Cisco CCNA Routing and Switching 200-120

Flash Cards and Exam Practice Pack
Eric Rivard

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

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Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack
Eric Rivard Copyright© 2014 Pearson Education, 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 1 2 3 4 5 6 7 8 9 0 First Printing July 2013 Library of Congress Control Number: 2013941281 ISBN-13: 978-1-58720-400-5 ISBN-10: 1-58720-400-2

Warning and Disclaimer
This book is designed to provide information about late-stage preparation for the Cisco CCNA 200-120 exam. 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.

Trademark Acknowledgments
All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark.

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Corporate and Government Sales
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Feedback Information
At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community. Readers’ feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through e-mail at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message. We greatly appreciate your assistance. Publisher: Paul Boger Business Operation Manager, Cisco Press: Jan Cornelssen Associate Publisher: Dave Dusthimer Executive Editor: Brett Bartow Senior Development Editor: Christopher A. Cleveland Managing Editor: Sandra Schroeder Copy Editor: John Edwards Senior Project Editor: Tonya Simpson Technical Editors: Brian D’Andrea, Desiree Lindfield Editorial Assistant: Vanessa Evans Proofreader: Sarah Kearns Book Designer: Mark Shirar Composition: Mary Sudul

iv Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

About the Author
Eric Rivard is a professional services manager for CDW overseeing an industry expert team of consultants who implement advanced Cisco, Microsoft, data center, virtualization, and storage solutions to enterprise customers. Over the years, he has taught professionals in both academic and industry settings on topics of SCADA, Windows, networking, and IT security. Eric has 15 years of experience in the IT industry, ranging from a network administrator to senior Cisco engineer to IT director. Eric is also a professor at National University, teaching networking and IT classes. He is the author of the first, second, and third editions of the CCNA Flash Card Practice Pack. He holds a B.S. in information technology from the University of Phoenix and a master’s in business management from Redlands University. Eric also volunteers serving the young men ages 12 through 18 in his church. Eric is an Eagle Scout and currently works with the Boy Scouts in his area. He lives with his wife and five children in Oceanside, California.

About the Technical Reviewers
Brian D’Andrea started his career working as a bench technician for a large computer manufacturer. He then progressed to a consultant position for various financial and medical institutions across Pennsylvania, New Jersey, and Delaware. He is now a long-time instructor and courseware developer of Cisco courses that include CCNA Routing & Switching, CCDA, CCNA Security, CCNP Routing & Switching, and CCDP. He has been privileged to be part of several Cisco Press–published materials. He enjoys sharing his knowledge and 17 years of experience in the information technology field. Desiree Lindfield is a Cisco Certified Systems Instructor (CCSI) and provides official Cisco training for Boson and Global Knowledge. She has delivered technical training for numerous vendors and technologies for teams located around the globe. In addition to training, Desiree serves on a team of consultants providing design, installation, and troubleshooting services. Recent implementations include Nexus 7000 switches and the Cisco Unified Computing System. Desiree is a regular attendee of Cisco Live, B-Sides, and Defcon conferences.

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Dedications
I dedicate this edition to my beloved family: my beautiful wife, Tammy, and my children, Ellie, Collin, Reegin, Averie, and Sadie. I am the man I am today because of you. You are my everything! Tammy, I could not have found a more perfect partner to spend my life and all eternity with. I am deeply in love with you. Thank you for your support, understanding, love, and patience. To my children, you are such a blessing to your mother and me and we love you more than you will ever know. Always remember how special you are. Always choose the right path and help others. I love you so much! Finally, I would like to dedicate this edition to my father-in-law, Paul M. Hatch. Thank you for your love, support, and righteous example through the years. I feel so blessed to be called your son. We love you. God be with you until we meet again.

Acknowledgments
First and foremost, I would like to thank my Father in Heaven for Your love and tender mercies. You have always been there for me. To my beautiful wife, thank you for being understanding during the long nights and hours I had to put in while working on this edition. It is not easy raising five kids, let alone trying to do it on your own while I was working late. You are an amazing mother and woman. To my children, everything I do, I do for you. Thank you for being such great kids. I am lucky to be your father. To my parents, brothers, and in-laws. You guys are so amazing and I love you dearly. I am truly blessed to have you in my life. To Brett Bartow, Executive Editor, thank you for your efforts in ensuring that this project was a success. It is always a pleasure to work with you. To Christopher Cleveland, thank you for your efforts and working with me on this edition. To the team at Cisco Press that helped with all the behind-the-scenes work to make this edition happen, thank you. To the technical reviewers, Brian and Desiree, thank you for your hard work and time. Your efforts were paramount.

vi Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Contents
Introduction Part I: ICND1 Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9 Section 10 Section 11 Section 12 Exploring the Functions of Networking Introducing Local-Area Networks 40 100 4 viii

Understanding Ethernet and Switch Operations Understanding TCP/IP Routing 174 210 132

