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13 Cards in this Set

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  • Back

List the AP states in order

AP boots, WLC discovery, CAPWAP tunnel, WLC join, Download image, Download Config, Run state, Reset

What does an AP do to discover the WLC?

AP sends a unicast CAPWAP Discovery Request to a controller’s IPaddress over UDP port 5246 or a broadcast to the local subnet

If the AP and controllers lie on different subnets, you can configure the local routerto relay any broadcast requests on UDP port 5246 to specific controller addresses. Use thefollowing configuration commands:

router(config)# ip forward-protocol udp 5246

router(config)# interface vlan nrouter

(config-int)# ip helper-address WLC1-MGMT-ADDRrouter

(config-int)# ip helper-address WLC2-MGMT-ADDR

Describe the steps of the WLC discovery process:

1. Broadcast on the local subnet

2. Use locally stored WLC addresses

3. Use DHCP

4. Use DNS

5. Reset and try again

Describe the steps of the WLC selection process:

1. Try primed address

2. Try the master controllers

3. Try the least-loaded controller

Joining a WLC involves sending it a CAPWAP Join Request and waiting for it to returna CAPWAP Join Response. From that point on, the AP and WLC build a

DTLS tunnel tosecure their CAPWAP control messages.

Describe the keepalive interval from the AP to the controller

Keepalives are sent from the AP to the controller every 30 seconds. If the controller does not answer back, the AP will escalate the test by sending four more keepalives at 3 second intervals. If these keepalives are not answered, the controller is declared to be down.

If an AP is configured for a primary and secondary controller, and the primary fails then recovers, what is the default behavior?

The AP will not rejoin the primary, unless it is configured to do so.

Describe WLC Stateful Switchover

-Version 7.5 and later supports SSO. Both controllers must have an identical image installed

-Active controller is purchased with the license to support the AP count, backup controller is purchased with the High-Availability license

-When the active unit fails, the hot standby unit assumes the role of the active controller. A new CAPWAP tunnel does not have to be built.

SSO typically takes how long?

-500 msec in the case of a crash or power failure

-Up to 4 seconds if a network failure has occured

The active and standby controller must share the following addresses:

-Mobility MAC

-Virtual Management IP

The hot standby controller mirrors the active controller through-

keepalives that are sent every 100 msec.

If keepalives are not answered, what is sent?

ICMP echo requests, to determine the type of failure that has occurred/