800. the router encapsulates the IPv4 packet into the proper data link frame format used by the exit interface (HDLC. 2. 2.10 and the MAC address that is returned in the ARP reply. Reach the Destination (1. PPP. .5) The following processes take place when the frame arrives at R3: 1. 4.2. which means that the Ethernet frame contains an IPv4 packet in the data portion of the frame.2.4: R2 Forwards the Packet to R3 Video Go to the online course and play the animation of a packet being sent from R2 to R3. R3 de-encapsulates the data link PPP frame.4. R2 sets the data link destination address to an equivalent of a broadcast (MAC address: FF:FF:FF:FF:FF:FF). R3 copies the data link PPP frame into its buffer. it examines the destination MAC address. 3. PC2.

1. the router sends an ICMP Unreachable message to the source IP address of the packet. If there is a default route. Remote network: If the destination IP address of the packet belongs to a remote network.2. the router searches its routing table for a network address that matches the destination IP address of the packet. the packet is forwarded to the Gateway of Last Resort. If the router does not have a default route. No route determined: If the destination IP address of the packet does not belong to either a connected or remote network.1. The routing table search results in one of three path determinations: Q Directly connected network: If the destination IP address of the packet belongs to a device on a network that is directly connected to one of the interfaces of the router.2.2. that packet is forwarded directly to the destination device. Video 1. Q Q . To determine the best path. This means that the destination IP address of the packet is a host address on the same network as the interface of the router. Path Determination (1. Routing Decisions (1. A Gateway of Last Resort is set when a default route is configured on a router.2. load balancing.6: Match Layer 2 and Layer 3 Addressing Go to the online course to perform this practice activity.2) This section discusses the best path to send packets. Interactive Graphic Activity 1. then the packet is discarded. If the packet is discarded.5: R3 Forwards the Packet to PC2 Video Go to the online course and play the animation of a packet being sent from R3 to PC2.Chapter 1: Routing Concepts 43 The animation in the online course illustrates how R3 forwards the packet to PC2.1) A primary function of a router is to determine the best path to use to send packets. and the concept of administrative distance. the router determines if there is a Gateway of Last Resort available.2. then the packet is forwarded to another router. Remote networks can only be reached by forwarding packets to another router.

Figure 1-29 Packet Forwarding Decision Process Best Path (1. The following lists some dynamic protocols and the metrics they use: Q Q Routing Information Protocol (RIP) : Hop count Open Shortest Path First (OSPF): Cisco routers use a cost based on cumulative bandwidth from source to destination . Metrics can be based on either a single characteristic or several characteristics of a path. The best path to a network is the path with the lowest metric. or a metric. combining them into a single metric.44 Routing Protocols Companion Guide The logic flowchart in Figure 1-29 illustrates the router packet-forwarding decision process. Dynamic routing protocols typically use their own rules and metrics to build and update routing tables. Whenever multiple paths to the same network exist.2. A metric is the quantitative value used to measure the distance to a given network. for each path through the network. each path uses a different exit interface on the router to reach that network. The best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a network. Some routing protocols can base route selection on multiple metrics.2) Determining the best path involves the evaluation of multiple paths to the same destination network and selecting the optimum or shortest path to reach that network.2. The routing algorithm generates a value.

one for each equal cost path. The router forwards packets using the multiple exit interfaces listed in the routing table.3: Equal Cost Load Balancing Video Go to the online course and play the animation showing an example of equal cost load balancing . This is called equal cost load balancing. Load Balancing (1. delay.2. Unequal cost load balancing is when a router distributes traffic over network interfaces.2: Hop Count vs. Video 1. Equal cost load balancing can be configured to use both dynamic routing protocols and static routes. Cisco routers can load balance up to four equal cost paths. The routing table contains the single destination network. Note EIGRP supports unequal cost load balancing by using the variance command. The animation in the online course provides an example of equal cost load balancing. then the router forwards the packets using both paths equally. By default. load balancing can increase the effectiveness and performance of the network.2.3) What happens if a routing table has two or more paths with identical metrics to the same destination network? When a router has two or more paths to a destination with equal cost metrics. load.Chapter 1: Routing Concepts 45 Q Enhanced Interior Gateway Routing Protocol (EIGRP): Bandwidth. Bandwidth as a Metric Video Go to the online course and play the animation showing how a network path may be different depending on the metric being used.2. reliability The animation in the online course highlights how the path may be different depending on the metric being used. If configured correctly. but has multiple exit interfaces. EIGRP supports equal cost load balancing and is also the only routing protocol to support unequal cost load balancing.2. The maximum number of equal cost paths depends on the routing protocol and IOS version. even those that are different distances from the destination address. Video 1.2.2.

Table 1-5 lists various routing protocols and their associated ADs. the router chooses the route with the lowest AD. each routing protocol may decide on a different path to reach the destination based on that routing protocol’s metrics. RIP chooses a path based on hop count. a static route has an AD of 1.2.4) It is possible for a router to be configured with multiple routing protocols and static routes.46 Routing Protocols Companion Guide Administrative Distance (1. the lower the AD. a directly connected route with an AD of 0 takes precedence over a static route with an AD of 1. If this occurs. both routing protocols may learn of the same destination network. However. Table 1-5 Default Administrative Distances Administrative Distance 0 1 5 20 90 100 110 115 120 170 200 255 Route Source Connected Static EIGRP summary route External BGP Internal EIGRP IGRP OSPF IS-IS RIP External EIGRP Internal BGP Unknown . How does the router know which route to use? Cisco IOS uses what is known as the administrative distance (AD) to determine the route to install into the IP routing table. For example. For example. When a router has the choice of a static route and an EIGRP route. if both RIP and EIGRP are configured on a router.2. The AD represents the “trustworthiness” of the route. the static route takes precedence. Given two separate routes to the same destination. whereas EIGRP chooses a path based on its composite metric. Similarly. the more trustworthy the route source. the routing table may have more than one route source for the same destination network. whereas an EIGRP-discovered route has an AD of 90.

5: Order the Steps in the Packet Forwarding Process Go to the online course to perform these four practice activities. The Routing Table (1. The routing table contains network or next-hop associations. To do this. In the following sections.3. Remote routes: These are remote networks connected to other routers. a routing table is a data file in RAM that is used to store route information about directly connected and remote networks.3) The primary function of a router is to forward packets toward their destination network.1. you will learn how a router builds the routing table. . Routes to these networks can be either statically configured or dynamically configured using dynamic routing protocols. Analyze the Routing Table (1.Chapter 1: Routing Concepts 47 Interactive Graphic Activity 1. Q Specifically. you will learn the three basic routing principles.2. Routers add a directly connected route when an interface is configured with an IP address and is activated.3. The next-hop association can also be the outgoing or exit interface to the next destination. Then. Router Operation (1. the destination IP address of the packet.1) The routing table of a router stores information about: Q Directly connected routes: These routes come from the active router interfaces. a router needs to search the routing information stored in its routing table.1) A good understanding of routing tables is crucial for any network administrator.2. These associations tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the next hop on the way to the final destination. Figure 1-30 identifies the directly connected networks and remote networks of router R1.

Static routes: Added when a route is manually configured and the exit interface is active. Q . and which specific interface to use to get to a predefined destination. Dynamic routing protocol: Added when routing protocols that dynamically learn about the network. including how the route was learned. are implemented and networks are identified. Entries in the routing table can be added as: Q Local Route interfaces: Added when an interface is configured and active. This allows the router to efficiently determine when it receives a packet for the interface instead of being forwarded. A router provides additional route information.2) On a Cisco IOS router. common codes include: Q L: Identifies the address assigned to a router’s interface.1. For instance. This entry is only displayed in IOS 15 or newer for IPv4 routes and all IOS releases for IPv6 routes.48 Routing Protocols Companion Guide Figure 1-30 Directly Connected and Remote Network Routes Routing Table Sources (1. the show ip route command can be used to display the IPv4 routing table of a router. Q Q Q The sources of the routing table entries are identified by a code. such as EIGRP or OSPF.3. how long the route has been in the table. The code identifies how the route was learned. Directly connected interfaces: Added to the routing table when an interface is configured and active. C: Identifies a directly connected network.

2. Note Other codes are beyond the scope of this chapter.1.1.3.3. Remote Network Routing Entries (1.Chapter 1: Routing Concepts 49 Q Q Q S: Identifies a static route created to reach a specific network.1. Figure 1-32 displays an IPv4 routing table entry on R1 for the route to remote network 10.0. .1. Figure 1-31 Note Routing Table of R1 The entire output of the show ip route command in Figure 1-31 can be viewed in the online course on page 1. Figure 1-31 shows a sample routing table of R1.3) As a network administrator. it is imperative to know how to interpret the content of an IPv4 and IPv6 routing table. O: Identifies a dynamically learned network from another router using the OSPF routing protocol. D: Identifies a dynamically learned network from another router using EIGRP.

Metric: Identifies the value assigned to reach the remote network. Administrative distance: Identifies the trustworthiness of the route source. Q Q Q Q Interactive Graphic Activity 1. Lower values indicate preferred routes.4: Interpret the Content of a Routing Table Entry Go to the online course to perform this practice activity.50 Routing Protocols Companion Guide Figure 1-32 Remote Network Entry Identifiers The entry identifies the following information: Q Q Q Route source: Identifies how the route was learned.3.1. Next-hop: Identifies the IPv4 address of the next router to forward the packet to. Lower values indicate preferred route source. . Destination network: Identifies the address of the remote network. Outgoing interface: Identifies the exit interface to use to forward a packet toward the final destination. Route timestamp: Identifies how much time has passed since the route was learned.

the network of that interface is added to the routing table as a directly connected network. etc. directly connected interface actually creates two routing table entries.3.2) An active. without any configured interfaces. properly configured. whenever an interface is configured with an IP address and enabled.Chapter 1: Routing Concepts 51 Directly Connected Routes (1. as shown in Figure 1-33.10.168. Directly Connected Route Table Entries (1. the interface must: Q Q Q Be assigned a valid IPv4 or IPv6 address Be activated with the no shutdown command Receive a carrier signal from another device (router.1) A newly deployed router.) When the interface is up. it is automatically added as a directly connected network. Figure 1-33 Empty Routing Table Before the interface state is considered “up/up” and added to the IPv4 routing table.2. host.0.3.2) How does a router add its interfaces to the routing table? Well. has an empty routing table. Directly Connected Interfaces (1.2. Figure 1-34 displays the IPv4 routing table entries on R1 for the directly connected network 192. switch.3. .

Local route (L) entries have always been a part of the IPv6 routing table. Destination network: The address of the remote network.255.3. configuring the following commands on R1 would enable the directly connected Gigabit Ethernet 0/0 interface and generate the following messages: R1(config)# interface gigabitethernet 0/0 R1(config-if)# description Link to LAN 1 R1(config-if)# ip address 192. ‘C’ identifies a directly connected network.255.0 . Outgoing interface: Identifies the exit interface to use when forwarding packets to the destination network. The entries contain the following information: Q Route source: Identifies how the route was learned. local route routing table entries (L) were not displayed in the IPv4 routing table. ‘L’ identifies the IPv4 address assigned to the router’s interface.2.168. Layer 1 and 2 informational messages are automatically generated. Directly connected interfaces have two route source codes. For example. Directly Connected Examples (1.1 255. Q Q Note Prior to IOS 15.10.3) When directly connected interfaces are enabled.52 Routing Protocols Companion Guide Figure 1-34 Directly Connected Network Entry Identifiers The routing table entry for directly connected interfaces is simpler than the entries for remote networks.

configuring the following commands on R1 would enable the directly connected IPv6 Gigabit Ethernet 0/0 interface and generate the following messages: R1(config)# ipv6 unicast-routing R1(config)# interface gigabitethernet 0/0 R1(config-if)# description Link to LAN 1 .0/24 is directly connected. For example.4) Enabling directly connected IPv6 interfaces also generates Layer 1 and Layer 2 informational messages.10.0/24 is variably subnetted. changed state to up *Jan 30 22:04:51.3.200.899: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0. 2 masks C L 192.224/30 is directly connected. GigabitEthernet0/1 209. The following provides an example of the routing table with the directly connected interfaces of R1 configured and activated: R1# show ip route | begin Gateway Gateway of last resort is not set 192.899: %LINK-3-UPDOWN: Interface GigabitEthernet0/0.168. GigabitEthernet0/1 192.10. Serial0/0/0 209. 2 masks C L R1# 209.168.2.2.11. 2 subnets.Chapter 1: Routing Concepts 53 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# *Jan 30 22:04:47.168. the routing table automatically adds the connected (‘C’) and local (‘L’) entries.165. GigabitEthernet0/0 192.168. changed state to up R1(config)# As each interface is enabled.0/24 is variably subnetted.168. changed state to down R1(config)# *Jan 30 22:04:50.1/32 is directly connected. GigabitEthernet0/0 192.200.3: Configure and Activate the Interfaces on R2 Go to the online course to use the Syntax Checker in the fifth graphic to configure the interfaces of the R2 router.11. 2 subnets. Serial0/0/0 Interactive Graphic Activity 1.168.165.0/24 is variably subnetted.3.225/32 is directly connected.1/32 is directly connected.0/24 is directly connected. Directly Connected IPv6 Example (1.11. 2 masks C L 192.200.551: %LINK-3-UPDOWN: Interface GigabitEthernet0/0. 2 subnets.165.10.

OSPF NSSA ext 2 C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0.ISIS L1 I2 .ISIS interarea.EIGRP external. OI .Connected. In an IPv6 network. ON1 . ND . H .Per-user Static route B . .ISIS summary. Figure 1-35 displays how the show ipv6 route command can be combined with a specific network destination to display the details of how that route was learned by the router. OE1 .default .NHRP. I1 . D . receive R1# When the show ipv6 route command reveals a ‘C’ next to a route.Redirect. ON2 . Local routes are used by the routing table to efficiently process packets with a destination address of the interface of the router.OSPF Inter. An ‘L’ indicates the local route. NDp . the local route has a /128 prefix. changed state to down *Feb 3 21:38:40. IA . that indicates that this is a directly connected network.BGP. DCE .279: %LINK-3-UPDOWN: Interface GigabitEthernet0/0.ND Default.54 Routing Protocols Companion Guide R1(config-if)# ipv6 address 2001:db8:acad:1::1/64 R1(config-if)# no shutdown R1(config-if)# exit *Feb 3 21:38:37.ND Prefix. Notice that there is also a route installed to the FF00::/8 network.Static.OSPF Intra. directly connected L 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/1. directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0.RIP.967: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0. S . R .5 entries Codes: C . receive C 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/1.OSPF ext 2.Destination NDr .ISIS L2. This route is required for multicast routing.967: %LINK-3-UPDOWN: Interface GigabitEthernet0/0. receive L FF00::/8 [0/0] via Null0.Local. U . changed state to up *Feb 3 21:38:41.OSPF ext 1 OE2 . O .EIGRP EX . changed state to up R1(config)# The following provides an example of the routing table with the directly connected interfaces of R1 configured and activated: R1# show ipv6 route IPv6 Routing Table . IS .OSPF NSSA ext 1. L .

100-byte ICMP Echos to 2001:DB8:ACAD:3::2. This is because R1 does not have an entry in the routing table to reach the 2001:DB8:ACAD:4::/64 network. Sending 5. 100-byte ICMP Echos to 2001:DB8:ACAD:4::1. timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5).Chapter 1: Routing Concepts 55 Figure 1-35 Show the IPv6 Route Entry The following displays how connectivity to R2 can be verified using the ping command: R1# ping 2001:db8:acad:3::2 Type escape sequence to abort. R1 requires additional information to reach a remote network. Remote network route entries can be added to the routing table using either: Q Q Static routing Dynamic routing protocols . Sending 5. timeout is 2 seconds: % No valid route for destination Success rate is 0 percent (0/1) R1# The pings are unsuccessful. round-trip min/avg/max = 12/13/16 ms R1# Notice what happens when the G0/0 LAN interface of R2 is the target of the ping command: R1# ping 2001:db8:acad:4::1 Type escape sequence to abort.

and no CPU cycles are used to calculate and communicate routes. A static route is identified in the routing table with the code ‘S’. Statically Learned Routes (1. To configure an IPv4 default static route.3.3.1) After directly connected interfaces are configured and added to the routing table.2.0. Statically learned routes must be manually configured by an administrator.5: Investigating Directly Connected Routes The network in the activity is already configured. A default static route is useful when a router has only one exit point to another router. .0. They define an explicit path between two networking devices.0. Static routes are manually configured. Unlike a dynamic routing protocol.3. The main disadvantage to using static routes is the lack of automatic reconfiguration if the network topology changes.0 0. There are two common types of static routes in the routing table: Q Q Static route to a specific network Default static route A static route can be configured to reach a specific remote network. use the ip route 0.56 Routing Protocols Companion Guide Packet Tracer Activity Packet Tracer Activity 1. such as when the router connects to a central router or service provider. Static Routes (1.0. IPv4 static routes are configured using the ip route network mask {next-hop-ip | exit-intf} global configuration command.0 {exit-intf | next-hop-ip} global configuration command. This topic introduces how to enter remote routes manually.3) Routers can dynamically learn about remote networks using a routing protocol or statically. A default static route is similar to a default gateway on a host. Static routes use less bandwidth than dynamic routing protocols.3. then static or dynamic routing can be implemented. You will log in to the routers and use show commands to discover and answer the questions below about the directly connected routes. The default static route specifies the exit point to use when the routing table does not contain a path for the destination network. static routes are not automatically updated and must be manually reconfigured if the network topology changes. The benefits of using static routes include improved security and resource efficiency.

In fact. Figure 1-36 Static and Default Route Scenario Static Route Examples (1.0. “Gateway of last resort is 0.3.3.0 to network 0.0. while the asterisk (*) identifies this route as a possible candidate to be the default route.0.0.2) Figure 1-37 shows the configuration of an IPv4 default static route on R1 to the Serial 0/0/0 interface.” Figure 1-37 Entering and Verifying a Static Default Route . The ‘S’ signifies that the route source is a static route.Chapter 1: Routing Concepts 57 Figure 1-36 provides a simple scenario of how default and static routes can be applied. Notice that the configuration of the route generated an ‘S*’ entry in the routing table. it has been chosen as the default route as evidenced by the line that reads.0.

168. notice how different they look in the routing table.3. Figure 1-38 Note Entering and Verifying Static Routes The entire output of the show ip route command in Figure 1-38 can be viewed in the online course on page 1.0/24 has been configured using the exit interface while the route to 192.3.10. Also notice that because these static routes were to specific networks. For instance.3. the output indicates that the Gateway of Last Resort is not set.3.0/24 has been configured using the next-hop IPv4 address.2: Entering and Verifying the Static and Default Routes on R1 and R2 Go to the online course to use the Syntax Checker in the third and fourth graphics to configure a default static route on router R1 and a static route on router R2.3. Figure 1-38 shows the configuration of two static routes from R2 to reach the two LANs on R1.168.11. there are some differences in how they operate. Although both are acceptable. Note Static and default static routes are discussed in detail in the next chapter. The route to 192.3.2 graphic number 2.58 Routing Protocols Companion Guide Note The entire output of the show ip route command in Figure 1-37 can be viewed in the online course on page 1.2 graphic number 1. Interactive Graphic Activity 1. .

8 entries Codes: C . DCE .ISIS L1 I2 .ISIS L2.OSPF Intra.NHRP. H .Connected. directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0. D .Destination NDr .OSPF NSSA ext 2 S ::/0 [1/0] via Serial0/0/0.Redirect. there is no asterisk (*) or Gateway of Last Resort explicitly identified.3. OI .default .OSPF NSSA ext 1. The ‘S’ signifies that the route source is a static route. directly connected L 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/1. receive C 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/1.RIP.EIGRP EX . use the ipv6 route ::/0 {ipv6-address | interface-type interface-number} global configuration command. IS .Per-user Static route B .EIGRP external. To configure a default static IPv6 route. Unlike the IPv4 static route.ISIS interarea. L .OSPF Inter. The following configures a default static route on R1 exiting out of the Serial 0/0/0 interface: R1(config)# ipv6 route ::/0 s0/0/0 R1(config)# exit R1# Notice in the following output that the default static route configuration generated an ‘S’ entry in the routing table. receive C 2001:DB8:ACAD:3::/64 [0/0] via Serial0/0/0.OSPF ext 1 OE2 . They are used and configured like IPv4 static routes. receive . O .3) Like IPv4. ON1 . R1# show ipv6 route IPv6 Routing Table .ND Default. directly connected L 2001:DB8:ACAD:3::1/128 [0/0] via Serial0/0/0. IPv6 supports static and default static routes. ON2 .ND Prefix.OSPF ext 2. U .3. ND .BGP. IA . receive L FF00::/8 [0/0] via Null0.ISIS summary. directly connected C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0. R . OE1 .Local. S .Chapter 1: Routing Concepts 59 Static IPv6 Route Examples (1. I1 . NDp .Static.

H .ISIS L2.NHRP. O .default .EIGRP external.EIGRP EX .OSPF ext 2. R . The following example configures two static routes from R2 to reach the two LANs on R1: R2(config)# ipv6 route 2001:DB8:ACAD:1::/64 2001:DB8:ACAD:3::1 R2(config)# ipv6 route 2001:DB8:ACAD:2::/64 s0/0/0 R2(config)# ^Z R2# The route to the 2001:0DB8:ACAD:2::/64 LAN is configured with an exit interface. directly connected L 2001:DB8:ACAD:4::1/128 [0/0] via GigabitEthernet0/0. DCE . while the route to the 2001:0DB8:ACAD:1::/64 LAN is configured with the next-hop IPv6 address. receive C 2001:DB8:ACAD:5::/64 [0/0] via GigabitEthernet0/1.OSPF ext 1 OE2 .OSPF NSSA ext 2 S 2001:DB8:ACAD:1::/64 [1/0] via 2001:DB8:ACAD:3::1 S 2001:DB8:ACAD:2::/64 [1/0] via Serial0/0/0.Redirect. receive .ISIS L1 I2 . directly connected C 2001:DB8:ACAD:3::/64 [0/0] via Serial0/0/0.Static.ND Prefix. D . The following output displays the routing table with the new static routes installed: R2# show ipv6 route IPv6 Routing Table . OE1 .OSPF Inter. directly connected L 2001:DB8:ACAD:5::1/128 [0/0] via GigabitEthernet0/1.ISIS interarea. IA .Destination NDr . S . ND . The next-hop IPv6 address can be either an IPv6 global unicast or linklocal address. OI . static routes are routes explicitly configured to reach a specific remote network. ON1 . I1 .OSPF NSSA ext 1.9 entries Codes: C .ND Default.OSPF Intra.Per-user Static route B .RIP. ON2 .Local. Static IPv6 routes are configured using the ipv6 route ipv6-prefix/prefixlength {ipv6-address | interface-type interface-number} global configuration command.BGP.Connected. directly connected L 2001:DB8:ACAD:3::2/128 [0/0] via Serial0/0/0.ISIS summary. IS . L . receive C 2001:DB8:ACAD:4::/64 [0/0] via GigabitEthernet0/0. U . NDp .60 Routing Protocols Companion Guide Like IPv4.

Sending 5. and identified as a network learned by a specific dynamic routing protocol. routers exchange routes and update their routing tables. timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5). Routers have converged after they have finished exchanging and updating their routing tables. During network discovery. including network discovery and maintaining routing tables.1) Dynamic routing protocols are used by routers to share information about the reachability and status of remote networks. . Network discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. R2 responds and provides R1 with its networks.Chapter 1: Routing Concepts 61 L FF00::/8 [0/0] via Null0.3.4) You just saw how a router can be manually configured with static routes to reach remote networks. receive R2# The following confirms remote network connectivity to the 2001:0DB8:ACAD:4::/64 LAN on R2 from R1: R1# ping 2001:db8:acad:4::1 Type escape sequence to abort. In this simplified message exchange. Figure 1-39 provides a simple scenario of how two neighboring routers would initially exchange routing information. 100-byte ICMP Echos to 2001:DB8:ACAD:4::1. Dynamic Routing (1. a dynamic routing protocol allows the routers to automatically learn about these networks from other routers. In this section you will see how a dynamic routing protocol can be used to achieve the same result. Instead of depending on manually configured static routes to remote networks on every router.4. These networks. Dynamic routing protocols perform several activities. are added to the routing table of the router. Routers then maintain the networks in their routing tables. R1 introduces itself and the networks it can reach. round-trip min/avg/max = 12/13/16 ms R1# Dynamic Routing Protocols (1. and the best path to each.3.

For these reasons.4. the other routing protocols supported by the IOS are beyond the scope of the CCNA certification. Note The focus of this course is on EIGRP and OSPF.2) A router running a dynamic routing protocol does not only make a best path determination to a network. it also determines a new best path if the initial path becomes unusable (or if the topology changes). RIP will be discussed only for legacy reasons. . Cisco ISR routers can support a variety of dynamic IPv4 routing protocols.62 Routing Protocols Companion Guide Figure 1-39 Dynamic Routing Scenario IPv4 Routing Protocols (1. use the router ? command in global configuration mode as shown in Figure 1-40. including: Q Q Q Q EIGRP: Enhanced Interior Gateway Routing Protocol OSPF: Open Shortest Path First IS-IS: Intermediate System-to-Intermediate System RIP: Routing Information Protocol To determine which routing protocols are supported by the IOS. Routers that use dynamic routing protocols automatically share routing information with other routers and compensate for any topology changes without involving the network administrator. dynamic routing protocols have an advantage over static routes.3.

there are three ‘D’ entries in the routing table: Q The entry beginning with ‘D*EX’ identifies that the source of this entry was EIGRP (‘D’). R2 advertises that it is the default gateway to other networks.3) In this dynamic routing example.Chapter 1: Routing Concepts 63 Figure 1-40 Supported IPv4 Routing Protocols IPv4 Dynamic Routing Examples (1. .3. Figure 1-41 Verifying Dynamic Routes Along with the connected and link-local interfaces. The route is a candidate to be a default route (‘*’).4. assume that R1 and R2 have been configured to support the dynamic routing protocol EIGRP. The output in Figure 1-41 displays the routing table of R1 after the routers have exchanged updates and converged. and the route is an external route (‘EX’) forwarded by EIGRP. The routers also advertise directly connected networks.

ISR routers can support dynamic IPv6 routing protocols.4. you must configure the ipv6 unicastrouting global configuration command.3. IPv6 Routing Protocols (1.4. Most of the modifications in the routing protocols are to support the longer IPv6 addresses and different header structures. there are two ‘D’ entries (EIGRP routes) in the routing table. IPv6 Dynamic Routing Examples (1. .3.4) As shown in Figure 1-42. as shown in the following output. including: Q Q Q RIPng (RIP next generation) OSPFv3 EIGRP for IPv6 Figure 1-42 Supported IPv6 Routing Protocols Support for dynamic IPv6 routing protocols is dependent on hardware and IOS version.5) Routers R1 and R2 have been configured with the dynamic routing protocol EIGRP for IPv6.) To view the routing table on R1. The output displays the routing table of R1 after the routers have exchanged updates and converged.64 Routing Protocols Companion Guide Q The other two ‘D’ entries are routes installed in the routing table based on the update from R2 advertising its LANs. To enable IPv6 routers to forward traffic. enter the show ipv6 route command. (This is the IPv6 equivalent of EIGRP for IPv4. Along with the connected and local routes.

ND Prefix.Connected. directly connected L 2001:DB8:ACAD:3::1/128 [0/0] via Serial0/0/0.RIP. R .BGP.ISIS L1 I2 .default . I1 . ON2 . OE1 . U .Local.OSPF Inter. directly connected L 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/1.Destination NDr .EIGRP EX . Serial0/0/0 D 2001:DB8:ACAD:5::/64 [90/2172416] via FE80::D68C:B5FF:FECE:A120.OSPF Intra.NHRP. IA . Serial0/0/0 L FF00::/8 [0/0] via Null0. DCE .Chapter 1: Routing Concepts 65 R1# show ipv6 route IPv6 Routing Table .ISIS interarea.OSPF NSSA ext 1. O . L .ISIS summary.ND Default. D .Static. receive D 2001:DB8:ACAD:4::/64 [90/2172416] via FE80::D68C:B5FF:FECE:A120. directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0. ON1 .OSPF NSSA ext 2 C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0. NDp . receive R1# . receive C 2001:DB8:ACAD:3::/64 [0/0] via Serial0/0/0.Per-user Static route B . S .ISIS L2.OSPF ext 1 OE2 .9 entries Codes: C . OI .EIGRP external.OSPF ext 2. receive C 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/1. ND .Redirect. H . IS .

1. This chapter introduced the router. The routing table includes network addresses for its own interfaces. follow these guidelines: Q Start with the Ashland router—use its routing table to identify ports and IP addresses/networks. Q Q In addition. Dynamic routing protocols automatically adjust to changes without any intervention from the network administrator. Dynamic routing protocols require more CPU processing and also use a certain amount of link capacity for routing updates and messages. A remote network is a network that can only be reached by forwarding the packet to another router. In many cases.4. With the help of a classmate. Each interface is a member or host on a different IP network.66 Routing Protocols Companion Guide Summary (1. Add any other intermediary and end devices as specified by the tables. Static routes do not have as much overhead as dynamic routing protocols.4) Class Activity 1. The routing table is a list of networks known by the router. however. record answers from your group to the reflection questions provided with this activity. The main purpose of a router is to connect multiple networks and forward packets from one network to the next. This means that a router typically has multiple interfaces. which are the directly connected networks. static routes can require more maintenance if the topology is constantly changing or is unstable. Be prepared to share your work with another group and/or the class. a routing table will contain both static and dynamic routes. as well as network addresses for remote networks. To assist you with this activity. draw a network topology using the information from the tables. . Add the Richmond router—use its routing table to identify ports and IP addresses/networks.1: We Really Could Use a Map! Scenario Use the Ashland and Richmond routing tables shown in the file provided with this activity. Remote networks are added to the routing table in one of two ways: either by the network administrator manually configuring static routes or by implementing a dynamic routing protocol. Cisco IOS uses what is known as the administrative distance (AD) to determine the route to install into the IP routing table.

Practice The following activities provide practice with the topics introduced in this chapter. For example.0.1.5: Configuring and Verifying a Small Network Packet Tracer Activity 1.4.9: Mapping the Internet Lab 1.Chapter 1: Routing Concepts 67 Routers make their primary forwarding decision at Layer 3.8: Using Traceroute to Discover the Network Packet Tracer Activity 1. The Packet Tracer Activities PKA files are found in the online course. The Labs and Class Activities are available in the companion Routing Protocols Lab Manual (978-1-58713-322-0). and 3. Router interfaces participate in Layer 2 processes associated with their encapsulation.5: Configuring IPv4 and IPv6 Interfaces Packet Tracer Activity 1.3.1.6: Configuring Basic Router Settings with IOS CLI Lab 1. Class Activities Class Activity 1.9: Documenting the Network Packet Tracer Activity 1. an Ethernet interface on a router participates in the ARP process like other hosts on that LAN.4. The routing table is actually a hierarchical structure that is used to speed up the lookup process when locating routes and forwarding packets. the network layer.1.1.1.1.1.1. Layer 3 IP packets are encapsulated into a Layer 2 data link frame and encoded into bits at Layer 1.1.3.1.1.4. and dynamically learned routes. Components of the IPv6 routing table are very similar to the IPv4 routing table.2: Do We Really Need a Map? Class Activity 1. router interfaces participate in Layers 1.7: Configuring Basic Router Settings with CCP Packet Tracer Activity Packet Tracer Activities Packet Tracer Activity 1.5: Investigating Directly Connected Routes . 2.4. The Cisco IP routing table is not a flat database.1: We Really Could Use a Map! Labs Lab 1. it is populated using directly connected interfaces. For instance.2. static routes. However.2.

Routing information about a path from one network to another implies routing information about the reverse. If one router has certain information in its routing table. “Answers to the ‘Check Your Understanding’ Questions. show ip config D. Flash: Permanently stores the bootstrap program B. C. NVRAM: Permanently stores the operating system image D. The appendix. RAM: Stores the routing tables and ARP cache 2.” lists the answers. R1(config)# enable secret quiz B. Every router makes its routing decisions alone. Which routing principle is correct? A. R1(config)# enable secret password quiz 4. Every router makes its routing decisions based on the information it has in its own routing table and the information in its neighbor routing tables. or return. based on the information it has in its own routing table. all adjacent routers have the same information. . R1(config)# password secret quiz C. ROM: Permanently stores the startup configuration file C. Which command can a technician use to determine whether router serial ports have IP addresses that are assigned to them? A. Which of the following matches a router component with its function? A. show ip interface brief 3. R1(config)# enable password secret quiz D.68 Routing Protocols Companion Guide Check Your Understanding Questions Complete all the review questions listed here to test your understanding of the topics and concepts in this chapter. Which of the following commands will set and automatically encrypt the privileged EXEC mode password to “quiz”? A. B. show controllers all C. 1. D. path. show interfaces ip brief B.

but no routing protocols or static routes have been configured yet. ipv6 enable B. If the packet is destined for a remote network. Which statements are correct regarding how a router forwards packets? (Choose two. Which command is used to explicitly configure a local IPv6 address on a router interface? A. A network engineer is configuring a new router. ipv6 address ipv6-address/prefix-length C. Update and maintain routing tables C.) A. F. What two tasks do dynamic routing protocols perform? (Choose two. B. the router forwards the packet to the switch on the next-hop VLAN. D. ipv6 address ipv6-address/prefix-length eui-64 D. If the packet is destined for a remote network. 8. If the packet is destined for a directly connected network. If the packet is destined for a remote network. C.Chapter 1: Routing Concepts 69 5. the router forwards the packet out the exit interface indicated by the routing table. Remote network routes C. the router forwards the packet based on the information in the router host table. the router sends the packet to the next-hop IP address in the routing table. If the packet is destined for a directly connected network. Default routes B. the router forwards the packet based on the destination MAC address. Directly connected routes D. What routes are present in the routing table? A. Assign IP addressing 6. The interfaces have been configured with IP addresses and activated. If the packet is destined for a directly connected network. Discover hosts B.) A. Network discovery E. the router forwards the packet out all interfaces that might be a next hop to that network. No route as the routing table is empty 7. E. ipv6 address ipv6-address/prefix-length link-local . Propagate host default gateways D.

E. D 0.0.2. 6 12.0. 2 B. Metrics represent a composite value of the amount of packet loss occurring for all routing protocols. Serial0/0/0 C. . The metric is always determined based on hop count. B. C 0. Routes with the smallest metric to the destination indicate the best path.2.0 0. What two statements correctly describe the concepts of administrative distance and metric? (Choose two. S* 0. A router first installs routes with higher administrative distances in its routing table. Administrative distance refers to the trustworthiness of a particular route.0/0 is directly connected. A metric is the quantitative value that a routing protocol uses to measure a given route.0.0. S* 0. The network administrator configured the ip route 0. Serial0/0/0 B. B.0.0/0 [1/0] via 192. How many equal-cost paths can a dynamic routing protocol use for load balancing by default? A. How will this command appear in the routing table.0/0 is directly connected. Metrics are used by the router to determine whether a packet has an error and should be dropped. C. 3 C. Which statement is true regarding metrics used by routing protocols? A.0. Metrics are used by the router to determine whether a packet has an error and should be dropped.0/0 [1/0] via 192.70 Routing Protocols Companion Guide 9. A metric is a Cisco-proprietary means to convert distances to a standard unit.0. D.) A.168. 10.0.0. D.0.2 D. assuming that the Serial 0/0/0 interface is up? A.2 11.0 serial 0/0/0 command on the router. C.168. 4 D.0.0.

Destination port 14. What type of IPv6 address must be configured on an IPv6-enabled interface? 23. 18. What are the three basic ways a router learns about networks? 20. A serial interface has been configured with an IP address and the clock rate. What are two important functions that a router performs? 17. 15. the show ip interface brief command indicates that the interface is administratively down. However. What must be done to correct the problem? 22. which type of message does it send first to determine the MAC address of the other device? . DHCP server address hostname D. Default gateway C. Source and destination Layer 2 address B. What purposes does it serve? 19. 16. Destination Layer 3 address D. What three pieces of information must be configured on a host to forward packets to remote networks? (Choose three. Clock rate B.) A. and outline the purpose of each. IP address F. what address continually changes from hop to hop? A. Source Layer 3 address C. Describe the router bootup process from power on to final configuration. When a packet travels from router to router to its destination. Describe the steps necessary to configure basic settings on a router. Describe the importance of the routing table.Chapter 1: Routing Concepts 71 13. Describe the internal router hardware components. DNS server address E. When a computer is pinging another computer for the first time. Subnet mask 21.