Managing Traffic Using Access Lists Enabling Internet Connectivity 232

Managing Network Device Security Implementing VLANs and Trunks WAN Technologies Implementing OSPF Introducing IPv6 352 378 312 334

248 282

ICND1 Quick Reference Guide Part II: ICND2 Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9

VLANs and Trunk Links

492 508

Building Redundant Switched Topologies Troubleshooting Basic Connectivity 556

Implementing an EIGRP-Based Solution

582 610

Implementing a Scalable Multiarea OSPF-Based Network Wide-Area Networks and Point-to-Point Communication Links 648 Establishing a WAN Connection Using Frame Relay Introducing VPN Solutions 708 724 682

Network Device Management 750

ICND2 Quick Reference Guide

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Icons

Bridge

Switch

Router

Access Server

ISDN Switch

Multilayer Switch

DSU/CSU

Personal Computer

File Server

Data Service Unit/ Channel Service Unit

Modem

Network Switch

WAN Cloud

VLAN

Hub

Network Cloud or Broadcast Domain Circuit Switched Line

Ethernet

Fast Ethernet

Serial Line

Access Point

Wireless Connection

Command Syntax Conventions
The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows:

Boldface indicates commands and keywords that are entered literally, as shown. In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command). Italics indicate arguments for which you supply actual values. Vertical bars (|) separate alternative, mutually exclusive elements. Square brackets [ ] indicate optional elements. Braces { } indicate a required choice. Braces within brackets [{ }] indicate a required choice within an optional element.

■ ■ ■ ■ ■

viii Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Introduction
Since the Cisco career certification programs were announced in 1998, they have been the most sought-after and prestigious certifications in the networking industry. For many, passing the ICND exams is crucial in building a rewarding career in networking or obtaining career advancement. Notorious as being some of the most difficult certifications in the networking industry, Cisco exams can cause much stress to the ill-prepared. Unlike other certification exams, the Cisco exams require that students truly understand the material instead of just memorizing answers. This pack is best used after you have used another, primary method of study for the CCNA certification, and need a mode of self-assessment and review to bring you confidently to test day.

The Purpose of Flash Cards
For years, flash cards have been recognized as a quick and effective study aid. They have been used to complement classroom training and significantly boost memory retention. The flash cards in this pack serve as a final preparation tool for the CCNA exam. They work best when used in conjunction with official study aids for the CCNA exam. They might also be useful to you as a quick desk- or field-reference guide.

Who These Flash Cards Are For
These flash cards are designed for network administrators, network engineers, Cisco Networking Academy Program students, and any professional or student looking to advance his or her career through achieving Cisco CCNA certification.

How to Use These Flash Cards
Review one section at a time, reading each flash card until you can answer it correctly on your own. When you can correctly answer every card in a given section, move on to the next. These flash cards are a condensed form of study and review. Don’t rush to move through each section. The amount of time you spend reviewing the cards directly affects how long you’ll be able to retain the information needed to pass the test. A couple of days before your exam, review each section as a final refresher. Although these flash cards are designed to be used as a final-stage study aid (30 days before the exam), they can also be used in the following situations:

Pre-study evaluation: Before charting out your course of study, read one or two questions at the beginning and end of every section to gauge your competence in the specific areas. Reinforcement of key topics: After you complete your study in each area, read through the answer cards (on the left side of the pages) to identify key topics and to reinforce concepts.

Introduction

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Identify areas for last-minute review: In the days before an exam, review the study cards and carefully note your areas of weakness. Concentrate your remaining study time on these areas. Post-study quiz: By flipping through this book at random and viewing the questions on the right side of the pages, you can randomize your self-quiz to be sure that you’re prepared in all areas. Desk reference or field guide to core concepts (Quick Reference Guide sections only): Networking professionals, sales representatives, and help-desk technicians alike can benefit from a handy, simple-to-navigate book that outlines the major topics aligned with the CCNA certification.

Quick Reference Guide
At the end of each part of the book, after the flash cards, you will find the Quick Reference Guide, which can serve as both a study guide for the CCNA exam and as a companion reference to the text. For readers who seek CCNA certification, this Quick Reference Guide is well suited to reinforce the concepts learned in the text rather than as a sole source of information. For readers who have either already obtained CCNA certification or simply need a basic overview, the study sheets in this guide can serve as a standalone reference.

What Is Included on the CD-ROM
The CD-ROM included with this book provides you with access to the Pearson IT Certification Practice Test (PCPT) software as well as the Pearson IT Certification Cert Flash Cards Online application. The PCPT software comes complete with more than 200 exam-realistic practice test questions that help you assess your knowledge and exam-readiness. The software is fully customizable, enabling you to focus on individual topic areas or take completed, timed exams. You can work in study mode, which allows you to review answers and full explanations, or in practice exam mode, which simulates the actual exam experience. You can take notes on questions or bookmark questions to create your own custom question databases. This powerful assessment engine also tracks your performance and provides feedback on a chapter-by-chapter basis, laying out a complete assessment of your knowledge to help you focus your student where it is needed most. The Cert Flash Cards Online allows you to access all the flash cards from the book in a customizable online application. This flexible application lets you enter your answer to each question and compare what you entered to the correct answer. You can choose to view cards in order or at random, and you can create custom sets from the entire bank of cards. The engine provides you with the ability to mark each question correct or incorrect and provides a detailed score report by category for each session. You can even write notes on each question and then get a printable PDF of all your notes aligned to the relevant questions. Best of all, the application is accessible by any device that has an Internet connection, allowing you to study at home on your desktop or on the go on your smartphone or tablet.

