[c-nsp] Weird problem with 2960S and desktop switch

[Peter Rathlev]

On Wed, 2014-01-08 at 10:14 +0100, Garry wrote:
> This is configured:
> 
> spanning-tree portfast bpduguard default
> errdisable recovery cause bpduguard

This is sensible. It precludes connecting switches to access ports, but
you don't want that without explicit configuration anyway.

> Apart from the fact that the default BPDU guard does as it is supposed
> to, my actual problem is why the switch goes down when I remove it on
> that port, thus allowing the switch to be connected ... I reckon I might
> have to go on site and check on the console when the switch is connected
> (and BPDU guard disabled) to find out whether there are any hints as to
> what is going wrong ...

If the error recovered by itself after 40-50 seconds it might "just"
have been an STP event. Maybe a root election. If things come back by
themselves the output from "show spanning-tree vlan 1 detail" might give
some clues. Look for who is root bridge, when the last change occurred
and from what ports you are receiving BPDUs.

If the problem didn't resolve itself until the switch was disconnected
then it might very well have been a loop. You would very probably see a
lot of output drops on all interfaces with a loop.

-- 
Peter