Multicast traffic stops

[Volodymyr Khrystenko]

Hi.

What will happen with sparse multicast network when source just stops forwarding? I mean how react the RP, tree states on interfaces and so on?

Will they just be deleted because of timeout or reaction will be faster? Thanks

[Steve Fuller]

Hi,

When the source stops sending traffic to the multicast group the (S,G) state will age out in the router closest to the source after approximately 3 minutes 30 seconds. This router will stop sending the periodic Join(S,G) messages to the RP and so the (S,G) state will also time out of the PIM routers on the path to the RP and the RP itself.

If there is still a receiver for the group, the (*,G) state will remain in the router closest to the receiver, the PIM routers on the path to the RP and the RP itself. When the receiver leaves the group, the (*,G) state will also age out after approximately 3 minutes 30 seconds.

Regards

[Harold Ritter]

Hi Steve,

Just a small rectification. The DR does not send PIM joins to the RP. It does refresh the RP by sending null-register messages though.

Regards

[Steve Fuller]

Hi Harold,

Thanks for the clarification. Time to review the Cisco IP Multicast Training Materials again to remind myself.

Regards

[Volodymyr Khrystenko]

I have some hesitations though. When closest router to the source registers with RP, it stops sending null-register message (there is no need in it). Only after switchover ti source tree, the messages start to be transmitted again. Ok, closest router stops sending null-registers (because there is no source). What next? RP has timers for it? It is not join/prune process. Thanks.

[Harold Ritter]

Hi Volodymyr,

If the RP is not in the forwarding path and it stops receiving the null-register message, then entry in the mroute will eventually time out.

Regards