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You can find the definitions in the Glossary.CHAPTER 2 Static Routing Objectives Upon completion of this chapter. you will be able to answer the following questions: Q What are the advantages and disadvantages of static routes? Can you explain the purpose of different types of static routes? Can you configure IPv4 and IPv6 static routes by specifying a next-hop address? How is legacy classful addressing used in network implementation? What is the purpose of CIDR in replacing classful addressing? Q How do you design and implement a hierarchical addressing scheme? How do you configure an IPv4 and IPv6 summary network address to reduce the number of routing table entries? Can you configure a floating static route to provide a backup connection? How does a router process packets when a static route is configured? How do you troubleshoot common static and default route configuration issues? Q Q Q Q Q Q Q Q Key Terms This chapter uses the following key terms. stub network page 77 80 quad-zero route stub router page 93 summary static route page floating static route page 106 page 128 page 128 page 81 summary route recursive lookup page 86 fully specified static route page 89 route summarization .

several important IOS commands and the resulting output will be examined. To attend the event. Choose a preferred route to arrive at the arena in time to see every second of the huge sporting event. which route would you choose to deliver data communications for your small. easiest route or the alternative. Routers learn about remote networks either dynamically.74 Routing Protocols Companion Guide Introduction (2. In many cases.2: Which Way Should We Go? A huge sporting event is about to take place in your city. An introduction to the routing table using both directly connected networks and static routes will be included. This chapter will also contrast classful routing and the widely implemented classless routing methods.1. . such as the amount of traffic or congestion. Alternative. routers use a combination of both dynamic routing protocols and static routes. using static routes. using routing protocols. There are two routes you can take to drive to the event: Q Q Highway route: It is easy to follow and fast driving speeds are allowed.to medium-sized business? Would your network route be the fastest. Depending on conditions.pdf and be prepared to justify your answers to the class or with another group. moving information across an internetwork from source to destination. This chapter focuses on static routing. In this chapter. discuss these options. or manually. Static routes are very common and do not require the same amount of processing and overhead as dynamic routing protocols. direct route: You found this route using a city map. direct route? Justify your choice. Routers are the devices responsible for the transfer of packets from one network to the next. you make concise plans to arrive at the sports arena on time to see the entire game. CIDR and VLSM have helped conserve the IPv4 address space using subnetting and summarization techniques. Complete the modeling activity . this just may be the way to get to the arena on time! With a partner.1. sample topologies will be used to configure IPv4 and IPv6 static routes and to present troubleshooting techniques. Compare your optional preferences to network traffic.1) Routing is at the core of every data network. In the process.0. Class Activity 2. It will cover Classless Inter-Domain Routing (CIDR) and the variable-length subnet mask (VLSM) methods.0.

Reach Remote Networks (2. Static routes are used in networks of all sizes.1.1) As previously stated. For this reason.Chapter 2: Static Routing 75 Static Routing Implementation (2. and are used along with a dynamic routing protocol. static routes are widely used in networks today. . Figure 2-1 Static and Default Route Scenario A network administrator can manually configure a static route to reach a specific network. A static route does not change until the administrator manually reconfigures it. a good understanding of static routes is a requirement for implementing routing on a network. static routes are not automatically updated and must be manually reconfigured any time the network topology changes. Figure 2-2 provides a sample scenario of dynamic routing using EIGRP. Dynamically: Remote routes are automatically learned using a dynamic routing protocol. Unlike a dynamic routing protocol.1.1) A router can learn about remote networks in one of two ways: Q Manually: Remote networks are manually entered into the route table using static routes. Q Figure 2-1 provides a sample scenario of static routing.

resulting in better security. Configuration can be error-prone.2) Static routing provides some advantages over dynamic routing.76 Routing Protocols Companion Guide Figure 2-2 Dynamic Routing Scenario Why Use Static Routing? (2. No CPU cycles are used to calculate and communicate routes. Does not scale well with growing networks. maintenance becomes cumbersome.1. Static routes use less bandwidth than dynamic routing protocols.1. dynamic and static routing features are compared. Notice that the advantages of one method are the disadvantages of the other. especially in large networks. as routers do not exchange routes. Q Q Static routing has the following disadvantages: Q Q Q Q Q Initial configuration and maintenance is time-consuming. The path a static route uses to send data is known. . Administrator intervention is required to maintain changing route information. including: Q Q Static routes are not advertised over the network. In Table 2-1. Requires complete knowledge of the whole network for proper implementation.

However. link bandwidth Route depends on the current topology More secure No extra resources needed Route to destination is always the same Static routes are useful for smaller networks with only one path to an outside network. They also provide security in a larger network for certain types of traffic or links to other networks that need more control. When to Use Static Routes (2. Notice in the figure that any network attached to R1 would only have one . memory. the administrative distance (AD) of a static route is 1. This may result in the router having multiple paths to a destination network via static routes and dynamically learned routes. Default routes are used to send traffic to any destination beyond the next upstream router. It is important to understand that static and dynamic routing are not mutually exclusive. Rather. and the router has only one neighbor. most networks use a combination of dynamic routing protocols and static routes. a static route will take precedence over all dynamically learned routes. A stub network is a network accessed by a single route. Therefore.3) Static routing has three primary uses: Q Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly.Chapter 2: Static Routing 77 Table 2-1 Dynamic Routing Versus Static Routing Dynamic Routing Static Routing Increases with the network size Administrator intervention required Configuration Complexity Generally independent of the network size Topology Changes Scaling Security Resource Usage Predictability Automatically adapts to topology changes Suitable for simple and complex Suitable for simple topologies topologies Less secure Uses CPU.1. Routing to and from stub networks. Q Q Figure 2-3 shows an example of a stub network connection and a default route connection.1. Using a single default route to represent a path to any network that does not have a more specific match with another route in the routing table.

1.1) Static routes are most often used to connect to a specific network or to provide a Gateway of Last Resort for a stub network. whether to networks attached to R2. a default static route can be configured on R1 to point to R2 as the next hop for all other networks. Figure 2-3 Stub Networks and Stub Routers In this example.16.4: Identify the Advantages and Disadvantages of Static Routing Interactive Graphic Go to the online course to perform this practice activity. Activity 2. This means that network 172.2.1.1. Static Route Applications (2. They can also be used to: Q Reduce the number of routes advertised by summarizing several contiguous networks as one static route Create a backup route in case a primary route link fails Q The following types of IPv4 and IPv6 static routes will be discussed: Q Q Standard static route Default static route . because R1 has only one way to send out non-local traffic. or to destinations beyond R2.0 is a stub network and R1 is a stub router. a static route can be configured on R2 to reach the R1 LAN. Running a routing protocol between R2 and R1 is a waste of resources. Additionally.3.78 Routing Protocols Companion Guide way to reach other destinations.

16.0. A default static route is simply a static route with 0.0/0 as the destination IPv4 address.2.3) A default static route is a route that matches all packets. . a static route can be used to connect to any network.Chapter 2: Static Routing 79 Q Q Summary static route Floating static route Standard Static Route (2. but in fact.1. Note The example is highlighting a stub network. A default route identifies the gateway IP address to which the router sends all IP packets that it does not have a learned or static route for. Static routes are useful when connecting to a specific remote network.3.1.0.2) Both IPv4 and IPv6 support the configuration of static routes.2. Figure 2-4 shows that R2 can be configured with a static route to reach the stub network 172. Figure 2-4 Connecting to a Stub Network Default Static Route (2.0/24. Configuring a default static route creates a Gateway of Last Resort.

20. Default static routes are used: Q When no other routes in the routing table match the packet destination IP address. A common use is when connecting a company’s edge router to the ISP network. Q In Figure 2-6.0/16 networks. This condition is known as a stub router.2.0.80 Routing Protocols Companion Guide Note All routes that identify a specific destination with a larger subnet mask take precedence over the default route.23.4) To reduce the number of routing table entries. The multiple static routes all use the same exit interface or next-hop IP address. When a router has only one other router to which it is connected. Q Refer to Figure 2-5 for a sample scenario of implementing default static routing. In other words.0. . multiple static routes can be summarized into a single summary static route if: Q The destination networks are contiguous and can be summarized into a single network address. Figure 2-5 Connecting to a Stub Router Summary Static Route (2.1. R1 would require four separate static routes to reach the 172. Instead. one summary static route can be configured and still provide connectivity to those networks.0/16 to 172. when a more specific match does not exist.

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Figure 2-6 Using One Summary Static Route

Floating Static Route (2.1.2.5)
Another type of static route is a floating static route. Floating static routes are static routes that are used to provide a backup path to a primary static or dynamic route, in the event of a link failure. The floating static route is only used when the primary route is not available. To accomplish this, the floating static route is configured with a higher administrative distance than the primary route. Recall that the administrative distance represents the trustworthiness of a route. If multiple paths to the destination exist, the router will choose the path with the lowest administrative distance. For example, assume that an administrator wants to create a floating static route as a backup to an EIGRP-learned route. The floating static route must be configured with a higher administrative distance than EIGRP. EIGRP has an administrative distance of 90. If the floating static route is configured with an administrative distance of 95, the dynamic route learned through EIGRP is preferred to the floating static route. If the EIGRP-learned route is lost, the floating static route is used in its place. In Figure 2-7, the Branch router typically forwards all traffic to the HQ router over the private WAN link. In this example, the routers exchange route information using EIGRP. A floating static route, with an administrative distance of 91 or higher, could be configured to serve as a backup route. If the private WAN link fails and the EIGRP route disappears from the routing table, the router selects the floating static route as the best path to reach the HQ LAN.
Activity 2.1.2.6: Identify the Type of Static Route

Interactive Graphic

Go to the online course to perform this practice activity.

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Figure 2-7 Configuring a Backup Route

Configure Static and Default Routes (2.2)
Recall that a router can learn about remote networks in one of two ways:
Q Q

Manually, from configured static routes Automatically, from a dynamic routing protocol

This chapter focuses on configuring static routes. Dynamic routing protocols are introduced in the next chapter. Even with the implementation of a dynamic routing protocol, static routes are also commonly used.

Configure IPv4 Static Routes (2.2.1)
Routers can be configured for both IPv4 and IPv6 static routes. This section will focus on the configuration of IPv4 static routes. IPv4 static routes are manually configured routing entries for reaching IPv4 networks. The configuration of IPv6 static routes is covered later in this chapter.

ip route Command (2.2.1.1)
Static routes are configured using the ip route global configuration command. The syntax of the command is:
Router(config)# ip route network-address subnet-mask { ip-address | interface-type interface-number [ ip-address ]} [ distance ] [ name name ] [ permanent ] [ tag tag ]

Chapter 2: Static Routing 83

The following parameters are required to configure static routing:
Q

network-address: Destination network address of the remote network to be added to the routing table; often this is referred to as the prefix. subnet-mask: Subnet mask, or just mask, of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks.

Q

One or both of the following parameters must also be used:
Q

ip-address: The IP address of the connecting router to use to forward the packet to the remote destination network. Commonly referred to as the next hop. interface-type interface-number or exit-intf: The outgoing interface to use to forward the packet to the next hop.

Q

As shown in Table 2-2, the command syntax commonly used is ip route networkaddress subnet-mask {ip-address | exit-intf}. The distance parameter is used to create a floating static route by setting an administrative distance that is higher than a dynamically learned route.
Table 2-2 Parameter network-address subnet-mask iproute Command Syntax Description Destination network address of the remote network to be added to the routing table.
Q Q

Subnet mask of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks. Commonly referred to as the next-hop router’s IP address. Typically used when connecting to a broadcast media (i.e., Ethernet). Commonly creates a recursive lookup. Use the outgoing interface to forward packets to the destination network. Also referred to as a directly attached static route. Typically used when connecting in a point-to-point configuration.

ip-address

Q Q Q

exit-intf

Q

Q Q

Note The remaining parameters are not relevant for this chapter or for CCNA studies.

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Next-Hop Options (2.2.1.2)
Figure 2-8 and the subsequent outputs display the topology and the routing tables of R1, R2, and R3. Notice that each router has entries only for directly connected networks and their associated local addresses. None of the routers have any knowledge of any networks beyond their directly connected interfaces.

Figure 2-8 Verify the Routing Table of R1, R2, R3
R1# show ip route | begin Gateway Gateway of last resort is not set 172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks C L C L R1# R2# show ip route | begin Gateway Gateway of last resort is not set 172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks C L C L 172.16.1.0/24 is directly connected, GigabitEthernet0/0 172.16.1.1/32 is directly connected, GigabitEthernet0/0 172.16.2.0/24 is directly connected, Serial0/0/0 172.16.2.2/32 is directly connected, Serial0/0/0 192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks C L R2# R3# show ip route | include C Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP C C R3# 192.168.1.0/24 is directly connected, Serial0/0/1 192.168.2.0/24 is directly connected, GigabitEthernet0/0 192.168.1.0/24 is directly connected, Serial0/0/1 192.168.1.2/32 is directly connected, Serial0/0/1 172.16.2.0/24 is directly connected, Serial0/0/0 172.16.2.1/32 is directly connected, Serial0/0/0 172.16.3.0/24 is directly connected, GigabitEthernet0/0 172.16.3.1/32 is directly connected, GigabitEthernet0/0

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For example, R1 has no knowledge of networks:
Q Q Q

172.16.1.0/24: LAN on R2 192.168.1.0/24: Serial network between R2 and R3 192.168.2.0/24: LAN on R3

Figure 2-9 displays a successful ping from R1 to R2. Figure 2-10 displays an unsuccessful ping to the R3 LAN. This is unsuccessful because R1 does not have an entry in its routing table for the R3 LAN network.

Figure 2-9 Verify Connectivity from R1 to R2

Figure 2-10 Verify Connectivity from R1 to R3 LAN

The next hop can be identified by an IP address, exit interface, or both. How the destination is specified creates one of the three following route types:
Q Q Q

Next-hop route: Only the next-hop IP address is specified. Directly connected static route: Only the router exit interface is specified. Fully specified static route: The next-hop IP address and exit interface are specified.

Configure a Next-Hop Static Route (2.2.1.3)
In a next-hop static route, only the next-hop IP address is specified. The output interface is derived from the next hop. For example, in Figure 2-11, three next-hop static routes are configured on R1 using the IP address of the next hop, R2.

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Figure 2-11 Configuring Next-Hop Static Routes on R1

Before any packet is forwarded by a router, the routing table process must determine the exit interface to use to forward the packet. This is known as route resolvability. The route resolvability process will vary depending upon the type of forwarding mechanism being used by the router. CEF (Cisco Express Forwarding) is the default behavior on most platforms running IOS 12.0 or later. Figure 2-12 details the basic packet forwarding process in the routing table for R1 without the use of CEF. When a packet is destined for the 192.168.2.0/24 network, R1: 1. Looks for a match in the routing table and finds that it has to forward the packets to the next-hop IPv4 address 172.16.2.2, as indicated by the label 1 in Figure 2-12. Every route that references only a next-hop IPv4 address and does not reference an exit interface must have the next-hop IPv4 address resolved using another route in the routing table with an exit interface. 2. R1 must now determine how to reach 172.16.2.2; therefore, it searches a second time for a 172.16.2.2 match. In this case, the IPv4 address matches the route for the directly connected network 172.16.2.0/24 with the exit interface Serial 0/0/0, as indicated by the label 2 in Figure 2-12. This lookup tells the routing table process that this packet is forwarded out of that interface. It actually takes two routing table lookup processes to forward any packet to the 192.168.2.0/24 network. When the router performs multiple lookups in the routing table before forwarding a packet, it is performing a process known as a recursive lookup. Because recursive lookups consume router resources, they should be avoided when possible.

R1 looks for a match in the routing table. a static route using a next-hop IP address requires only a single lookup when CEF is enabled on the router. . CEF eliminates the need for recursive lookup for next-hop IP address lookups.4) When configuring a static route. three directly connected static routes are configured on R1 using the exit interface. either directly or indirectly. By combining the information from these two tables. and an adjacency table that includes Layer 2 addressing information. In Figure 2-13. The routing table for R1 in Figure 2-14 shows that when a packet is destined for the 192. Configure a Directly Connected Static Route (2.2. In other words. to a valid exit interface. another option is to use the exit interface to specify the next-hop address. prior to CEF. Note CEF provides optimized lookup for efficient packet forwarding by using two main data structures stored in the data plane: an FIB (Forwarding Information Base). which is a copy of the routing table. In older IOS versions.168. this method is used to avoid the recursive lookup problem. it is a candidate for insertion in the routing table) only when the specified next hop resolves.Chapter 2: Static Routing 87 Figure 2-12 Verify the Routing Table of R1 A recursive static route is valid (that is.0/24 network.1.2.

Figure 2-13 Configure Directly Connected Static Routes on R1 Figure 2-14 Verify the Routing Table of R1 .88 Routing Protocols Companion Guide and finds that it can forward the packet out of its Serial 0/0/0 interface. No other lookups are required.

prior to CEF.0/24 networks using the exit interface S0/0/1.4 Part 2: Configure Directly Connected Static Routes on R3 Go to the online course to use the Syntax Checker in the fourth graphic to configure static routes to the 172. instead of two searches. Only a directly connected interface can have an administrative distance of 0.0/24 network using exit interface S0/0/0. Interactive Graphic Activity 2.255.0 GigabitEthernet 0/1 . Interactive Graphic Activity 2.5) In a fully specified static route. CEF is not enabled.0/24.16.1.16.168.3. Configure a Fully Specified Static Route (2.1.2. and 172. Suppose that the network link between R1 and R2 is an Ethernet link and that the GigabitEthernet 0/1 interface of R1 is connected to that network. Although the routing table entry indicates “directly connected.1. For multipoint/broadcast interfaces.” the administrative distance of the static route is still 1. 172.Chapter 2: Static Routing 89 Notice how the routing table looks different for the route configured with an exit interface than the route configured with a recursive entry. a directly connected static route can be implemented using the following command: R1(config)# ip route 192. the use of the default CEF forwarding mechanism makes this practice unnecessary.16. it is more suitable to use static routes that point to a next-hop address. The next hop must be directly connected to the specified exit interface.16. Configuring a directly connected static route with an exit interface allows the routing table to resolve the exit interface in a single search.2. both the output interface and the next-hop IP address are specified. This form of static route is used when the output interface is a multi-access interface and it is necessary to explicitly identify the next hop. Although static routes that use only an exit interface on point-to-point networks are common. This is another type of static route that is used in older IOS versions.2. To eliminate the recursive lookup.1. as shown in Figure 2-15.0 255.3. Note For point-to-point interfaces.0/24.2. you can use static routes that point to the exit interface or to the next-hop address.4 Part 1: Configure Directly Connected Static Routes on R2 Go to the online course to use the Syntax Checker in the third graphic to configure a static route to the 172.2.255.

including hosts and even multiple routers. As shown in Figure 2-16. this may cause unexpected or inconsistent results.2. . Depending upon the topology and the configurations on other routers. the router will not have sufficient information to determine which device is the next-hop device. Note With the use of CEF. By only designating the Ethernet exit interface in the static route. the router at the other end of the link. this static route may or may not work. there may be many different devices sharing the same multi-access network. It is recommended that when the exit interface is an Ethernet network. A static route using a next-hop address should be used. R1 does not know the next-hop IPv4 address and therefore it cannot determine the destination MAC address for the Ethernet frame. However. when forwarding packets to R2. a fully specified static route is no longer necessary. a fully specified static route is used including both the exit interface and the next-hop address.2.16. the exit interface is GigabitEthernet 0/1 and the next-hop IPv4 address is 172.90 Routing Protocols Companion Guide Figure 2-15 Configure Fully Specified Static Routes on R1 However. With Ethernet networks. The difference between an Ethernet multi-access network and a point-to-point serial network is that a pointto-point network has only one other device on that network. R1 knows that the packet needs to be encapsulated in an Ethernet frame and sent out the GigabitEthernet 0/1 interface.

2.1.0/24.5 Part 2: Configure Fully Specified Static Routes on R3 Go to the online course to use the Syntax Checker in the fourth graphic to configure a static route to the 172.3.16.5 Part 1: Configure Fully Specified Static Routes on R2 Interactive Graphic Go to the online course to use the Syntax Checker in the third graphic to configure a static route to the 172.2. Verify a Static Route (2.16.1. useful commands to verify static routes include: Q Q Q show ip route show ip route static show ip route network .1.1. 172. and 172.1.2.0/24.2.0/24 networks using the exit interface S0/0/1 and next-hop address 192.0/24 network using the exit interface/next-hop pair: G0/1 172.16.1.168. Interactive Graphic Activity 2.Chapter 2: Static Routing 91 Figure 2-16 Verify the Routing Table of R1 Activity 2.2.16.3.2.16.6) Along with ping and traceroute.

1 Routing entry for 192.0 ip route 192.168.168.168.0 R1# 255. the output is filtered using the pipe and begin parameter.255.16.16. Figure 2-17 Verify the Routing Table of R1 The following displays sample output of the show ip route 192.2 172.2 . In the example.2 Route metric is 0. distance 1.255. The output reflects the use of static routes using the next-hop address.0 172.1.2.255. metric 0 Routing Descriptor Blocks: *172.168.1 command: R1# show ip route 192.16.0/24 Known via "static".255.2.168.92 Routing Protocols Companion Guide Figure 2-17 displays sample output of the show ip route static command.16.2.2.2 172.2.2.255.2.0 255.0 ip route 192.16.0 255. traffic share count is 1 R1# The following output verifies the ip route configuration in the running configuration with the output filtered using the pipe and section parameter: R1# show running-config | section ip route ip route 172.2.1.255.

Chapter 2: Static Routing 93 Interactive Graphic Activity 2. Rather than storing all routes to all networks in the routing table. A default route is used when no other routes in the routing table match the destination IP address of the packet.0.1. The basic command syntax of a default static route is: Q ip route 0.2. Default Static Route (2.0.6 Part 2: Verify the Static Routing Settings on R3 Go to the online course to use the Syntax Checker in the third graphic to display only the static routes in the routing table of R3.1) A default route is a static route that matches all packets.0.6 Part 1: Verify the Static Routing Settings on R2 Go to the online course to use the Syntax Checker in the third graphic to display only the static routes in the routing table of R2. then the default route is used as the Gateway of Last Resort.0. Routers commonly use default routes that are either configured locally or learned from another router.0. In other words. . if a more specific match does not exist.0. the command syntax for a default static route is similar to any other static route. using a dynamic routing protocol.0 { ip-address | exit-intf } Note An IPv4 default static route is commonly referred to as a quad-zero route.0 and the subnet mask is 0.2. Default static routes are commonly used when connecting: Q Q An edge router to a service provider network A stub router (a router with only one upstream neighbor router) As shown in Table 2-3.2. except that the network address is 0.0 0.2.0.2. a default route entry can be used to forward packets to another router.0. Interactive Graphic Activity 2.0. a router can store a single default route to represent any network that is not in the routing table. Configure IPv4 Default Routes (2.1.2) If a router does not have a route entry in its routing table for a destination network. The use of a static default route is common with dynamic routing protocols and will be discussed in later chapters.

0. Q Q Commonly referred to as the next-hop router’s IP address.e. any packets not matching more specific route entries are forwarded to 172. However. With the configuration shown in the example.94 Routing Protocols Companion Guide Table 2-3 Parameter 0. As displayed in the ..0.2.0 ip-address Default Static Route Syntax Description Matches any network address.2. Therefore.2.0.2. the show ip route static command output displays the contents of the routing table. it would be more efficient to configure a default static route. Matches any subnet mask.0. Typically used when connecting to a broadcast media (i. Ethernet). Note the asterisk (*) next to the route with code ‘S’. R1 is a stub router because it is only connected to R2.0 0. Also referred to as a directly attached static route. exit-intf Q Q Configure a Default Static Route (2.3) In Figure 2-19. Use the outgoing interface to forward packets to the destination network.2) R1 can be configured with three static routes to reach all of the remote networks in the example topology. The example in Figure 2-18 configures a default static route on R1.16.2. Figure 2-18 Configuring a Default Static Route Verify a Default Static Route (2.2.

A /0 mask in this route entry indicates that none of the bits are required to match. Recall that the subnet mask in a routing table determines how many bits must match between the destination IP address of the packet and the route in the routing table. There are four different static routes that are used in this activity: a recursive static route. a fully specified static route. Figure 2-19 Verifying the Routing Table of R1 The key to this configuration is the /0 mask. the asterisk indicates that this static route is a candidate default route. a directly connected static route. A static route is a route that is entered manually by the network administrator to create a route that is reliable and safe. and a default route. Packet Tracer Activity 2.2. which is why it is selected as the Gateway of Last Resort. A binary 0 indicates that the bits do not have to match. . you will configure static and default routes. The default static route matches all packets for which a more specific match does not exist.2.Chapter 2: Static Routing 95 Codes table in Figure 2-19.4: Configuring IPv4 Static and Default Routes Packet Tracer Activity In this activity. A binary 1 indicates that the bits must match.

3) This section focuses on the configuration of IPv6 static routes.1) Static routes for IPv6 are configured using the ipv6 route global configuration command.5: Configuring IPv4 Static and Default Routes In this lab.2. IPv4 static routes are manually configured routes for reaching IPv4 networks. IPv6 static routes are similar to IPv4 static routes. Use the outgoing interface to forward packets to the destination network. IPv6 static routes can also be implemented as: Q Q Standard IPv6 static route Default IPv6 static route . The ipv6 route Command (2.e. Q Q prefix-length ipv6-address Commonly referred to as the next-hop router’s IP address.. Typically used when connecting in a point-to-point configuration. Also referred to as a directly attached static route.2. exit-intf Q Q Q Most of the parameters are identical to the IPv4 version of the command.2.2.3. Prefix length of the remote network to be added to the routing table. Typically used when connecting to a broadcast media (i.96 Routing Protocols Companion Guide Lab 2. Ethernet). whereas IPv6 static routes are configured for reaching IPv6 networks. you will complete the following objectives: Q Q Q Q Part 1: Set Up the Topology and Initialize Devices Part 2: Configure Basic Device Settings and Verify Connectivity Part 3: Configure Static Routes Part 4: Configure and Verify a Default Route Configure IPv6 Static Routes (2. Table 2-4 shows the simplified version of the command syntax: Router(config)# ipv6 route ipv6-prefix/prefix-length { ipv6-address | exit-intf } Table 2-4 Parameter ipv6-prefix IPv6 Command Syntax Description Destination network address of the remote network to be added to the routing table.

.Chapter 2: Static Routing 97 Q Q Summary IPv6 static route Floating IPv6 static route As with IPv4. or fully specified. these routes can be configured as recursive. directly connected.3.2. and R3.3. Next-Hop Options (2. Figure 2-20 displays the enabling of IPv6 unicast routing. Each router has entries only for directly connected networks and their associated local addresses.1 Part 1: Enabling IPv6 Unicast Routing on R2 Interactive Graphic Go to the online course to use the Syntax Checker in the third graphic to enable IPv6 unicast routing on R2. Interactive Graphic Activity 2.3. The ipv6 unicast-routing global configuration command must be configured to enable the router to forward IPv6 packets. R2.1 Part 2: Enabling IPv6 Unicast Routing on R3 Go to the online course to use the Syntax Checker in the third graphic to enable IPv6 unicast routing on R3. Figure 2-20 Enabling IPv6 Unicast Routing Activity 2.2) The following example displays the routing tables of R1.2.2.

receive C 2001:DB8:ACAD:5::/64 [0/0] via Serial0/0/1. receive R2# R3# show ipv6 route <output omitted> C 2001:DB8:ACAD:3::/64 [0/0] via GigabitEthernet0/0. receive R3# . R1# show ipv6 route <output omitted> C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0. directly connected L 2001:DB8:ACAD:4::1/128 [0/0] via Serial0/0/0. directly connected L 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/0. directly connected L 2001:DB8:ACAD:4::2/128 [0/0] via Serial0/0/0. receive C 2001:DB8:ACAD:4::/64 [0/0] via Serial0/0/0. receive L FF00::/8 [0/0] via Null0. receive C 2001:DB8:ACAD:5::/64 [0/0] via Serial0/0/1. directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0. receive R1# R2# show ipv6 route <output omitted> C 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/0. directly connected L 2001:DB8:ACAD:5::1/128 [0/0] via Serial0/0/1.98 Routing Protocols Companion Guide None of the routers have any knowledge of any networks beyond their directly connected interfaces. receive L FF00::/8 [0/0] via Null0. directly connected L 2001:DB8:ACAD:5::2/128 [0/0] via Serial0/0/1. receive L FF00::/8 [0/0] via Null0. receive C 2001:DB8:ACAD:4::/64 [0/0] via Serial0/0/0. directly connected L 2001:DB8:ACAD:3::1/128 [0/0] via GigabitEthernet0/0.

This is unsuccessful because R1 does not have an entry in its routing table for that network. 100-byte ICMP Echos to 2001:DB8:ACAD:3::1.Chapter 2: Static Routing 99 For example. Figure 2-21 Verify Connectivity from R1 to R2 R1# ping ipv6 2001:DB8:ACAD:3::1 Type escape sequence to abort. Sending 5. R1 has no knowledge of networks: Q Q Q 2001:DB8:ACAD:2::/64: LAN on R2 2001:DB8:ACAD:5::/64: Serial network between R2 and R3 2001:DB8:ACAD:3::/64: LAN on R3 Figure 2-21 displays a successful ping from R1 to R2. timeout is 2 seconds: % No valid route for destination Success rate is 0 percent (0/1) R1# . And the subsequent output shows an unsuccessful ping to the R3 LAN.

When a packet is destined for the 2001:DB8:ACAD:3::/64 network. How the destination is specified creates one of three route types: Q Q Q Next-hop static IPv6 route: Only the next-hop IPv6 address is specified. CEF is the default behavior on most platforms running IOS 12. before any packet is forwarded by the router. Every route that references . in Figure 2-22. For instance. exit interface. Figure 2-23 details the basic packet forwarding route resolvability process in the routing table for R1 without the use of CEF.3) In a next-hop static route. Looks for a match in the routing table and finds that it has to forward the packets to the next-hop IPv6 address 2001:DB8:ACAD:4::2.3. Directly connected static IPv6 route: Only the router exit interface is specified. only the next-hop IPv6 address is specified. the routing table process must resolve the route to determine the exit interface to use to forward the packet. The route resolvability process will vary depending upon the type of forwarding mechanism being used by the router.100 Routing Protocols Companion Guide The next hop can be identified by an IPv6 address. Figure 2-22 Configure Next-Hop Static IPv6 Routes As with IPv4. Configure a Next-Hop Static IPv6 Route (2.2. The output interface is derived from the next hop. R1: 1.0 or later. three next-hop static routes are configured on R1. or both. Fully specified static IPv6 route: The next-hop IPv6 address and exit interface are specified.

it is a candidate for insertion in the routing table) only when the specified next hop resolves. it is performing a process known as a recursive lookup.3 Part 1: Configure Next-Hop Static IPv6 Routing on R2 Interactive Graphic Go to the online course to use the Syntax Checker in the third graphic to configure an IPv6 route to network 2001:DB8:ACAD:1::/64 using the next-hop address 2001:DB8:ACAD:4::1. Activity 2. This lookup tells the routing table process that this packet is forwarded out of that interface. In this case. . it searches a second time looking for a match. 2. A recursive static IPv6 route is valid (that is.3. When the router has to perform multiple lookups in the routing table before forwarding a packet. either directly or indirectly. R1 must now determine how to reach 2001:DB8:ACAD:4::2. to a valid exit interface. therefore. the IPv6 address matches the route for the directly connected network 2001:DB8:ACAD:4::/64 with the exit interface Serial 0/0/0. it actually takes two routing table lookup processes to forward any packet to the 2001:DB8:ACAD:3::/64 network.Chapter 2: Static Routing 101 only a next-hop IPv6 address and does not reference an exit interface must have the next-hop IPv6 address resolved using another route in the routing table with an exit interface.2. Figure 2-23 Verifying an IPv6 Next-Hop Lookup Therefore.

Configure a Directly Connected Static IPv6 Route (2.2. R1 looks for a match in the routing table and finds that it can forward the packet out of its Serial 0/0/0 interface.2.3. No other lookups are required. three directly connected static routes are configured on R1 using the exit interface. . to avoid the recursive lookup problem. and 2001:DB8:ACAD:4::/64 using the next-hop address 2001:DB8:ACAD:5::2.102 Routing Protocols Companion Guide Interactive Graphic Activity 2. Figure 2-24 Configure Directly Connected Static IPv6 Routes on R1 The IPv6 routing table for R1 in the following output shows that when a packet is destined for the 2001:DB8:ACAD:3::/64 network. For instance. This is an alternative used in older IOS versions or whenever CEF is disabled.3 Part 2: Configure Next-Hop Static IPv6 Routing on R3 Go to the online course to use the Syntax Checker in the fourth graphic to configure an IPv6 route to networks 2001:DB8:ACAD:1::/64. 2001:DB8:ACAD:2::/64.4) When configuring a static route on point-to-point networks. in Figure 2-24.3. an alternative to using the next-hop IPv6 address is to specify the exit interface.

ND Default. receive S 2001:DB8:ACAD:5::/64 [1/0] via Serial0/0/0.Destination.ISIS L2 IA . DCE . I2 . and 2001:DB8:ACAD:4::/64 networks using exit interface S0/0/1.Connected. IS .8 entries Codes: C . I1 .EIGRP external ND .ND Prefix. directly connected L 2001:DB8:ACAD:4::1/128 [0/0] via Serial0/0/0. NDr .BGP. OE1 . Recall that with the use of the CEF forwarding mechanism. 2001:DB8:ACAD:2::/64. directly connected C 2001:DB8:ACAD:4::/64 [0/0] via Serial0/0/0. R .ISIS L1. OI . D . Interactive Graphic Activity 2.2. OE2 . U . . receive R1# Notice how the routing table looks different for the route configured with an exit interface than the route configured with a recursive entry.3.OSPF ext 2 ON1 .OSPF ext 1.OSPF NSSA ext 1.OSPF Inter.ISIS summary.OSPF Intra. EX .OSPF NSSA ext 2 C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0.Per-user Static route B .Local. Activity 2. NDp .RIP.Chapter 2: Static Routing 103 R1# show ipv6 route IPv6 Routing Table . receive S 2001:DB8:ACAD:2::/64 [1/0] via Serial0/0/0. static routes with an exit interface are considered unnecessary. S .ISIS interarea. Configuring a directly connected static route with an exit interface allows the routing table to resolve the exit interface in a single search instead of two searches.3.2.Redirect O . directly connected S 2001:DB8:ACAD:3::/64 [1/0] via Serial0/0/0.Static. ON2 .default . A single lookup is performed using a combination of the FIB and adjacency table stored in the data plane.4 Part 1: Configure Directly Connected Static IPv6 Routes on R2 Interactive Graphic Go to the online course to use the Syntax Checker in the third graphic to configure an IPv6 route to network 2001:DB8:ACAD:1::/64 using exit interface S0/0/0. directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0.4 Part 2: Configure Directly Connected Static IPv6 Routes on R3 Go to the online course to use the Syntax Checker in the fourth graphic to configure an IPv6 route to the 2001:DB8:ACAD:1::/64.EIGRP. L . directly connected L FF00::/8 [0/0] via Null0.

this would be used if CEF were not enabled on the router and the exit interface was on a multi-access network. The next-hop link-local address may be a valid address on multiple networks connected to the router. Unlike IPv4. a static route using only a next-hop IPv6 address would be the preferred method even when the exit interface is a multi-access network. With CEF. Therefore.5) In a fully specified static route. a fully specified static route is configured using R2’s link-local address as the next-hop address. there is a situation in IPv6 when a fully specified static route must be used. Notice that IOS requires that an exit interface be specified. Notice that both the next-hop link-local address and the exit interface are included. Similar to fully specified static routes used with IPv4. If the IPv6 static route uses an IPv6 link-local address as the next-hop address. Serial0/0/0 . R1# show ipv6 route static S being 2001:DB8:ACAD:2::/64 2001:DB8:ACAD:2::/64 (1/0) via FE80::2.104 Routing Protocols Companion Guide Configure a Fully Specified Static IPv6 Route (2. Figure 2-25 shows an example of a fully qualified IPv6 static route using an IPv6 link-local address as the next-hop address. Figure 2-25 Configure a Fully Specified Static IPv6 Route on R1 The following output shows the IPv6 routing table entry for this route.2. both the output interface and the next-hop IPv6 address are specified. a fully specified static route including the exit interface must be used. Link-local addresses are only unique on a given link or network. In Figure 2-25. it is necessary that the exit interface be included. The reason a fully specified static route must be used is because IPv6 link-local addresses are not contained in the IPv6 routing table.3.

