All things related to multicast

[Bill Owens <>]

On Thu, Jun 07, 2012 at 11:02:44AM -0700, Michael Knezevich wrote:
>    What do you think could be causing this?  It's clearly something on a
>    timer, but I don't know what, or what to do about it.  Is it at our end?
>     Any advice on how to troubleshoot would be appreciated.

I'd suggest starting at your local router and watching the multicast state. 
If you're on a Cisco, these commands may show something interesting:

- check IGMP with
    show ip igmp groups
- check multicast forwarding state with
    show ip mroute S G
    show ip mroute S G count

The S and G are source and group IP addresses. If you see the state coming up 
and remaining in place, then move to the next hop towards the source. At some 
point you should find a router where the state is established and then 
disappears. At that point look closely at the link between the two routers, 
especially if there are ACLs installed on either side. You might have 
something that permits establishment of the state, but blocks the keepalives, 
or that breaks the connection in one direction and not the other.

If the router acting as your RP is *not* in the shortest path, I'd also look 
at whether the traffic is beginning to flow along the RP-tree, and failing 
once the path switches over to the shortest path tree. 

Good luck,
Bill.