When a network port encounters an error. This port is automatically shutdown to ensure network stability. When error-disable is enabled.
The predefined error are as follows;
Primary function of error-disable is fault detection. Secondary you can set up recovery, per predefined error. This can be done by ;
errdisable recovery cause
Be sure to set the recovery interval to your specific needs;
errdisable recovery interval 60
Whenever a port is disabled due to an error-disable condition you should see something like ;
somerouter#show interface GigabitEthernet1/6
GigabitEthernet1/6 is down, line protocol is down (err-disabled)
--//output omitted for brevity//--
Interesting to see that the port is in down/down status with an err-disabled condition.
If you do not resolve the root cause the log will be flooded with
Jan 10 08:51:35.074 CET: %PM-4-ERR_RECOVER: Attempting to recover from link-flap err-disable state on Gi1/6
Jan 10 08:51:37.179 CETT: %PM-4-ERR_DISABLE: link-flap error detected on Gi1/6, putting Gi1/6 in err-disable state
To resolve the problme one has to know the root cause, for this you’ll have to issue the command “show errdisable recovery”. First you see a list of errors where recovery is enabled, or disabled. (See column ‘Timer Status’)
somerouter#sh errdisable recovery
ErrDisable Reason Timer Status
Timer interval: 60 seconds
Interfaces that will be enabled at the next timeout:
Interface Errdisable reason Time left(sec)
--------- ----------------- --------------
Gi1/6 link-flap 47
Root cause for the problem with interface Gi1/6 lies in link-flap. This is somewhat cryptic but will give you an idea where to find the solution.
Possible root causes are;
faulty optics (sfp/gbic)
wrong speed/duplex settings
In this particular case I suspected the speed/duplex settings.
Jan 10 11:20:31.589 CET: %LINK-5-CHANGED: Interface GigabitEthernet1/6, changed state to administratively down
Jan 10 11:20:33.703 CET: %LINK-3-UPDOWN: Interface GigabitEthernet1/6, changed state to up
Jan 10 11:20:33.712 CET: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/6, changed state to up
Link was forced down and up to get rid of the error-disable condition.
Terminal monitor was turned on to instantly see what is going on.
Logging tells me that the port is admin down and that changed to up.
Et voilà, line protocol is also changed to up.
Root cause found and resolved.