[c-nsp] Odd problem with N7K and multicast

[John Neiberger]

We ran into an interesting problem this morning and I've been told that
we've run into this same problem a couple of times before with other N7Ks.
This is ASM. We have a receiver and a source connected to the N7K. The RP
is a 7600 elsewhere. The N7K was rebooted (upgraded to 6.1(3), actually)
and when it came back up, the receiver could not join the source.

There was a *,G entry on the N7K and we could see the IGMPv2 join coming
from the receiver. Up on the RP, we could also see the *,G route there.
However, there was no S,G and there should have been since the source was
active.

Here's where it gets weird. The workaround is for a second receiver to send
an SSM join (IGMPv3) directly to the source. This sets up the S,G state on
the N7K and suddenly everything starts working. Even the RP starts showing
the S,G route that should have been there all along.

It seems as if the N7K has a problem with Source-to-RP communication. I
have no idea what else it could be. At least we have a workaround, but it
is still quite frustrating when dealing with several sources that all have
to jiggled manually like that.

Have any of you seen this before?