Hello,
I am labbing some auto-rp multicast stuff and I have a question about the IGMP join messages specifically related to the 224.0.1.40 MC group.
So here goes…
In the lab I have 3 routers with PIM-SM config’d:
RTR A — P2P frame-relay— RTR B —fast ethernet— RTR C
(Lo 0)
RTR A is the candidate RP and the mapping agent and on the fast ethernet interface RTR B is the IGMP querier on all interfaces.
So from what i have read so far and observing the workings of the routers, RTR A the RP candidate and mapping agent sends out MC to groups in dense mode, so RTR B has received the RP mapping info. On RTR B I also noticed it sends out IGMP general queries on the loopback and fast ethernet, but not serial. RTR B will receive an IGMP membership report for group 224.0.1.40 on its loopback interface.
So my question lies with the IGMP membership report for 224.0.1.39 & 40 – do routers send membership reports for 224.0.1.39 & 40???
I am thinking that routers don’t send membership reports for 224.0.1.39 & 40. Thought process – when a router first comes up, it doesn’t know where the RP is to forward the membership report to, that makes sense. But a router could respond to a IGMP general query message if a neighbor asked and eventually every router would figure out where the RP is, eliminating the need of autorp listerner or sparse-dense mode. SO…I have not yet found a definitive answer, but my guess would be that routers don’t send membership reports for 224.0.1.39 & 40.
BUT… one piece of info is messing up my theory — on RTR B I am getting a membership report for 224.0.1.40 on the loopback interface, but not on the fast ethernet interface. Any insight into this would be greatly appreciated…
Thank,
Sanjay