[c-nsp] Reasons for "random" ISIS flapping?

[Peter Rathlev]

On Wed, 2013-08-07 at 10:34 +0200, Adam Vitkovsky wrote:
> So in case Router-A does not see the hellos for 800ms or 1s it will
> thorn down the adjacency on his side and will try to reinitialize it
> by sending the IIH but this time with an empty TLV 6. 
> When e.g. Router-B will receive such an IIH it will realize that its
> neighbor has forgot him and will thorn down the adjacency to
> participate in the new adjacency formation procedure with Router-A. 
> 
> So the question seems to be why Router-A stops receiving IIHs or BFD
> hellos for a split second from time to time while no one else notices
> any problems until they learn that Router-A dropped the adjacency. 

Ah, thank you (and Saku too) for this explanation. It makes a lot of
sense and clearly points at ROUTR-A not receiving (or internally losing)
the hello packets.

> Maybe some ingress buffers overruns or some CoPP. 

The device in question has no control-plane policy. (Sub-optimal, I
know.) And we see no input queue drops on the receiving side or output
drops on the sending side. Since it's dark fiber between all the devices
I consider the possibility of simply "lost" packets low.

-- 
Peter