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Section 3
Understanding Ethernet and Switch Operations
Ethernet is the technology of choice for today’s LANs. It is fast, has low costs, and is easy to maintain. Today’s Ethernet standards support speeds of 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps, and 40 Gbps. Ethernet functions at Layers 1 and 2 of the Open Systems Interconnection (OSI) model. As such, Ethernet standards specify cabling, signaling, and data link layer addressing. Because most LANs use Ethernet as the primary Layer 2 technology, most switches today are Ethernet switches. This section covers the fundamentals of Ethernet technologies and describes how switches operate.

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Question 1
What does BASE mean in 100BASE-T and 1000BASE-T?

Question 2
What is carrier sense multiple access collision detect (CSMA/CD)?

Question 3
What is UTP cabling?

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Answer 1
BASE in 100BASE-T and 1000BASE-T refers to the baseband signaling method. Baseband is a network technology in which only one carrier frequency is used. This means that when a device transmits, it uses the entire bandwidth on the wire and does not share it during the single time interval.

Answer 2
CSMA/CD describes the Ethernet access method. In CSMA/CD, many stations can transmit on the same cable, and no station has priority over any other. Before a station transmits, it listens on the wire (carrier sense) to make sure that no other station is transmitting. If no other station is transmitting, the station transmits across the wire. If a collision occurs, the transmitting stations detect the collision and run a random backoff algorithm. The random backoff algorithm is a random time that each station waits before retransmitting.

Answer 3
Unshielded twisted-pair (UTP) cabling is a type of twisted-pair cable that relies solely on the cancellation effects produced by the twisted wire pairs to limit electromagnetic interference (EMI) and radio frequency interference (RFI). UTP cable is often installed using an RJ-45 connector, and UTP cabling must follow precise specifications dictating how many twists are required per meter of cable. The advantages of UTP are ease of installation and low cost. A disadvantage of UTP is that it is more prone to EMI than other types of media.

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Question 4
What is the maximum cable length for UTP?

Question 5
What is a straight-through Ethernet cable, and when would you use it?

Question 6
What is a crossover Ethernet cable, and when would you use it?

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Answer 4
The maximum length is 100 meters or 328 feet.

Answer 5
A straight-through Ethernet cable is wired the same way at both ends. This cable uses pins 1, 2, 3, and 6. The send and receive wires are not crossed. You should use a straight-through Ethernet cable when connecting dissimilar devices (for example, data terminal equipment [DTE] to data communications equipment [DCE]). Examples include connecting PCs (DTE) to switches or hubs (DCE) or a router (DTE) to a switch or a hub (DCE).

Answer 6
A crossover Ethernet cable is a cable that has the send and receive wires crossed at one of the ends. In a Category 5 cable, the 1 and 3 wires are switched and the 2 and 6 wires are switched at one end of the cable. You should use a crossover cable when connecting similar devices (DCE to DCE or DTE to DTE), such as connecting a router to a router, a switch to a switch or hub, a hub to a hub, or a PC to a PC.

NOTE In today’s networks, most Catalyst switches have auto-mdix, which can automatically detect the type of cable connected to the interface and automatically configure the connection appropriately.

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Question 7
What are the different UTP categories?

Question 8
What is the difference between single-mode fiber (SMF) and multimode fiber (MMF)?

Question 9
What are three ways that LAN traffic is transmitted?

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Answer 7
The categories of UTP cable are as follows:
■ ■ ■ ■ ■ ■ ■ ■

Category 1: Used for telephone communications. Category 2: Capable of data transmission speeds of up to 4 Mbps. Category 3: Used in 10BASE-T networks. Speeds up to 10 Mbps. Category 4: Used in Token Ring networks. Speeds up to 16 Mbps. Category 5: Capable of data transmission speeds of up to 100 Mbps. Category 5e: Supports speeds of up to 1 Gbps. Category 6: Consists of four pairs of 24-gauge copper wires. Speeds up to 1 Gbps. Category 6a: Supports speeds up to 10 Gbps.

Answer 8
The primary difference between SMF and MMF is the ability of the fiber to send light for a long distance at high bit rates. In general, MMF supports shorter distances than SMF.

Answer 9
LAN traffic is transmitted one of the following three ways:

Unicast: Unicasts are the most common type of LAN traffic. A unicast frame is a frame intended for only one host. Broadcast: Broadcast frames are intended for all hosts within a broadcast domain. Stations view broadcast frames as public service announcements. All stations receive and process broadcast frames. Multicast: Multicasts are traffic in which one transmitter tries to reach only a subset, or group, of the entire segment.

