[c-nsp] TCN's - Causing brief outages on ASR1K

[Lukas Tribus]

> A TCN will cause all the learned MAC addresses to be flushed by the 
> switiches, but it will not "block" traffic. So the TCN on its own 
> should not be the cause of OSPF and LDP flaps. 

Thats the case if the TCN originated by an isolated event on one part
of the network that doesn't relate to this part, yes.

But if the TCN is only part of a larger STP problem, like a
complete root-change, then the "portfast trunk" config
will indeed improve reconvergence.

"Portfast trunk" however doesn't affect how STP handles TCAM
entries when a TCN comes in.


TCN's are not the problem, but one of the symptoms.