Lessons · Network switches · err-disabled ports
The switch shut the port itself
err-disabled means the switch disabled the port on its own, because something it was told to guard against happened: a port security violation, a BPDU on a guarded port, a loop it detected. It stays down until somebody clears it.
Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.
What it is for
It is not a fault to be fixed by trying the cable again; it is the switch having done its job. Read as a broken port, it costs twenty minutes of swapping leads while the reason sits in the log saying exactly what was caught.
How to think about it
The status column tells you who shut it. `disabled` is a port somebody typed shutdown on. `err-disabled` is a port the switch shut without being asked, and the difference is the whole diagnosis -- so find out WHY before putting it back, because a guarded port with a switch on the end of it needs the switch moved, not the port reopened.
Worked example
enableThe # prompt.
show interfaces statusEvery port and its state. This is the column that matters.
configure terminalSwitch(config)#.
interface gi0/5Switch(config-if)#.
shutdownDown, because you said so.
endSwitch#.
show interfaces statusGi0/5 now reads `disabled`. That word means a person did this. `err-disabled` is the one the switch writes without being asked, and you have just made the state it is NOT.
configure terminalBack in.
interface gi0/5Switch(config-if)#.
no shutdownAnd up. Off and on again, in that order, is also the manual way back from err-disabled -- with the difference that if the cause is still there, it will shut itself again within seconds.
endSwitch#.
Your turn
Put the port the switch shut back into service.
no
Console into a switch
The trap
Configuring errdisable recovery so ports come back on a timer and calling that the fix. It hides the count: a port recovering every five minutes all week looks healthy on Friday and is a fault nobody has looked at.