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Question 10
How many bits are in an Ethernet address?

Question 11
What portion of the MAC address is vendor specific?

Question 12
What portion of the MAC address is vendor assigned?

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Answer 10
Also called a MAC address, an Ethernet address is the Layer 2 address associated with the Ethernet network adapter. Typically burned into the adapter, the MAC address is usually displayed in a hexadecimal format, such as 00-0d-65-ac-50-7f.

Answer 11
The first half or first 24 bits of the MAC address are vendor specific. A MAC address is 48 bits and is displayed in hexadecimal. The first half of the address identifies the vendor or manufacturer of the card. This is called the Organizational Unique Identifier (OUI). The last half of the address identifies the card address.

Answer 12
The last 24 bits are vendor assigned.

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Question 13
What are the first 24 bits in a MAC address called?

Question 14
What is an example of a Layer 2 address?

Question 15
What is an example of a Layer 3 address?

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Answer 13
These bits are the Organizational Unique Identifier (OUI).

Answer 14
An example is a MAC address.

Answer 15
An example is an IP address.

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Question 16
If a sending device does not know the MAC address of the destination device, what protocol is used to find the MAC address of the receiving device?

Question 17
Host A wants to send data to host B. Host B is on a different segment from host A. The two segments are connected to each other through a router. What will host B see as the source MAC address for all frames sent from host A?

Question 18
Switching uses a process outlined by the IEEE as transparent bridging. What are the five processes transparent bridges use for determining what to do with a frame?

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Answer 16
Address Resolution Protocol (ARP) is used to find the MAC address of the receiving device. ARP is a local broadcast sent to all devices on the local segment to find the MAC address of a host.

Answer 17
Because host B is on a different segment that is separated by a router, the MAC address of all frames sent from host A will be the MAC address of the router. Anytime a frame passed through a router, a router rewrites the MAC address to the MAC address of the router’s exit interface for the segment and then sends the frame to the local host. In this case, the router will change the source MAC address of the frame sent from host A with the MAC address of its interface connecting to the segment host B is on. Host B will see that the frame came from the MAC address of the router with the IP address of host A.

Answer 18
The five processes of transparent bridging as defined in IEEE 802.1d are 1. Learning 2. Flooding 3. Filtering 4. Forwarding 5. Aging

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Question 19
What is the transparent bridging learning process?

Question 20
What is the transparent bridging flooding process?

Question 21
What is the transparent bridging filtering process?

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Answer 19
When a frame enters a switch, the switch adds the source Ethernet MAC address and source port into its MAC address table. The process of recording the source MAC address and the source port in the table whenever a switch sees a frame is called the learning process.

Answer 20
When a switch receives a unicast frame and it does not have the destination MAC address and port in its bridging table, or a broadcast or multicast frame, the switch will forward this frame out all ports, except the port it received the unicast frame on. This is called the flooding process.

Answer 21
The filtering process occurs when a switch receives a frame and the source and destination hosts reside on the same interface. When this occurs, the switch filters or discards the frame.

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Question 22
What is the transparent bridging forwarding process?

Question 23
What is the transparent bridging aging process?

Question 24
For what two purposes does the Ethernet protocol use physical addresses?

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Answer 22
A switch forwards a frame when the destination address is in the switch’s MAC address table and the source and destination are on different interfaces. This is the forwarding process.

Answer 23
When a switch learns a source address, it time-stamps the entry in the MAC address table. Every time the switch sees a frame from the same source, the timestamp is updated. The aging process occurs when the switch does not see a frame from the source before the aging timer expires. When this happens, the switch removes the entry from the MAC address table.

Answer 24
Ethernet uses physical addresses to
■ ■

Uniquely identify devices at Layer 2 Allow communication between different devices on the same Layer 2 network

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Question 25
What will an Ethernet switch do if it receives a unicast frame with a destination MAC that is listed in the switch table?

Question 26
Under what conditions would a switch flood a frame?

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Answer 25
The switch will forward the frame to a specific port. Switches use the transparent bridging process to determine how to handle frames. The process is as follows: 1. A frame is received. 2. If the destination is a broadcast or multicast, the switch will forward the frame to all ports except to the port the frame was received. 3. If the destination is a unicast and the address is not in the MAC address table, the switch forwards the frame to all ports except the receiving port. 4. If the destination is a unicast, the address is in the MAC address table, and the associated interface in the MAC address table is not the receiving interface, the switch forwards the frame to the correct interface. 5. If the above rules do not occur, filter the frame.

Answer 26
A switch will flood a frame if the MAC address table is full, if the destination MAC address has not been learned by the switch, or if the frame is a broadcast or multicast frame.

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Question 27
What is the switch MAC address table used for?

Question 28
Describe full-duplex transmission.

