[c-nsp] Possible spanning tree issue

[Pete Templin]

On 6/4/13 3:56 PM, Michael Sprouffske wrote:
> I attached a new switch to the network and it took down our contact
> center that doesn't touch this switch nor does the phone system.  Is
> this spanning tree doing this?  I don't see anything in the logs that
> show a change in spanning tree.
>
> I also had an employee unplug a switch by accident and it took down
> our contact center.  This switch is all by itself and does not
> directly touch the phone system nor is it in the path of the phone
> system.  I feel like this shouldn't have happened.

You won't see anything in the logs regarding STP changes unless you're 
running a debug before/during/after and you are logging at the debug 
level.  Do "sh spann det | inc gy changes" on a switch and see if one or 
more VLANs had a topology change about the time this event happened.  If 
it's more recent than that, the commands after the next paragraph may 
become quite important.

At this very moment, I would highly suggest that you stop whatever else 
you're doing and embark on a priority-1 project to assess and define 
your STP root placement.  I suspect, reading between the lines of your 
post, that you haven't done much to select where it is, and you're 
experiencing a change in root placement.  I'd strongly suggest assessing 
whether any of the following make sense in your environment:

Global:
spanning-tree vlan 1-4094 pri 8192
spanning-tree portfast default
spanning-tree portfast bpdufilter default

Interface:
no spanning-tree portfast
spanning-tree portfast trunk
spanning-tree bpduguard enable
spanning-tree guard root

pt