[c-nsp] 2970 turns into a hub for a few moments

[Vincent De Keyzer]

> > Well, since there have been no topology changes [...]
> 
> Are all access ports configured with 'spanning-tree portfast'?
> Otherwise, you might be seeing a lot more TCNs than you're
> expecting...

OK, you guys win. I have just correlated the last two breaks with a flood of
TC BPDUs (seen with TCP dump on the interface of both firewalls)... 

But then, what's the catch? It's OK for me to configure 'spanning-tree
portfast' on all access ports, but why has it been working OK up to now, and
why has this suddenly become an issue with the Packet Filters?

Vincent