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Answer 27
The switch MAC address table forwards traffic out the appropriate interface. Because switches operate at Layer 2 of the OSI model, they switch traffic by MAC address. Instead of flooding traffic out all interfaces, a switch learns the MAC address of devices on each interface and only forwards traffic destined to the host on the interface. The learned MAC addresses are stored in the switch’s MAC address table.

Answer 28
Full-duplex transmission is achieved by setting switch interfaces, router ports, and host NICs to full duplex. Microsegmentation, where each network device has its own dedicated segment to the switch, ensures that full duplex will work properly. Because the network device has its own dedicated segment, it does not have to worry about sharing the segment with other devices. With full-duplex transmission, the device can send and receive at the same time, effectively doubling the amount of bandwidth between nodes. Three points to remember about the operation of full-duplex communication are
■ ■ ■

There are no collisions in full-duplex mode. A dedicated switch port is required for each full-duplex node. The host network card and the switch port must be capable of operating in fullduplex mode.

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Question 29
What are the advantages of using full-duplex Ethernet instead of half-duplex?

Question 30
How does replacing a hub with a switch affect CSMA/CD behavior in an Ethernet network?

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Answer 29
Full-duplex provides faster data transfer by being able to send and receive simultaneously and operates without collisions.

NOTE By enabling full-duplex on a port, you are disabling CSMA/CD on the
segment.

Answer 30
It effectively eliminates collisions. Replacing a hub with a switch effectively eliminates collisions because each switch port is a separate collision domain. One device per switch port and configured for full-duplex operation eliminates the need for CSMA/CD.

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Question 31
What command allows you to view the duplex and speed settings configured for a switch port?

Question 32
Can a network hub be connected to a switch port in full-duplex mode?

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Answer 31
To view the duplex and speed setting configured for a switch port, enter the show interface interface-id command, as follows:
Cat2960# show interface f0/1 FastEthernet0/1 is up, line protocol is up Hardware is Fast Ethernet, address is 0019.e81a.4801 (bia 0019.e81a.4801) MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Auto-duplex, Auto-speed, media type is 10/100BaseTX input flow-control is off, output flow-control is unsupported ARP type: ARPA, ARP Timeout 04:00:00

Answer 32
No. Because a hub shares access to the segment, it must connect to a switch port in half-duplex mode to be able to detect collisions.

NOTE CSMA/CD is not enforced when full-duplex is configured.

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Question 33
When troubleshooting a switch interface operating in full-duplex mode, which error condition can be immediately ruled out?

Question 34
An end user complains of slow access to the network. You issue the show interface command on the port the end user is connected to and you see a lot of collisions and runts on the interface. What is most likely the cause of the problem?

Question 35
An end user complains of slow access to the network. You issue the show interface command on the port the user is connected to and you see a lot of collisions and cyclic redundancy check (CRC) errors on the interface. What can be several causes for the problem?

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Answer 33
Collisions can be ruled out. Remember, collisions occur only on half-duplex links. There are no collisions on fullduplex links.

Answer 34
A duplex mismatch is most likely the cause. Although there are many things that can cause network slowness, the key here is when you issue the show interface command, you see many collisions and runts. A duplex mismatch will not only cause the end user to experience network slowness but also cause many collisions and runts on the switch interface.

Answer 35
The most likely causes of the problem are a bad network cable, damaged media, or EMI. Excessive collisions and CRC errors usually indicate a problem with the network cable attached to the port, or outside interference.

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Question 36
You connect two switches using a straight-through UTP Cat 6 cable. The port link lights between the switches are not coming on. What is the problem?

Question 37
You have a port on your switch that is not working properly. You enter the show interface command on the faulty port and the port status says “errDisable.” What are some possible causes for this error?

Question 38
Traffic between two switches is slow. You issue the show interface command on the uplink between the two switches and you see the following:
!output omitted! 0 input packets with dribble condition detected 180749 packets output, 8004302 bytes, 0 underruns 0 output errors, 45345 collisions, 0 interface resets 0 babbles, 45345 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

What are several possibilities for this problem?

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Answer 36
The problem is with the cable. A straight-through cable is used to connect data terminal equipment (DTE) devices to data communications equipment (DCE) devices. A switch is considered a DCE device, and so are hubs. DTE devices include computers, printers, servers, and routers. For two like devices to connect to each other, a crossover cable is needed. In this case, replacing the cable with a crossover cable will fix the problem.

Answer 37
If you are having connectivity issues and the port state shows “errDisable,” the following issues can be causing this error:
■ ■ ■ ■ ■

EtherChannel misconfiguration. Duplex mismatch. Bridge protocol data unit (BPDU) port guard has been enabled on the port. Unidirectional Link Detection (UDLD). A native VLAN mismatch.

Answer 38
The switch port is receiving a lot of late collisions. The problem can be a duplex mismatch or a faulty port, or the distance between the two switches might exceed the cable specifications.

NOTE Duplex mismatches occur when the connecting ends are set to different duplex modes, or when one end’s duplex is configured and the other end is set to autonegotiation.