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Interactive Graphic

Activity 2.2.3.5: Configure a Fully Specified IPv6 Route on R2

Go to the online course to use the Syntax Checker in the third graphic to configure a fully specified static IPv6 route to the R1 LAN using the R1 link-local address as the next-hop address.

Verify IPv6 Static Routes (2.2.3.6)
Along with ping and traceroute, useful commands to verify static routes include:
Q Q Q

show ipv6 route show ipv6 route static ipv6 route network

The following displays sample output of the show ipv6 route static command. The output reflects the use of static routes using next-hop global unicast addresses.
R1# show ipv6 route static IPv6 Routing Table - default - 8 entries Codes: C - Connected, L - Local, S - Static, U - Per-user Static route B - BGP, R - RIP, I1 - ISIS L1, I2 - ISIS L2 IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2 ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2 S 2001:DB8:ACAD:2::/64 [1/0] via 2001:DB8:ACAD:4::2, Serial0/0/0 S 2001:DB8:ACAD:3::/64 [1/0] via 2001:DB8:ACAD:4::2, Serial0/0/0 S 2001:DB8:ACAD:5::/64 [1/0] via 2001:DB8:ACAD:4::2, Serial0/0/0 R1#

The following output displays sample output from the show ip route 2001:DB8:ACAD:3::1 command:
R1# show ipv6 route 2001:0DB8:ACAD:3::1 Routing entry for 2001:DB8:ACAD:3::/64 Known via "static", distance 1, metric 0 Route count is 1/1, share count 0 Routing paths: 2001:DB8:ACAD:4::2, Serial0/0/0 Last updated 00:19:11 ago R1#

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The following output verifies the ipv6 route configuration in the running configuration with the output filtered using the pipe and section parameter:
R1# show running-config | section ipv6 route ipv6 route 2001:DB8:ACAD:2::/64 Serial0/0/0 2001:DB8:ACAD:4::2 ipv6 route 2001:DB8:ACAD:3::/64 Serial0/0/0 2001:DB8:ACAD:4::2 ipv6 route 2001:DB8:ACAD:5::/64 Serial0/0/0 2001:DB8:ACAD:4::2 R1#

Configure IPv6 Default Routes (2.2.4)
Similar to IPv4, an IPv6 default route entry can be used to forward packets to another router when there is not a specific IPv6 route in the IPv6 routing table.

Default Static IPv6 Route (2.2.4.1)
A default route is a static route that matches all packets. Instead of routers storing routes for all of the networks in the Internet, they can store a single default route to represent any network that is not in the routing table. Routers commonly use default routes that are either configured locally or learned from another router, using a dynamic routing protocol. They are used when no other routes match the packet’s destination IP address in the routing table. In other words, if a more specific match does not exist, then use the default route as the Gateway of Last Resort. Default static routes are commonly used when connecting:
Q Q

A company’s edge router to a service provider network. A router with only an upstream neighbor router. The router has no other neighbors and is, therefore, referred to as a stub router.

As shown in Table 2-5, the command syntax for a default static route is similar to any other static route, except that the ipv6-prefix/prefix-length is ::/0, which matches all routes. The basic command syntax of a default static route is:
Q

ipv6 route ::/0 { ipv6-address | exit-intf }

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Table 2-5 Parameter ::/0

Default Static IPv6 Route Syntax Description Matches any IPv6 prefix regardless of prefix length.
Q Q

ipv6-address

Commonly referred to as the next-hop router’s IP address. Typically used when connecting to a broadcast media (i.e., Ethernet). Use the outgoing interface to forward packets to the destination network. Also referred to as a directly attached static route.

exit-intf

Q Q

Configure a Default Static IPv6 Route (2.2.4.2)
R1 can be configured with three static routes to reach all of the remote networks in our topology. However, R1 is a stub router because it is only connected to R2. Therefore, it would be more efficient to configure a default static IPv6 route. The example in Figure 2-26 displays a configuration for a default static IPv6 route on R1.

Figure 2-26 Default Static IPv6 Route Syntax

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Verify a Default Static Route (2.2.4.3)
In the following output, the show ipv6 route static command output displays the contents of the routing table:
R1# show ipv6 route static IPv6 Routing Table - default - 6 entries Codes: C - Connected, L - Local, S - Static, U - Per-user Static route B - BGP, R - RIP, I1 - ISIS L1, I2 - ISIS L2 IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2 ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2 S ::/0 [1/0] via 2001:DB8:ACAD:4::2, Serial0/0/0 R1#

Unlike IPv4, IPv6 does not explicitly state that the default IPv6 is the Gateway of Last Resort. The key to this configuration is the ::/0 mask. Recall that the ipv6 prefix-length in a routing table determines how many bits must match between the destination IP address of the packet and the route in the routing table. The ::/0 mask indicates that none of the bits are required to match. As long as a more specific match does not exist, the default static IPv6 route matches all packets. The following output displays a successful ping to the R3 LAN interface:
R1# ping 2001:0DB8:ACAD:3::1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2001:DB8:ACAD:3::1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 28/28/28 ms R1#

Packet Tracer Activity

Packet Tracer Activity 2.2.4.4: Configuring IPv6 Static and Default Routes

In this activity, you will configure IPv6 static and default routes. A static route is a route that is entered manually by the network administrator to create a route that is reliable and safe. There are four different static routes used in this activity: a recursive static route; a directly connected static route; a fully specified static route; and a default route.

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Lab 2.2.4.5: Configuring IPv6 Static and Default Routes

In this lab, you will complete the following objectives:
Q Q

Part 1: Build the Network and Configure Basic Device Settings Part 2: Configure IPv6 Static and Default Routes

Review of CIDR and VLSM (2.3)
Recall that VLSM (variable-length subnet mask) subnetting is similar to the traditional subnetting. The difference is that with VLSM, the network is first subnetted, and then subnets are subnetted again. This can occur in several iterations. CIDR (Classless Inter-Domain Routing) was introduced by IETF in 1993 to replace class network assignments. VLSM and CIDR helped make the allocation of the limited IPv4 address space more efficient.

Classful Addressing (2.3.1)
Although CIDR and classless addressing obsoleted classful addressing, an understanding of classful addressing is still important. Routing protocols such as RIP and EIGRP can both be configured to summarize on classful network boundaries. The IPv4 routing table is also structured in a classful hierarchy.

Classful Network Addressing (2.3.1.1)
Released in 1981, RFC 790 and RFC 791 describe how IPv4 network addresses were initially allocated based on a classification system. In the original specification of IPv4, the authors established the classes to provide three different sizes of networks for large, medium, and small organizations. As a result, class A, B, and C addresses were defined with a specific format for the high order bits. High order bits are the far left bits in a 32-bit address. As shown in Table 2-6:
Q

Class A addresses begin with 0: Intended for large organizations; includes all addresses from 0.0.0.0 (00000000) to 127.255.255.255 (01111111). The 0.0.0.0 address is reserved for default routing and the 127.0.0.0 address is reserved for loopback testing. Class B addresses begin with 10: Intended for medium-to-large organizations; includes all addresses from 128.0.0.0 (10000000) to 191.255.255.255 (10111111). Class C addresses begin with 110: Intended for small-to-medium organizations; includes all addresses from 192.0.0.0 (11000000) to 223.255.255.255 (11011111).

Q

Q

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The remaining addresses were reserved for multicasting and future uses:
Q

Class D Multicast addresses begin with 1110: Multicast addresses are used to identify a group of hosts that are part of a multicast group. This helps reduce the amount of packet processing that is done by hosts, particularly on broadcast media (i.e., Ethernet LANs). Routing protocols such as RIPv2, EIGRP, and OSPF use designated multicast addresses (RIP = 224.0.0.9, EIGRP = 224.0.0.10, OSPF = 224.0.0.5, and 224.0.0.6). Class E Reserved IP addresses begin with 1111: These addresses were reserved for experimental and future use.
High Order Bits High Order Bits 0xxxxxxx 10xxxxxx 110xxxxx 111xxxx 1111xxxx Start 0.0.0.0 128.0.0.0 192.0.0.0 224.0.0.0 240.0.0.0 End 127.255.255.255 191.255.255.255 223.255.255.255 239.255.255.255 255.255.255.255

Q

Table 2-6 Class Class A Class B Class C

Class D (Multicast) Class E (Reserved)

Links: “Internet Protocol,” http://www.ietf.org/rfc/rfc791.txt “IPv4 Multicast Address Space Registry,” http://www.iana.org/assignments/ multicast-addresses

Classful Subnet Masks (2.3.1.2)
As specified in RFC 790, each network class has a default subnet mask associated with it. As shown in Figure 2-27, class A networks used the first octet to identify the network portion of the address. This is translated to a 255.0.0.0 classful subnet mask. Because only 7 bits were left in the first octet (remember, the first bit is always 0), this made 2 to the 7th power, or 128 networks. The actual number is 126 networks, because there are two reserved class A addresses (i.e., 0.0.0.0/8 and 127.0.0.0/8). With 24 bits in the host portion, each class A address had the potential for over 16 million individual host addresses.

With the first two bits already established as 1 and 0. class B networks used the first two octets to identify the network portion of the network address. which identifies the class. each class C network only had 8 bits in the host portion. 21 bits remained for assigning networks for over 2 million class C networks. 14 bits remained in the first two octets for assigning networks. (Recall that two addresses were reserved for the network and broadcast addresses.) Figure 2-28 Class B Networks As shown in Figure 2-29. class C networks used the first three octets to identify the network portion of the network address. With the first three bits established as 1 and 1 and 0. Because each class B network address contained 16 bits in the host portion. or 254 possible host addresses. it controlled 65. An advantage of assigning specific default subnet masks to each class is that it made routing update messages smaller. which resulted in 16.534 addresses.384 class B network addresses. Classful routing protocols do not include the subnet mask information in their updates. The receiving router applies the default mask based on the value of the first octet. But.Chapter 2: Static Routing 111 Figure 2-27 Class A Networks As shown in Figure 2-28. .

This is due to the router receiving the routing update determining the subnet mask simply by examining the value of the first octet in the network address.3. such as RIPv1.3) Using classful IP addresses meant that the subnet mask of a network address could be determined by the value of the first octet.1.0 to the routing table.16.0. or by applying its ingress interface mask for subnetted routes.1. The subnet mask was directly related to the network address. When R2 receives the update.1.1. only need to propagate the network address of known routes and do not need to include the subnet mask in the routing update. Routing protocols. Therefore. In Figure 2-30. the first three bits of the address. In the example.0 belongs to the same major classful network as the outgoing interface.112 Routing Protocols Companion Guide Figure 2-29 Class C Networks Classful Routing Protocol Example (2. it applies the receiving interface subnet mask (/24) to the update and adds 172. R1 sends an update to R2. Figure 2-30 Classful Routing Update: R1 to R2 .16. it sends an RIP update to R2 containing subnet 172. or more accurately.16. R1 knows that subnet 172.

When sending updates to R3. and the U.5% of the total address space. and each of these networks could support up to 65. Postal Service owns 56. Ridiculously. in many cases. B. General Electric owns 3. In the early days of the Internet. R2 sends an update to R3.3.Chapter 2: Static Routing 113 In Figure 2-31. 172.0/8. Up to 16.16.0.0. However. Apple Computer owns 17. each of these organizations could provide addresses for up to 16 million hosts. Very large organizations were allocated entire class A address blocks.4) The classful addressing specified in RFCs 790 and 791 resulted in a tremendous waste of address space.0/8. class C addresses were often too small for most midsize organizations. and 172.0.16. As illustrated in Figure 2-32: Q Class A had 50% of the total address space. R2 summarizes subnets 172. Only the largest organizations and governments could ever hope to use all 65.2.16.1. organizations were assigned an entire classful network address from the A.0/24.0.16.1. it applies the classful mask for a class B network.0.384 organizations could be assigned a class B network address. Q Q Q .000 addresses.S. or C class. For example.0. Class C had 12.0.0/24 into the major classful network 172. In fact.3. Because R3 does not have any subnets that belong to 172.534 hosts. only 126 organizations could be assigned a class A network address. Some companies and governmental organizations still have class A addresses. Like class A networks.16.0/8. but were limited in the total number of hosts that they could connect. which is /16. many IP addresses in the class B address space were wasted.0. Many more organizations were able to get class C networks.0/24. Class B had 25% of the total address space. Figure 2-31 Classful Routing Update: R2 to R3 Classful Addressing Waste (2. Classes D and E are used for multicasting and reserved addresses.0.0.

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Figure 2-32 Classful IP Address Allocation = Inefficient

The overall result was that the classful addressing was a very wasteful addressing scheme. A better network addressing solution had to be developed. For this reason, Classless Inter-Domain Routing (CIDR) was introduced in 1993.

CIDR (2.3.2)
To help solve the limitation of the IPv4 address space, at least for a relatively short term, CIDR replaced classful addressing to make the distribution of IPv4 addresses more efficient.

Classless Inter-Domain Routing (2.3.2.1)
Just as the Internet was growing at an exponential rate in the early 1990s, so was the size of the routing tables that were maintained by Internet routers under classful IP addressing. For this reason, the IETF introduced CIDR in RFC 1517 in 1993. CIDR replaced the classful network assignments, and address classes (A, B, and C) became obsolete. Using CIDR, the network address is no longer determined by the value of the first octet. Instead, the network portion of the address is determined by the subnet mask, also known as the network prefix, or prefix length (i.e., /8, /19, etc.). ISPs are no longer limited to a /8, /16, or /24 subnet mask. They can now more efficiently allocate address space using any prefix length, starting with /8 and larger (i.e., /8, /9, /10, etc.). Figure 2-33 shows how blocks of IP addresses can be assigned to a network based on the requirements of the customer, ranging from a few hosts to hundreds or thousands of hosts.

Chapter 2: Static Routing 115

Figure 2-33 CIDR = Efficient

CIDR also reduces the size of routing tables and manages the IPv4 address space more efficiently using:
Q

Route summarization: Also known as prefix aggregation, routes are summarized into a single route to help reduce the size of routing tables. For instance, one summary static route can replace several specific static route statements. Supernetting: Occurs when the route summarization mask is a smaller value than the default traditional classful mask.

Q

Note A supernet is always a route summary, but a route summary is not always a supernet.

Classless Inter-Domain Routing (2.3.2.2)
In Figure 2-34, notice that ISP1 has four customers, and that each customer has a variable amount of IP address space. The address space of the four customers can be summarized into one advertisement to ISP2. The 192.168.0.0/20 summarized or aggregated route includes all the networks belonging to Customers A, B, C, and D. This type of route is known as a supernet route. A supernet summarizes multiple network addresses with a mask that is smaller than the classful mask.

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Figure 2-34 Summarizing Supernet Routes

Determining the summary route and subnet mask for a group of networks can be done in the following three steps:

How To

Step 1. Step 2.

List the networks in binary format. Count the number of far left matching bits. This identifies the prefix length or subnet mask for the summarized route. Copy the matching bits and then add zero bits to the rest of the address to determine the summarized network address.

Step 3.

The summarized network address and subnet mask can now be used as the summary route for this group of networks. Summary routes can be configured by both static routes and classless routing protocols.
Note If a routing table contains both a summarized route and a more specific route, a route with a longer subnet mask (prefix length), the more specific route is always preferred.

Chapter 2: Static Routing 117

Static Routing CIDR Example (2.3.2.3)
Creating smaller routing tables makes the routing table lookup process more efficient, because there are fewer routes to search. If one static route can be used instead of multiple static routes, the size of the routing table is reduced. In many cases, a single static route can be used to represent dozens, hundreds, or even thousands of routes. Summary CIDR routes can be configured using static routes. This helps to reduce the size of routing tables. In Figure 2-35, R1 has been configured to reach the identified networks in the topology. Although acceptable, it would be more efficient to configure a summary static route.

Figure 2-35 Six Static Routes

Figure 2-36 provides a solution using CIDR summarization. The six static route entries could be reduced to a 172.16.0.0/13 entry. The example removes the six static route entries and replaces them with a summary static route.

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Figure 2-36 One Summary Static Route

Classless Routing Protocol Example (2.3.2.4)
Classful routing protocols cannot send supernet routes. This is because the receiving router automatically applies the default classful subnet mask to the network address in the routing update. If the topology in Figure 2-37 contained a classful routing protocol, then R3 would only install 172.16.0.0/16 in the routing table.

Figure 2-37 Classless Routing Update

Chapter 2: Static Routing 119

Propagating VLSM and supernet routes requires a classless routing protocol such as RIPv2, OSPF, or EIGRP. Classless routing protocols advertise network addresses with their associated subnet masks. With a classless routing protocol, R2 can summarize networks 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16, and 172.19.0.0/16, and advertise a supernet summary static route 172.16.0.0/14 to R3. R3 then installs the supernet route 172.16.0.0/14 in its routing table.
Note When a supernet route is in a routing table, for example, as a static route, a classful routing protocol does not include that route in its updates.

VLSM (2.3.3)
Along with CIDR, VLSM helped more efficiently allocate the IPv4 address space. VLSM permits network administrators to subnet one or more specific subnets, allowing for different sized subnets. With VLSM, network administrators are no longer required to create a one-size-fits-all subnet.

Fixed-Length Subnet Masking (2.3.3.1)
With fixed-length subnet masking (FLSM), the same number of addresses is allocated for each subnet. If all the subnets have the same requirements for the number of hosts, these fixed-size address blocks would be sufficient. However, most often that is not the case.
Note FLSM is also referred to as traditional subnetting.

The topology shown in Figure 2-38 requires that network address 192.168.20.0/24 be subnetted into seven subnets: one subnet for each of the four LANs (Buildings A to D), and one for each of the three WAN connections between routers.

Figure 2-38 Network Topology: Basic Subnets

there are 28 unused addresses in each of these subnets. while the Host portion highlights 5 host bits providing 30 usable host IP addresses per subnet. it results in significant waste of unused addresses. Figure 2-39 Basic Subnet Scheme Although this traditional subnetting meets the needs of the largest LAN and divides the address space into an adequate number of subnets. under the Host portion.120 Routing Protocols Companion Guide Figure 2-39 highlights how traditional subnetting can borrow 3 bits from the Host portion in the last octet to meet the subnet requirement of seven subnets. This scheme creates the needed subnets and meets the host requirement of the largest LAN. Figure 2-40 Unused Addresses on WAN Subnets . the Subnet portion highlights how borrowing 3 bits creates 8 subnets. This inefficient use of addresses is characteristic of traditional subnetting of classful networks. only two addresses are needed in each subnet for the three WAN links. this limits future growth by reducing the total number of subnets available. For example. As shown in Figure 2-40. Because each subnet has 30 usable addresses. this results in 84 unused addresses (28 × 3). For example. Further.

or using variablelength subnet masking (VLSM). The formulas to calculate the number of hosts per subnet and the number of subnets created still apply. As shown in Figure 2-42. VLSM subnetting is similar to traditional subnetting in that bits are borrowed to create subnets. Each subnet in a traditional scheme uses the same subnet mask. This process can be repeated multiple times to create subnets of various sizes. The difference is that subnetting is not a single-pass activity. and then the subnets are subnetted again. With VLSM.2) In traditional subnetting the same subnet mask is applied for all the subnets. this example is a good model for showing how subnetting a subnet can be used to maximize address utilization. As illustrated in Figure 2-41. Figure 2-41 Traditional Subnetting Creates Equal Sized Subnets With VLSM the subnet mask length varies depending on how many bits have been borrowed for a particular subnet.Chapter 2: Static Routing 121 Applying a traditional subnetting scheme to this scenario is not very efficient and is wasteful. Subnetting a subnet.3. traditional subnetting creates subnets of equal size. Variable-Length Subnet Masking (2. was designed to avoid wasting addresses. the network is first subnetted.3. thus the “variable” part of variable-length subnet mask. VLSM allows a network space to be divided into unequal parts. This means that each subnet has the same number of available host addresses. In fact. .

Figure 2-43 shows the network 10.4.0/16 subnet divided into /24 subnets. 10.122 Routing Protocols Companion Guide Figure 2-42 Subnets of Varying Sizes VLSM in Action (2.255.0. VLSM is simply subnetting a subnet.3.2.0.0/16.0/16 subnet is subnetted again with the /24 mask.0/16.0.3.1. .10 address would now be a member of the more specific subnet 10.2. and so forth through 10. VLSM can be thought of as sub-subnetting. Figure 2-43 shows the 10. those subnets can be further subnetted. 10.0. that is. The 10.0. Individual host addresses are assigned from the addresses of sub-subnets.0.0/16. The 10.0.4.0. subnetted a second time using three different subnet masks: Q Q Q Q The 10.0.0/8 that has been subnetted using the subnet mask of /16.0/16 subnet is subnetted again with the /24 mask. 10. After a network address is subnetted. The 10.0.1.4.0. For example.0/16.3) VLSM allows the use of different masks for each subnet. which makes 256 subnets.1.0/24.1. Any of these /16 subnets can be subnetted further. Four of these /16 subnets are displayed in Figure 2-43.0/16 subnet is subnetted again with the /20 mask.0. Figure 2-43 shows four subnets.3.1.0/16 subnet is subnetted again with the /28 mask The 10.

3.255.0. Figure 2-44 Subnetting 10.0.4) Another way to view the VLSM subnets is to list each subnet and its sub-subnets.Chapter 2: Static Routing 123 Figure 2-43 VLSM Subnets Subnetting Subnets (2.0.0.0.0.0/8 network is the starting address space and is subnetted with a /16 mask.0.0/16.0/8 to 10. Borrowing 8 bits (going from /8 to /16) creates 256 subnets that range from 10. the 10.0. In Figure 2-44.0.3.0/16 to 10.0/16 .

1.1.0. The subnets ranging from 10.0. This creates 256 subnets with a /24 mask. thus creating 4.0/16.0.3. Figure 2-45 Subnetting 10.0/24 to 10.2. the 10.0/16 subnet is further subnetted by borrowing 8 more bits. The subnets ranging from 10.0/24 to 10.1.3.0/16.124 Routing Protocols Companion Guide In Figure 2-45.0.0.1. The subnets ranging from 10.240/28 are subnets of the subnet 10.1.0.0.0.3.0/24 In Figure 2-46.0/16 to 10.0.0/16 to 10.255.0.0/16 subnet is further subnetted with a /28 mask.2.255.0/16 subnet is also further subnetted with a /24 mask allowing 254 host addresses per subnet.096 subnets and allowing 14 host addresses per subnet.0. the 10. the 10.0/16.2.3.1.2.2.0.0/28 to 10. Figure 2-46 Subnetting 10.0/24 In Figure 2-47.0.255.0/24 are subnets of the subnet 10. .0/24 are subnets of the subnet 10. This mask allows 254 host addresses per subnet.2.

4.0.0/20 VLSM Example (2. The subnets ranging from 10.4.0/16 to 10. as shown in Figure 2-50.0. allowing more networks. These /20 subnets are big enough to subnet even further. Using traditional subnetting.3.Chapter 2: Static Routing 125 Figure 2-47 Subnetting 10.0.0/16 to 10.0.0/28 In Figure 2-48. there are many wasted addresses in the WAN segments.0.4. the sample topology in Figure 2-49 requires seven subnets.0/20 are subnets of the subnet 10.3.240.094 host addresses per subnet.0/16 subnet is further subnetted with a /20 mask. the first seven address blocks are allocated for LANs and WANs. the 10.0/16. This scheme results in 8 subnets with 30 usable addresses each (/27).3. For example.4. .0.5) Careful consideration must be given to the design of a network addressing scheme.0/20 to 10.0. While this scheme works for the LAN segments. Figure 2-48 Subnetting 10.3.4. thus creating 16 subnets and allowing 4.4.

192.224/30 . to use the address space more efficiently.168. Figure 2-51 Subnetting 192. the address blocks can be assigned in a way that minimizes waste and keeps unused blocks of addresses contiguous.0/24 to 192.20.20. Designing the addressing scheme in this way leaves three unused /27 subnets and five unused /30 subnets.168. The first 3 subnets were assigned to WAN links.20.168. To keep the unused blocks of addresses together.228/30.20.224/30.20.20. As shown in Figure 2-51.0/27 If an addressing scheme is designed for a new network.168.20.168. the last /27 subnet is further subnetted to create the /30 subnets.232/30. creating subnets 192.168.168. It can be more difficult to do this when adding to an existing network.224/27 to 192. /30 subnets are created for WAN links.126 Routing Protocols Companion Guide Figure 2-49 Basic Topology Figure 2-50 Subnetting 192. and 192.

255.255.229 255.225 255.65 255.20.255.226 255.255.224 R4(config-if)# exit R4(config)# interface serial 0/0/0 R4(config-if)# ip address 192.20.224 R2(config-if)# exit R2(config)# interface serial 0/0/0 R2(config-if)# ip address 192.168.168.168.20.255.1 255. Configuring VLSM on R1: R1(config)# interface gigabitethernet 0/0 R1(config-if)# ip address 192.255.20.255.20.255.252 R1(config-if)# end R1# Configuring VLSM on R2: R2(config)# interface gigabitethernet 0/0 R2(config-if)# ip address 192.255.255.20.255.252 R3(config-if)# end R3# Configuring VLSM on R4: R4(config)# interface gigabitethernet 0/0 R4(config-if)# ip address 192.20.234 255.168.33 255.252 R2(config-if)# exit R2(config)# interface serial 0/0/1 R2(config-if)# ip address 192.255.255.255.168.168.255.255.255.255.Chapter 2: Static Routing 127 The next four CLI outputs display sample configurations on all four routers to implement the VLSM addressing scheme.252 R2(config-if)# end R2# Configuring VLSM on R3: R3(config)# interface gigabitethernet 0/0 R3(config-if)# ip address 192.168.230 255.252 R3(config-if)# exit R3(config)# interface serial 0/0/1 R3(config-if)# ip address 192.168.255.224 R1(config-if)# exit R1(config)# interface serial 0/0/0 R1(config-if)# ip address 192.20.224 R3(config-if)# exit R3(config)# interface serial 0/0/0 R3(config-if)# ip address 192.20.168.252 R4(config-if)# end R4# .233 255.20.168.255.97 255.

4) Summary static routes can be used to help minimize the number of static routes in the routing table.3. you will complete the following objectives: Q Q Q Part 1: Examine the Network Requirements Part 2: Design the VLSM Address Scheme Part 3: Cable and Configure the IPv4 Network Configure Summary and Floating Static Routes (2. is the process of advertising a contiguous set of addresses as a single address with a less-specific.1. Configure IPv4 Summary Routes (2. shorter subnet mask. you are given a network address to develop a VLSM addressing scheme for the network shown in the included topology. CIDR is a form of route summarization and is synonymous with the term supernetting.3.3.128 Routing Protocols Companion Guide Packet Tracer Activity Packet Tracer Activity 2.4. The configuration of a summary static route is similar to the configuration of other IPv4 static routes. Using summary static routes can also make management of a large number of static routes easier and less prone to errors.6: Designing and Implementing a VLSM Addressing Scheme In this activity.3.7: Designing and Implementing Addressing with VLSM In this lab.1) A single IPv4 static summary route can be used to replace multiple static routes when those routes can be summarized with a common prefix length. also known as route aggregation.4. . Lab 2.1) Route summarization. Floating static routes can be used as a backup route for another static route or a dynamic routing protocol. Route Summarization (2.

0/16 to 172.0.20.23. Count the number of far left matching bits to determine the mask for the summary route.20.0/16—can be summarized into the single network address and prefix 172.0/16 to 172.0/16.0.20. This type of summarization helps reduce the number of entries in routing updates and lowers the number of entries in local routing tables. Figure 2-54 displays R1 configured with a summary static route to reach networks 172.0. It also helps reduce bandwidth utilization for routing updates and results in faster routing table lookups.0. Figure 2-52 Basic Topology Calculate a Summary Route (2. R1 requires a summary static route to reach networks in the range of 172. In Figure 2-52.0.20. 172. Figure 2-53 shows that the matching bits with zeros at the end results in the network address 172. Figure 2-53 lists networks 172.Chapter 2: Static Routing 129 CIDR ignores the limitation of classful boundaries.1.21.252.4.20.0. for the summarized route: /14 or 255.0/16 in binary format.20.0/16. List the networks in binary format.23. 172. and allows summarization with masks that are smaller than that of the default classful mask. This is the prefix. .0/16 to 172.0.23. or subnet mask. Step 2.0. The four networks—172.0.0/16.0. Copy the matching bits and then add zero bits to determine the summarized network address.0.2) Summarizing networks into a single address and mask can be done in three steps.23.0.0/16.0.0.0/14. Step 3. and 172.0. Figure 2-53 highlights the 14 far left matching bits. as shown in Figure 2-53: How To Step 1.22.0/16.

All routers have connectivity using static routes. Q Consider the example in Figure 2-55.130 Routing Protocols Companion Guide Figure 2-53 Calculating a Route Summary Figure 2-54 One Summary Static Route Summary Static Route Example (2. .1.4.3) Multiple static routes can be summarized into a single static route if: Q The destination networks are contiguous and can be summarized into a single network address. The multiple static routes all use the same exit interface or next-hop IP address.

0/24 is subnetted. Step 3. Write out the networks to summarize in binary.0 is directly connected.16. R3# show ip route static | begin Gateway Gateway of last resort is not set 172.0. identifying the summary boundary. 3 subnets S S S R3# 172. Serial0/0/1 172.1. Serial0/0/1 Figure 2-56 displays the steps to summarize those three networks: How To Step 1. it is 22.16.2. Notice that it has three static routes that can be summarized because they share the same two first octets. Step 2. Count the number of far left matching bits. Serial0/0/1 172. work to the right. start with the far left bit. To find the subnet mask for summarization. After the summary route is identified. in our example. . replace the existing routes with the one summary route. copy the matching 22 bits and add all 0 bits to the end to make 32 bits.0 is directly connected. To find the network address for summarization.0.252.16.3. Step 4. This number identifies the subnet mask for the summarized route as /22 or 255.16.0 is directly connected.Chapter 2: Static Routing 131 Figure 2-55 Basic Topology The following output displays the static routing table entries for R3. finding all the bits that match consecutively until a column of bits that do not match is found.255.

4.255.16.0 255.2.0/22 is subnetted.16. .1.0.0 s0/0/1 R3(config)# The following output confirms that the summary static route is in the routing table of R3: R3# show ip route static | begin Gateway Gateway of last resort is not set 172.16.0.252.0 s0/0/1 R3(config)# no ip route 172.0 255.255.132 Routing Protocols Companion Guide Figure 2-56 Summarize the Networks The following output shows how the three existing routes are removed and then the new summary static route is configured: R3(config)# no ip route 172.1.255.255. 1 subnets S R3# 172.0 is directly connected.0 255.4: Determine the Summary Network Address and Prefix Go to the online course to perform this practice activity.16.0 255.16.0.3.0 s0/0/1 R3(config)# no ip route 172.255. Serial0/0/1 Interactive Graphic Activity 2.255.16.255.0 s0/0/1 R3(config)# ip route 172.

4. After calculating summary routes for each LAN.4. you must summarize a route which includes all networks in the topology in order for the ISP to reach each LAN. R1 currently has four static IPv6 routes to reach networks 2001:DB8:ACAD:1::/64 to 2001:DB8:ACAD:4::/64.6: Configuring IPv4 Route Summarization – Scenario 2 In this activity. . summarizing IPv6 addresses is actually similar to the summarization of IPv4 addresses.1) Similar to IPv4. The multiple static routes all use the same exit interface or next-hop IPv6 address.2. Configure IPv6 Summary Routes (2.4. The calculation and configuration of an IPv6 summary static route is similar to the configuration of an IPv4 static summary route.1) Aside from the fact that IPv6 addresses are 128 bits long and written in hexadecimal.4. you will calculate and configure summary routes. Multiple static IPv6 routes can be summarized into a single static IPv6 route if: Q The destination networks are contiguous and can be summarized into a single network address. Packet Tracer Activity Packet Tracer Activity 2. is the process of advertising a contiguous set of addresses as a single address.5: Configuring IPv4 Route Summarization – Scenario 1 In this activity. you will calculate and configure summary routes. also known as route aggregation. Summarize IPv6 Network Addresses (2.1. a single IPv6 static summary route can be used to replace multiple IPv6 static routes with a common prefix length.Chapter 2: Static Routing 133 Packet Tracer Activity Packet Tracer Activity 2. Q Refer to the network in Figure 2-57.1. Route summarization. It just requires a few extra steps due to the abbreviated IPv6 addresses and hex conversion. Route summarization. is the process of advertising a contiguous set of addresses as a single address. also known as route aggregation.

EX .OSPF NSSA ext 1.BGP.OSPF ext 2 ON1 .Redirect O .ISIS summary. OI . R .EIGRP external ND . D . DCE .OSPF NSSA ext 2 S 2001:DB8:ACAD:1::/64 [1/0] via 2001:DB8:FEED:1::2 S 2001:DB8:ACAD:2::/64 [1/0] via 2001:DB8:FEED:1::2 S 2001:DB8:ACAD:3::/64 [1/0] via 2001:DB8:FEED:1::2 S 2001:DB8:ACAD:4::/64 [1/0] via 2001:DB8:FEED:1::2 R1# Calculate IPv6 Network Addresses (2.default . OE1 .ISIS L1. IS .ISIS interarea. NDr .Local.Static.Per-user Static route B .Destination. S .RIP.ISIS L2 IA . OE2 .ND Prefix. I1 .2.Connected.2) Summarizing IPv6 networks into a single IPv6 prefix and prefix length can be done in seven steps as shown in Figures 2-58 to 2-64: .EIGRP. L .OSPF Inter.OSPF ext 1. NDp . I2 . ON2 . U .ND Default.OSPF Intra.134 Routing Protocols Companion Guide Figure 2-57 Basic Topology The following output displays the IPv6 static routes installed in the IPv6 routing table: R1# show ipv6 route static IPv6 Routing Table .4.7 entries Codes: C .

Step 4. Convert the differing section from hex to binary. Step 7. Count the number of far left matching bits to determine the prefix length for the summary route. Step 3. Step 5. List the network addresses (prefixes) and identify the part where the addresses differ. Figure 2-58 Identify the Part Where the Addresses Differ Figure 2-59 Identify the Part Where the Addresses Differ – Expanded View Figure 2-60 Convert the Section from Hex to Binary . Expand the IPv6 if it is abbreviated. Step 6. Convert the binary section back to hex. Append the prefix of the summary route (result of Step 4). Step 2. Copy the matching bits and then add zero bits to determine the summarized network address (prefix).Chapter 2: Static Routing 135 How To Step 1.

136 Routing Protocols Companion Guide Figure 2-61 Count the Number of Far Left Matching Bits Figure 2-62 Add Zero Bits to Determine the Summarized Network Address Figure 2-63 Convert the Binary Section Back to Hex .

Figure 2-65 displays how the four existing routes are removed and then the new summary static IPv6 route is configured.Chapter 2: Static Routing 137 Figure 2-64 Count the Number of Far Left Matching Bits Configure an IPv6 Summary Address (2. replace the existing routes with the single summary route.2. Figure 2-65 Remove Static Routes and Configure Summary IPv6 Route .3) After the summary route is identified.4.

ND Prefix.Connected. OI . or many other reasons. NDp .4 entries Codes: C . ON2 . OE1 .OSPF NSSA ext 2 S 2001:DB8:ACA8::/45 [1/0] via 2001:DB8:FEED:1::2 R1# Packet Tracer Activity Packet Tracer Activity 2. hardware issues. Floating Static Routes (2.BGP.Destination.ISIS L1. R . DCE . Lab 2. IS .OSPF NSSA ext 1.OSPF Inter. L . U .1) Floating static routes are static routes that have an administrative distance greater than the administrative distance of another static route or dynamic routes.3. A floating static route can be used as a backup route when there is a secondary path available. OE2 . you will calculate. D .5: Calculating Summary Routes with IPv4 and IPv6 In this lab.RIP.EIGRP external ND .4. R1 is configured with a loopback interface.4: Configuring IPv6 Route Summarization In this activity.3) There may be times when a primary route fails due to physical layer problems. Instead of adding a LAN or another network to R1.4. NDr .4.ND Default. a misconfiguration.2.ISIS interarea.Redirect O . I1 . .ISIS L2 IA .OSPF ext 2 ON1 .OSPF ext 1.138 Routing Protocols Companion Guide The following output confirms that the summary static route is in the routing table of R1: R1# show ipv6 route static IPv6 Routing Table . They are very useful when providing a backup to a primary link. and verify a summary route for all the networks R1 can access through R2.Local.2. you will complete the following objectives: Q Q Part 1: Calculate IPv4 Summary Routes Part 2: Calculate IPv6 Summary Routes Configure Floating Static Routes (2.4. as shown in Figure 2-66. S . I2 .Per-user Static route B .Static.EIGRP. EX . configure.ISIS summary.OSPF Intra. we can use a loopback interface to simplify testing when verifying routing.default .

