[c-nsp] Multicast state behavior differences between 7600 and ASR9k

[John Neiberger]

We're seeing a little weirdness that we're having trouble deciphering.
We have a multicast source connected to a 7600 and we're using SSM. If
the source starts sending, an mroute entry is created in the mroute
table immediately, whether or not anything is joining the group. So,
prior to anything actually joining the group, we can see which groups
that source is sending to simply by doing a "show ip mroute".

The behavior is different on the ASR9k. On that platform, there are no
entries in the mrib when the source is sending. The mrib entries are
not created until something joins the group. Once the receiver leaves
the group, the mrib entries disappear. This is not expected behavior
and we've had a few people from Cisco say that multicast state should
be created if the source is sending, whether or not anything is
joining.

Do any of you have any idea why this behavior is different on the ASR?

Thanks!
John