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Question 39
What is the cause of multiple collisions on a port?

Question 40
While troubleshooting a switched network, you see the following on a switch interface that is having connectivity problems:
!output omitted! 5 minute input rate 10000 bits/sec, 8 packets/sec 5 minute output rate 10000 bits/sec, 7 packets/sec 1476671 packets input, 363178961 bytes, 0 no buffer Received 20320 broadcasts (12683 multicast) 2345 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

What could be the cause of the problem?

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Answer 39
Multiple collisions are the number of times the transmitting port had more than one collision before successfully transmitting a frame. If you experience multiple collisions on a port, the problem usually lies with an oversaturated medium.

Answer 40
The switch is receiving a lot of runts. Runts are frames smaller than 64 bytes with a bad frame check sequence (FCS). Bad cabling or inconsistent duplex settings usually cause runts.

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400 Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Section 3
Understanding Ethernet and Switch Operations
Ethernet was developed in the 1970s by Digital Equipment Corporation (DEC), Intel, and Xerox. Later, the IEEE defined new standards for Ethernet called Ethernet 802.3. 802.3 is the standard that is in use today.

Ethernet
Ethernet is one of the most widely used LAN standards. As Figure 3-1 shows, Ethernet operates at Layers 1 and 2 of the OSI model. Figure 3-1 Physical and Data Link Layers
Frame Relay

Data Link

Ethernet

802.3

Physical

The physical layer (Layer 1) defines cabling, connection specifications, and topology. The data link layer (Layer 2) has the following functions:
■ ■ ■

Provides physical addressing Provides support for connection-oriented and connectionless services Provides frame sequencing and flow control

One sublayer performs data-link functions: the MAC sublayer. Figure 3-2 shows the Media Access Control (MAC) sublayer (802.3). The MAC sublayer is responsible for how data is sent over the wire. The MAC address is a 48-bit address expressed as 12 hex digits.

HDLC EIA/TIA-232 v.35

Section 3: Understanding Ethernet and Switch Operations

401

Figure 3-2 MAC Sublayer
MAC Layer - 802.3 #Bytes 8 Preamble 6 Dest Add 6 Source Add 2 Length Variable Data 4 FCS

0000.0C

xx.xxxx

Ethernet II Uses "Type" Here and Does Not Use 802.2.

IEEE Assigned

Vendor Assigned MAC Address

The MAC sublayer defines the following:
■ ■ ■ ■ ■ ■

Physical addressing Network topology Line discipline Error notification Orderly delivery of frames Optional flow control

Ethernet LAN Connection Media
The term Ethernet encompasses several LAN implementations. Physical layer implementations vary, and all support various cabling structures. The following four main categories of Ethernet exist:

Ethernet (DIX) and IEEE 802.3: Operate at 10 Mbps over coaxial cable, unshielded twisted-pair (UTP) cable, or fiber. The standards are referred to as 10BASE2, 10BASE5, 10BASE-T, and 10BASE-F. Fast Ethernet or 100-Mbps Ethernet: Operates over UTP or fiber. Gigabit Ethernet: An 802.3 extension that operates over fiber and copper at 1000 Mbps, or 1 gigabit per second (Gbps). 10-Gigabit Ethernet: Defined in 802.3ae, runs in full-duplex mode only, over fiber.

■ ■

402 Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Network Media Types
Network media refers to the physical path that signals take across a network. The most common types of media are as follows:

Twisted-pair cable: Used for telephony and most Ethernet networks. Each pair makes up a circuit that can transmit signals. The pairs are twisted to prevent interference (crosstalk). The two categories of twisted-pair cables are unshielded twisted-pair (UTP) and shielded twisted-pair (STP). UTP cable is usually connected to equipment with an RJ-45 connector. UTP (see Figure 3-3) has a small diameter that can be an advantage when space for cabling is at a minimum. It is prone to electrical noise and interference because of the lack of shielding. Examples of categories of UTP cable exist: CAT 1, CAT 2, CAT 3, CAT 4, CAT 5, CAT 5e, CAT 6, CAT 6a, CAT 7, and so on.

Figure 3-3 UTP

Unshielded Twisted Pairs
Twisted Pair

Outer Jacket

Color-Coded Plastic Insulation

Fiber-optic cable: Allows the transmission of light signals. This offers better support in bandwidth over other types of cables. The two types of fiber-optic cables are multimode and single-mode, defined as follows:

Multimode: With this type of fiber, several modes (or wavelengths) propagate down the fiber, each taking a slightly different path. Multimode fiber is used primarily in systems with transmission distances less than 2 km. Single-mode: This type of fiber has only one mode in which light can propagate. Single-mode fiber is typically used for long-distance and high-bandwidth applications.