For example. the floating static route can take over. It is also encapsulation independent. meaning it can be used to forward packets out any interface. the static route “floats” and is not used when the route with the better administrative distance is active. static routes have an administrative distance of 1. A floating static route can be used to provide a backup route to multiple interfaces or networks on a router. In this way. However. An important consideration of a floating static route is that it is affected by convergence time. regardless of encapsulation type. and traffic can be sent through this alternate route. making them preferable to routes learned from dynamic routing protocols. . if the preferred route is lost.Chapter 2: Static Routing 139 Figure 2-66 Why Configure a Floating Static Route? By default. A route that is continuously dropping and re-establishing a connection can cause the backup interface to be activated unnecessarily. the administrative distances of some common dynamic routing protocols are: Q Q Q Q Q EIGRP = 90 IGRP = 100 OSPF = 110 IS-IS = 115 RIP = 120 The administrative distance of a static route can be increased to make the route less desirable than that of another static route or a route learned through a dynamic routing protocol.

0. R1# show ip route static | begin Gateway Gateway of last resort is 0. .0.168.3. In this scenario.2) IPv4 static routes are configured using the ip route global configuration command and specifying an administrative distance.140 Routing Protocols Companion Guide Configure a Floating Static Route (2. If no administrative distance is configured.0.0 to network 0.2 Interactive Graphic Activity 2. R1 is also configured with a floating static default pointing to R3 with an administrative distance of 5.2. Figure 2-67 Configure a Floating Static Route to R3 R1 is configured with a default static route pointing to R2. the preferred route from R1 is to R2. Note that the backup route to R3 is not present in the routing table.4.1. The following output verifies that the default route to R2 is installed in the routing table.4.2: Configure a Default Static Route on R3 Go to the online course to use the Syntax Checker in the third graphic to configure a default route using the next-hop address 192. therefore. The connection to R3 should be used for backup only. the default value (1) is used.2. This value is greater than the default value of 1 and. unless the preferred route fails. Because no administrative distance is configured. the default value (1) is used for this static route.0.0.16. Refer to the topology in Figure 2-67.0 S* R1# 0.0. this route floats and is not present in the routing table.3.0/0 [1/0] via 172.

A look at the routing table verifies that the .939: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0. Figure 2-68 Verify the Path to the R3 LAN What would happen if R2 failed? To simulate this failure. changed state to administratively down *Feb 21 16:33:43. both serial interfaces of R2 are shut down. traffic from R1 to R3 should go through R2.939: %LINK-5-CHANGED: Interface Serial0/0/0.4. changed state to down R2(config-if)# int s0/0/1 R2(config-if)# shut R2(config-if)# *Feb 21 16:33:42. changed state to administratively down *Feb 21 16:33:36.3) Because the default static route on R1 to R2 has an administrative distance of 1. The output in Figure 2-68 confirms that traffic between R1 and R3 flows through R2. as shown in the following output: R2(config)# int s0/0/0 R2(config-if)# shut *Feb 21 16:33:35. changed state to down Notice in the following output that R1 automatically generates messages indicating that the serial interface to R2 is down.543: %LINK-5-CHANGED: Interface Serial0/0/1.Chapter 2: Static Routing 141 Test the Floating Static Route (2.3.543: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1.

It has a manually configured administrative distance greater than that of the primary route and therefore would not be in the routing table until the primary route fails.435: %LINK-3-UPDOWN: Interface Serial0/0/0.168. *Feb 21 16:35:58.4: Configuring a Floating Static Route In this activity. Tracing the route to 192.142 Routing Protocols Companion Guide default route is now pointing to R3 using the floating static default route configured for next-hop 10. .1 VRF info: (vrf in name/id.0.2.0 S* R1# 0. and then restore connectivity to the primary route.0. changed state to down *Feb 21 16:35:59.2.168. changed state to down R1# R1# show ip route static | begin Gateway Gateway of last resort is 0. A floating static route is used as a backup route. you will configure a floating static route.10. You will test failover to the backup route.0.0/0 [5/0] via 10.4.10.0 to network 0.2 4 msec 4 msec * R1# Note Configuring IPv6 floating static routes is outside of the scope of this chapter. this section discusses how to troubleshoot some of the common problems you might encounter.2.0.5) Now that you have learned how to configure different types of static routes.10.435: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0.10. When a static route is no longer needed. Troubleshooting exercises are an excellent method to help better understand network protocols and configurations.2 The output confirms that traffic now flows directly between R1 and R3: R1# traceroute 192.1 Type escape sequence to abort.0. Packet Tracer Activity Packet Tracer Activity 2. vrf out name/id) 1 10.10.3. that static route should be deleted from the running and startup configuration files.10.0. Troubleshoot Static and Default Route Issues (2.

Chapter 2: Static Routing 143 Packet Processing with Static Routes (2.168. Examine Figure 2-69. The frame is forwarded out of the FastEthernet 0/0 interface. which includes the PC3 MAC address.5. The packet arrives on the Serial 0/0/0 interface on R2. The frame is forwarded out of the Serial 0/0/1 interface. If no entry exists. 4.0/24 out of the FastEthernet 0/0 interface. Because the link to R3 is a point-topoint link.2.0/24 out of the Serial 0/0/1 interface. R1 adds an “all 1s” address for the Layer 2 destination address. 192. 7.2. 11. 5.0/24. 9. R1 uses the default static route. R2 de-encapsulates the frame and looks for a route to the destination. 8. you need to learn about the process that a packet goes through as it is forwarded by a router.10 to find the Layer 2 Media Access Control (MAC) address for PC3. therefore.1) Now that you have configured static routes. R3 has a connected route to 192. 10. R3 de-encapsulates the frame and looks for a route to the destination. 6. R3 encapsulates the packet in a new frame with the MAC address of the FastEthernet 0/0 interface as the source Layer 2 address and the MAC address of PC3 as the destination MAC address. R1 does not have a specific route to the destination network. and PC3 responds with an ARP reply. The frame is forwarded out of the Serial 0/0/0 interface. R2 encapsulates the packet in a new frame. R2 adds an “all 1s” address for the Layer 2 destination address. . R3 looks up the ARP table entry for 192.168. The packet arrives on the Serial 0/0/1 interface on R3.1. 3.168. R2 has a static route to 192.2. Because the link to R2 is a point-topoint link. The packet arrives on the FastEthernet 0/0 interface of R1. 2.5.168.1) The following example describes the packet forwarding process with static routes. where PC1 is sending a packet to PC3: 1. The packet arrives on the network interface card (NIC) interface of PC3. R3 sends an Address Resolution Protocol (ARP) request out of the FastEthernet 0/0 interface. R1 encapsulates the packet in a new frame.2. Static Routes and Packet Forwarding (2.

1 6 172. Networks are subject to forces that can cause their status to change quite often: Q Q An interface fails.16. It is always best to look for the most obvious and simplest issues first. begin looking for more complicated possibilities like an error in the static route configuration. When this has been verified.5. such as an interface still in shutdown mode or an interface with the wrong IP address.144 Routing Protocols Companion Guide 172.2) Troubleshooting is a skill that develops as you gain experience.1 Fa0/0 .2 .1.1. begin by making sure that you can ping your own interface and other devices on your own directly connected networks.3.2.16.0/24 PC2 Fa0/0 . . A service provider drops a connection.1) When end-to-end connectivity is a problem.1 . begin testing connectivity to remote networks from other devices.2 S0/0/1 DCE 192.168.2.5.1 4 S0/0/0 DCE 7 S0/0/1 .0/24 Fa0/0 . Troubleshooting a Missing Route (2.168.0/24 172.2.1 192.16. After these items have been verified.0/24 1 2 3 8 9 10 11 PC1 PC3 Figure 2-69 Static Routes and Packet Forwarding Troubleshoot IPv4 Static and Default Route Configuration (2.0/24 5 S0/0/0 .

Common IOS troubleshooting commands include: Q Q Q Q Q ping traceroute show ip route show ip interface brief show cdp neighbors detail Figure 2-70 displays the result of an extended ping from the source interface of R1 to the LAN interface of R3. Network administrators are responsible for pinpointing and solving the problem. When there is a change in the network.Chapter 2: Static Routing 145 Q Q Links become oversaturated. connectivity may be lost. An administrator enters a wrong configuration. Figure 2-70 Extended Ping . a network administrator must be familiar with tools to help isolate routing problems quickly. An extended ping is when the source interface or source IP address is specified. To find and solve these issues.

Two-port Mac Relay Device ID netlab-cs5 R2 R1# Local Intrfce Gig 0/0 Ser 0/0/0 Holdtme 156 153 Capability S I R S I Platform Port ID WS-C2960. I .2.168.16.Phone.Source Route Bridge S .0/24 [1/0] via 172.2.16.2.3. C .2 4 msec 4 msec 8 msec 2 192.1. GigabitEthernet0/0 172.Repeater. B .Remote.16.3.168.Fas 0/1 CISCO1941 Ser 0/0/0 .146 Routing Protocols Companion Guide The following output displays the result of a traceroute from R1 to the R3 LAN: R1# traceroute 192. P .0/24 is directly connected.1/32 is directly connected.1/32 is directly connected.0/24 is directly connected. D .16. R1# show cdp neighbors Capability Codes: R .Host.Router. GigabitEthernet0/0 192. r .Trans Bridge. T .Switch. H .IGMP.168. but it cannot be pinged.2.2 172. 5 subnets. This command validates Layer 2 (and therefore Layer 1) connectivity.168. M .0/24 [1/0] via 172. if a neighbor device is listed in the command output.2 The following output provides a quick status of all interfaces on the router: R1# show ip interface brief Interface IP-Address OK? Method Status YES unset Protocol Embedded-Service-Engine0/0 unassigned GigabitEthernet0/0 GigabitEthernet0/1 Serial0/0/0 Serial0/0/1 R1# 172.3.1 12 msec 12 msec * R1# The following output displays the routing table of R1: R1# show ip route | begin Gateway Gateway of last resort is not set 172.1.2.16.1 unassigned 172.0/24 [1/0] via 172.16.2.168.16.1 VRF info: (vrf in name/id.1 Type escape sequence to abort.16.1 unassigned administratively down down up YES manual up YES unset administratively down down up YES manual up YES unset administratively down down The show cdp neighbors command in the following output provides a list of directly connected Cisco devices.2 192.0. Serial0/0/0 172.16.16.2.0/16 is variably subnetted. then Layer 3 addressing should be investigated.CVTA. 2 masks S C L C L S S R1# 172.16.16.2. Serial0/0/0 172.1.2. vrf out name/id) 1 172. Tracing the route to 192.2. For example.

This loop would continue until the time to live (TTL) value decrements to zero.2 4 msec 4 msec 8 msec 2 172. the user at PC1 reports that he cannot access resources on the R3 LAN. R1# traceroute 192.5. R1 returns it to R2.2. the router would then send an Internet Control Message Protocol (ICMP) Destination Unreachable message to R1.2. For some reason.16.2) Finding a missing (or misconfigured) route is a relatively straightforward process. R2 forwards the traceroute back to R1.1 VRF info: (vrf in name/id. For instance.Chapter 2: Static Routing 147 Solve a Connectivity Problem (2.16. Tracing the route to 192.2.16.1 Type escape sequence to abort. Figure 2-71 Verify Connectivity to the R3 LAN A traceroute in the following output reveals that R2 is not responding as expected.168.16. in which case.2. vrf out name/id) 1 172.2.2.16. This can be confirmed by pinging the LAN interface of R3 using the LAN interface of R1 as the source (see Figure 2-71).1 20 msec 16 msec 20 msec 5 172.168.2 12 msec 8 msec 8 msec 4 172. in this example.2 16 msec 16 msec 16 msec .1 12 msec 12 msec 12 msec 3 172. if the right tools are used in a methodical manner.2.2. The results show that there is no connectivity between these LANs.

2. Using the configured next-hop address.16.168.0 172. the static route to the 192.3. because it is the router displaying a strange forwarding pattern. As a last step in confirmation.2. End with CNTL/Z.168.1 R2(config)# The following output verifies that R1 can now reach the LAN interface of R3.2.1.255.2. one per line.255. Serial0/0/0 172.1.16.1 R2# R2# conf t Enter configuration commands.255.2.1 192.168. A static route to the 192. the routing table in the following output reveals that the 192.2.1.0/24 network is connected to R3.2 20 msec R1# The next step is to investigate the routing table of R2. Therefore.168. 2 masks C L S R2# 192. R2# show running-config | section ip route ip route 172. The incorrect route is removed and the correct route is then entered.0/24 network has been configured using the next-hop address 172.168.2.168. Serial0/0/1 192.168.168. not 172.255.2.3.16.2.16.1 ip route 192.168.16.1.2.2. It is clear from the topology that the 192.255.168.2.2.0/16 is variably subnetted.0 255.2.16.16.168.0/24 [1/0] via 172. R2# show ip route | begin Gateway Gateway of last resort is not set 172.0 255. 5 subnets.1.0 172.2.148 Routing Protocols Companion Guide 6 172.0/24 is directly connected.16.2.0/24 network are sent back to R1. Serial0/0/1 192. Serial0/0/0 172. 2 subnets.2.255.0/24 is variably subnetted.1.168.1.0 172.1.2/32 is directly connected. Using the show ip route | begin Gateway command.1 R2(config)# ip route 192.16.0/24 is directly connected.16.16. GigabitEthernet0/0 172.2.168. packets destined for the 192.1.1. .0/24 network is configured incorrectly.0/24 LAN. R2(config)# no ip route 192. the user on PC1 should also test connectivity to the 192.1/32 is directly connected.255.0 192.0.16.16.0/24 is directly connected.1 The following shows output from the running configuration that reveals the incorrect ip route statement.2.2.1 20 msec 20 msec 24 msec 7 172.168.16.0/24 1/0] via 172.0 255. not R1.16.0 255.2.255.2/32 is directly connected. GigabitEthernet0/0 172.16.0/24 network on R2 must use next-hop 192. 2 masks C L C L S 172.168.

3.2.1 !!!!! Success rate is 100 percent (5/5). Packet Tracer Activity Packet Tracer Activity 2.5. Locate the issue or issues.168. Locate the problem.1 source g0/0 Type escape sequence to abort.2. timeout is 2 seconds: Packet sent with a source address of 172. round-trip min/avg/max = 28/28/28 ms R1# Packet Tracer Activity Packet Tracer Activity 2.5. PC1 reports that it cannot access resources at Server. determine the best solution.5: Troubleshooting Static Routes In this lab.1. and verify connectivity. implement the solution. the network is already addressed using VLSM and configured with static routes. 100-byte ICMP Echos to 192. decide on an appropriate solution. Lab 2.2. Sending 5.Chapter 2: Static Routing 149 R1# ping 192. you will complete the following objectives: Q Q Q Part 1: Build the Network and Configure Basic Device Settings Part 2: Troubleshoot Static Routes in an IPv4 Network Part 3: Troubleshoot Static Routes in an IPv6 Network .16.3: Solving the Missing Route In this activity.2. But there is a problem.4: Troubleshooting VLSM and Route Summarization In this activity.5. and resolve the issue.2.168.

.1: Make it Static Go to the online course to perform this practice activity. this manual operation can become quite cumbersome. Try to write the route statements without the assistance of completed labs. get together with another group and compare your written answers. etc. Scenario 2 IPv6 default static route from R3 directing all data through your S0/0/1 interface to the next-hop address on R2. Discuss any differences found in your comparisons. In this chapter. As the use of IPv6 addressing becomes more prevalent. Scenario 3 IPv6 default static route from R2 directing all data through your S0/0/1 interface to the next-hop address on R3.1.6) Class Activity 2. in large networks. Packet Tracer files. Scenario 1 IPv6 default static route from R2 directing all data through your S0/0/0 interface to the next-hop address on R1.2: Packet Tracer Skills Integration Challenge The network administrator asked you to implement IPv4 and IPv6 static and default routing in the test environment shown in the topology.pdf file provided specifically for this activity.6. even when a dynamic routing protocol is implemented. Work with a partner to write an IPv6 statement for each of the three scenarios. use the topology as shown in the . Configure each static and default route as directly connected. However. To prove that you are able to direct IPv6 traffic correctly and review the IPv6 default static route curriculum concepts.6. Static routes are still used. it is important for network administrators to be able to direct network traffic between routers.150 Routing Protocols Companion Guide Summary (2.1. Static routes are easily configured. Remote networks are networks that can only be reached by forwarding the packet to another router. you learned how IPv4 and IPv6 static routes can be used to reach remote networks. When complete. Packet Tracer Activity Packet Tracer Activity 2.

such as Ethernet. A floating static route can be configured to back up a main link by manipulating its administrative value. both a next-hop IP address and an exit interface can be configured on the static route.0. it is usually more efficient to configure the static route with an exit interface.6. Class Activities Class Activity 2. VLSM subnetting is similar to traditional subnetting in that bits are borrowed to create subnets.1: Make it Static . When a next-hop IP address is used. The Packet Tracer Activities PKA files are found in the online course. With VLSM. the network is first subnetted. Practice The following activities provide practice with the topics introduced in this chapter. Whether the static route is configured with a next-hop IP address or exit interface.0.0 network address and a 0.0. as well as an exit interface. the routing table process must resolve this address to an exit interface.2: Which Way Should We Go? Class Activity 2.0. This administrative distance also applies to static routes configured with a next-hop address. CIDR also manages the IPv4 address space more efficiently. Static routes have a default administrative distance of 1.0 subnet mask for IPv4. The Labs and Class Activities are available in the companion Routing Protocols Lab Manual (978-1-58713-322-0).1. This process can be repeated multiple times to create subnets of various sizes. several static routes can be configured as a single summary route. and then the subnets are subnetted again. configured with a 0. the static route is not included in the routing table.1. Using CIDR. If there is not a more specific match in the routing table. the routing table uses the default route to forward the packet to another router. This means fewer entries in the routing table and results in a faster routing table lookup process.Chapter 2: Static Routing 151 Static routes can be configured with a next-hop IP address.0. The ultimate summary route is a default route. if the exit interface that is used to forward that packet is not in the routing table. A static route is only entered in the routing table if the next-hop IP address can be resolved through an exit interface. and the prefix/prefix-length ::/0 for IPv6. which is commonly the IP address of the next-hop router. On point-to-point serial links. On multi-access networks.

152 Routing Protocols Companion Guide Labs Lab 2.5.2.2.4.” lists the answers.3.4.5: Configuring IPv6 Static and Default Routes Lab 2.5: Configuring IPv4 Route Summarization – Scenario 1 Packet Tracer Activity 2.2.0/24 172.3: Solving the Missing Route Packet Tracer Activity 2.10/24 and 10.168.0.5: Configuring IPv4 Static and Default Routes Lab 2.40.5.4.3.2: Packet Tracer Skills Integration Challenge Check Your Understanding Questions Complete all the review questions listed here to test your understanding of the topics and concepts in this chapter.16.6.1.2.4: Configuring a Floating Static Route Packet Tracer Activity 2.0/8 networks? (Choose two.4: Configuring IPv6 Route Summarization Packet Tracer Activity 2.4.3.1.3.0.2.2.5.4.0.0/8 Figure 2-72 Topology for Quiz Question 1 .6: Designing and Implementing a VLSM Addressing Scheme Packet Tracer Activity 2.2.0.2.2/24 10.16. Refer to Figure 2-72. The appendix. “Answers to the ‘Check Your Understanding’ Questions.2.2.3.5: Calculating Summary Routes with IPv4 and IPv6 Lab 2.5: Troubleshooting Static Routes Packet Tracer Activity Packet Tracer Activities Packet Tracer Activity 2.40.1.4.2.6: Configuring IPv4 Route Summarization – Scenario 2 Packet Tracer Activity 2.4: Configuring IPv6 Static and Default Routes Packet Tracer Activity 2.) 192.1/24 S0/1/0 S0/0/0 172.168.4: Troubleshooting VLSM and Route Summarization Packet Tracer Activity 2. Which two commands must be configured to allow communications between the 192.4: Configuring IPv4 Static and Default Routes Packet Tracer Activity 2.1.7: Designing and Implementing IPv4 Addressing with VLSM Lab 2. 1.4.

0.255. Next-hop addresses can only be used with IPv4 static routes. there is no need for a recursive lookup when using static routes with next-hop addresses.0.) A.1 .0 172.0.1.1 2. Router(config)# ipv4 route 0.40.1 B. Less memory and processing requirements than a dynamic routing protocol B. Which global configuration command configures an IPv4 static default route using the next-hop address 10.0 172.0. Used to indicate a default route or a Gateway of Last Resort F.255.0. D.1 E.255.0 255.0.0.0. Ensures that there is always a path available C.0 s0/0/0 C.0.16. Routers configured with static routes using a next-hop address must either have the exit interface listed in the route or have another route with the network of the next hop and an associated exit interface.0. A(config)# ip route 10.168. 3.1 C. Used to dynamically find the best path to a destination network D.0.2 F.0.168. Which two statements are true concerning configuring static routes using nexthop addresses? (Choose two.0.0.0.0.1.0. A(config)# ip route 10.255.0 192. B.Chapter 2: Static Routing 153 A.0.) A.0.0.1? A.1 D.40.168. B# ip route 192.0.0. Used for routers that connect to stub networks E.16.0.0.1. the exit interface must also be included in the configuration.0.0 10.0.2 B.0 0.0.0. C. Router(config)# ip route 0. When configuring a static route with a next-hop address.0 255. B(config)# ip route 192.40. B(config)# ip route 192. Reduces configuration time on large networks 4.0 255.0 172.0.0/0 10.1 D.16. Router(config)# ip route 0.0.0. Router(config)# ip route 0.255.255. A(config)# ip route 10.0.0.0 10.0.0 0.0 255.1.0 255.0.0 255.0 10.0 10.0. Which of the following are three characteristics of a static route? (Choose three. With CEF enabled.168. They cannot be used for IPv6 static routes.

0.0 10.0. Router# show ip route static B.15. Router(config)# ipv6 route ::/0 2001:DB8:ACAD:1::1 D. Router# show ipv6 route static D.0 10.0. What type of static route can be configured to be a backup route in case the pri- mary route fails? A.0 8.0. Which global configuration command configures an IPv6 static default route using the next-hop address 2001:DB8:ACAD:1::1? A.12. Backup static route D. True/False: Static routes are commonly configured along with a dynamic routing protocol.0. Floating static route B. Default route C. Router(config)# ipv6 route 0. Router# show static ipv6 route .0.0 2001:DB8:ACAD:1::1 B. 10.0 0. Router# show ip static route C.14.13. Router(config)# ip route ::/0 2001:DB8:ACAD:1::1 6. 7.0. True/False: A static route configured with an exit interface has an administrative distance of 0. Router(config)# ip route 0/0 2001:DB8:ACAD:1::1 C. the same as a directly connected network.0 10. Summarize the following addresses using the shortest valid subnet mask: 10.154 Routing Protocols Companion Guide 5.0. Which command will only display the IPv6 static routes in the IPv6 routing table? A. Summary route 9.

CHAPTER 3 Routing Dynamically Objectives Upon completion of this chapter. administrative distance. you will be able to answer the following questions: Q What is the purpose of dynamic routing protocols? How does dynamic routing compare with static routing? How do dynamic routing protocols share route information and achieve convergence? What are the differences between the categories of dynamic routing protocols? How does the algorithm used by distance vector routing protocols determine the best path? What are the different types of distance vector routing protocols? How do you configure the RIP routing protocol? How do you configure the RIPng routing protocol? Q How does the algorithm used by link-state routing protocols determine the best path? How do link-state routing protocols use information sent in link-state updates? What are the advantages and disadvantages of using link-state routing protocols? How do you determine the source route. dynamic routing protocols page 158 page 158 Interior Gateway Routing Protocol (IGRP) page 159 Enhanced IGRP (EIGRP) page 159 page 159 Routing Information Protocol (RIP) Advanced Research Projects Agency Network (ARPANET) page 158 Open Shortest Path First (OSPF) page 158 Border Gateway Protocol (BGP) data structures page 159 Intermediate System-to-Intermediate System (IS-IS) page 159 routing protocol messages page 160 . and metric for a given route? How do you explain the concept of a parent/ child relationship in a dynamically built routing table? How do you describe the differences between the IPv4 route lookup process and the IPv6 route lookup process? Can you determine which route will be used to forward a packet upon analyzing a routing table? Q Q Q Q Q Q Q Q Q Q Q Q Q Key Terms This chapter uses the following key terms. You can find the definitions in the Glossary.

156 Routing Protocols Companion Guide algorithm page 160 page 170 page 171 page 171 page 172 page 172 page 172 page 174 automatic summarization passive-interface default static route RIPng page 196 page 193 convergence page 194 page 195 classful routing protocols classless routing protocols autonomous system (AS) Dijkstra’s algorithm page 201 page 201 page 204 Interior Gateway Protocols (IGP) Exterior Gateway Protocols (EGP) distance vector routing protocols link-state routing protocols discontiguous network shortest path first (SPF) link-state packet (LSP) SPF tree page 211 page 174 event-driven updates OSPFv3 page 214 page 213 page 177 variable-length subnet mask (VLSM) page 179 metrics page 180 page 185 page 185 ultimate route level 1 route page 220 page 220 page 221 page 221 page 222 supernet route bounded triggered updates Hello keepalive mechanism level 1 parent route level 2 child route .

2: How Much Does This Cost? This modeling activity illustrates the network concept of routing cost. outdoor track area.0. and the metrics routing protocols use to determine the best path for network traffic. The remaining four team members will actively participate in the following scenarios. In a large network with numerous networks and subnets. a user may have a router and two or more computers. Activity 1 The tallest person in the group establishes a start and finish line by marking 15 steps from start to finish. It explores the benefits of using dynamic routing protocols. and the student file for this activity will be required per group. and work range from small. A school or university classroom. Network professionals must understand the different routing protocols available in order to make informed decisions about when to use static or dynamic routing. Routes to remote networks can be learned by the router in two ways: static routes and dynamic routes. how different routing protocols are classified.1. play. .1. One person will function as the photographer and event recorder. indicating the distance of the team route. At work. Implementing dynamic routing protocols can ease the burden of configuration and maintenance tasks and give the network scalability. configuring and maintaining static routes between these networks requires a great deal of administrative and operational overhead. You will be a member of a team of five students who travel routes to complete the activity scenarios. Class Activity 3.Chapter 3: Routing Dynamically 157 Introduction (3. as selected by each group. At home. school parking lot. Routers forward packets by using information in the routing table. Other topics covered in this chapter include the characteristics of dynamic routing protocols and how the various routing protocols differ.1) The data networks that we use in our everyday lives to learn. This operational overhead is especially cumbersome when changes to the network occur. an organization may have multiple routers and switches servicing the data communication needs of hundreds or even thousands of PCs. This chapter introduces dynamic routing protocols. a stopwatch. Each student will take 15 steps from the start line toward the finish line and then stop on the 15th step—no further steps are allowed. or any other location can serve as the venue for these activities. They also need to know which dynamic routing protocol is most appropriate in a particular network environment. such as a down link or implementing a new subnet. local networks to large.0. One digital camera or bring your own device (BYOD) with camera. hallway. global internetworks.

The following sections describe several important benefits that dynamic routing protocols provide.158 Routing Protocols Companion Guide Note Not all of the students may reach the same distance from the start line due to their height and stride differences. Activity 2 A new start and finish line will be established. The photographer will take a group picture of the entire team’s final location after taking the 15 steps required. time permitting. this time. As networks evolved and became more complex. One of the first routing protocols was Routing Information Protocol (RIP). however.1. Each team member will count the steps taken to complete the route. Group answers can be discussed as a class. record the time that it took to complete the full route and how many steps were taken.1. as recounted by each team member and recorded on the team’s student file. The RIP routing protocol was updated to accommodate growth in the network environment. Dynamic Routing Protocols (3. teams will use the digital picture taken for Activity 1 and their recorded data from Activity 2 file to answer the reflection questions. a longer distance for the route will be established than the distance specified in Activity 1. The Evolution of Dynamic Routing Protocols (3. No maximum steps are to be used as a basis for creating this particular route. The recorder will time each student and. but some of the basic algorithms within the protocol were used on the Advanced Research Projects Agency Network (ARPANET) as early as 1969.1) Dynamic routing protocols have been used in networks since the late 1980s. new routing protocols emerged. students will walk the new route from beginning to end twice. However. at the end of each team member’s route. into RIPv2.1) Dynamic routing protocols play an important role in today’s networks. One at a time. the newer version of RIP still does not scale to the larger network implementations of today. RIP version 1 (RIPv1) was released in 1988. After both activities have been completed. two advanced routing protocols were developed: Open Shortest Path First (OSPF) . dynamic routing protocols are typically used with static routes. In many networks. To address the needs of larger networks.

BGP is also used between ISPs and their larger private clients to exchange routing information. algorithms. there was the need to connect different internetworks and provide routing between them. . as shown by the IPv6 row in Table 3-1.2) Routing protocols are used to facilitate the exchange of routing information between routers. Additionally. thus. This information is kept in RAM. IPv6 has emerged. The purpose of dynamic routing protocols includes: Q Q Q Q Discovery of remote networks Maintaining up-to-date routing information Choosing the best path to destination networks Ability to find a new best path if the current path is no longer available The main components of dynamic routing protocols include: Q Data structures: Routing protocols typically use tables or databases for their operations. Table 3-1 Routing Protocol Classification Interior Gateway Protocols Distance Vector IPv4 IPv6 RIPv2 RIPng EIGRP EIGRP for IPv6 Link-State OSPFv2 OSPFv3 IS-IS IS-IS for IPv6 Exterior Gateway Protocols Path Vector BGP-4 MBGP With the advent of numerous consumer devices using IP. which also scales well in larger network implementations. A routing protocol is a set of processes. newer versions of the IP routing protocols have been developed.1. RIP is the simplest of dynamic routing protocols and is used in this section to provide a basic level of routing protocol understanding. Cisco developed the Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP).Chapter 3: Routing Dynamically 159 and Intermediate System-to-Intermediate System (IS-IS). The Border Gateway Protocol (BGP) is now used between Internet service providers (ISPs). Table 3-1 classifies the protocols. the IPv4 addressing space is nearly exhausted.1. Purpose of Dynamic Routing Protocols (3. and messages that are used to exchange routing information and populate the routing table with the routing protocol’s choice of best paths. To support the communication based on IPv6.

1. Routing protocols determine the best path.1. . This exchange allows routers to automatically learn about new networks and also to find alternate paths when there is a link failure to a current network.1.1. and routing algorithm used by EIGRP. or route. Algorithm: An algorithm is a finite list of steps used to accomplish a task. routing protocol messages. That route is then added to the routing table. Video 3.3: Routers Dynamically Share Updates Video Go to the online course and play the animation of three routers sharing updates dynamically. to each network. and perform other tasks to learn and maintain accurate information about the network. A primary benefit of dynamic routing protocols is that routers exchange routing information when there is a topology change.3) Routing protocols allow routers to dynamically share information about remote networks and automatically add this information to their own routing tables. Figure 3-1 Components of Routing Protocols The Role of Dynamic Routing Protocols (3. exchange routing information.160 Routing Protocols Companion Guide Q Routing protocol messages: Routing protocols use various types of messages to discover neighboring routers. Q Figure 3-1 highlights the data structures. Routing protocols use algorithms for facilitating routing information and for best path determination.

which is a network with only one default route out and no knowledge of any remote networks. static routing is still used in networks today. Despite the benefits of dynamic routing. Q Q Figure 3-2 provides a sample static routing scenario. This section compares static routing and dynamic routing. However. static routing still has its place.2. . including CPU time and network link bandwidth. networks typically use a combination of both static and dynamic routing. There are times when static routing is more appropriate and other times when dynamic routing is the better choice. Network professionals must understand when to use static or dynamic routing. Using Static Routing (3.1) Before identifying the benefits of dynamic routing protocols. however.1.2) Routing tables can contain directly connected. Static routing has several primary uses. Dynamic routing certainly has several advantages over static routing. Activity 3. the expense of using dynamic routing protocols is dedicating part of a router’s resources for protocol operation.1. manually configured static routes and routes learned dynamically using a routing protocol. dynamic routing protocols require less administrative overhead.1. Dynamic versus Static Routing (3. Routing to and from a stub network.4: Identify Components of a Routing Protocol (EIGRP) Interactive Graphic Go to the online course to perform these three practice activities. including: Q Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. consider the reasons why network professionals use static routing.1. Accessing a single default route (which is used to represent a path to any network that does not have a more specific match with another route in the routing table). Networks with moderate levels of complexity may have both static and dynamic routing configured. In fact.Chapter 3: Routing Dynamically 161 Compared to static routing.

. Managing the static configurations in large networks can become time consuming.162 Routing Protocols Companion Guide Figure 3-2 Static Routing Scenario Static Routing Scorecard (3. unlike with dynamic routing protocols. No advertisements are sent. extra resources (CPU and memory) are not required. Static Routing Advantages and Disadvantages Disadvantages Suitable for simple topologies or for special purposes such as a default static route. Very secure. therefore. It is very predictable.2) Static routing is easy to implement in a small network. Table 3-2 highlights the advantages and disadvantages of static routing. Managing the static configurations can become time consuming. No routing algorithm or update mechanisms are required. If a link fails. If a link fails. Static routes do not send update messages and. a static route cannot reroute traffic. Table 3-2 Advantages Easy to implement in a small network. manual intervention is required to re-route traffic. which makes them fairly easy to troubleshoot. Therefore. as the route to the destination is always the same. The disadvantages of static routing include: Q Q Q They are not easy to implement in a large network. a static route cannot reroute traffic. Configuration complexity increases dramatically as the network grows.1.2. Static routes stay the same. require very little overhead. Therefore.

2. Figure 3-3 Small Dynamic Routing Scenario What if the company grew and now has four regions and 28 routers to manage.Chapter 3: Routing Dynamically 163 Using Dynamic Routing Protocols (3.1.3) Dynamic routing protocols help the network administrator manage the timeconsuming and exacting process of configuring and maintaining static routes. as shown in Figure 3-4? What happens when a link goes down? How do you ensure that redundant paths are available? Figure 3-4 Large Dynamic Routing Scenario Dynamic routing is the best choice for large networks like the one shown in Figure 3-4. Dynamic Routing Scorecard (3. They are scalable and automatically determine better routes if there is a .1.4) Dynamic routing protocols work well in any type of network consisting of several routers.2. Imagine maintaining the static routing configurations for the seven routers in Figure 3-3.

Dynamic Routing Advantages and Disadvantages Disadvantages Can be more complex to initially implement.2. Additional configuration settings such as passive interfaces and routing protocol authentication are required to increase security. and link bandwidth.5: Compare Static and Dynamic Routing Interactive Graphic Go to the online course to perform this practice activity. Activity 3. It is also less secure than static routing because the interfaces identified by the routing protocol send routing updates out. RAM. Routes taken may differ between packets. they are simpler to configure in a large network. and link bandwidth. Although there is more to the configuration of dynamic routing protocols.1. Route depends on the current topology. Automatically adapts topology to reroute traffic if possible. Generally independent of the network size.1. Notice how dynamic routing addresses the disadvantages of static routing. Routing Protocol Operating Fundamentals (3. Requires additional resources such as CPU. There are disadvantages to dynamic routing. They all exchange routing updates and converge to build routing tables that are used by the router to make packet forwarding decisions.164 Routing Protocols Companion Guide change in the topology. The routing algorithm uses additional CPU.3) All routing protocols basically perform the same tasks. Table 3-3 Advantages Suitable in all topologies where multiple routers are required. This section provides an overview of routing protocol fundamentals. Less secure due to the broadcast and multicast routing updates. Dynamic routing requires knowledge of additional commands. Table 3-3 highlights the advantages and disadvantages of dynamic routing. memory. .

