2.1.a Implement and troubleshoot switch administration

2.1.a [ii] errdisable recovery

If the configuration shows a port as enabled, but software on the switch detects an error situation on the port, the software shuts down that port . In other words, the port is automatically disabled by the switch operating system software because of an error condition that is encountered on the port.

When a port is error disabled, it is effectively shut down and no traffic is sent or received on that port. The port LED is set to the amber and if you issue the show interfaces command, the port status shows err-disabled. Here is an example of what an error-disabled port looks like from the command-line interface (CLI) of the switch:

Switch# show interfaces gigabitethernet 5/ 1 status

Port   Name    Status    Vlan   Duplex   Speed   Type

Gi4/ 1 err-disabled 100 full 1000 1000BaseSX

Or, if the interface has been disabled because of an error condition, you can see messages that are similar to these in both the console and the syslog:

%SPANTREE-SP-2-BLOCK_BPDUGUARD:

Received BPDU on port GigabitEthernet4/ 1 with BPDU Guard enabled. Disabling port.

%PM-SP-4-ERR_DISABLE: bpduguard error detected on Gi4/ 1, putting Gi4/ 1 in err-disable state

In order to recover a port from the errdisable state, first identify and correct the underlying cause, and then re-enable the port. If you re-enable the port before you fix the actual problem, the ports could just become error disabled again. After you fix the root problem, the ports are still disabled if you have not configured errdisable recovery on the switch. In this case, you must re-enable the ports manually.

Issue the shutdown command and then the no shutdown interface mode command on the associated interface in order to manually re-enable the ports.

Major reasons for errdisable are:

● EthernetChannel misconfiguration

● Duplex mismatch

● BPDU port guard

● UDLD

● Link-flap error

● Loopback error

● Port security violation

● L2tp guard

● Incorrect SFP cable

● 802.1X security violation

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1492-1509).  . Kindle Edition.
http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/69980-errdisable-recovery.html