Section 3: Understanding Ethernet and Switch Operations

403

UTP Implementation
An RJ-45 connector is used with UTP cabling. Figure 3-4 shows an RJ-45 connector and its pin connections, following the T568B standards. Figure 3-4 RJ-45 Connector
Wire Pair T is Tip R is Ring Pair 2 T2 Pair 2 R2 Pair 3 T3 Pair 1 R1 Pair 1 T1 Pair 3 R3 Pair 4 T4 Pair 4 R4

Pin 1 2 3 4 The RJ-45 Connector 5 6 7 8

The two types of Ethernet cables are straight-through and crossover. Straightthrough cables are typically used to connect different devices (data terminal equipment [DTE] to data communications equipment [DCE]), such as switch-to-router connections. Figure 3-5 shows the pins for a straight-through cable. Figure 3-5 Straight-Through Wiring
Cable 10 BASE TX 100BASE T Straight-Through

Hub/Switch Pin Label 1 RD+ 2 RD– 3 TD+ 4 NC 5 NC 6 TD– 7 NC 8 NC

Server/Router Pin Label 1 TD+ 2 TD– 3 RD+ 4 NC 5 NC 6 RD– 7 NC 8 NC

404 Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Crossover Ethernet cables are typically used to connect similar devices (DTE to DTE or DCE to DCE), such as switch-to-switch connections. Exceptions to this rule are switch-to-hub connections or router-to-PC connections, which use a crossover cable. Figure 3-6 shows the pins for a crossover cable. Figure 3-6 Crossover Wiring
Cable 10 BASE T/ 100BASE T Crossover

Hub/Switch Pin Label 1 RD+ 2 RD– 3 TD+ 4 NC 5 NC 6 TD– 7 NC 8 NC

Hub/Switch Pin Label 1 RD+ 2 RD– 3 TD+ 4 NC 5 NC 6 TD– 7 NC 8 NC

Role of CSMA/CD in Ethernet
All stations on an Ethernet segment are connected to the same media. Therefore, all devices receive all signals. When devices send signals at the same time, a collision occurs. A scheme is needed to detect and compensate for collisions. Ethernet uses a method called carrier sense multiple access collision detect (CSMA/CD) to detect and limit collisions. In CSMA/CD, many stations can transmit on the Ethernet media, and no station has priority over any other. Before a station transmits, it listens to the network (carrier sense) to make sure that no other station is transmitting. If no other station is transmitting, the station transmits across the media. If a collision occurs, the transmitting stations detect the collision and run a backoff algorithm. The backoff algorithm computes a random time that each station waits before retransmitting.

Ethernet LAN Traffic
Three major types of network traffic exist on a LAN:

Unicasts: The most common type of LAN traffic. A unicast frame is a frame intended for only one host. Broadcasts: Intended for all hosts. Stations view broadcast frames as public service announcements. All stations receive and process broadcast frames. Multicasts: Traffic in which one transmitter tries to reach only a subset, or group, of the entire segment.

Section 3: Understanding Ethernet and Switch Operations

405

Ethernet Addresses
The Ethernet address, or MAC address, is the Layer 2 address of the network adapter of the network device. Typically burned into the adapter, the MAC address is usually displayed in a hexadecimal format such as 00-0d-65-ac-50-7f. As shown in Figure 3-7, the MAC address is 48 bits and consists of the following two components:

Organizational Unique Identifier (OUI): 24 bits. This is IEEE assigned and identifies the manufacturer of the card. Vendor-assigned: 24 bits. Uniquely identifies the Ethernet hardware.

Figure 3-7 MAC Addresses
OUI 24-Bits Vendor Assigned 24-bits

48-bit MAC Address

Switching Operation
Ethernet switches perform four major functions when processing packets: learning, forwarding, filtering, and flooding. Switches perform these functions by the following methods:

MAC address learning: Switches learn the MAC addresses of all devices on the Layer 2 network. These addresses are stored in a MAC address table. Forwarding and filtering: Switches determine which port a frame must be sent out to reach its destination. If the address is known, the frame is sent only on that port, filtering other ports from receiving the frame. If it’s unknown, the frame is flooded to all ports except the one it originated from. Flooding: Switches flood all unknown frames, broadcasts, and some multicasts to all ports on the switch except the one it originated from.

A switch uses its MAC address table when forwarding frames to devices. When a switch is first powered on, it has an empty MAC address table. With an empty MAC address table, the switch must learn the MAC addresses of attached devices. This learning process is outlined as follows using Figure 3-8: 1. Initially, the switch MAC address table is empty.

406 Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

Figure 3-8 Frame Forwarding by a Switch
MAC Address Table E0: 0260.8c01.1111 E3: 0260.8c01.4444 A E0 0260.8c01.1111 E2 B E3 D E1 0260.8c01.2222 C

0260.8c01.3333

0260.8c01.4444

2. Station A with the MAC address 0260.8c01.1111 sends a frame to station C. When the switch receives this frame, it does the following: a. b. Because the MAC table is empty, the switch must flood the frame to all other ports (except E0, the interface the frame was received). The switch notes the source address of the originating device and associates it with port E0 in its MAC address table entry.