1.1.2. it applies the saved configuration.1: Routing Protocol Operation Video Go to the online course and play the animation of two routers sharing routing updates. The router shares routing messages and routing information with other routers that are using the same routing protocol. The router sends and receives routing messages on its interfaces. When a router detects a topology change. In general. Video 3. It does not even know that there are devices on the other end of its links. it knows nothing about the network topology.Chapter 3: Routing Dynamically 165 Dynamic Routing Protocol Operation (3. Video 3. the operations of a dynamic routing protocol can be described as follows: 1. then the router initially discovers its own directly connected networks.2: Directly Connected Networks Detected Video Go to the online course to view an animation of the initial discovery of connected networks for each router. Notice how the routers proceed through the boot process and then discover any directly connected networks and subnet masks. 3.1.1. After a router boots successfully. Cold Start (3. If the IP addressing is configured correctly.3.0. This information is added to their routing tables as follows: Q R1 adds the 10. When a router powers up.0 available through interface Serial 0/0/0.0. .0 network available through interface FastEthernet 0/0 and adds 10.1) All routing protocols are designed to learn about remote networks and to quickly adapt whenever there is a change in the topology.3.3. The only information that a router has is from its own saved configuration file stored in NVRAM. 2.3.1. Routers exchange routing information to learn about remote networks.2) All routing protocols follow the same patterns of operation. 4. the routing protocol can advertise this change to other routers. The method that a routing protocol uses to accomplish this depends upon the algorithm it uses and the operational characteristics of that protocol.

2. a listing of the different updates that R1.0 available through interface Serial 0/0/1. the next step is for the router to begin exchanging routing updates to learn about any remote routes.166 Routing Protocols Companion Guide Q R2 adds the 10.0 network available through interface Serial 0/0/0 and adds 10.3. The router sends an update packet out all interfaces that are enabled on the router. and R3 send and receive during initial convergence is provided: . Q With this initial information. the router checks it for new network information.0. If a routing protocol is configured.3) After initial boot up and discovery.0 network available through interface Serial 0/0/1 and adds 10. the router also receives and processes similar updates from other connected routers. the routing table is updated with all directly connected networks and the interfaces those networks reside on. At the same time. Notice that only the directly connected networks are listed in each router’s respective routing table. Any networks that are not currently listed in the routing table are added. R2.0.0. Upon receiving an update. Network Discovery (3. The update contains the information in the routing table. Figure 3-5 depicts an example topology setup between three routers.3. the routers then proceed to find additional route sources for their routing tables. R1. R3 adds the 10.3. Figure 3-5 Initial Routing Table Before Exchange Based on this topology.1.4.0 available through interface FastEthernet 0/0. R2.0. and R3. which currently comprises all directly connected networks.

0.0.0 out the Serial 0/0/0 interface Sends an update about network 10.0 in the routing table via Serial 0/0/1 with a metric of 1 Q Q Q R3: Q Q Q Sends an update about network 10.2.0 out the Serial 0/0/1 interface Receives an update from R1 about network 10.0 and increments the hop count by 1 Stores network 10.3.2. Figure 3-6 Routing Table After Initial Exchange .0.0 out the Serial 0/0/0 interface Sends an update about network 10.0.Chapter 3: Routing Dynamically 167 R1: Q Q Q Sends an update about network 10.0.0.4.3.1.1.4.0.0 in the routing table via Serial 0/0/1 with a metric of 1 Q Figure 3-6 displays the routing tables after the initial exchange.0.4.0 out the FastEthernet 0/0 interface Receives an update from R2 about network 10.0.0.3.0.1.0 in the routing table via Serial 0/0/0 with a metric of 1 Q R2: Q Q Q Sends an update about network 10.0 out the Serial 0/0/1 interface Sends an update about network 10.2.0.0 and increments the hop count by 1 Stores network 10.0 out the FastEthernet 0/0 interface Receives update from R2 about network 10.0 and increments the hop count by 1 Stores network 10.0.3.0 in the routing table via Serial 0/0/0 with a metric of 1 Receives an update from R3 about network 10.0 and increments the hop count by 1 Stores network 10.2.0.

1. There is no change. therefore.0 with a metric of 1.4. therefore. the routing information remains the same.0.0.1.0 in the routing table via Serial 0/0/0 with a metric of 2 Same update from R2 contains information about network 10.1.2.0 out of Serial 0/0/0 interface Sends an update about networks 10. Q . Each router again checks the updates for new information.0.0 out of Serial 0/0/1 interface Receives an update from R1 about network 10. each router knows about the connected networks of its directly connected neighbors.3.0 and 10. After initial discovery is complete.168 Routing Protocols Companion Guide Video 3.1.0.0 and increments the hop count by 1 Stores network 10. Exchanging the Routing Information (3.3.0? Full knowledge and a converged network do not take place until there is another exchange of routing information.0.4.0.0.0. R2.4. Q Q Q R2: Q Q Q Sends an update about networks 10.0.3.0 out the Serial 0/0/0 interface Sends an update about networks 10.0 and that R3 does not yet know about 10. each router continues the convergence process by sending and receiving the following updates.0 and 10.0.1. the routing information remains the same. did you notice that R1 does not yet know about 10.0.0.4) At this point the routers have knowledge about their own directly connected networks and about the connected networks of their immediate neighbors. the routers exchange the next round of periodic updates. Receives an update from R3 about network 10.1. the routing information remains the same.0. After this first round of update exchanges. therefore. However.0.4.0. and R3 starting the initial exchange.3. Continuing the journey toward convergence. There is no change.0 and 10.0 out the FastEthernet 0/0 interface Receives an update from R2 about network 10. There is no change.3.3: Initial Exchange Video Go to the online course and play the animation of R1. R1: Q Q Sends an update about network 10.2.0.4.

1.0 out the Serial 0/0/1 interface Sends an update about networks 10. therefore.0. the routing information remains the same. For example.0 with a metric of 1. Split horizon prevents information from being sent out the same interface from which it was received.0 and 10. After routers within a network have converged. the router can then use the information within the route table to determine the best path to reach a destination.0 out the FastEthernet 0/0 interface Receives an update from R2 about network 10. Q Q Q Figure 3-7 displays the routing tables after the routers have converged.Chapter 3: Routing Dynamically 169 R3: Q Q Sends an update about network 10.4.2.1. Different routing protocols have different ways of calculating the best path.0 out of Serial 0/0/0.1. Figure 3-7 Routing Table After Convergence Video 3.3. because R2 learned about network 10. There is no change.3.0 through Serial 0/0/0.0.2. and R3 sending the latest routing table to their neighbors.0. R2 does not send an update containing the network 10.0.4: Next Update Video Go to the online course and play an animation of R1.0.0. R2.0.0. .0 and increments the hop count by 1 Stores network 10.0 in the routing table via Serial 0/0/1 with a metric of 2 Same update from R2 contains information about network 10.1. Distance vector routing protocols typically implement a routing loop prevention technique known as split horizon.1.

6: Investigating Convergence This activity will help you identify important information in routing tables and witness the process of network convergence. routing protocols can be rated based on the speed to convergence. such as RIP. Convergence is the time it takes routers to share information.170 Routing Protocols Companion Guide Achieving Convergence (3.3.3. Figure 3-8 Converging Packet Tracer Activity Packet Tracer Activity 3. the faster the convergence. such as EIGRP and OSPF. The routers share information with each other. calculate best paths. Convergence properties include the speed of propagation of routing information and the calculation of optimal paths. most networks require short convergence times. and update their routing tables.1.1. as shown in Figure 3-7. the better the routing protocol. but must independently calculate the impacts of the topology change on their own routes. Generally. older protocols. Because they develop an agreement with the new topology independently. whereas modern protocols. . As shown in Figure 3-8.5) The network has converged when all routers have complete and accurate information about the entire network. they are said to converge on this consensus. A network is not completely operable until the network has converged. therefore. are slow to converge. converge more quickly. Convergence is both collaborative and independent. The speed of propagation refers to the amount of time it takes for routers within the network to forward routing information.

Classifying Routing Protocols (3.Chapter 3: Routing Dynamically 171 Types of Routing Protocols (3. These routing protocols have evolved into the classless routing protocols. classless protocol EIGRP: IGP. This section gives an overview of the most common IP routing protocols. classful protocol IGRP (legacy): IGP. link-state protocol. this section gives a very brief overview of each protocol.1) Routing protocols can be classified into different groups according to their characteristics. link-state. Link-state routing protocols are classless by nature. classless protocol Q Q Q Q Q The classful routing protocols. link-state. For now. respectively. IPv4 routing protocols are classified as follows: Q Q RIPv1 (legacy): IGP. routing protocols can be classified by their: Q Q Q Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP) Operation: Distance vector protocol. Most of these routing protocols will be examined in detail in other chapters. distance vector.4. distance vector. . distance vector. path-vector. RIPv1 and IGRP. Specifically.1. classless protocol IS-IS: IGP. RIPv2 and EIGRP. classful protocol developed by Cisco (deprecated from 12. are legacy protocols and are only used in older networks. classless protocol BGP: EGP. Figure 3-9 displays a hierarchical view of dynamic routing protocol classification.4) Table 3-1 showed how routing protocols can be classified according to various characteristics.1. classless protocol developed by Cisco OSPF: IGP.2 IOS and later) RIPv2: IGP. or path-vector protocol Behavior: Classful (legacy) or classless protocol For example. distance vector.

EIGRP. IGPs include RIP. most engineers simply refer to BGP. and IS-IS. An AS is also known as a routing domain. OSPF. instead. .4. Companies.1. It is also referred to as inter-AS routing. Exterior Gateway Protocols (EGP): Used for routing between autonomous systems. The Border Gateway Protocol (BGP) is the only currently viable EGP and is the official routing protocol used by the Internet.2) An autonomous system (AS) is a collection of routers under a common administration such as a company or an organization. and even service providers use an IGP on their internal networks. and static routing. BGP. Typical examples of an AS are a company’s internal network and an ISP’s network. The example in Figure 3-10 provides simple scenarios highlighting the deployment of IGPs.172 Routing Protocols Companion Guide Figure 3-9 Routing Protocol Classification IGP and EGP Routing Protocols (3. organizations. two types of routing protocols are required: Q Interior Gateway Protocols (IGP): Used for routing within an AS. It is also referred to as intra-AS routing. Service providers and large companies may interconnect using an EGP. therefore. the term EGP is rarely used. The Internet is based on the AS concept. Q Note Because BGP is the only EGP available.

It interconnects with other autonomous systems and service providers using BGP to explicitly control how traffic is routed. connects to two different service providers).. BGP is not required because it is single-homed (i. it uses RIP as the IGP. Because it is multihomed (i. AS-3: This is a small organization with older routers within the AS. therefore. AS-2: This is a medium-sized organization and it uses OSPF as the IGP.4.. it uses BGP to explicitly control how traffic enters and leaves the AS.e.Chapter 3: Routing Dynamically 173 Figure 3-10 IGP versus EGP Routing Protocols There are five individual autonomous systems in the scenario: Q ISP-1: This is an AS and it uses IS-IS as the IGP. Q Q Q Q Note BGP is beyond the scope of this course and is not discussed in detail. static routing is implemented between the AS and the service provider. It interconnects with other autonomous systems and service providers using BGP to explicitly control how traffic is routed. and more . Instead. Distance Vector Routing Protocols (3. ISP-2: This is an AS and it uses OSPF as the IGP.e. delay. bandwidth. AS-1: This is a large organization and it uses EIGRP as the IGP. it uses BGP to explicitly control how traffic enters and leaves the AS. connects to one service provider).1. cost.3) Distance vector means that routes are advertised by providing two characteristics: Q Distance: Identifies how far it is to the destination network and is based on a metric such as the hop count. It is also multihomed.

16. using a link-state routing protocol is like having a complete map of the network topology.0/24 is one hop and that the direction is out of the interface Serial 0/0/0 toward R2. Distance vector routing protocols do not have an actual map of the network topology. Link-state routing protocols do not use periodic updates. To continue our analogy of sign posts. a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.4.3. The sign posts along the way from source to destination are not necessary. Distance vector protocols use routers as sign posts along the path to the final destination. in Figure 3-11. There are four distance vector IPv4 IGPs: Q Q Q RIPv1: First generation legacy protocol RIPv2: Simple distance vector routing protocol IGRP: First generation Cisco proprietary protocol (obsolete and replaced by EIGRP) EIGRP: Advanced version of distance vector routing Q Link-State Routing Protocols (3. because all link-state routers are using an identical map of the network. After the network has .1. RIP-enabled routers send periodic updates of their routing information to their neighbors. Figure 3-11 The Meaning of Distance Vector A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there.174 Routing Protocols Companion Guide Q Vector: Specifies the direction of the next-hop router or exit interface to reach the destination For example. R1 knows that the distance to reach network 172.4) In contrast to distance vector routing protocol operation. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology.

a link-state update is only sent when there is a change in the topology. in Figure 3-12. They were created when network addresses were allocated based on classes (i.0 network goes down.16. B. or . class A.3.4.0 network goes down. the link-state update is sent when the 172. Classless routing protocols include subnet mask information in the routing updates.1.4: Link-State Protocol Operation Video Go to the online course and play the animation to see how a link-state update is only sent when the 172.5) The biggest distinction between classful and classless routing protocols is that classful routing protocols do not send subnet mask information in their routing updates.3.Chapter 3: Routing Dynamically 175 converged. Figure 3-12 Link-State Protocol Operation Video 3.4.1.16.e.. usually occurring in large networks Fast convergence of the network is crucial The administrators have good knowledge of the implemented link-state routing protocol There are two link-state IPv4 IGPs: Q Q OSPF: Popular standards-based routing protocol IS-IS: Popular in provider networks Classful Routing Protocols (3. Link-state protocols work best in situations where: Q Q Q The network design is hierarchical. For example. The two original IPv4 routing protocols developed were RIPv1 and IGRP.

0/30).2. it only forwards the class B network address 172. because the network mask could be determined based on the first octet of the network address.0. Note Only RIPv1 and IGRP are classful. At that time.16.0.16.0/30 and 192. Classful routing protocols also create problems in discontiguous networks. refer to the topology in Figure 3-13.0. Classful addressing has never been a part of IPv6.2.1. All other IPv4 and IPv6 routing protocols are classless.0.16.176 Routing Protocols Companion Guide C).0 via R1 . It then creates and adds an entry for the class B 172.168.0/24) are both subnets of the same class B network (172.0/16). They are separated by different classful network addresses (192. When R1 forwards an update to R2.1.0. A discontiguous network is when subnets from the same classful major network address are separated by a different classful network address. Figure 3-13 R1 Forwards a Classful Update to R2 Notice that the LANs of R1 (172.168.16. To illustrate the shortcoming of classful routing.0/24) and R3 (172. Figure 3-14 R2 Adds the Entry for 172. R2 receives and processes the update. as shown in Figure 3-14. a routing protocol did not need to include the subnet mask in the routing update.16.0/16 network in the routing table.16. The fact that RIPv1 and IGRP do not include subnet mask information in their updates means that they cannot provide variable-length subnet masks (VLSMs) and Classless Inter-Domain Routing (CIDR). RIPv1 does not include the subnet mask information with the update.

a ping to 172.0. IPv6 routing protocols are classless. For example. This is known as load balancing. and IS-IS) all include the subnet mask information with the network address in routing updates.Chapter 3: Routing Dynamically 177 When R3 forwards an update to R2. When R1 forwards an update to R2.16.6) Modern networks no longer use classful IP addressing and the subnet mask cannot be determined by the value of the first octet. Figures 3-16 through 3-18 illustrate how classless routing solves the issues created with classful routing. Classless routing protocols support VLSM and CIDR.4.16. This pattern would continue until the ping command is done.U.1 would return “U. In the discontiguous network design of Figure 3-16.0.16. OSPF. the classless protocol RIPv2 has been implemented on all three routers. and R3 would return a Destination Unreachable (U) error code to R2. The second ping would exit out of R2’s Serial 0/0/0 interface toward R1. EIGRP.0/16 to its routing table.0 via R3 Discontiguous networks have a negative impact on a network. it also does not include the subnet mask information and therefore only forwards the classful network address 172.1. .0/24.16.16.1. The classless IPv4 routing protocols (RIPv2. All IPv6 routing protocols are considered classless because they include the prefix-length with the IPv6 address.U” because R2 would forward the first ping out its Serial 0/0/1 interface toward R3. When there are two entries with identical metrics in the routing table. as shown in Figure 3-15. RIPv2 includes the subnet mask information with the update 172.). Classless Routing Protocols (3.0. R2 receives and processes the update and adds another entry for the classful network address 172. and R1 would return a successful code (.0. Figure 3-15 R2 Adds the Entry for 172. the router shares the load of the traffic equally among the two links.1. The distinction whether a routing protocol is classful or classless typically only applies to IPv4 routing protocols.

1. and adds another child route entry 172.0/24.16.1 would now be successful.16. The first line displays the classful network address 172. The second entry displays the VLSM network address 172.2.1.0.2.2. and adds two entries in the routing table. Figure 3-17 R2 Adds the Entry for the 172.0/24 under the parent route entry 172. Figure 3-18 Entry for the 172. processes. R2 receives.1.178 Routing Protocols Companion Guide Figure 3-16 R1 Forwards a Classless Update to R2 In Figure 3-17.0. processes.0/24 Network via R1 When R3 forwards an update to R2.16. RIPv2 includes the subnet mask information with the update 172.16.16.16.0 with the /24 subnet mask of the update. . Parent routes never include an exit interface or next-hop IP address.16. as shown in Figure 3-18.0. This is referred to as the child route.0 with the exit and next-hop address. R2 receives. This is known as the parent route.16.0/24 Network via R3 A ping from R2 to 172.

Resource usage: Resource usage includes the requirements of a routing protocol such as memory space (RAM). Classless routing protocols support VLSM and better route summarization.1. Classful or classless (use of VLSM): Classful routing protocols do not include the subnet mask and cannot support variable-length subnet mask (VLSM). Q Q Q Q Table 3-4 summarizes the characteristics of each routing protocol. Scalability: Scalability defines how large a network can become. based on the routing protocol that is deployed.Chapter 3: Routing Dynamically 179 Routing Protocol Characteristics (3. the more preferable the protocol.7) Routing protocols can be compared based on the following characteristics: Q Speed of convergence: Speed of convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence. The larger the network is. CPU utilization. Table 3-4 Comparing Routing Protocols Distance Vector RIPv1 Speed of Convergence Scalability – Size of Network Use of VLSM Resource Usage Implementation and Maintenance Slow Small No Low Simple RIPv2 Slow Small Yes Low Simple IGRP Slow Small No Low Simple Link-State EIGRP Fast Large Yes Medium Complex OSPF Fast Large Yes High Complex IS-IS Fast Large Yes High Complex . and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation. Classless routing protocols include the subnet mask in the updates. in addition to the packet forwarding processes. the more scalable the routing protocol needs to be. Implementation and maintenance: Implementation and maintenance describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed. Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.4.

the RIP routing protocol has been enabled on all routers and the network has converged. Different routing protocols use different metrics. assume that PC1 wants to send a packet to PC2. whereas OSPF would choose the path with the highest bandwidth. Video 3. Therefore. For example. Therefore. the routing protocol must be able to evaluate and differentiate between the available paths. which would then forward it to R2. This is accomplished through the use of routing metrics. the best route to reach the PC2 network would be to send it to R3. the OSPF routing protocol has been enabled on all routers and the network has converged.180 Routing Protocols Companion Guide Routing Protocol Metrics (3. .8: Routing Protocols and Their Metrics Video Go to the online course and play the animation showing that RIP would choose the path with the least number of hops.4. the routing metrics are used to determine the overall “cost” of a path from source to destination.1.4. Routing protocols determine the best path based on the route with the lowest cost. the best route to reach the PC2 network would be to send it directly to R2 even though the link is much slower that all other links.8) There are cases when a routing protocol learns of more than one route to the same destination. Figure 3-19 RIP Uses Shortest Hop Count Path In Figure 3-20. when the packet arrives on R1. In Figure 3-19. To select the best path. A metric is a measurable value that is assigned by the routing protocol to different routes based on the usefulness of that route. RIP makes a routing protocol decision based on the least number of hops. when the packet arrives on R1. The metric used by one routing protocol is not comparable to the metric used by another routing protocol. OSPF makes a routing protocol decision based on the best bandwidth. In situations where there are multiple paths to the same remote network. Two different routing protocols might choose different paths to the same destination.1.

and troubleshooting these protocols.1. The router is only aware of the network addresses of its own interfaces and the remote network addresses it can reach through its neighbors.Chapter 3: Routing Dynamically 181 Figure 3-20 OSPF Uses Faster Links Interactive Graphic Activity 3.4.9: Classify Dynamic Routing Protocols Go to the online course to perform this practice activity. Some distance vector routing protocols send periodic updates. it continues to send updates. Routers using distance vector routing are not aware of the network topology. Understanding the operation of distance vector routing is critical to enabling.4. RIPv1 reaches all of . Distance Vector Dynamic Routing (3. Interactive Graphic Activity 3.1. and functionality of distance vector routing protocols. Distance Vector Technologies (3.2) This section describes the characteristics. verifying. Interactive Graphic Activity 3.1.1. RIP does this even if the topology has not changed.1) Distance vector routing protocols share updates between neighbors.11: Match the Metric to the Protocol Go to the online course to perform this practice activity.4. operations. RIP sends a periodic update to all of its neighbors every 30 seconds.10: Compare Routing Protocols Go to the online course to perform this practice activity. For example. Neighbors are routers that share a link and are configured to use the same routing protocol.2.

. As shown in Figure 3-21. Figure 3-21 Distance Vector Routing Protocols Distance Vector Algorithm (3. EIGRP only sends an update when needed.2. a broadcast.182 Routing Protocols Companion Guide its neighbors by sending updates to the all-hosts IPv4 address of 255. The algorithm is used to calculate the best paths and then send that information to the neighbors. The algorithm used for the routing protocols defines the following processes: Q Q Mechanism for sending and receiving routing information Mechanism for calculating the best paths and installing routes in the routing table Mechanism for detecting and reacting to topology changes Q Video 3.1. Every network device has to process a broadcast message.255. The broadcasting of periodic updates is inefficient because the updates consume bandwidth and consume network device CPU resources.2: Routers Route Packets Video Go to the online course and play the animation to see how the RIP routing protocol adds and deletes routes from a routing table. Additionally. use multicast addresses so that only neighbors that need updates will receive them. RIPv1 and IGRP are listed only for historical accuracy.2.1. instead. EIGRP can also send a unicast message to only the affected neighbor. RIPv2 and EIGRP.2) At the core of the distance vector protocol is the routing algorithm. the two modern IPv4 distance vector routing protocols are RIPv2 and EIGRP.255.255. instead of periodically.

RIPv1 has the following key characteristics: Q Q Q Routing updates are broadcasted (255. and make path determination decisions. . Jr.Chapter 3: Routing Dynamically 183 In the animation in the online course.2. R1 and R2 are configured with the RIP routing protocol.255.2. IGRP and EIGRP use the Diffusing Update Algorithm (DUAL) routing algorithm developed by Dr.3: Identify Distance Vector Terminology Go to the online course to perform this practice activity. For example: Q RIP uses the Bellman-Ford algorithm as its routing algorithm. It is based on two algorithms developed in 1958 and 1956 by Richard Bellman and Lester Ford. This section highlights similarities and differences between RIP and EIGRP. The hop count is used as the metric for path selection. Garcia-Luna-Aceves at SRI International. The algorithm on each router makes its calculations independently and updates the routing table with the new information. In this case. each router learns about a new network. A hop count greater than 15 hops is deemed infinite (too far). the algorithm constructs a triggered update and sends it to R1. R1 then removes the network from the routing table. That 15th hop router would not propagate the routing update to the next router.1) The Routing Information Protocol (RIP) was a first generation routing protocol for IPv4 originally specified in RFC 1058.J. Q Interactive Graphic Activity 3.255. J. The algorithm sends and receives updates.1. When the LAN on R2 goes down. send updates to neighbors.2) There are two main distance vector routing protocols. Routing Information Protocol (3. Both R1 and R2 then glean new information from the update.255) every 30 seconds. Different routing protocols use different algorithms to install routes in the routing table. It is easy to configure. Types of Distance Vector Routing Protocols (3.2.2. making it a good choice for small networks.

and reliability are used to create a composite metric.9 Yes Yes Yes Yes RIP updates are encapsulated into a UDP segment. 255.0.184 Routing Protocols Companion Guide In 1993. the IPv6-enabled version of RIP was released. delay.255.2.0. It used the following design characteristics: Q Q Bandwidth.0. because it includes the subnet mask in the routing updates. load.255. developed by Cisco in 1984. Q Q Q Table 3-5 summarizes the differences between RIPv1 and RIPv2.255 No No No No 224. with both source and destination port numbers set to UDP port 520. Secure: It supports an authentication mechanism to secure routing table updates between neighbors. instead of the broadcast address 255. Reduced routing entries: It supports manual route summarization on any interface.0. RIPng is based on RIPv2. The maximum number of hops is 15. RIPv2 introduced the following improvements: Q Classless routing protocol: It supports VLSM and CIDR. Table 3-5 RIPv1 versus RIPv2 RIPv1 RIPv2 Characteristics and Features Metric Updates Forwarded to Address Supports VLSM Supports CIDR Supports Summarization Supports Authentication Both use hop count as a simple metric. Increased efficiency: It forwards updates to multicast address 224. It still has a 15-hop limitation and the administrative distance is 120.255. Routing updates are broadcast every 90 seconds.255.2) The Interior Gateway Routing Protocol (IGRP) was the first proprietary IPv4 routing protocol.255.2. by default. RIPv1 evolved to a classless routing protocol known as RIP version 2 (RIPv2). . Enhanced Interior Gateway Routing Protocol (3. In 1997.9.

especially in large networks with many routes. IGRP was replaced by Enhanced IGRP (EIGRP). 255. reduces routing updates. whenever a change occurs. If a primary route fails. Reliability and load can also be included in the metric calculation if configured. instead of the periodic updates. Table 3-6 IGRP versus EIGRP IGRP EIGRP Characteristics and Features Metric Both use a composite metric based on bandwidth and delay. EIGRP increases efficiency. Maintains a topology table: Maintains all the routes received from neighbors (not only the best paths) in a topology table.255.10 Yes Yes Yes Yes Updates Forwarded to Address Supports VLSM Supports CIDR Supports Summarization Supports Authentication EIGRP also introduced: Q Bounded triggered updates: It does not send periodic updates. Q Q Q . EIGRP also introduced support for VLSM and CIDR. Only routing table changes are propagated. Rapid convergence: In most cases. the router can use the alternate route identified. It uses less bandwidth.Chapter 3: Routing Dynamically 185 In 1992.255. Hello keepalive mechanism: A small Hello message is periodically exchanged to maintain adjacencies with neighboring routers. This reduces the amount of load the routing protocol places on the network.0. Bounded triggered updates means that EIGRP only sends to the neighbors that need it. This means a very low usage of network resources during normal operation. Like RIPv2. it is the fastest IGP to converge because it maintains alternate routes. enabling almost instantaneous convergence.0.255 No No No No 224. The switchover to the alternate route is immediate and does not involve interaction with other routers. DUAL can insert backup routes into the EIGRP topology table. Table 3-6 summarizes the differences between IGRP and EIGRP. and supports secure message exchange.

3.3.2. For this reason. Packet Tracer Activity Packet Tracer Activity 3.186 Routing Protocols Companion Guide Q Multiple network layer protocol support: EIGRP uses Protocol Dependent Modules (PDM).1) Although RIP is rarely used in modern networks. Interactive Graphic Activity 3. or it can travel through R4 and R5. Configuring the RIP Protocol (3.2. The process by which routers select the best path depends on the routing protocol. R2. We will examine the behavior of two distance vector routing protocols. As well. it is useful as a foundation for understanding basic network routing. Enhanced Interior Gateway Routing Protocol (EIGRP) and Routing Information Protocol version 2 (RIPv2). and troubleshoot RIPv2. you will learn how to configure. which means that it is the only protocol to include support for protocols other than IPv4 and IPv6. this section provides a brief overview of how to configure basic RIP settings and to verify RIPv2. Router RIP Configuration Mode (3.2.2.1. understanding how RIP operates and knowing its implementation will make learning other routing protocols easier.3: Compare RIP and EIGRP Go to the online course to perform this practice activity. verify. it is still important to your networking studies because it might be encountered in a network implementation. Refer to the reference topology in Figure 3-22 and the addressing table in Table 3-7.3) Although the use of RIP has decreased in the past decade.4: Comparing RIP and EIGRP Path Selection PCA and PCB need to communicate. RIP and RIPng Routing (3. The path that the data takes between these end devices can travel through R1. . and R3.1) In this section. such as legacy IPX and AppleTalk.

0 R2 G0/0 S0/0/0 S0/0/1 R3 G0/0 S0/0/1 In this scenario. To enable RIP. use the no router rip global configuration command.1 192.4. Instead. Figure 3-23 displays a partial list of the various RIP commands that can be configured. remote network access is currently impossible.1.255.0 255. and version. This command stops the RIP process and erases all existing RIP configurations.255. use the router rip command to enter router configuration mode. all routers have been configured with basic management features and all interfaces identified in the reference topology are configured and enabled.255. as shown in the following output.168.255.2.255.168.1 192.1 192.1 192. therefore. This command does not directly start the RIP process. R1(config)# router rip R1(config-router)# To disable and eliminate RIP.255. passiveinterface.255.255.5.0 255.255. There are no static routes configured and no routing protocols enabled.0 255.255. R1# conf t Enter configuration commands. one per line.Chapter 3: Routing Dynamically 187 Figure 3-22 Table 3-7 Device R1 RIP Reference Topology Addressing Table Interface G0/0 S0/0/0 IP Address 192.255.255.168.2 192. This section covers the two highlighted commands as well as network.0 255.3. End with CNTL/Z. RIPv2 is used as the dynamic routing protocol.168.255.168.0 255.168.0 255.255.1 Subnet Mask 255.4.2.2 192. . it provides access to the router configuration mode where the RIP routing settings are configured.168.

3. But the router still needs to know which local interfaces it should use for communication with other routers.168.1.168. the router is instructed to run RIP. Associated interfaces now both send and receive RIP updates. but instead corrects the input and enters the classful network address. For example.0 in the running configuration file. Remember RIPv1 is a classful routing protocol for IPv4. Q Note If a subnet address is entered.1. The IOS does not give an error message. This command: Q Enables RIP on all interfaces that belong to a specific network.1.1. . use the network network-address router configuration mode command. Advertises the specified network in RIP routing updates sent to other routers every 30 seconds. Advertising Networks (3.2) By entering the RIP router configuration mode.3. as well as which locally connected networks it should advertise to those routers.188 Routing Protocols Companion Guide Figure 3-23 Note RIP Configuration Options The entire output in Figure 3-23 can be viewed in the online course on page 3. To enable RIP routing for a network. Enter the classful network address for each directly connected network. the IOS automatically converts it to the classful network address.32 command would automatically be converted to network 192. entering the network 192.1 graphic number 4.

1.0 R1(config-router)# network 192. 2. Examining Default RIP Settings (3. These are the networks that R1 includes in its RIP updates. R1(config)# router rip R1(config-router)# network 192. the network command is used to advertise the R1 directly connected networks.3.2.3) The output of the show ip protocols command in Figure 3-24 displays the IPv4 routing protocol settings currently configured on the router.1. RIP routing is configured and running on router R1. R1 is currently summarizing at the classful network boundary. The values of various timers. 3. for example.Chapter 3: Routing Dynamically 189 In the following command sequence.168.2: Advertising the R2 and R3 Networks Go to the online course to use the Syntax Checker in the second graphic to configure a similar configuration on R2 and R3. 4. .168. The classful networks are advertised by R1.0 R1(config-router)# Interactive Graphic Activity 3. Figure 3-24 Verifying RIP Settings on R1 This output confirms that: 1.3. 5. The version of RIP configured is currently RIPv1.1. the next routing update is sent by R1 in 16 seconds.

including their next-hop IP address. In Figure 3-25. flushed after 240 Redistributing: rip Default version control: send version 1. when a RIP process is configured on a Cisco router.1. it is running RIPv1. Note This command is also very useful when verifying the operations of other routing protocols (i. next due in 16 seconds Invalid after 180 seconds.e. EIGRP and OSPF). hold down 180. the associated AD that R2 uses for updates sent by this neighbor.190 Routing Protocols Companion Guide 6. Figure 3-25 Verifying RIP Routes on R1 Interactive Graphic Activity 3.4) By default.3: Advertising the R2 and R3 Networks Go to the online course to use the Syntax Checker in the third graphic to verify the R2 and R3 RIP settings and routes. The show ip route command displays the RIP routes installed in the routing table.3. receive any version Interface GigabitEthernet0/0 Serial0/0/0 Send 1 1 Recv 1 2 1 2 Triggered RIP Key-chain .3. The RIP neighbors are listed. R1 now knows about the highlighted networks.1. Enabling RIPv2 (3.. as shown in the following output: R1# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is "rip" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Sending updates every 30 seconds. and when the last update was received from this neighbor.

168. . Use the version 2 router configuration mode command to enable RIPv2. as shown in Figure 3-26.1.2.2 Distance 120 Last Update 00:00:15 Distance: (default is 120) R1# However.0 Routing Information Sources: Gateway 192. The RIP process now includes the subnet mask in all updates.168.Chapter 3: Routing Dynamically 191 Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 192. it can interpret both RIPv1 and RIPv2 messages.168. while configuring no version returns the router to the default setting of sending version 1 updates but listening for version 1 or version 2 updates.0 192. Note Configuring version 1 enables RIPv1 only. even though the router only sends RIPv1 messages. Figure 3-26 Enable and Verify RIPv2 on R1 Notice how the show ip protocols command verifies that R2 is now configured to send and receive version 2 messages only. making RIPv2 a classless routing protocol.2. A RIPv1 router ignores the RIPv2 fields in the route entry.

GigabitEthernet0/0 192. the version 2 command must be configured on all routers in the routing domain. 2 masks C L R1# 192. R2 and R3 are still sending RIPv1 updates.2.168.168. RIPv2 automatically summarizes networks at major network boundaries by default.1. Activity 3. Disabling Auto Summarization (3.3.4: Enable and Verify RIPv2 on R2 and R3 Interactive Graphic Go to the online course to use the Syntax Checker in the fourth graphic to enable RIPv2 on R2 and R3.0/24 is directly connected.0/24 is variably subnetted. GigabitEthernet0/0 192. Therefore.2.2. Serial0/0/0 192. Figure 3-27 Verify RIPv2 Route Summarization . Serial0/0/0 There are no RIP routes because R1 is now only listening for RIPv2 updates.192 Routing Protocols Companion Guide The following output verifies that there are no RIP routes still in the routing table: R1# show ip route | begin Gateway Gateway of last resort is not set 192.0/24 is directly connected.168.0/24 is variably subnetted.1.1.168.168.1. just like RIPv1.5) As shown in Figure 3-27. 2 masks C L 192.1.1/32 is directly connected. 2 subnets.168. 2 subnets.3.1/32 is directly connected.

Note RIPv2 must be enabled before automatic summarization is disabled. Wasted resources: All devices on the LAN must process the update up to the transport layers. at which point the devices will discard the update. When automatic summarization has been disabled. Sending out unneeded updates on a LAN impacts the network in three ways: Q Wasted bandwidth: Bandwidth is used to transport unnecessary updates. RIPv2 now includes all subnets and their appropriate masks in its routing updates. The show ip protocols output now states that automatic network summarization is not in effect. refer to the topology in Figure 3-22.1.3. However.659: %SYS-5-CONFIG_I: Configured from console by console R1# show ip protocols | section Automatic Automatic network summarization is not in effect R1# This command has no effect when using RIPv1. For instance. RIP updates are forwarded out all RIP-enabled interfaces. RIPv2 no longer summarizes networks to their classful address at boundary routers.6) By default.3. R1 has no way of knowing this and. Q . switches also forward the updates out all ports. use the no auto-summary router configuration mode command as shown in the following command sequence: R1(config)# router rip R1(config-router)# no auto-summary R1(config-router)# end R1# *Mar 10 14:11:49. RIP updates really only need to be sent out interfaces connecting to other RIP-enabled routers. sends an update every 30 seconds. Interactive Graphic Activity 3.5: Disable Automatic Summarization on R2 and R3 Go to the online course to use the Syntax Checker in the third graphic to disable automatic summarization on R2 and R3. Because RIP updates are either broadcasted or multicasted.Chapter 3: Routing Dynamically 193 To modify the default RIPv2 behavior of automatic summarization. RIP sends updates out of its Gigabit Ethernet 0/0 interface even though no RIP device exists on that LAN. as a result. Configuring Passive Interfaces (3.1.

