Cisco® CCNP Switch Exam Cram Notes : Troubleshooting err-disable recovery

1. Layer2 Technologies

1.1 Configure and verify switch administration

1.1.c Troubleshoot Err-disable recovery:

Errdisable is a feature that automatically disables a port on a Cisco Catalyst switch. There are several reasons for which an administrator can configure ErrDisable on a switch port. These include the following:

1. Duplex Mismatch

2. Loopback Error

3. Link Flapping (up/down)

4. Port Security Violation

5. Unicast Flodding

6. UDLD Failure

7. Broadcast Storms

8. BPDU Guard

1. When a port is in error-disabled state, it is effectively shutdown and no traffic is sent or received on that port.

2. show interfaces command, the port status shows as Errdisabled.

3. To recover a port that is in an Errdisable state, manual intervention is required, and the administrator must access the switch and configure the specific port with 'shutdown' followed by the 'no shutdown' command.

The error disabled feature is supported on most Catalyst switches running the Cisco IOS software. Including all the following models:

Catalyst 2940/2950/2960/2960S
Catalyst 3550/3560/3560-E/3750/3750-E
Catalyst 4000/4500/4507R
Catalyst 6000/6500

There are a number of reasons a port can enter the Errdisable state. One common reason is the Port Security error.

Of all the errors, Port Security is more a feature rather than an error. Port Security allows the restriction of MAC Addresses on an interface configured as a layer 2 port. This effectively prevents others connecting unwanted hubs or switches on the network. Port Security allows us to specify a single MAC Address to be connected to a specific port, thus restricting access to a specific computer. Some times, it is desirable to restart the switch port automatically after ErrDisabled. This is possible using ErrDisable recovery command as shown in the example below.

The following commands enable the autorecovery feature 30 seconds after a port security violation:

Switch(config)#errdisable recovery cause psecure-violation
Switch(config)#errdisable recovery interval 30

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