3. The switch continues to learn addresses in this manner, continually updating the table. As the MAC table becomes more complete, the switching becomes more efficient, because frames are forwarded to specific ports rather than being flooded out all ports.

Maximizing the Benefits of Switching
Microsegmentation
Microsegmentation is a network design (functionality) where each workstation or device on a network gets its own dedicated segment (collision domain) to the switch. Each network device gets the full bandwidth of the segment and does not have to share the segment with other devices. Microsegmentation reduces and can even eliminate collisions because each segment is its own collision domain. Microsegmentation is implemented by installing LAN switches. Benefits of microsegmentation are as follows:
■ ■ ■

Collision-free domains from one larger collision domain Efficient use of bandwidth by enabling full-duplex communication Low latency and high frame-forwarding rates at each interface port

Section 3: Understanding Ethernet and Switch Operations

407

Duplex Communication
Duplexing is the mode of communication in which both ends can send and receive information. With full-duplex, bidirectional communication can occur at the same time. Half-duplex is also bidirectional communication, but signals can flow in only one direction at a time. Table 3-1 provides a comparative summary of full-duplex and half-duplex. Table 3-1 Full-Duplex and Half-Duplex Half-Duplex Can send and receive, but not simultaneously. The Ethernet segment is susceptible to collisions. Multipoint and point-to-point attachments. The medium is considered shared.

Full-Duplex Can send and receive data at the same time. Collision-free. Point-to-point connection only. Uses a dedicated switched port with separate circuits.

Efficiency is rated at 100 percent in both Efficiency is typically rated at 50 to 60 directions. percent. Both ends must be configured to run in full-duplex mode. The duplex setting must match on devices sharing a segment.

Configuring and Verifying Port Duplex
The default port settings on a Catalyst 2960 switch are as follows:
■ ■

Duplex: auto Speed: auto

The default auto setting means that the switch will automatically try to negotiate the duplex and speed of connected interfaces. To change the default settings, use the following commands:
Switch(config)# interface g0/1 Switch(config-if)# duplex {auto | full | half} Switch(config-if)# speed {10 | 100 | 1000 | auto}

408 Cisco CCNA Routing and Switching 200-120 Flash Cards and Exam Practice Pack

To view duplex and speed settings, use the show interface interface-id command, as follows:
Cat2960# show interface f0/1 FastEthernet0/1 is up, line protocol is up Hardware is Fast Ethernet, address is 0019.e81a.4801 (bia 0019.e81a.4801) MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Auto-duplex, Auto-speed, media type is 10/100BaseTX input flow-control is off, output flow-control is unsupported ARP type: ARPA, ARP Timeout 04:00:00

Troubleshooting Common Switch Issues
When troubleshooting switch issues, remember the following:
■ ■ ■ ■

Switches operate at Layer 2 of the OSI model. Switches provide an interface to the physical media. Problems generally are seen at Layer 1 and Layer 2. Layer 3 issues could be regarding IP connectivity to the switch for management purposes.

Identifying and Resolving Media Issues
Common switch Layer 1 issues include the following:
■ ■ ■

Bad wires or damaged wires. EMI is introduced. Malfunctioning equipment.

Bad wiring and EMI commonly show up as excessive collisions and noise. This is displayed by excessive collisions and runts when issuing the show interface command, as follows:
SwitchA# show interface g0/1 GigabitEthernet0/1 is up, line protocol is up (connected) Hardware is Gigabit Ethernet Port, address is 000d.65ac.5040 (bia 000d.65ac.5040) MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, reliability 255/255, txload 1/255, rxload 1/255 <Text-Ommited> 5 minute output rate 10000 bits/sec, 7 packets/sec

Section 3: Understanding Ethernet and Switch Operations

409

1476671 packets input, 363178961 bytes, 0 no buffer Received 20320 broadcasts (12683 multicast) 542 runts, 0 giants, 0 throttles 3 input errors, 3 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 1680749 packets output, 880704302 bytes, 0 underruns 8 output errors, 1874 collisions, 15 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

Identifying and Resolving Access Port Issues
Common port access issues are as follows:
■ ■ ■

Media-related issues Duplex mismatch Speed mismatch

Media-Related Issues
Media-related issues might be reported as an access issue; for example, a user might say that she cannot access the network. Media issues should be isolated and identified as indicated in the previous topic.

Duplex Issues
The following items can create duplex issues:

One end set to full-duplex and the other set to half-duplex results in a duplex mismatch. One end set to full-duplex and auto-negotiation on the other:
■ ■

Auto-negotiation can fail, and the end reverts to half-duplex. Results in a duplex mismatch.

One end set to half-duplex and auto-negotiation on the other:
■ ■

Auto-negotiation can fail, and the end reverts to half-duplex. Both ends set to half-duplex causes no mismatch.

Speed Issues
The following items can create speed issues:
■ ■

One end set to one speed and the other set to another results in a mismatch. One end set to a higher speed and auto-negotiation on the other:
■ ■

Auto-negotiation will fail, and the end will revert to a lower speed. Results in a mismatch.

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