. Figure 3-28 Configuring and Verifying a Passive Interface on R1 The show ip protocols command is then used to verify that the Gigabit Ethernet interface was passive. Notice that the Gigabit Ethernet 0/0 interface is no longer listed as sending or receiving version 2 updates. To address these problems. an interface can be configured to stop sending routing updates. The command stops routing updates out the specified interface. which means that this network is still included as a route entry in RIP updates that are sent to R2. Use the passive-interface router configuration command to prevent the transmission of routing updates through a router interface but still allow that network to be advertised to other routers.0 is still listed under Routing for Networks. The configuration in Figure 3-28 identifies the R1 Gigabit Ethernet 0/0 interface as passive.1. Routing updates can be modified and sent back to the router. This is referred to as configuring a passive interface. but instead is now listed under the Passive Interface(s) section.194 Routing Protocols Companion Guide Q Security risk: Advertising updates on a broadcast network is a security risk. Also notice that the network 192. and R3 to forward RIP updates out of their LAN interfaces. the network that the specified interface belongs to is still advertised in routing updates that are sent out other interfaces. There is no need for R1.168. However. Note All routing protocols support the passive-interface command. corrupting the routing table with false metrics that misdirect traffic. RIP updates can be intercepted with packet sniffing software. R2.

3.Chapter 3: Routing Dynamically 195 Interactive Graphic Activity 3. Interfaces that should not be passive can be re-enabled using the no passive-interface command. Figure 3-29 Propagating a Default Route on R1 Similar default static routes could be configured on R2 and R3. all interfaces can be made passive using the passive-interface default command.1. As an alternative. To propagate a default route. The default-information originate router configuration command. by propagating the static default route in RIP updates. Propagating a Default Route (3. Notice that R1 now has a Gateway of Last Resort and default route installed in its routing table. the default static route needs to be advertised to all other routers that use the dynamic routing protocol. Therefore. the edge router must be configured with: Q A default static route using the ip route 0.1. . R1 is single-homed to a service provider.0 exit-intf next-hop-ip command. Q The example in Figure 3-30 configures a fully specified default static route to the service provider.7) In the topology in Figure 3-29.0.0. all that is required for R1 to reach the Internet is a default static route going out of the Serial 0/0/1 interface. To provide Internet connectivity to all other networks in the RIP routing domain.0.0. and then the route is propagated by RIP.0 0.6: Configuring and Verifying a Passive Interface on R2 and R3 Go to the online course to use the Syntax Checker in the third graphic to configure a passive interface on R2 and R3. This instructs R1 to originate default information. but it is much more scalable to enter it one time on the edge router R1 and then have R1 propagate it to all other routers using RIP.3.

In this activity.3.3. you will configure a default route.196 Routing Protocols Companion Guide Figure 3-30 Configuring and Verifying a Default Route on R1 Interactive Graphic Activity 3. Configuring the RIPng Protocol (3.7: Verifying the Gateway of Last Resort on R2 and R3 Go to the online course to use the Syntax Checker in the third graphic to verify that the default route has been propagated to R2 and R3.1) As with its IPv4 counterpart. It is also useful as a foundation for understanding basic network routing.3.1. you will learn how to configure. and verify full connectivity. it is useful as a foundation for understanding basic network routing. Advertising IPv6 Networks (3. Refer to the reference topology in Figure 3-31. configure RIP version 2 with appropriate network statements and passive interfaces.2) In this section.1. Packet Tracer Activity Packet Tracer Activity 3. verify. and troubleshoot RIPng. this section provides a brief overview of how to configure basic RIPng. RIPng is rarely used in modern networks.2. For this reason.8: Configuring RIPv2 Although RIP is rarely used in modern networks.3. .

Chapter 3: Routing Dynamically 197 Figure 3-31 Enabling RIPng on the R1 Interfaces In this scenario. To propagate a default route. ipv6 unicast-routing must be configured. therefore. . there is no network network-address command available in RIPng. remote network access is currently impossible.3.2. Instead. R1 would have to be configured with: Q A default static route using the ipv6 route 0::/0 2001:DB8:FEED:1::1 global configuration command. IPv6 unicast routing is enabled and the Gigabit Ethernet 0/0 and Serial 0/0/0 interfaces are enabled for RIPng using the domain name RIP-AS: R1(config)# ipv6 unicast-routing R1(config)# R1(config)# interface gigabitethernet 0/0 R1(config-if)# ipv6 rip RIP-AS enable R1(config-if)# exit R1(config)# R1(config)# interface serial 0/0/0 R1(config-if)# ipv6 rip RIP-AS enable R1(config-if)# no shutdown R1(config-if)# Interactive Graphic Activity 3. For example. assume that R1 had an Internet connection from a Serial 0/0/1 interface to IP address 2001:DB8:FEED:1::1/64. use the ipv6 rip domain-name enable interface configuration command. In the following output. Unlike RIPv2. There are no static routes configured and no routing protocols enabled. The process to propagate a default route in RIPng is identical to RIPv2 except that an IPv6 default static route must be specified. In fact. To enable an IPv6 router to forward IPv6 packets. RIPng is enabled on an interface and not in router configuration mode. all routers have been configured with basic management features and all interfaces identified in the reference topology are configured and enabled.1: Enabling RIPng on the R2 and R3 Interfaces Go to the online course to use the Syntax Checker in the second graphic to enable RIPng on the R2 and R3 interfaces.

2. That RIPng routing is configured and running on router R1.198 Routing Protocols Companion Guide Q The ipv6 rip domain-name default-information originate interface configuration mode command. Figure 3-33 Verifying Routes on R1 . The output confirms that R1 now knows about the highlighted RIPng networks. Figure 3-32 Verifying RIPng Settings on R1 However. the Serial 0/0/1 interface of R1 would have to be configured with the ipv6 rip RIP-AS default-information originate command. 2. The show ipv6 route command displays the routes installed in the routing table as shown in Figure 3-33.3. For example. Examining the RIPng Configuration (3. The interfaces configured with RIPng. the command does confirm the following parameters: 1. the show ipv6 protocols command does not provide the same amount of information as its IPv4 counterpart.2) In Figure 3-32. This would instruct R1 to be the source of the default route information and propagate the default static route in RIPng updates sent out of the RIPngenabled interfaces.

This is because there is a difference in the way RIPv2 and RIPng calculate the hop counts. In RIPng. Packet Tracer Activity Packet Tracer Activity 3. Appending the rip keyword to the command as shown in Figure 3-34 only lists RIPng networks. This is because the metric (hop count) that is displayed in the IPv4 routing table is the number of hops required to reach the remote network (counting the next-hop router as the first hop). R2 advertises its LAN with a metric of 1. therefore. Similarly it considers the R3 LAN to be three hops away. With RIPv2 (and RIPv1).2.3. Figure 3-34 Verifying RIPng Routes on R1 Interactive Graphic Activity 3. RIPng is based on RIPv2 and has the same administrative distance and 15-hop limitation. Therefore.Chapter 3: Routing Dynamically 199 Notice that the R2 LAN is advertised as two hops away.2: Verifying RIPng Settings and Routes on R2 and R3 Go to the online course to use the Syntax Checker in the fourth graphic to verify RIPng settings and routes on R2 and R3.2.2. This activity will help you become more familiar with RIPng.3: Configuring RIPng RIPng (RIP Next Generation) is a distance vector routing protocol for routing IPv6 addresses.4: Configuring RIPv2 In this lab.3. you will complete the following objectives: Q Q Part 1: Build the Network and Configure Basic Device Settings Part 2: Configure and Verify RIPv2 Routing . Lab 3.3. R1 considers the R2 LAN to be two hops away. it adds another hop count of 1 to the metric. When R1 receives the update. the metric to the R2 LAN would be one hop. the sending router already considers itself to be one hop away.

whereas link-state routing protocols have the reputation of being very complex. even intimidating.4. the link-state process is simpler to understand than distance vector concepts.1.200 Routing Protocols Companion Guide Q Q Part 3: Configure IPv6 on Devices Part 4: Configure and Verify RIPng Routing Link-State Dynamic Routing (3. and functionality of link-state routing protocols.1) This section describes the characteristics. verifying. Link-State Routing Protocol Operation (3. However.1) Link-state routing protocols are also known as shortest path first protocols and are built around Edsger Dijkstra’s shortest path first (SPF) algorithm. The IPv4 link-state routing protocols are shown Figure 3-35: Q Q Open Shortest Path First (OSPF) Intermediate System-to-Intermediate System (IS-IS) Figure 3-35 Link-State Routing Protocols . Understanding the operation of link-state routing is critical to enabling.4. In many ways. The SPF algorithm is discussed in more detail in a later section. Shortest Path First Protocols (3. link-state routing protocols and concepts are not difficult to understand.4) Distance vector routing protocols are thought to be simple to understand. and troubleshooting these protocols. operations.

Just like RIP and EIGRP. Figure 3-36 Dijkstra’s Shortest Path First Algorithm The cost of the shortest path for R2 to send packets to the LAN attached to R3 is 27. In Figure 3-36. each router calculates the SPF algorithm and determines the cost from its own perspective. In other words. the basic functionality and configuration of link-state routing protocols is equally straightforward. each path is labeled with an arbitrary value for cost.2) All link-state routing protocols apply Dijkstra’s algorithm to calculate the best path route. basic OSPF operations can be configured using the: Q Q router ospf process-id global configuration command network command to advertise networks Dijkstra’s Algorithm (3. All links are represented with a solid black line. from source to destination.Chapter 3: Routing Dynamically 201 Link-state routing protocols have the reputation of being much more complex than their distance vector counterparts. the graphics throughout this section show the connections of the SPF tree. . Each router determines its own cost to each destination in the topology. This algorithm uses accumulated costs along each path. which is determined by the SPF tree. to determine the total cost of a route. For this reason. Note The focus of this section is on cost. However. Specifically.4. not the topology. the cost is R2 to R1 (20) plus R1 to R3 (5) plus R3 to LAN (2).1. The algorithm is commonly referred to as the shortest path first (SPF) algorithm.

However. Observe the shortest path for each router to reach each of the LANs. It might be assumed that R1 would send directly to R4 instead of to R3. Table 3-8 Destination R1 LAN R3 LAN R4 LAN R5 LAN R2 SPF Tree Shortest Path R2 to R1 R2 to R1 to R3 R2 to R5 to R4 R2 to R5 Cost 22 27 22 12 . as shown in Tables 3-8 through 3-11.202 Routing Protocols Companion Guide SPF Example (3. look at the path to the R5 LAN. For example.3) The table in Figure 3-37 displays the shortest path and the accumulated cost to reach the identified destination networks from the perspective of R1. Figure 3-37 R1 SPF Tree The shortest path is not necessarily the path with the least number of hops.1.4. the cost to reach R4 directly (22) is higher than the cost to reach R4 through R3 (17).

Chapter 3: Routing Dynamically 203 Table 3-9 Destination R1 LAN R2 LAN R4 LAN R5 LAN R3 SPF Tree Shortest Path R3 to R1 R3 to R1 to R2 R3 to R4 R3 to R4 to R5 Cost 7 27 12 22 Table 3-10 Destination R1 LAN R2 LAN R3 LAN R5 LAN R4 SPF Tree Shortest Path R4 to R3 to R1 R4 to R5 to R2 RR4 to R3 R4 to R5 Cost 17 22 12 12 Table 3-11 Destination R1 LAN R2 LAN R3 LAN R4 LAN R5 SPF Tree Shortest Path R5 to R4 to R3 to R1 R5 to R2 R5 to R4 to R3 R5 to R4 Cost 27 12 22 12 Link-State Updates (3. Information about the state of those links is known as link-states. a link is an interface on a router.1) So exactly how does a link-state routing protocol work? With link-state routing protocols. This section discusses how OSPF exchanges LSUs to discover the best routes. .2) Link-state updates (LSUs) are the packets used for OSPF routing updates.4.4. Link-State Routing Process (3.2.

its own directly connected networks. R1 lost power briefly and had to restart. Note This process is the same for both OSPF for IPv4 and OSPF for IPv6. Each router learns about its own links and its own directly connected networks. They then flood the LSPs to their neighbors until all routers in the area have received the LSPs.4. Each router stores a copy of each LSP received from its neighbors in a local database. As the previously configured interfaces become active. including neighbor ID. This is done by detecting that an interface is in the up state. Regardless of the routing protocols used. . Link-state routers do this by exchanging Hello packets with other linkstate routers on directly connected networks. Refer to the topology in Figure 3-38. assume that R1 was previously configured and had full connectivity to all neighbors. 4. For purposes of this discussion. 5. Each router is responsible for meeting its neighbors on directly connected networks. Each router uses the database to construct a complete map of the topology and computes the best path to each destination network.2) The first step in the link-state routing process is that each router learns about its own links. The examples in this section refer to OSPF for IPv4. However.204 Routing Protocols Companion Guide All routers in an OSPF area will complete the following generic link-state routing process to reach a state of convergence: 1. 3. link type. these directly connected networks are now entries in the routing table. and bandwidth. Each router builds a link-state packet (LSP)containing the state of each directly connected link. Link and Link-State (3. This is done by recording all the pertinent information about each neighbor. 2. The SPF algorithm is used to construct the map of the topology and to determine the best path to each network. Those neighbors store all LSPs received in a database. Like having a road map. When a router interface is configured with an IP address and subnet mask. During boot up R1 loads the saved startup configuration file. the interface becomes part of that network. Each router floods the LSP to all neighbors. the router now has a complete map of all destinations in the topology and the routes to reach them. R1 learns about its own directly connected networks.2.

0.4.0. and the link must be in the up state before the link-state routing protocol can learn about a link.0.0/16 Serial 0/0/0: 10.2.1.0/16 Serial 0/0/1: 10. such as Ethernet (broadcast) or Serial point-to-point link The cost of that link Any neighbor routers on that link . Also. Figure 3-38 shows R1 linked to four directly connected networks: Q Q Q Q FastEthernet 0/0: 10. like distance vector protocols.3. the link-state information includes: Q Q Q Q The interface’s IPv4 address and subnet mask The type of network. the interface must be properly configured with an IPv4 address and subnet mask.0.0/16 Serial 0/1/0: 10. the interface must be included in one of the network router configuration statements before it can participate in the link-state routing process.Chapter 3: Routing Dynamically 205 Figure 3-38 R1 Links As with distance vector protocols and static routes.0/16 As shown in Figures 3-39 through 3-42.

206 Routing Protocols Companion Guide Figure 3-39 Link-State of Interface Fa0/0 Figure 3-40 Link-State of Interface S0/0/0 Figure 3-41 Link-State of Interface S0/0/1 .

Say Hello (3. R1 sends Hello packets out its links (interfaces) to discover if there are any neighbors.4.3) The second step in the link-state routing process is that each router is responsible for meeting its neighbors on directly connected networks. A neighbor is any other router that is enabled with the same linkstate routing protocol. In Figure 3-43. we are using arbitrary cost values to simplify the demonstration. Routers with link-state routing protocols use a Hello protocol to discover any neighbors on their links.Chapter 3: Routing Dynamically 207 Figure 3-42 Note Link-State of Interface S0/1/0 Cisco’s implementation of OSPF specifies the OSPF routing metric as the cost of the link based on the bandwidth of the outgoing interface. Figure 3-43 R1 Sends Hello Packets . For the purposes of this chapter.2.

A simplified version of the LSP from R1 displayed in Figure 3-45 would contain the following: 1. they form an adjacency.4. If a router stops receiving Hello packets from a neighbor. Because R1 does not receive a Hello on this interface. There are no neighbors out the FastEthernet 0/0 interface. that neighbor is considered unreachable and the adjacency is broken. Ethernet network 10. R3. These small Hello packets continue to be exchanged between two adjacent neighbors and serve as a keepalive function to monitor the state of the neighbor. and R4 Reply with Hello Packets Video 3. When two link-state routers learn that they are neighbors. Figure 3-44 R2.3: Neighbor Discovery—Hello Packets Video Go to the online course and play the animation to view the link-state neighbor discovery process with Hello packets.0. it can build its LSPs that contain the link-state information about its links. and R4 reply to the Hello packet with their own Hello packets because these routers are configured with the same link-state routing protocol. Serial point-to-point network.208 Routing Protocols Companion Guide In Figure 3-44.0/16.2.4) The third step in the link-state routing process is that each router builds an LSP containing the state of each directly connected link. Cost 20 .1. 10. it does not continue with the link-state routing process steps for the FastEthernet 0/0 link.0. R1 -> R2.2. After a router has established its adjacencies. Building the Link-State Packet (3.4.2. R2.0/16. Cost 2 2. R3. R1.

0. it immediately sends that LSP out all other interfaces except the interface that received the LSP. .4.5) The fourth step in the link-state routing process is that each router floods the LSP to all neighbors. Cost 5 4.0/16.Chapter 3: Routing Dynamically 209 3.2. who then store all LSPs received in a database. 10. Serial point-to-point network. Figure 3-46 R1 Floods Its LSP Whenever a router receives an LSP from a neighboring router.0/16. Serial point-to-point network. This process creates a flooding effect of LSPs from all routers throughout the routing area.3.4. R1 -> R4. Each router floods its link-state information to all other link-state routers in the routing area as shown in Figure 3-46. R1 -> R3. Cost 20 Figure 3-45 Building the LSP Flooding the LSP (3. 10.0.

0/16.. These LSPs are stored in the link-state database. such as sequence numbers and aging information.4. link-state routing protocols reach convergence very quickly. router restart) Whenever there is a change in the topology (e. all routers receive an LSP from every other link-state router in the routing area.2.0.0.0. Table 3-12 Link-State Database R1 Link-states: Connected to network 10. This information is used by each router to determine if it has already received the LSP from another router or if the LSP has newer information than what is already contained in the link-state database.0. Eventually. to help manage the flooding process.g. Remember that LSPs do not need to be sent periodically.6) The final step in the link-state routing process is that each router uses the database to construct a complete map of the topology and computes the best path to each destination network. cost = 2 Connected to R2 on network 10. Table 3-12 displays the link-state database content of R1. cost = 5 Connected to R4 on network 10.. cost = 20 Connected to R3 on network 10.2. a link going down or coming up. An LSP only needs to be sent: Q During initial startup of the routing protocol process on that router (e.g. In the animation. a neighbor adjacency being established or broken) Q In addition to the link-state information.5: Routers Route Packets Video Go to the online course and play the animation to view the LSP flooding. Link-state routing protocols calculate the SPF algorithm after the flooding is complete.2.1.0/16. Building the Link-State Database (3. other information is included in the LSP.2.3.4. cost = 20 .210 Routing Protocols Companion Guide Video 3.0/16. As a result. the LSPs are flooded almost immediately after being received without any intermediate calculations. This process allows a router to keep only the most current information in its link-state database.0/16.

0.0/16. cost = 2 Connected to R1 on network 10.0. cost = 20 Connected to R3 on network 10.2.7. R1 has learned the link-state information for each router in its routing area.7) Each router in the routing area uses the link-state database and SPF algorithm to construct the SPF tree. cost = 10 R3 Link-states: Connected to network 10.0/16. Notice that R1 also includes its own link-state information in the link-state database.6.0/16. R1 can now use the database and the shortest path first (SPF) algorithm to calculate the preferred path or shortest path to each network. The SPF algorithm then calculates the shortest paths to reach each individual network.0/16. .8.Chapter 3: Routing Dynamically 211 R2 Link-states: Connected to network 10.0. cost = 5 Connected to R4 on network 10.0/16.0/16. With a complete link-state database.7. cost = 10 As a result of the flooding process.0.5.10. To begin. the SPF algorithm interprets each router’s LSP to identify networks and associated costs.9.0/16.2.0/16.0. cost = 10 R5 Link-states: Connected to network 10.0. cost = 10 Connected to R4 on network 10.4. resulting in the SPF tree as shown in Figure 3-47.0.0.3.0. cost = 2 Connected to R1 on network 10. resulting in the SPF tree. For example.9.0/16. cost = 2 Connected to R1 on network 10.0.0/16. using the link-state information from all other routers.10.0.0/16. cost = 10 R4 Link-states: Connected to network 10. R1 now has a complete topology view of the link-state area. R1 can now begin to construct an SPF tree of the network.0. Building the SPF Tree (3.0/16.4.0/16.11.0. cost = 2 Connected to R2 on network 10. cost = 20 Connected to R5 on network 10. cost = 10 Connected to R5 on network 10.

8) Using the shortest path information determined by the SPF algorithm.2. Packets are now forwarded according to these entries in the routing table.4. .2. the link-state databases used to construct those trees must be identical on all routers.7 in Figures 1 through 6. such as static routes. To ensure proper routing.212 Routing Protocols Companion Guide Note The entire process can be viewed in the online course on page 3.4. Figure 3-47 Resulting SPF Tree of R1 Each router constructs its own SPF tree independently from all other routers. Adding OSPF Routes to the Routing Table (3. these paths can now be added to the routing table. Figure 3-48 Populate the Routing Table The routing table also includes all directly connected networks and routes from any other sources. Figure 3-48 shows the routes that have now been added to R1’s IPv4 routing table.

The LSP contains only the information regarding the affected link.2. Because link-state routing protocols exchange link-states.1) There are several advantages of link-state routing protocols compared to distance vector routing protocols.3) This section discusses the advantages of using link-state routing protocols and compares the two types of link-state routing protocols. Hierarchical design: Link-state routing protocols use the concept of areas. The SPF algorithm requires more CPU time than distance vector algorithms such as Bellman-Ford. allowing for better route aggregation (summarization) and the isolation of routing issues within an area.4. Multiple areas create a hierarchical design to networks. link-state routing protocols immediately flood the LSP out all interfaces except for the interface from which the LSP was received. but can also be an issue on unstable networks.Chapter 3: Routing Dynamically 213 Interactive Graphic Activity 3. In contrast. Event-driven updates: After the initial flooding of LSPs. Bandwidth requirements: The flooding of link-state packets can adversely affect the available bandwidth on a network.3. or SPF tree of the network topology.4. Q Q Q Link-state protocols also have a few disadvantages compared to distance vector routing protocols: Q Memory requirements: Link-state protocols require additional memory to create and maintain the link-state database and SPF tree.9: Building the Link-State Database and SPF Tree Go to the online course to perform this practice activity. Why Use Link-State Protocols? (3. Why Use Link-State Routing Protocols? (3. link-state routing protocols do not send periodic updates. link-state routing protocols only send out an LSP when there is a change in the topology. Processing requirements: Link-state protocols can also require more CPU processing than distance vector routing protocols. because linkstate protocols build a complete map of the topology. Using the SPF tree. the SPF algorithm can build an SPF tree of the network. each router can independently determine the shortest path to every network.4. Q Q . Q Builds a topological map: Link-state routing protocols create a topological map. Unlike some distance vector routing protocols. RIP needs to process each routing update and update its routing table before flooding the routing update out other interfaces. This should only occur during initial startup of routers. Fast convergence: When receiving an LSP.

CPU. and bandwidth. only those routers in the affected area receive the LSP and run the SPF algorithm. The use and configuration of multiple areas can reduce the size of the link-state databases. area 0. there are three separate routing domains: area 1.3. but this is done with a type of LSP that does not cause them to rerun their SPF algorithm. Only those routers in area 51 need to update their link-state databases.3. The development of OSPF began in 1987 and there are two current versions in use: Q Q OSPFv2: OSPF for IPv4 networks (RFC 1247 and RFC 2328) OSPFv3: OSPF for IPv6 networks (RFC 2740) . When there is a change in the topology.2) Modern link-state routing protocols are designed to minimize the effects on memory. in Figure 3-49. Open Shortest Path First (OSPF) is the most popular implementation. Protocols that Use Link-State (3. Routers in other areas learn that this route is down.214 Routing Protocols Companion Guide Link-State Protocols Support Multiple Areas (3. Multiple areas can also limit the amount of link-state information flooding in a routing domain and send LSPs only to those routers that need them. create a new SPF tree. For example.4. the LSP with the information about this downed link is only flooded to other routers in that area. and area 51. Figure 3-49 Create Areas to Minimize Router Resource Usage If a network in area 51 goes down. and update their routing tables.4. It was designed by the Internet Engineering Task Force (IETF) OSPF Working Group. OSPF and IS-IS. This can help isolate an unstable link to a specific area in the routing domain. rerun the SPF algorithm. Routers in other areas can update their routing tables directly.3) There are only two link-state routing protocols.

OSPFv3 includes support for both IPv4 and IPv6. The first incarnation of this routing protocol was developed at Digital Equipment Corporation (DEC) and is known as DECnet Phase V. Radia Perlman was the chief designer of the IS-IS routing protocol. included support for IP networks.1.5) As a network administrator. For example.5. There are many pro-OSPF and pro-IS-IS factions who discuss and debate the advantages of one routing protocol over the other. regardless of your level of familiarity with a particular routing protocol. Parts of an IPv4 Route Entry (3. The Routing Table (3. you might encounter a situation in which the routing table has all of the routes you would expect to see. . IS-IS was originally designed for the OSI protocol suite and not the TCP/IP protocol suite. OSPF and IS-IS share many similarities and also have many differences.5. Understanding the structure and lookup process of the routing table will help you diagnose any routing table issue. Routing Table Entries (3. Later. or Dual IS-IS. IS-IS was designed by International Organization for Standardization (ISO) and is described in ISO 10589. Knowing how to step through the lookup process of a destination IP address for a packet will enable you to determine whether the packet is being forwarded as expected. it is important to know the routing table in depth when troubleshooting network issues.1) The topology displayed in Figure 3-50 is used as the reference topology for this section. Integrated IS-IS.1) A routing table consists of directly connected networks and routes learned statically or dynamically. if and why the packet is being sent elsewhere. Although IS-IS has been known as the routing protocol used mainly by ISPs and carriers. This section examines these two types of routing table entries. Both routing protocols provide the necessary routing functionality. or whether the packet has been discarded.Chapter 3: Routing Dynamically 215 Note With the OSPFv3 Address Families feature. but packet forwarding is not performing as expected. more enterprise networks are beginning to use IS-IS.

0. Figure 3-51 Note Routing Table of R1 The routing table hierarchy in Cisco IOS was originally implemented with the classful routing scheme. and dynamic routes. R3 is also introducing a 192. Although the routing table incorporates both classful and classless addressing. . Therefore. Q Q Figure 3-51 displays the IPv4 routing table of R1 with directly connected.0/16 supernet route.168. R2. it is propagating a default static route to R2 and R3.216 Routing Protocols Companion Guide Figure 3-50 Reference Topology Notice that in the topology: Q R1 is the edge router that connects to the Internet. static. R1. the overall structure is still built around this classful scheme. and R3 contain discontiguous networks separated by another classful network.

16.1. L identifies that this is a local route.0. Directly connected interfaces have two route source codes. Notice that two routing table entries are automatically created when an active router interface is configured with an IP address and subnet mask.Chapter 3: Routing Dynamically 217 Directly Connected Entries (3. . Local routes are automatically created whenever an interface is configured with an IP address and activated. Directly connected networks are automatically created whenever an interface is configured with an IP address and activated. Figure 3-52 Directly Connected Interfaces of R1 Figure 3-53 displays one of the routing table entries on R1 for the directly connected network 172. Figure 3-53 Directly Connected Routes of R1 The entries contain the following information: Q Route source: Identifies how the route was learned. These entries were automatically added to the routing table when the GigabitEthernet 0/0 interface was configured and activated.2) As highlighted in Figure 3-52. C identifies a directly connected network.1.5. the routing table of R1 contains three directly connected networks.

R: Identifies that the route was learned dynamically from another router using the RIP routing protocol. Q Note Local routing table entries did not appear in routing tables prior to IOS release 15. D: Identifies that the route was learned dynamically from another router using the EIGRP routing protocol.3) Figure 3-54 displays an IPv4 routing table entry on R1 for the route to remote network 172. O: Identifies that the route was learned dynamically from another router using the OSPF routing protocol. Q Q Q Remote Network Entries (3.5. .0 on R3. Figure 3-54 Remote Network Route Entry on R1 The entry identifies the following information: Q Q Route source: Identifies how the route was learned. Destination network: Identifies the address of the remote network. Outgoing interface: Identifies the exit interface to use when forwarding packets to the destination network. common codes for remote networks include: Q S: Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route.218 Routing Protocols Companion Guide Q Destination network: The address of the remote network and how that network is connected. the route source identifies how the route was learned. For instance. As with directly connected networks.4. The routing table stores information about both directly connected and remote routes. A router typically has multiple interfaces configured.1.16.

Chapter 3: Routing Dynamically 219 Q Q Administrative distance: Identifies the trustworthiness of the route source. Special terms are applied when discussing the contents of a routing table. Lower values indicate preferred routes.5. Route timestamp: Identifies from when the route was last heard.2) The structure or format of the routing table might seem obvious until you take a closer look.5. it is crucial to understand the output generated by the routing table.5. Metric: Identifies the value assigned to reach the remote network. Routing Table Terms (3. as shown in Figure 3-55.4: Identify Parts of an IPv4 Routing Table Entry Go to the online course to perform this practice activity. Therefore.1.2. Figure 3-55 Routing Table of R1 . Understanding the structure of the routing table will help you verify and troubleshoot routing issues because you will understand the routing table lookup process. Q Q Q Interactive Graphic Activity 3. Dynamically Learned IPv4 Routes (3.1) A dynamically built routing table provides a great deal of information. Next hop: Identifies the IPv4 address of the next router to forward the packet to. Outgoing interface: Identifies the exit interface to use to forward a packet toward the final destination.

In Figure 3-56. Directly connected. a level 1 route can be a: Q Network route: A network route has a subnet mask equal to that of the classful mask. and local routes are ultimate routes. dynamically learned. Notice that all of these routes specify either a next-hop IPv4 address or an exit interface.2) An ultimate route is a routing table entry that contains either a next-hop IPv4 address or an exit interface. Within this structure.5.2. Figure 3-56 Ultimate Routes of R1 Level 1 Route (3.3) A level 1 route is a route with a subnet mask equal to or less than the classful mask of the network address.5. Routes are discussed in terms of: Q Q Q Q Ultimate route Level 1 route Level 1 parent route Level 2 child routes Ultimate Route (3.2. The routing table is actually a hierarchical structure that is used to speed up the lookup process when locating routes and forwarding packets. the hierarchy includes several levels. .220 Routing Protocols Companion Guide The Cisco IP routing table is not a flat database. the highlighted areas are examples of ultimate routes. Therefore.

Default route: A default route is a static route with the address 0. for example.4) As illustrated in Figure 3-59.0.Chapter 3: Routing Dynamically 221 Q Supernet route: A supernet route is a network address with a subnet mask less than the classful mask. a level 1 parent route is a level 1 network route that is subnetted. Figure 3-58 Example of Level 1 Routes Level 1 Parent Route (3.5. Figure 3-57 Sources of Level 1 Routes Figure 3-58 highlights level 1 routes. static route. or a dynamic routing protocol. . a summary address.0. Figure 3-57 highlights how level 1 routes are also ultimate routes.0/0. A parent route can never be an ultimate route. Q The source of the level 1 route can be a directly connected network.2.

As illustrated in Figure 3-61. a level 1 parent route is a level 1 network route that is subnetted. Each entry displays the classful network address. . The routing table basically provides a heading for the specific subnets it contains. and the number of different subnet masks that the classful address has been subdivided into.2.5. Figure 3-60 Level 1 Parent Routes of R1 Level 2 Child Route (3. the number of subnets.5) A level 2 child route is a route that is a subnet of a classful network address.222 Routing Protocols Companion Guide Figure 3-59 Level 1 Parent Route Figure 3-60 highlights the level 1 parent routes in the routing table of R1.

A level 1 parent route is the classful network address of the subnet route. Note The routing table hierarchy in Cisco IOS has a classful routing scheme. as shown in Figure 3-62. This is the case even if a classless routing protocol is the source of the subnet route. a static route. . Figure 3-63 highlights the level 2 child routes in the routing table of R1. Figure 3-62 Child Routes Are Ultimate Routes Like a level 1 route. Level 2 child routes are also ultimate routes. or a dynamically learned route.Chapter 3: Routing Dynamically 223 Figure 3-61 Level 2 Child Routes A level 1 parent route contains level 2 child routes. the source of a level 2 route can be a directly connected network.

. the router examines the IPv4 header.1) When a packet arrives on a router interface. In Figure 3-64. Interactive Graphic Activity 3.3) Now that you understand the structure of the routing table.5. this section will help you understand the routing table lookup process.224 Routing Protocols Companion Guide Figure 3-63 Note Example of Level 2 Child Routes The entire output in Figure 3-63 can be viewed in the online course on page 3.6: Identify Parent and Child IPv4 Routes Go to the online course to perform this practice activity. The IPv4 Route Lookup Process (3.5.5. identifies the destination IPv4 address. and proceeds through the router lookup process.5 graphic number 3.5.2.3.2. Route Lookup Process (3. the router examines level 1 network routes for the best match with the destination address of the IPv4 packet.

Figure 3-65 Match Level 2 Child Routes 3. If the best match is a level 1 ultimate route. In Figure 3-65.Chapter 3: Routing Dynamically 225 Figure 3-64 Match Level 1 Routes Specifically. if there is one. including the default route. proceed to the next step. If the best match is a level 1 parent route. 4. the router proceeds as follows: 1. then this route is used to forward the packet. . the router examines child routes (the subnet routes) of the parent route for a best match. 2. proceed to the next step. In Figure 3-66. If there is a match with a level 2 child route. the router continues searching level 1 supernet routes in the routing table for a match. If there is not a match with any of the level 2 child routes. that subnet is used to forward the packet.

5. . a packet is destined for 172. for any of these routes to be considered a match there must be at least the number of matching bits indicated by the subnet mask of the route.0/26 has the longest match and is therefore chosen to forward the packet.3. Remember that an IPv4 packet only contains the IPv4 address and not the subnet mask.0. If there is not a match with any route in the routing table. Of the three routes. or the longest match. the router uses that route to forward the packet.0. A recursive lookup is performed on the next-hop IP address until the route is resolved to an exit interface.2) What is meant by the router must find the best match in the routing table? Best match is equal to the longest match. In Figure 3-67. 172. and 172. The subnet mask of the route in the routing table is used to determine the minimum number of far left bits that must match.16. the router drops the packet. Note A route referencing only a next-hop IP address and not an exit interface must be resolved to a route with an exit interface.0.226 Routing Protocols Companion Guide Figure 3-66 Match Supernet and Then Default Route 5. The route with the greatest number of equivalent far left bits.16.16. Remember.0/26.16.0/18. The router has three possible routes that match this packet: 172. The best match is the route in the routing table that has the most number of far left matching bits with the destination IPv4 address of the packet.10.0. 6. Best Route = Longest Match (3. a minimum number of far left bits must match between the IPv4 address of the packet and the route in the routing table. If there is now a lesser match with a level 1 supernet or default routes. is always the preferred route.16. 172.0/12.0. For there to be a match between the destination IPv4 address of a packet and a route in the routing table.

5. This section examines the IPv6 routing table.Chapter 3: Routing Dynamically 227 Figure 3-67 Matches for Packets Destined to 172.3: Determine the Longest Match Route Go to the online course to perform this practice activity.0. There is no level 1 parent of level 2 child routes. it is populated using directly connected interfaces. For instance.3. All routers have redundant paths to various networks. Analyze an IPv6 Routing Table (3. IPv6 Routing Table Entries (3. It also consists of directly connected networks and routes learned statically or dynamically. The topology displayed in Figure 3-68 is used as the reference topology for this section.5. the entries are displayed somewhat differently than IPv4 entries. EIGRP for IPv6 has been configured on all three routers. R2. and dynamically learned routes. Notice that in the topology: Q R1. R2 is the edge router and connects to the ISP. however.16. static routes. However. all routes are effectively level 1 ultimate routes.10 Interactive Graphic Activity 3.4. Because IPv6 is classless by design. and R3 are configured in a full mesh topology.1) Components of the IPv6 routing table are very similar to the IPv4 routing table.5. a default static route is not being advertised.4) The IPv6 routing table shares many similarities with the IPv4 routing table. Q Q .

it still contains the relevant route information. The three entries were added when the interfaces were configured and activated. .228 Routing Protocols Companion Guide Figure 3-68 Reference IPv6 Topology Directly Connected Entries (3. Figure 3-69 IPv6 Routing Table of R1 Figure 3-70 highlights the connected network and local routing table entries of the directly connected interfaces.4.5.2) The routing table of R1 is displayed in Figure 3-69 using the show ipv6 route command. Although the command output is displayed slightly differently than in the IPv4 version.

The reference bandwidth is not a realistic representation of modern networks. . Outgoing interface: Identifies the exit interface to use when forwarding packets to the destination network. most trustworthy source. Metric: Identifies the value assigned to reach the remote network. IPv6 uses the same distances as IPv4. It is used only to provide a visual sense of link speed. Directly connected network: The IPv6 address of the directly connected network. Lower values indicate preferred routes.Chapter 3: Routing Dynamically 229 Figure 3-70 Directly Connected Routes on R1 As shown in Figure 3-71. directly connected route entries display the following information: Q Route source: Identifies how the route was learned. Q Q Q Q Note The serial links have reference bandwidths configured to observe how EIGRP metrics select the best route. A value of 0 indicates the best. Directly connected interfaces have two route source codes (C identifies a directly connected network while L identifies that this is a local route). Administrative distance: Identifies the trustworthiness of the route source.

. and the link between R2 and R3). The three entries were added by the EIGRP. R2 LAN.230 Routing Protocols Companion Guide Figure 3-71 Directly Connected Routes on R1 Remote IPv6 Network Entries (3. R3 LAN.3) Figure 3-72 highlights the routing table entries for the three remote networks (i.5.e.4. . Figure 3-72 Remote Networks Entries on R1 Figure 3-73 displays a routing table entry on R1 for the route to remote network 2001:DB8:CAFE:3::/64 on R3.

. Destination network: Identifies the address of the remote IPv6 network. For example. Activity 3. R (RIP). D (EIGRP). Lower values indicate preferred routes. if there are multiple matches in the routing table. Metric: Identifies the value assigned to reach the remote network. A match is made by matching the far left bits of the packet’s destination IPv6 address with the IPv6 prefix and prefix-length in the IPv6 routing table. the router examines the IPv6 header and identifies the destination IPv6 address. IPv6 uses the same distances as IPv4. The router examines level 1 network routes for the best match with the destination address of the IPv6 packet. The router then proceeds through the following router lookup process.4. Outgoing interface: Identifies the exit interface to use to forward a packet toward the final destination. the longest match is the best match.4: Identify Parts of an IPv6 Routing Table Entry Interactive Graphic Go to the online course to perform this practice activity. Common codes include O (OSPF). Just like IPv4.5.Chapter 3: Routing Dynamically 231 Figure 3-73 Remote Networks Entries on R1 The entry identifies the following information: Q Route source: Identifies how the route was learned. Q Q Q Q Q When an IPv6 packet arrives on a router interface. the router chooses the route with the longest match. Administrative distance: Identifies the trustworthiness of the route source. Next hop: Identifies the IPv6 address of the next router to forward the packet to. and S (Static route).

and as an Interior Gateway Protocol or an Exterior Gateway Protocol. Details… After studying the concepts presented in this chapter concerning IPv6. Distance vector protocols use routers as “sign posts” along the path to the final destination.1: IPv6 Details. routing protocols propagate that information throughout the routing domain. where all of the routers in the same routing domain or area have complete and accurate information about the network. maintaining up-to-date routing information. With a partner. as distance vector or link-state. Dynamic routing is the best choice for large networks and static routing is better for stub networks. use the IPv6 routing table diagram and the . one other group from the class. While dynamic routing protocols require less administrative overhead than static routing. Distance vector routing protocols do not have an actual map of the network topology. is called convergence. Networks typically use a combination of both static and dynamic routing. and ability to find a new best path if the current path is no longer available. . at least.1.6) Class Activity 3. Routing protocols are responsible for discovering remote networks. including CPU time and network link bandwidth. they do require dedicating part of a router’s resources for protocol operation. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Routing protocols can be classified as either classful or classless. The purpose of dynamic routing protocols includes: discovery of remote networks.pdf provided with this activity. you should be able to read a routing table easily and interpret the IPv6 routing information listed within it. When there is a change in the topology. The process of bringing all routing tables to a state of consistency. Record your answers to the Reflection questions. choosing the best path to destination networks.6. Then compare your answers with. Dynamic routing protocols are used by routers to facilitate the exchange of routing information between routers. Some routing protocols converge faster than others. as well as maintaining accurate network information.232 Routing Protocols Companion Guide Summary (3. A router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.

6. use show ipv6 protocols.3. The lower the administrative value. Different routing protocols may use different metrics. a link is an interface on a router. The algorithm is commonly referred to as the shortest path first (SPF) algorithm. Class Activities Class Activity 3. All link-state routing protocols apply Dijkstra’s algorithm to calculate the best path route.1. bandwidth.1: IPv6 Details. along with static routes and directly connected networks. When a router learns about a destination network from more than one routing source. Information about the state of those links is known as link-states. This algorithm uses accumulated costs along each path. delay. For IPv6. followed by static routes and then various dynamic routing protocols. The Packet Tracer Activities PKA files are found in the online course. Cisco routers use the administrative distance value to determine which source to use.1.0. Practice The following activities provide practice with the topics introduced in this chapter. Metrics can be determined by hops. Typically. a lower metric means a better path. the more preferred the route source.Chapter 3: Routing Dynamically 233 Metrics are used by routing protocols to determine the best path or shortest path to reach a destination network. from source to destination. Details… Lab Lab 3. The Labs and Class Activities are available in the companion Routing Protocols Lab Manual (978-1-58713-322-0). to determine the total cost of a route. The show ip protocols command displays the IPv4 routing protocol settings currently configured on the router. Each dynamic routing protocol has a unique administrative value. reliability.2.4: Configuring RIPv2 .2: How Much Does This Cost? Class Activity 3. Routers sometimes learn about multiple routes to the same network from both static routes and dynamic routing protocols. and load. With link-state routing protocols such as OSPF. A directly connected network is always the preferred source.

2.4: Comparing RIP and EIGRP Path Selection Packet Tracer Activity 3.6: Investigating Convergence Packet Tracer Activity 3.3. B.8: Configuring RIPv2 Packet Tracer Activity 3.3: Configuring RIPng Check Your Understanding Questions Complete all the review questions listed here to test your understanding of the topics and concepts in this chapter. E.” lists the answers. Link-state interior routing protocol: D. 2. Cisco advanced interior routing protocol: C.2. “Answers to the ‘Check Your Understanding’ Questions. Path vector exterior routing protocol: B. Match the description to the proper routing protocol. Growing the network usually does not present a problem. The configuration is less error prone. The appendix. The administrator has less work maintaining the configuration. C.) A. Routing protocols: RIP IGRP OSPF EIGRP BGP Description: A.2. What are two advantages of static routing over dynamic routing? (Choose two. Cisco distance vector interior routing protocol: . 1. Distance vector interior routing protocol: E. Static routing is more secure because routers do not advertise routes.3.1. No computing overhead is involved.1.234 Routing Protocols Companion Guide Packet Tracer Activity Packet Tracer Activities Packet Tracer Activity 3.3. D.

EIGRP internal routes B.) A. Administrative distance 6. RIPv1 E. The time required for the routers in one autonomous system to learn routes to destinations in another autonomous system D. Uptime C. Which of the following parameters are used to calculate metrics? (Choose two. Network discovery D. RIPv2 . Convergence time E. Which routing protocol has the most trustworthy administrative distance by default? A. The time required for the routers in the network to update their routing tables after a topology change has occurred C. The time required for routers running disparate routing protocols to update their routing tables 4. from one end of a network to the other end B. Assign IP addressing B. IS-IS C. Propagate host default routes E. Discover hosts C.Chapter 3: Routing Dynamically 235 3. OSPF D. The amount of time required for routers to share administrative configuration changes.) A. Hop count B. Which statement best describes convergence on a network? A. Bandwidth D. such as password changes. Dynamic routing protocols perform which two tasks? (Choose two. Update and maintain routing tables 5.

A level 1 parent route C. Lowest metric B. A change in the topology B. After examining its routing table for a best match with the destination address. which route will a router use to forward an IPv4 packet? A. The router update timer expiring 11. debug ip routing 8. The initial startup of the routing protocol process D. Router R1 is using the RIPv2 routing protocol and has discovered multiple unequal paths to reach a destination network. As soon as they are addressed and operational at Layer 2 D. Highest metric C. A level 2 parent route . Which command will show the administrative distance of routes? A. As soon as they are addressed and operational at Layer 3 E. When do directly connected networks appear in the routing table? A. When they are included in a static route B. A level 1 ultimate route D.236 Routing Protocols Companion Guide 7. Always when a no shutdown command is issued 9. Highest administrative distance E. show ip interfaces D. When they are used as an exit interface C. How will Router R1 determine which path is the best path to the destination network? A. By load-balancing between up to four paths 10. A level 2 supernet route E. Which of the following will trigger the sending of a link-state packet by OSPF? (Choose two.) A. show interfaces B. A level 1 child route B. show ip route C. A link to a neighbor router has become congested C. Lowest administrative distance D.

What are four ways of classifying dynamic routing protocols? 17. eBGP: B. which is based on the longest matching prefix. OSPF. 16. IPv6 does not use static routes to populate the routing table. EIGRP. RIP version 1 and IGRP: F. Allows for use of both 172. B. Sends subnet mask information in routing updates: D. unlike IPv4 route selection. Unlike IPv4. C.128/27 subnets in the same topology: 15. What are the most common metrics used in IP dynamic routing protocols? 18. OSPF: F. Does not support discontiguous networks: B. and BGP: C.16. EIGRP (External): D. The selection of IPv6 routes is based on the shortest matching prefix. Designate the following characteristics as belonging to either a classful routing protocol or a classless routing protocol.1. A. 13.Chapter 3: Routing Dynamically 237 12. Enter the proper administrative distance for each routing protocol. RIP: 14. which IPv4 routing tables do not. Does not send subnet mask in its routing updates: G.0/26 and 172. By design IPv6 is classless. IS-IS: E. What is the purpose of a passive interface? . Explain why static routing might be preferred over dynamic routing. so all routes are effectively level 1 ultimate routes. What is different between IPv6 routing table entries and IPv4 routing table entries? A.1. A.16. EIGRP (Internal): C. and why is it important? 19. What is administrative distance. D. IPv6 routing tables include local route entries. Supports discontiguous networks: E.

635 applying to interfaces. 600-601 editing named. 382. 574 logic. 574-575 outbound. 641 configuring. 592 modifying. 572 access control lists (ACLs). 591 internal logic.Index Symbols 2-WAY/DROTHER routers. 472 A ABRs (Area Border Routers). 604-605 entering criteria statements. 575. 635-637 verifying. 625-626 IPv6. 587. 400. 587-591 inbound. 591-603 creating named. 621-622 editing. 566-570. 574-575 logic. 597 ACEs (access control entries). 614-615 verifying. 637-645 creating. See ACLs (access control lists) access-list command. 628-629 extended. 643-645 logic operations. 572-573 processing packets with. 627-628 numbering and naming. 605-606 editing numbered. 588-589 securing VTY ports. 620-621 testing packets. 246. 596-599 commenting. 623-625 filtering traffic. 647 access control entries (ACEs). 584-586 guidelines for placement. 532 access-class command. 249 ACLs (access control lists). 625-627 standard IPv4. 572 Acknowledgement packets (EIGRP). 618-619 configuring. 611-614 sequence numbers. 616-625 creating named. 587 placing. 646-647 decision process. 611. 608-610 . 576-577 operation. 614 applying to interfaces. 626-627 packet filtering. 576. 595-596 logic. 622-623 guidelines for creation. 601-603 configuring. 603-611 placing. 591 applying to interfaces. 589-591 extended IPv4.

364-366 SPF (Shortest Path First). 188-189 IPv6. 359-360 load balancing. 575 TCP conversations. 680-681 active states. configuring IPv6. 577-584 calculating. 16-17 global unicast. 231 administrative distance information (remote network entries). 158 advertising networks. 219 advanced configuration. 290-296. 160 MD5 (Message Digest 5). 335-347 bandwidth utilization. 443 IPv6 summary. 298 AD (administrative distance). 579-580 keywords. 66 administrative distance information (IPv6 directly connected entries).724 ACLs (access control lists) statistics. 444-446 local-link. 114-119 classful. 347-353 troubleshooting. 625-629 common errors. OSPF. 302-308 dynamic routing protocols. 357-359 default route propagation. 16 adjacencies creating multiple. 580 activating Evaluation RTU (Right-to-Use) licenses. 394. 46-47 . 113-114 tables. 532 ARP (Address Resolution Protocol). 465 EIGRP. 16-17 subnets. EIGRP (Enhanced Interior Gateway Routing Protocol) authentication. 196-198 algorithms distance vector. 46-47 . 182-183 DUAL (Diffusing Update Algorithm). configuring. 582-584 matching ranges. 120 addressing classless. 42 ARPANET (Advanced Research Projects Agency Network). 581-582 IPv4 subnets. 42 addresses dynamically assigned IP. 606-607 versus extended. 353-357 Hello intervals. EIGRP. 568-570 troubleshooting. 229 administrative distance information (remote IPv6 network entries). 398 area area-id authentication message-digest command. 496 Area Border Routers (ABRs). CIDR. 400. 66 Address Resolution Protocol (ARP). EIGRP router IDs. 263 statically assigned IP. unused. 370-385 Advanced Research Projects Agency Network (ARPANET). 314-316 loopback. 359-360 Hold times. 361-364 manual summarization. 109-112 waste. 137-138 link-local. 277-278 adjacency database (OSPF). 607-608 verifying. 397 administrative distance (AD). routes. 629-635 wildcard masks. 364-370 auto-summarization. 201-203. 158 .

335-338 verifying. networks. 434 BDRs (Backup Designated Routers). 530 backbone OSPF routers. 686 Border Gateway Protocol (BGP). 433 default interface. 172 boot system command. 44 BGP (Border Gateway Protocol). 670-672. RIPv2. 159. 343. 364-366 OSPF (Open Shortest Path First). 137 . 387 automatic summarization. OSPF. 339. 242 Branch site devices. 532 C cables. MP5. 172 border routers. 533-534 attacks. 244-245. 382-385 auto-summary command. 469-471 best paths. 5 backing up Cisco IOS licenses. 134. 340-347 routing tables.calculating 725 ASBR (Autonomous System Boundary Router). 13 broadcast multi-access networks. OSPF. 462 OSPF (Open Shortest Path First). troubleshooting. 489-492 authentication EIGRP. 19 calculating EIGRP metrics. 429 auto-cost reference-bandwidth command. 463 B backbone (transit) area. 533-534 autonomous system numbers. Cisco IOS images. 347 . 427 auto-summarization EIGRP (Enhanced Interior Gateway Routing Protocol). 284-286 utilization. 192-193 Autonomous System Boundary Router (ASBR). 433. 287-290 IPv6 network addresses. 257-259 availability. 408-411 default election process. 384. OSPF two-layer area hierarchy. 364-368 configuring. 357 . See BDRs (Backup Designated Routers) backups. 369-370 MD5 (Message Digest 5) algorithm. 406. 357-359 reference. 430-433 EIGRP (Enhanced Interior Gateway Routing Protocol) metrics. console. 474-476 verifying adjacencies. network connections. 335 configuring. 365-368 verifying. disabling. EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP. 283 adjusting interface. 682 Backup Designated Routers (BDRs). 667-668 bandwidth. routers. 5. 492-501 auto-cost reference-bandwidth 1000 router command. 289 adjusting. EIGRP. 159. 185 bounded updates. 338-340 network topology. 427-430 bandwidth command. 472-473 verifying roles. 337 bounded triggered updates.

176 classless network addressing. 114-116 static routing. 171-174 classless EIGRP. 176 classless network addressing. 655-662 Cisco License Manager (CLM). 658-663 trains. 597 area area-id authentication message-digest. 669-670 TFTP servers as backup. 660-662 system image filenames. 655-656 mainline. 667-672 backups. 517 CLM (Cisco License Manager). 114-116 static routing. 671 managing system files. 240 Classless Inter-Domain Routing (CIDR). 110-111 classifying routing protocols. 655-662 technology. 117-119 classless routing protocols. 395 commands access-class. network connections. 109. 112-113. 611. 670-672 copying. 19 Cisco Express Forwarding (CEF). 550 wildcard masks. 654 EM (extended maintenance) release. 171. 660-661 licensing. 496 auto-cost reference-bandwidth. 581-582 CEF (Cisco Express Forwarding) packetforwarding mechanism. 678-680 managing images. 74. 675 Cisco License Registration Portal. 109. 673-674 uninstalling. 672 backing up. 11. 682-684 verification. 177-178. 478 clear ip ospf [ process-id ] process command. 675 clock rate command. 449 clear ipv6 ospf [ process-id ] process command. 655-656 standard maintenance release. 14 Classless Inter-Domain Routing (CIDR). 682 Evaluation RTU license. 647 access-list. 171. 654 naming conventions. 117-119 Cisco 1941 LEDs. 362 Central site devices. 24 Coltun. 674 purchasing. See CEF (Cisco Express Forwarding) Cisco IOS.726 calculating summary routes. Rob. multiarea OSPF. 667-669 boot system. 680-681 installing. 109-110 waste. 677-678 obtaining. 654-666 release families. 74. 175-177 classful subnet masks. 675 technology package. 427 . 676 classful network addressing. 663-666 system image packaging. 505 clear ipv6 ospf process command. 113-114 classful routing protocols. 86-87 load balancing. 184 clear ip ospf process command. 667 TFTP servers to upgrade. 675-677 process.

445 ipv6 bandwidth-percent eigrp. 445. 96-97 ipv6 router eigrp. 378-380. 308 debug eigrp fsm. 434 ip ospf database. 488 no ipv6 ospf hello-interval. 339. 641 no ipv6 ospf dead-interval. 303-306 default-information originate. 285. 327 ipv6 eigrp interface. 641 no passive-interface. 449 clear ipv6 ospf [ process-id ] process. 488 no ipv6 traffic-filter command. 641 ip access-group. 517 clock rate. 600 ip access-list extended. 327. 598 ip access-list. 36-38 interface. 194. 518 network network-address. 384. 424 ping. 474. 264-266. 195. 450. 24 copy. 444 ipv6 ospf authentication ipsec spi. 261-262. 596-597. 316-317 end. 347. 433-434 boot system. 605 history. 384 no bandwidth. 424. 317 OSPFv3 troubleshooting. 357.commands 727 auto-cost reference-bandwidth 1000 router. 513. 433 no ip access-group. 647 ipv6 address. 680. 197. 455. 195 eigrp router-id. 429 auto-summary. 595-597. 376. 188 no 10. 318-319 ipv6 ospf 10 area 0 command. 687 license install. 600. 343. 682 maximum-paths. 34. 478 clear ip ospf [ process-id ] process. 195. 641 ipv6 unicast-routing. 600 ip access-lists standard. 647 ip bandwidth-percent eigrp. 268-269. 605 ip access-list standard. 97. 315. 505 clear ipv6 ospf process. 362. 670-672. 29. 501. 511 ip ospf cost. 496 ipv6 route. 379. 450 ipv6 traffic-filter. 647 no ipv6 access-list. 605 no access-list. 305. 510 no router rip. 316 license accept end user agreement. 514-517 passive-interface. 357. 686 clear ip ospf process. 597 ip access-class. 387 network. 423 passive-interface default. 682-683 license save. 387 ip mtu size. 91 . 647 no auto-summary. 604. 187 no shutdown. 82-85 ipv6 access-list. 640. 387 ipv6 eigrp. 496 ip ospf message-digest-key key md5 password. 319. 420-422. 387 bandwidth. 327 ipv6 router ospf process-id. 670 debug. 509. 555 ip ospf message-digest-key. 647 ip access-group 1 out. 496 ip route. 451 ipv6 ospf area.

259-260 router eigrp. 342 show ip interface. 146 show flash. 263. 374. 503-505. 505-506. 489. 609. 12 troubleshooting EIGRP. 272-273. 397. 453. 370-372 troubleshooting OSPF. 388 show ip eigrp topology. 644. 438 show ip ospf neighbor. 678. 369-371. 553 show ip route. 327 router eigrp as-number. 670. 29-31. 682 show interface. 354-356. 601-603 composite metrics. 380. 31. 387 reload. 470. 444. 260. 271. 319-321. 29. 647 show ip interface brief. 233. 647 show running-config interface. 228. 283-285. 387-388. 263. 378. 670. 664-686 show flash0. 64. 677. 321. standard IPv4 ACLs. 376 show ip eigrp neighbors. 369 show ipv6 interface. 453-454. 644 show ipv6 interface brief. 644. 91 tracert. 595. 623. 603-604. 676. 377-378. 233. EIGRP. 397. 516 show ipv6 ospf interface. 361. 148 show ip route ospf. 338-347. 681-683 remark. 502. 397. 371. 269. 602 router. 30. 257. 638 show ipv6 interface gigabitethernet 0/0. 320-321. 437-438. 450-453. 554 show ip route | begin Gateway. 509. 555 show ip ospf interface. 517 show license. 327. 31. 371. 282. 34-36 show access-list. 456. 595. 647 show access-lists 1. 486. 281-282 . 554 show ip route static. 606. 505 show ip protocols. 58. 484 show ipv6 route ospf. 451-452. 505 show ip interface g0/0. 388. 687 show license feature. 300. 438. 679-681. 515 show ipv6 ospf interface brief. 509 show ip ospf interface brief. 32. 354. 286 show ip eigrp interfaces. 553 show ip ospf interface s0/0/0. 687 shutdown. 34 traceroute. 607-610. 502-505 commenting. 304 show ip eigrp topology all-links. 270-271. 49. 515 show ipv6 protocols. 502. 33. 455 show. 485. 305-306 terminal length number. 191-194.728 commands redistribute static. 356. 273-276. 29 filtering output. 503 show ip ospf database. 423. 92-94 show ipv6 eigrp neighbors. 622 show ip ospf. 298. 623. 489. 12. 436-437. 430 show ip ospf interface serial 0/0/1. 381-383. 514 show ipv6 route. 472. 375 router ospf process-id. 456. 32 show ipv6 ospf. 604 show cdp neighbors. 674 show license udi. 687 show running-config. 438. 435-436. 316. 375. 29-31 show version. 301. 451 show ipv6 ospf neighbor.

444-446 network topology. 591 D data storage. 443-444 router ID. 528 OSPF (Open Shortest Path First). 96-106 IPv6 summary. 29-31 verify IPv6 interface settings. 637-645 IPv6 static routes. 82-93 IPv6 ACLs. 368 MD5 authentication. 20 network devices. building. 591-603 static routes default IPv6. 147-149 console access. 462-480 single-area OSPFv2. routers. 308-319 IPv6. 434 criteria statements. 450-451 link-local addresses. 439-451 enabling on interfaces. 496-497 OSPFv3. requirements. 93-94 IPv4 static routes. 22-23 initial.databases 729 configuration EIGRP (Enhanced Interior Gateway Routing Protocol) auto-summarization. 96-105 multiarea OSPF. 411-413 . OSPF messages. OSPF (Open Shortest Path First). 280 copy command. synchronizing. 193-195 single-area OSPF. 670 copying Cisco IOS images. standard IPv4 ACLs. 106 IPv4 summary. 255-270 for IPv6. 414-424 standard IPv4 ACLs. 4-12 passive interface. 550-552 IPv4 default routes. 403 databases link-state. advanced. 338-340 for IPv4. 159 Database Description (DBD) packets. 140 interarea route summarization. 31-34 solving problems. dynamic routing protocols. 133-138 connections consoles. 669-670 cost metric. 446-450 RIP (Routing Information Protocol). 170 EIGRP. 616-625 floating static routes. 210-211 LSDB (large link-state database). 20 convergence dynamic routing protocols. 19-20 connection requirements. 6 data structures. 186-188 routers. 128-133 IPv6. 13-22 connectivity networks filtering show command output. 365-366 summary routes. 34-36 verify interface settings. 541-545 OSPF MP5 authentication. 425-434 manually setting. entering. 349-350 extended IPv4 ACLs.

303-306 decision process. 195 default OSPF interface bandwidth. 186-188 RIPng. 628-629 default DR/BDR election process. routing tables. 305. 94-95 troubleshooting. Edsger Wybe. 355-356 verification. 218 destination network information (remote IPv6 network entries). OSPF messages DBD (Database Description) packets. 486-489 debug command. 231 destination network information (remote network entries). 308 debug eigrp fsm command. 355-357 OSPF. 430-433 default route propagation. 286 denial-of-service (DoS) attacks. 183-196 configuring.730 DBD (Database Description) packets. 229 directly connected networks. 490 Down state. 173-174 EGRP (Exterior Gateway Routing Protocol). 181-182 distance vector routing protocols. 196-200 DMVPN (Dynamic Multipoint Virtual Private Network). 15-16 DoS (denial-of-service) attacks. 16 Dijkstra. 410 . 51-56 directly connected static IPv6 routes. 490 Designated Routers (DRs). 43 directly connected routes. 47 . 93-94 verifying. 240 documenting network addressing. 13-22 LEDs. OSPF messages. 474-476 default gateways. 102-103 discontinuous networks. 200-201. 18-19 Diffusing Update Algorithm (DUAL). 195-196 EIGRP. 79-80 configuring. 14-15 default-information originate command. 406 DROTHERs. 217-218 directly connected IPv6 route entries. OSPF. 353-354 IPv6. 403 Dead interval (OSPF). 144-146 delay metrics. routing tables. 221 static routing. ACLs (access control lists). 485 modifying. 181-183 algorithms. EIGRP (Enhanced Interior Gateway). 3. 177 distance vector dynamic routing. 182-183 technologies. See DUAL (Diffusing Update Algorithm) diagrams. See DRs (Designated Routers) destination network information (directly connected entries). 218 devices connecting to networks. topologies. 394 DijkstraDs algorithm. configuring. 184-186 RIP (Routing Information Protocol). 228-229 directly connected network information (IPv6 directly connected entries). 480-485 default routes. See SPF (shortest path first) directly connected IPv4 route entries.

604-605 EGP (Exterior Gateway Protocol). 184-186. 280 default route propagation. 184-186. 406. 240-242 bounded triggered updates. 240 configuring for IPv4. 240-245 classless. 353-354 IPv6. 408-411. 474-476 verifying adjacencies. 219-224 IPv4 route entries. 355-357 . 357-359 basic features. 369-370 autonomous system numbers. 75. 166-168 purpose. 159 network discovery. 290-296 convergence. 159-160 role. 163-166 achieving convergence. 227-231 versus static. 185 bounded updates. 158. 364-368 configuring. 386-388 authentication. 340-347 bandwidth utilization. 224-227 IPv6. 462 OSPF. 157-158. 326 EIGRP. 16-17 dynamically learned IPv4 routes. 240. 170 classifying. 365-368 verifying. 335 configuring. 171-173. 242 characteristics. 64 main components. 61. 158-159 IGP (Interior Gateway Protocol).EIGRP (Exterior Gateway Routing Protocol) 731 DRs (Designated Routers). 172-173 evolution. 171-174 distance vector protocols. 161-162 E editing extended IPv4 ACLs. 172-173 IPv4. 76-77. 241. 159. 16 Dynamic Multipoint Virtual Private Network (DMVPN). 257-259 auto-summarization. 333-334. 623-625 named standard ACLs. 244-245. 45. 472-473 verifying roles. 326. 215-219 IPv4 route lookup process. 302-308 FS (Feasible Successor). 160-161 routing information exchange. 355-356 verification. 66. 467-468 default election process. 232 EIGRP (Exterior Gateway Routing Protocol). 240 dynamic routing. 168-169 routing tables. 304-305 FSM (Finite State Machine). 219-224 Dynamic Host Configuration Protocol (DHCP). 62-64 IPv6. 173-174 EGP (Exterior Gateway Protocol). 232 protocols. 302-303 dynamically assigned IP addresses. 308-319 convergence. 215 dynamically learned IPv4 routes. 605-606 numbered standard ACLs. 469-471 DUAL (Diffusing Update Algorithm). 255-270 configuring for IPv6. 338-340 network topology. 277 . 335-338 verifying.

269-270 PDMs (protocol-dependent modules). 283 neighbor adjacencies. 370-374 basic commands. 378-385 verifying. IOS. 374-378 parameters. 251 OSPF messages. 359-360 initial route discover. 186. 185 Hold times. 304-305 Hello intervals. 253 packet headers. 361-364 manual summarization. 319-325 eigrp router-id command. 246. 361-364 EULA (End User License Agreement). 660-661 empty routing tables. See EIGRP (Enhanced Interior Gateway Routing Protocol) equal cost load balancing. 246-248 partial updates. 605 End User License Agreement (EULA). 242. length. 316-317 EM (extended maintenance) release. 268-269 verifying. 278-279. 39 end command. 302-308 FS (Feasible Successor). 374-375 neighbors. value). 297-302 troubleshooting. 245-247 Query. 280 bandwidth. 249-250 Reply. 281-282 delay. 375 routing tables. 277-278 network topology. 317 packets Acknowledgement. 347-353 configuring. 287-290 composite. 242 passive interface. 286 interface values. 243-244 topology table. 278-279 topology tables. 261-262. 242. 241. 252-255 TLV (type. 402 packets. 312-313 load balancing. 241 neighbor adjacency. 290-296 convergence. 246. 45 EIGRP. 359-360 hello keepalive mechanisms. 251-255 metrics. 255-256 no shutdown command. 284-286 calculating. 251 Hold Time. 51 encapsulation EIGRP messages. 349-350 verifying. 242-243 router ID. 277-280 IPv6 network topology. 370-372 interfaces. 261-263 RTP (Reliable Transport Protocol). 270-277 IPv6. 376-378 Layer 3 connectivity. 263-264 IPv4. 675 . 675 Enhanced Interior Gateway Routing Protocol (EIGRP). 246. 249 Hello. 250-251 Update. 351 messages encapsulating.732 EIGRP (Exterior Gateway Routing Protocol) DUAL (Diffusing Update Algorithm).

295. OSPF. 141-142 flooding LSAs (link-state advertisements). 406 ExStart state. 119-121 forwarding database (OSPF). 572-573 traffic. extended IPv4 ACLs. 294. 410 LSPs (link-state packets). 589-591 extended IPv4 ACLs applying to interfaces. configuring. 406 fully specified static IPv6 routes. 327 DUAL. configuring 733 Evaluation RTU (Right-to-Use) licenses. 614-615 verifying. 623-624 filtering traffic. 327 DUAL. 89-91 F fast switching packet-forwarding mechanism. 34-36 Finite State Machine (FSM). 87 FS (Feasible Successor). 232 external route summarization. 397 Forwarding Information Base (FIB). 621-622 editing. OSPF. IOS. 295. 472 FULL/DR routers. 6 floating static routes. 11. 119-121 Flash. 213 Exchange state. 659 . 327 feasible successor (FS). 680-681 event-driven updates. 660-661 Exterior Gateway Protocol (EGP). 327 FD (feasible distance). 618-619 configuring. 576. Dennis. 295 feasible distance (FD). 587 placing. 81 testing.fully specified static routes. OSPF. 620-621 filtering show command output. 327 feasibility condition (FC). 87 filtering packets. 622-623 extended maintenance (EM) release. 171-173. 302-303 FSs (feasibility successors). 616-625 creating named. 620-621 testing packets. 138-139 configuring. 546-547 Ferguson. 304-305 Feature Navigator (Cisco). 406 extended ACLs. 140 static routing. 209-210 FLSM (fixed-length subnet masking). 472 Full state. 327 feasibility successors (FSs). activating. 295 FULL/BDR routers. 294. 104-105 fully specified static routes. 11. 184-186. 304-305 FSM (Finite State Machine). 395 FIB (Forwarding Information Base). 302-303 fixed-length subnet masking (FLSM). multiarea OSPF. 10 FC (feasibility condition). configuring. 472 FULL/DROTHER DR/BDR routers.

257 IGP (Interior Gateway Protocol). 24 hybrid routing protocol. 40-41 hosts. 4-12 initial route discovery. 252-255 Hello intervals EIGRP. 376-378 values. 641 EIGRP troubleshooting. 597 interfaces applying extended IPv4 ACLs. 485-486 modifying. EIGRP messages. forwarding to. 159. 359-360 OSPF. EIGRP. 402-404 intervals. 24 history. 245-247 OSPF messages. 546-548 interface command. 277-280 Init state. 326 H headers. 445. 43 gateways. commands. 13 hops. 406-408 installation. 666 interarea route summarization. OSPF. 359-360 Home Office devices. 283 enabling OSPFv3 on. network connections. 450-451 loopback. 171-173. 14 global unicast addresses. 404-405 High-Speed WAN Interface Card (HWIC). 669-670 image backups. 19 HWIC (High-Speed WAN Interface Card). 667 TFTP servers to upgrade. EIRGP messages. 232. routers. 667-672 TFTP servers as backup.734 Gateway of Last Resort G Gateway of Last Resort. 185 Hello packets EIGRP. 16-17 HTTPS (HyperText Transfer Protocol Secure). enabling IP (Internet Protocol) on. 671 inbound ACLs. 395 IGRP (Interior Gateway Routing Protocol). 618-619 IPv6 ACLs to. 36-38 Hold Time. 486-489 hello keepalive mechanisms. EIGRP. 625-626 initial configuration. multiarea OSPF. 574 logic. Cisco IOS licensing. 253. 670-672 copying. 443 I-J IANA (Internet Assigned Numbers Authority). 19 images (Cisco IOS) boot system. 15 default. 667-669 managing. 242 HyperText Transfer Protocol Secure (HTTPS). 28 . 677-678 Integrated Services Routers (ISR).

647 ip access-list command. 16-17 switches. 357 . 453 passive. 682 Evaluation RTU license. 257 intervals EIGRP. 658-663 trains. 422-424 routers. 20-22 ip access-class command. 496 . 654 EM (extended maintenance) release. 14 statically and dynamically assigned. 673-674 uninstalling. 232. applying to. 511 ip ospf cost command. 485 Hello. 395 Interior Gateway Routing Protocol (IGRP). 680-681 installing. 16-17 ip bandwidth-percent eigrp command. 485-489 verifying settings. 660-662 system image filenames. 605 IP addresses. 600. 486-489 IOS (Internetwork Operating System). 655-656 standard maintenance release. 675-677 process. 159. 596-599 Interior Gateway Protocol (IGP). 641 ip access-group 1 out command. 359-360 OSPF Dead. 667-672 backups. 660-661 licensing. 600 ip access-list standard command. 647 ip access-lists standard command. 675 technology package. 682-684 verification. 171-173. 596-597 . 485-486 modifying. 159. 672 backing up. 671 managing system files naming conventions. 670-672 copying. 678-680 managing images. 667-669 boot system. 387 ip mtu size command. 600 ip access-list extended command. configuring.ip ospf message-digest-key key md5 password command 735 OSPF fine-tuning. 663-666 system image packaging. 24-29 standard IPv4 ACLs. 655-656 mainline. 496 ip ospf message-digest-key key md5 password command. 395 internal OSPF routers. single-area OSPF. 655-662 IP (Internet Protocol) enabling on hosts. 326 Intermediate System-to-Intermediate System (IS-IS). 674 purchasing. 434 ip ospf database command. 669-670 TFTP servers as backup. 667 TFTP servers to upgrade. 555 ip ospf message-digest-key command. 438 OSPFv3. 655-662 technology. Hello. 677-678 obtaining. 598 ip access-group command. 654-666 release families. verifying. 532 Internet Assigned Numbers Authority (IANA). enabling on.

270-277 loopback interfaces. 64 static routes configuring. 576. 25-28 routing protocols. 591 applying to interfaces. 3 ip route command. 596-599 commenting. 600-601 editing named. 53-56 EIGRP configuring for. 616-625 creating named. 587-591 interface configuring routers. 605-606 editing numbered. 575. 133-138 . configuring. 643-645 directly connected routes. configuring. 625-627 standard. 635-637 verifying. 608-610 statistics.736 IP packets IP packets. 607 verifying. 620-621 testing packets. 592 modifying. 604-605 entering criteria statements. 59-61 IPv4 ACLs extended. 603-611 placing. 28-29 router interfaces. 579-580 keywords. 28-29 loopback. 637-645 creating. 128-133 troubleshooting. 582-584 matching ranges. 25-28 router interfaces. 614-615 verifying. 96-106 configuring default. 623-625 filtering traffic. 575 static summary routes. 319-325 interface. 622-623 guidelines for creation. 24-25 routing protocols. 601-603 configuring. 606-607 versus extended. 641 configuring. 625-629 common errors. 595-596 logic. 581-582 IPv4 subnets. 106 configuring summary. 62-64 static routes. 591 internal logic. 82-85 IPv4 EIGRP configuring for. 614 applying to interfaces. 621-622 editing. configuring. 611-614 sequence numbers. 618-619 configuring. 28-29 numbering and naming. 255-270 verifying with. 584-586 guidelines for placement. 577-584 calculating. 576-577 processing packets with. 629-635 wildcard masks. 368 verifying for. 580 IPv6 ACLs applying to interfaces. configuring routers. 591-603 creating named. 308-319 configuring for authentication. 24-25. configuring. 588-589 securing VTY ports.

582-584 LANs (local-area networks). 674 purchasing. OSPF. 647 ipv6 address command. 496 ipv6 route command. 174-175. 682 licensing (IOS). 528 Layer 3 connectivity. EIGRP. 159. routing tables. 675 technology package. 444-446 Link-State Acknowledgement (LSAck) packets. OSPF. 108-109 ipv6 access-list command. 208 flooding. 682-684 verification. 682 Evaluation RTU license. 316 IS-IS (Intermediate System-to-Intermediate System). 96-97 ipv6 router eigrp command. 451 ipv6 ospf area command. 210-211 link-state dynamic routing. 666 license accept end user agreement command. 222-224 . 682-683 license save command.load balancing 737 verifying. 680. 672 backing up. 327 ipv6 eigrp interface command. 18-19 level 1 parent routes. 318-319 ipv6 ospf 10 area 0 command. 374-375 LEDs. 213-215 link-state updates (LSUs). routing tables. 398 link-state packets (LSPs) building. 403 link-state advertisements (LSAs). 387 ipv6 eigrp command. 209-210 Link-State Request (LSR) packets. See LSAs (link-state advertisements) link-state databases. 677-678 obtaining. 221-222 level 1 routes. 445 ipv6 bandwidth-percent eigrp command. 403-406 load balancing EIGRP. 640. 673-674 uninstalling. 203-208 OSPF messages. 105-106 verifying default. 197 . wildcard masks. 675-677 process. 450 ipv6 traffic-filter command. 395 ISR (Integrated Services Routers). OSPF messages. 528 large routing table. 242. 680-681 installing. 403 link-state routing protocols. 45 K-L keywords. 200-213 link-state operation. 315. routing tables. 97 . OSPF messages. 8 large link-state database (LSDB). 687 license install command. 361-364 equal cost. 361 routing packets. building. 444 ipv6 ospf authentication ipsec spi command. 220-221 level 2 child routes. 641 ipv6 unicast-routing command. troubleshooting. 327 ipv6 router ospf process-id command. 678-680 link-local addresses. 397 .

OSPF. configuring. 627-628 inbound. 465 flooding. 209-210 LSR (Link-State Request) packets. 28-29 LSAck (Link-State Acknowledgement) packets. 15 mainline trains (IOS). 397 . 534 operations. 351 maximum-paths command. 626 standard IPv4 ACLs. routers. EIGRP. OSPF Loading state. 538-539 LSDB (large link-state database). 403 LSUs (link-state updates). OSPF messages. 208 flooding. 535-536 type 2 network LSAs. OSPF messages. 387 MD5 (Message Digest 5) algorithm. 528 LSPs (link-state packets) building. 314-316 logic ACLs (access control lists). 28 IPv4. 287-290 composite. 203-208 OSPF messages. 252-255 OSPF. 8 local-link addresses. 397 metric information (remote IPv6 network entries). 6 Message Digest 5 (MD5) algorithm. 160 EIGRP encapsulating. 405 extensive flooding. 364-366 Media Access Control (MAC) addresses. 364-366 messages dynamic routing protocols. 402-404 routing protocol. 261 EIGRP router IDs. 410 multiarea OSPF. 281-282 delay.738 Loading state. 655-662 managing IOS system files. 398. 406 local-area networks (LANs). 286 interface values. 15 memory. 592 internal. 536-539 type 1 router LSA. 654-666 manual summarization. configuring IPv6. 283 OSPF. 280 bandwidth. 347-353 configuring. 401 encapsulating. 595-596 loopback addresses. 536 type 3 summary LSAs. 231 metrics. 44. 536-537 type 4 summary LSAs. 263 loopback interfaces. naming conventions. 425-434 . cost. 403-406 M MAC (Media Access Control) addresses. 251 packet headers. 284-286 calculating. 402 link-state updates. 219 EIGRP. 405-406 packets. 403 LSAs (link-state advertisements). 349-350 verifying. 625-626 outbound. 362. 537-538 type 5 external LSAs.

editing. 5 broadcast multiaccess. 166-168 network network-address command. 600-601 . 399-401 naming ACLs. 144-146 modifying standard IPv4 ACLs. troubleshooting. 537-538 type 5 external LSAs. 546-552 routing tables. 407-408 neighbor table (OSPF). 530-532 type 1 router LSAs. John. subnets addresses. 605-607 named extended IPv4 ACLs. 376. 109-110 waste. 435-436 OSPFv3. 489-501 troubleshooting single-area. 539-541 two-layer area hierarchy. 603-611 Moy. 541-545 implementing. 327 . 536-537 type 4 summary LSAs. creating. 180-181 missing routes. 133 advertising. 379. 496-497 example. 463 N named ACLs. 474. 538-539 verifying. CIDR. 528-530 configuring. 541-542 LSAs. 497-499 verifying. summarizing. 576-577 naming conventions. 113-114 classless. 188 networks. 15-16 network command. 499-501 multi-access networks. 455 MP5 (Message Digest 5) authentication. 455. 513. 420-422. 397 neighbors EIGRP adjacency. creating. 508-511 verifying. 463. 463-466 multiarea OSPF. IOS system files. 114-119 documenting. dynamic routing protocol. 545-546 calculating. 374-378 OSPF securing between routing events. 621-622 named standard IPv4 ACLs. 509. 532-534 route summarization. 277-278 troubleshooting. OSPF. 241 establishing. 536 neighbor adjacencies EIGRP. 492-496 configuring. 501. 536 type 3 summary LSAs. See also routing. 450. 534-535 router types. 451-452 network addressing classful. 264-266. 188-189 availability. 550 interarea. OSPF. 3-4. 266-268 network discovery.networks 739 routing protocols. 395. 518 wildcard mask. verifying. 552-559 versus single-area. 404. 535-536 type 2 network LSAs. 654-666 NBMA (nonbroadcast multi-access) networks.

187 no shutdown command. 13-22 filtering show command output. 196-198 multiaccess. 595-597 . 29-31 verify IPv6 interface settings. 220 routing protocols. 604-605 numbering ACLs. 312-313. configuring. 9-12 paths.740 networks connectivity. 255-256. 195. 465-466 NBMA (nonbroadcast multiaccess). 5 speed. 463 point-to-point. 376 NSSA (not-so-stubby area). 31-34 default gateways. 531 NSF (Nonstop Forwarding). 433 no ip access-group command. 161-162 IPv6. 6 not-so-stubby area (NSSA). 9 sending packets. 157-158 protocols. 641 no ipv6 ospf dead-interval command. 6 forwarding to next hop. 414. 34-36 verify interface settings. 641 no passive-interface command. 404. 488 no ipv6 traffic-filter command. 14-15 directly connected. editing. 463. 38-39 routes. OSPF. 443-444. 424. 536 point-to-multipoint. 647 no auto-summary command. 100-102 no 10 command. 29. 4-5 stub. 462 reliability. 285. 119-120 type 2 network LSAs. 43 reaching. 5 remote. 488 no ipv6 ospf hello-interval command. 219 next-hop static routes. 384 no bandwidth command. 43 discontinuous. 531 null authentication. 335-338 OSPF. 492 numbered ACLs. 85-87 . 3-8 data storage. 231 next hop information (remote network entries). 404. 510 no router rip command. 536 next hop information (remote IPv6 network entries). 376 Non-Volatile Random-Access Memory (NVRAM). 463. 39-40 switching functions. 462-465 subnets. advertising. 4 EIGRP. 576-577 NVRAM (Non-Volatile Random-Access Memory). 77-79 topologies. 158-170 versus static. 604. 536 Nonstop Forwarding (NSF). 605 no access-list command. 6 . 40-41 packet-forwarding mechanisms. 177 dynamic routing. 171-183 scalability. 75 routers. 647 no ipv6 access-list command. 317 nonbroadcast multi-access (NBMA) networks.

528-529 advanced configurations. 496-497 example. 462-465 null authentication. 462. 493 single-area. 158. 540-541 routers. 528-530 configuring. 402-404 MP5 authentication. 469-471 establishing neighbor adjacencies. 480-485 DRs (Designated Routers). 552-559 network topology. 469-471 classless. 534-539 route summarization. 397 LSUs (link-state updates). 541-545 implementing. 478-480 reduced calculations. 203-208 messages. 406 priorities. 499-501 multiarea. 455-456. adding routes to. 546-552 LSAs. 401 encapsulating. 398 LSDB (link-state database). 474-476 verifying adjacencies. 395-396 fine-tuning interfaces. See OSPF (Open Shortest Path First) operational states. 477-478 changing. 408-411 default election process. 402 link-state updates. 530 reference bandwidth. types. 492-496 configuring. 430-433 default route propagation. 427-430 route calculations. 407-408 evolution of. OSPF. 414-424 . 462-480 configuring. 521-522. 489-501 simple password authentication. 396-397 default interface bandwidth. 433 BDRs (Backup Designated Routers). 397 adjusting interface bandwidth. 485 Hello. 472-473 verifying roles. 28 routing tables.OSPF (Open Shortest Path First) 741 O Open Shortest Path First (OSPF). 530-532 verifying. 541-542 interarea route summarization. 472-473 verifying roles. 394-396 features. 539-541 two-layer area hierarchy. 497-499 verifying. 492 operational states. 395 cost metric. adjusting. 414 network types. 397 routing process. 434 data structures. 405-406 packets. 212-213 securing routing updates between neighbors. 44. 394. 406 OSPF (Open Shortest Path First). 425-434 manually setting. 532-534 routing protocol messages. 397 intervals Dead. 467-468 default election process. 485-489 forwarding database. 408-411. 474-476 verifying adjacencies. 485-486 modifying. 545-550 routing tables. 486-489 link-state operation. See also OSPFv3 adjacency database.

625-627 routing. 505-506 neighbor issues. 502-505 components. 41-43 AD (administrative distance). 9-12 packet headers. 143 link-state building. 208 flooding. filtering. 511. 572-573 forwarding. 452-453 routing table. 508-511 routing table issues. 43-47 load balancing. 422-424 troubleshooting. 246-250 Reply. 514 verifying interface settings. 514-520 verifying. 246-248 encapsulating. 411-413 troubleshooting commands. 250-251 Update. 246-249 Hello. 46-47 best paths. 402-404 processing. 439-451 enabling on interfaces. 626-627 outgoing interface (directly connected entries). 437-438 protocol settings. 245-247 Query. 218 outgoing interface information (IPv6 directly connected entries). 438 neighbors.742 OSPF (Open Shortest Path First) passive interfaces. 451 interfaces. 451-452 protocol settings. 444-446 modifying router ID. 449-450 network topology. show commands. ACLs (access control lists). 614-615 . 443-444 troubleshooting. 446-449 configuring single-area. 453 neighbors. 34-36 P packet-forwarding mechanisms. 252-255 packets. 246. 39-40 testing. 501-520 wildcard mask. 5-6. 3 EIGRP Acknowledgement. 229 outgoing interface information (remote IPv6 network entries). ACLs (access control lists). 214 configuring router ID. routers. 39 filtering. 450-451 link-local addresses. 574-575 outbound logic. EIGRP messages. 501 synchronizing databases. 231 outgoing interface information (remote network entries). extended IPv4 ACLs. 45 sending. 453-454 outbound ACLs. 420-421 single-area versus multiarea. 219 output. 399-401 SPF algorithm. 436-437 OSPFv3. 435-436 process information. 398 states. 209-210 OSPF messages. static routes.

423 passive-interface default command. 480-481 OSPFv3. 194. 171-173 EIGRP (Enhanced Gateway Routing Protocol). 375 partial updates. 62-64 IPv6. 44 load balancing. 319. 357-359 . 158-159 IPv4. ACLs (access control lists).protocols 743 PAK (Product Activation Key). 268 verifying. 663. 462 Point-to-Point Protocol (PPP) encapsulated frame. 478-480 process information. EIGRP. 163-166. 675. 587-591 point-to-multipoint networks. EIGRP. 335-347 bandwidth utilization. 334. 195. 186. 611-614 PPP (Point-to-Point Protocol) encapsulated frame. 61. 242-243 protocols. 477-478 changing. 45. 625-627 Product Activation Key (PAK). 386-388 authentication. 663. 158. 355-357 static OSPFv2. 687 propagating default routes EIGRP. See also specific protocols BGP (Border Gateway Protocol). 91 placing ACLs (access control lists). OSPF. 159. routes. 675. 181-183 evolution. 364-370 autonomous system numbers. 9-10 processing packets. 159-160 role. securing with IPv4 ACLs. EIGRP. 232 achieving convergence. 242 passive interface EIGRP. 160-161 routing information exchange. 66. 39 priorities. 112-113 dynamic routing. 424 passive states. 39 ports. 43-47 bets paths. 463 point-to-point networks. 161-162 EGP (Exterior Gateway Protocol). OSPF. 269-270 routing tables. 168-169 versus static. 422-424 passive-interface command. 257-259 auto-summarization. 355-356 verification. 159 network discovery. 482-484 protocol data unit (PDU). 172 classful routing. 9 routing packets. 277. 437-438 process switching packet-forwarding mechanism. configuring. troubleshooting. 240. 687 parameters. 45 PDMs (protocol-dependent modules). 159. 268-269. 193-195 single-area OSPFv2. 298 paths routers. 34. 378-380 routers. 170 distance vector. 378-380. verifying. EIGRP. 64 main components. 166-168 purpose. VTY. 353-354 IPv6. 15 protocol-dependent modules (PDMs). 242-243 ping command.

414-424 cost metric. 395-396 link-state operation. 171-173. 240-242 bounded updates. 159 IS-IS (Intermediate System-to-Intermediate System). 435-438 wildcard masks. 408-411 establishing neighbor adjacencies. 240 configuring for IPv4. 370-385 verifying for IPv6. 242. 261-263 RTP (Reliable Transport Protocol). 290-296. 270-277 hybrid routing. 277-278 network topology. 240-245 classless. 158. 398 messages. 433 adjusting reference bandwidth. 406 passive interfaces. 411-413 verifying. 255-256 packets. 353-357 DUAL (Diffusing Update Algorithm). 268-270 PDMs (protocol-dependent modules). 477-480 routing protocol messages. 263-264 verifying with IPv4. 44. 241. 280-290 neighbor adjacencies.744 protocols basic features. 308-319 convergence. 283 IPv6 network topology. 251-255 metrics. 396-397 default interface bandwidth. 242 IGP (Interior Gateway Protocol). 242 passive interface. 302-308 Hello intervals. 455-456 adjusting interface bandwidth. 425-434 data structures. 430-433 DRs (Designated Routers). 319-325 verifying process. 361-364 manual summarization. 242-243 Reliable Transport Protocol (RTP). 159 link-state. 312-313 load balancing. 414 operational states. 427-430 BDRs (Backup Designated Routers). 397 single-area versus multiarea. 243-244 topology tables. 420-421 . 399-401 SPF algorithm. 280 default route propagation. 255-270 configuring for IPv6. 398 synchronizing databases. 359-360 Hold times. 359-360 initial route discover. 245-251 partial updates. 297-302 troubleshooting. 277-280 interface values. 408-411 configuring. 407-408 evolution of. 241. 394-395 features. 395 IGRP (Interior Gateway Routing Protocol). 347-353 messages. 278-279. 241 router ID. 401-406 network topology. 422-424 priorities. 213-215 OSPF (Open Shortest Path First). 242 characteristics.

EIGRP. 241 characteristics. 75 remote routes. 446-449 configuring single-area. 218-219 remote network routing entries. 180-181 RIPng. 602 remote IPv6 route entries. 171. 489-501 troubleshooting. 450-451 link-local addresses. 5 Reliable Transport Protocol (RTP). routing tables. 173-174 EGP (Exterior Gateway Protocol). 172-173 EGRP (Exterior Gateway Routing Protocol). 439-451 enabling on interfaces. 449-450 network topology. 677 . 655-656 reliability. 462-480 default route propagation. 173-174 distance vector protocols. 6 recursive lookups. 531 release families. 183-196 single-area OSPF advanced configurations. 241-244 reload command. 250-251 reported distance (RD). 681-683 remark command. 49-50 remote networks. 295-296. 44. 249-250 RAM (Random-Access Memory). 246. 196-200 RIP (Routing Information Protocol). 427-430 regular (non-backbone) area. 6 ranges. 200-215 metrics. 443-444 verifying. 354-356. 501-520 purchasing Cisco IOS licensing. 177-178 distance vector. 530 reference bandwidth. 327 . 295-296. 444-446 modifying router ID. 246. 230-231 remote network route entries. matching. 171. 675 Q-R quad zero routes. wildcard masks. 86 redistribute static command. 327 Read-Only Memory (ROM). 485-489 securing routing updates between neighbors. 179 classful. Cisco IOS. 580 RD (reported distance). 480-485 fine-tuning interfaces. 93 Query packets (EIGRP). 451-454 RIP (Routing Information Protocol). 172-173 link-state. networks. 171. 171-174 classless.reported distance (RD) 745 OSPFv3 configuring router ID. OSPF two-layer area hierarchy. 174-175 link-state dynamic. routing tables. 43 reaching. OSPF. 387 reduced calculations. 184-186 IGP (Interior Gateway Protocol). 289 adjusting. 47 Reply packets (EIGRP). 175-177 classifying. 158 routing.

261-263 OSPFv3 configuring. 15 DROTHERs. 408-411. 375 router eigrp autonomous-system command. 455 routers. 229 route source information (remote IPv6 network entries). 327 router ID (OSPFv3) EIGRP. multiarea OSPF. 546-552 route timestamp information (remote network entries). 355-357 static OSPFv2. 192-193 configuring. 400 BDRs (Backup Designated Routers). 6 route lookup process. 217 route source information (IPv6 directly connected entries). disabling. 43-47 load balancing. 355-356 verification. 532-534 packet-forwarding mechanisms. 186-188 default static routes. 4-12 IRS (Integrated Services Routers). 472 initial configuration. 482-484 route source information (directly connected entries). 219 router command. 666 network attacks. 259-260 router eigrp as-number command. 467-476 forwarding to next hop. 449-450 router ospf process-id command. 158. 472 ABRs (Area Border Routers). 462 OSPF. 489-492 OSPF (Open Shortest Path First) types. 480-481 OSPFv3. 406. 24-25 IPv4 loopback interface. 408-411. 545-546 calculating. 410 DRs (designated routers). 469-476 border. 6 default gateways. propagating. 406. 550 interarea. 28-29 IPv6 interface. 218 route summarization. 263. 3-8 2-WAY/DROTHER. 45 . configuring. 25-28 data storage. 472 FULL/DR. 196-200 ROM (Read-Only Memory). 337 configuring. 224-227 route propagation EIGRP. 446-449 modifying. 183-196 automatic summarization. 22-23 IPv4 interface. 40-41 FULL/BDR. 231 route source information (remote network entries). 9-12 packets AD (administrative distance). 44. 462 OSPF.746 RIP (Routing Information Protocol) RIP (Routing Information Protocol). 193-195 RIPng. 353-354 IPv6. 257 router eigrp command. 46-47 best path for routing. 472 FULL/DROTHER DR/BDR. 260. routing tables. 195-196 passive interfaces.

386-388 authentication. configuring. 244-245. 75-81 primary uses. 240-242 . 106 switching functions. 181-183 EGP (Exterior Gateway Protocol). 133-138 packet forwarding. 82-85 configuring default. troubleshooting. 171. 277. 115-116 routing CIDR (Classless Inter-Domain Routing). 45 remote network entries. 173-174 dynamic. 96-106. 93-94 default. 179 classful. 77-78 standard routes. propagating. 663 passive interfaces. 9 sending packets. 41-43 AD (administrative distance). 168-169 packets. 46-47 best paths. 157 link-state. 159 characteristics. 143 troubleshooting. 535-536 routes active states. 177-178 distance vector. 176 classful routing protocols. 49-50 static. 78. 241. 43-47 paths. 82-93. 298 static. 51-56 missing. 41-43 sending. 78. 81 implementing. troubleshooting. 106-109 floating static routes. 240. 117-119 default routes. 175-177 classifying. 138-142 IPv4. 357-359 basic features. 171. 161-162 exchanging information. 79-80 default static routes. 215-231 versus static. 298 default. 364-370 autonomous system numbers. 59-61. 158-170 routing tables. 56-58 supernet. 159. 144-146 passive states.routing protocols 747 routing. 232. 39-40 stub. 334. 172-173 EGRP (Exterior Gateway Routing Protocol). 195-196 floating. See also protocols BGP (Border Gateway Protocol). 79 static routes. 193-195 paths. 39-40 PAK (Product Activation Key). 171-174 classless. 128-133 IPv6. 78. See RIP (Routing Information Protocol) routing protocols. 94-95 statically connected. 73-74 CIDR. 142-146 verifying default. 80 versus dynamic. 184-186. 200-215 protocols. 38-39 type 1 router LSA. 144-146 directly connected. 76-77 Routing Information Protocol (RIP). 75. 257-259 auto-summarization. summarizing. 82-106 summary static routes. 171. 112-113 dynamic. 335-347 bandwidth utilization.

278-279. 397 single-area versus multiarea. 241. 395-396 link-state operation. 243-244 topology tables. 414 operational states. 158. 242 passive interface. 241 router ID. 297-302 troubleshooting. 408-411 establishing neighbor adjacencies. 280-290 neighbor adjacencies. 361-364 manual summarization. 420-421 OSPFv3 configuring router ID. 398 messages. 408-411 configuring. 277-280 interface values. 159 link-state. 450-451 . 302-308 Hello intervals. 401-406 network topology. 277-278 network topology. 407-408 evolution of. 399-401 SPF algorithm. 290-296. 414-424 cost metric. 174-175 metrics. 283 IPv6 network topology. 446-449 configuring single-area. 439-451 enabling on interfaces. 241. 398 synchronizing databases. 245-251 partial updates. 359-360 Hold times. 270-277 hybrid. 427-430 BDRs (Backup Designated Routers). 308-319 convergence. 242. 435-438 wildcard masks. 172-173 IGRP (Interior Gateway Routing Protocol). 263-264 verifying with IPv4. 268-270 PDMs (protocol-dependent modules). 396-397 default interface bandwidth. 347-353 messages. 394-395 features.748 routing protocols bounded updates. 242-243 Reliable Transport Protocol (RTP). 255-256 packets. 242 characteristics. 312-313 load balancing. 280 default route propagation. 255-270 configuring for IPv6. 411-413 verifying. 159 IS-IS (Intermediate System-to-Intermediate System). 370-385 verifying for IPv6. 433 adjusting reference bandwidth. 359-360 initial route discover. 422-424 routing protocol messages. 430-433 DRs (Designated Routers). 353-357 DUAL (Diffusing Update Algorithm). 425-434 data structures. 251-255 metrics. 240 configuring for IPv4. 240-245 classless. 180-181 OSPF (Open Shortest Path First). 455-456 adjusting interface bandwidth. 261-263 RTP (Reliable Transport Protocol). 242 IGP (Interior Gateway Protocol). 319-325 verifying process. 406 passive interfaces.

158. 587-591 inbound. 575 TCP conversations. 241-244. 625-635 wildcard masks. 183-196 configuring. 47 adding OSPF routes to. 444-446 modifying router ID.show access-lists command 749 link-local addresses. 220-221 level 2 child routes. standard ACLs. 625-627 standard. 51 IPv4 route entries. 511. 607-610. 449-450 network topology. 572-573 processing packets with. 576 extended IPv4. 215-219 IPv4 route lookup process. 196-200 routing tables. 220 routing updates. 382-385 dynamically learned IPv4 routes. 514 sources. 682 scalability. 574-575 packet filtering. 222-224 missing network statement. 687 Shortest Path First (SPF) algorithm. 380-382 multiarea OSPF. 574 IPv6. 635-645 numbering and naming. troubleshooting. 574-575 outbound. 5 Secure Shell (SSH). 623. 588-614 standard versus extended. 116 ultimate route. 378-380 single-area OSPF. EIGRP. troubleshooting. 568-570 troubleshooting. 608-610 servers. 19 security ACLs (access control lists). See SPF (Shortest Path First) algorithm show access-list command. 43. 453-454 passive interface. 647 . 219-224 EIGRP. 224-227 IPv6. 584-586 guidelines for placement. 47-50 auto-summarization. EIGRP. 576-577 operation. TFTP. 443-444 verifying. 48-49 summarized routes. 326 S saving Cisco IOS licenses. 595 show access-lists 1 command. 575 standard IPv4. 566-570. 644. 186-188 RIPng. securing between neighbors. verifying. 378-385 empty. 577-584 authentication. routers. 646-647 extended. 39-40 sequence numbers. 539-541 OSPFv3. 614-625 guidelines for creation. 604 show access-lists command. 212-213 analyzing. 221-222 level 1 routes. troubleshooting. 227-231 large. networks. 528 level 1 parent routes. 451-454 RIP (Routing Information Protocol). 489-501 RTP (Reliable Transport Protocol). OSPF. 364-370 sending packets.

369 show ipv6 interface brief command. 397 . 320-321. 456. 553 show ip route | begin Gateway command. 374. 438. 451-452. 29. 514 show ipv6 route command. 686 show interface command. 316. 394. 516 show ipv6 ospf interface brief command. 595. 554 show ip route ospf command. 283. 338-347 . 502 show ip ospf neighbors command. 472. 489. 423. 505 show ip protocols command. 319-321. 193-194. 606. 29-31. 388 show ip eigrp topology all-links command. 380. 554 show ip route static command. 397 . 33. 270-271. 32 show ipv6 ospf command. 687 show running-config command. 553 show ip ospf interface command. 438 show ip ospf neighbor command. 469-471 . 528-529 BDRs (Backup Designated Routers). 32. 369-371. 622 show ip ospf command. 687 show license feature command. 451 show ipv6 ospf interface command. 282. 321. 638 show ipv6 interface command. 502. 381-383. 284-285 show ip eigrp interfaces command. 300. 356. 462. 485. 301. 435-436. 486. 555 show ip ospf interface brief command. 509 show ip ospf interface s0/0/0 command. 609. 271. 436-437 . 371. 505-506. 233. 272-273. 298. 273-276. 305-306 simple password authentication. 674 show license udi command. 647 show ip interface g0/0 command. 64. 304 show ip interface brief command. 505 show ip interface command. 503 show ip ospf database command. 484 show ipv6 route ospf command. 644. 623. 493 single-area OSPF. 327 . 489. 603-604. 233. 378. 388. 515 show ipv6 ospf neighbor command. 34-36 show flash0 command. 453-454. 670. 503-505. 456. 371. 682 show flash command. 29-31 show version command. 342 show ip eigrp topology command. 148 show ip route command. 437-438. 453. 377-378. 146 show commands. 515 show ipv6 protocols command. 644 show ipv6 interface gigabitethernet 0/0 command. 12. 470. 228. 438. 31.750 show cdp neighbors command show cdp neighbors command. 521-522. 430 show ip ospf interface serial 0/0/1 command. 517 show license command. OSPF. 31. 397 . 474-476 verifying adjacencies. 509. 375. 269. 472 verifying roles. 450-453. 678. 286 show interfaces command. 647 show running-config interface command. 387-388. 191. 29-30. 92-94 show ipv6 eigrp neighbors command. 376 show ip eigrp neighbors command. 276 filtering output. 676. 361. 58. 481. 354. 408-411 default election process. 49. 664-665. 444. 263. 679-681. 670. 687 shutdown command.

672 backing up. 405-406 packets. 675-677 process. 485-488 intervals Dead. 439-451 configuring router ID. 499-501 network topology. 485 Hello. 467-468 default election process. 462-480 cost metric. 398 messages. 446-449 enabling on interfaces. 449-450 network topology. 680-681 installing. 485-486 modifying. 474-476 verifying adjacencies. 492-496 configuring. 414-424 advanced configurations. 462-465 operational states. 502-505 components. 511-514 verifying interface settings. 478-480 routing protocol messages. 682 Evaluation RTU license.software licensing (IOS) 751 configuring. 469-470 establishing neighbor adjacencies. 486-489 link-state operation. 472-473 verifying roles. 675 technology package. 674 purchasing. 480-485 DRs (Designated Routers). 398 states. 453-454 software licensing (IOS). 411-413 troubleshooting. 425-434 data structures. 422-424 priorities. 436-437 versus multiarea. 677-678 obtaining. 408-411. 496-497 example. 501-520 commands. 452-453 routing table. 435-436 process information. 497-499 verifying. 450-451 link-local addresses. 508-511 routing table issues. 489-501 SPF algorithm. 477 changing. 437-438 protocol settings. 401 encapsulating. 453 neighbors. 501 synchronizing databases. 438 neighbors. 395-396 fine-tuning interfaces. 396-397 default route propagation. 407-408 features. 443-444 verifying interfaces. 673-674 . 451-452 protocol settings. 414 network types. 399-401 wildcard mask. 397 securing routing updates between neighbors. 420-421 single-area OSPFv3 configuring. 402-404 MP5 authentication. 406 passive interfaces. 402 link-state updates. 505-507 neighbor issues. 444-446 modifying router ID.

82-93 configuring summary. 80 versus dynamic. 596-599 commenting. 601-603 configuring. 678-680 speed. 106 . 587 standard IPv4 ACLs (access control lists) applying to interfaces. 73-74 CIDR. 394. 77-79 stub routers. 607-608 stub networks. ACLs (access control lists). 588-589 securing VTY ports. 4-5 SPF (shortest path first) algorithm. 96-106 verifying default. 605-606 editing numbered. 128-133 IPv6 configuring. 133-138 verifying. 592 modifying. 79 states. 81 implementing.752 software licensing (IOS) uninstalling. 78 configuring default static IPv6 routes. 105-106 summary static routes. 78 configuring default. 201-203. 600-601 editing named. 75-81 primary uses. 604-605 entering criteria statements. 195-196 floating. 138-139 configuring. 105-109 packet forwarding. OSPF. 575. 117-119 configuring IPv4. 608-610 statistics. 595-596 logic. 96-106 configuring default routes. 143 troubleshooting. 77-78 standard routes. 591-603 creating named. 16-17 statically connected routes. 85 default routes. networks. propagating. 94-95 static routing. 59-61 configuring. 93-94 default. 79 static routes. 140 testing. 108-109 verifying IPv6 static routes. 611-614 sequence numbers. 529 trees. 591 internal logic. 682-684 verification. 93-94 configuring IPv6 static routes. 398. static routing. 660-662 standard routes. 141-142 IPv4. 76-77. 606-607 standard maintenance release. 56-58 static routes. 82-93 configuring IPv4 default. IOS. 79-80 floating static routes. 106 configuring IPv4. 19 standard ACLs. 603-611 placing. 94-95 verifying default static IPv6 routes. 142-143 configuration. building. 211-212 SSH (Secure Shell). 607-608 verifying. 501 statically assigned IP addresses. 144-146 verifying default. 106 configuring summary. 161-162 statistics.

224-227 IPv6. enabling IP on. 16 routing adding OSPF routes to. 120-121 VLSM. IOS. 397 . 382-385 dynamically learned IPv4 routes. 335-347 troubleshooting routing tables. 123-125 VLSMs (variable length subnet masks). 212-213 analyzing. 222-224 missing network statement. 47-50 auto-summarization. 295 DUAL. 550 static IPv4. 38-39 synchronizing OSPF databases. 658-663 T T (technology) trains. 304-305 summarized routes. 220 verifying OSPFv3. 20-22 switching functions. 20-22 switches. static routing. 293 FSs (feasibility successors). 221-222 level 1 routes. 524 sources. 511. 119 subnet masks. 51 IPv4 route entries. 215-219 IPv4 route lookup process. routing tables. 539-541 passive interface. 378-385 ultimate route.tables 753 subnet masking FLSM (fixed-length subnet masking). 119-121 subnetting. 380-382 multiarea OSPF. 80 supernet routes. 116 troubleshooting EIGRP. routers. 14 classful. 116 summarizing auto-summarization EIGRP (Enhanced Interior Gateway Routing Protocol). 347-353 supernet routes. 219-224 empty. EIGRP. 221 summarizing. 227-231 large. 179 subnetting subnets. 115-116 summary routes calculating. 121-128. 528 level 1 parent routes. 278-279. 220-221 level 2 child routes. 48-49 summarized routes. 411-413 system files (IOS). 128-133 static IPv6. configuring. 378-380 single-area OSPF. managing. 297-302 OSPF. configuring. 176. 382-385 manual summarization. 120 VLSMs (variable-length subnet masks). 109 successors. 133-138 summary static routes. 453-454 topology EIGRP. 654-666 system image filenames (IOS). 74. 110-111 subnets. 123-125 unused addresses. 655-662 tables addressing. 663-666 system image packaging (IOS). 115-116 SVI (switched virtual interface).

414-444 subnets. multiarea OSPF. 19 terminal length number command. 676-677 unused addresses. IOS licensing technology package. 246-248 updates EIGRP. length. 673-674 terminal emulation software. 655-662 transit (backbone) area. length. extended IPv4 ACLs. 34 testing floating static routes. 144-146 two-layer area hierarchy. 16 OSPF networks. 406 type 1 router LSAs. value). 251-255 U UDIs (Unique Device Identifiers). EIGRP messages. 278-279. data fields. 120 Update packets (EIGRP). 242 event-driven. subnets. 91 tracert command. 297-302 OSPF. 213 link-state. filtering. 625-629 common errors. 376-378 Layer 3 connectivity. 370-374 basic commands. 537-538 type 5 external LSAs. 374-375 neighbors. 141-142 TFTP servers. OSPF. 147-149 default routes. 45. 144-146 EIGRP. 119-120 topology table EIGRP. 375 routing tables. 655-662 technology. Cisco IOS mainline. 142-143 configuration. EIGRP messages. 397 traceroute command. 251-255 topologies. 514 static routes. 676-677 ultimate route. 620-621 trains. 370-372 interfaces. 508-511 routing table issues. 4 diagrams. 501-520 neighbor issues. 530 troubleshooting ACLs (access control lists). IOS licensing. 374-378 parameters. 378-385 OSPF (Open Shortest Path First) commands. 220 unequal cost load balancing. 505-506 single-area OSPF. data fields. 667 upgrades.754 technology package. OSPF two-layer area hierarchy. 535-536 type 2 network LSAs. 682-684 Unique Device Identifiers (UDIs). 629-635 connectivity problems. 405-406 . 502-505 components. 538-539 type. 536 type 3 summary LSAs. 511. value (TLV). routing tables. 536-537 type 4 summary LSAs. OSPF. 687 Cisco IOS images. 530-532 Two-way state. 242 uninstalling Cisco IOS licenses. 12 traffic. 671 TLV (type.

577-584 IPv4 subnets. 74. 451-452 protocol settings. 270-277 default static routes. 436-437 OSPFv3 interfaces. 266-268 single-area OSPFv2. 319-325 passive interface. 643-645 manual summary routes.wildcard masks 755 V Variable Length Subnet Mask (VLSM). 8 waste. 472-473 DR/BDR roles. 123-125 VTY ports. 269-270 with IPv4. 437-438 protocol settings. 579-580 matching ranges. 369-370 for IPv6. 469-471 EIGRP authentication. 484-485 propagated default routes. 355-357 standard ACLs. 108-109 virtual links. 119-128. default IPv6. 452-453 routing table. 420-421 . classful addressing. 453-454 propagated default route. 464 VLSMs (Variable Length Subnet Masks). 176. 109. 622-623 IPv6 ACLs. 8 wildcard masks ACLs (access control lists). 351 multiarea OSPF. 606-607 static routes. 611-614 W-Z WANs (wide-area networks). 582-584 network command. 552-559 OSPF interface settings. See VLSM (Variable Length Subnet Mask) verifying auto-summarization. 179 subnetting subnets. securing with standard IPv4 ACLs. 453 neighbors. 678-680 DR/BDR adjacencies. 580 calculating. 435-436 process information. 340-347 Cisco IOS licensing. 438 neighbors. 113-114 wide-area networks (WANs). 481-482 propagated IPv6 route. 581-582 keywords. 94-95 extended IPv4 ACLs.

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