2

Imagine you have a ring of routers, all of which are routing multicast with PIM Sparse mode, pretend there's a single Rendevouz Point (RP) "Router A" for any multicast on 239.10.10.0/24. If a stream with the address 239.20.20.20 is then injected into this ring, what is the expected behavior?

enter image description here

2

If there is no RP for the second multicast group, the new multicast stream will not be routed because the routers have no place to send the stream.

Based on the RP configuration in your previous question:

ip pim autorp listener
ip pim send-rp-announce Loopback0 scope 12 group-list 1
ip pim send-rp-discovery scope 12
!
access-list 1 permit 239.10.10.0 0.0.0.255
!

this RP will not be an RP for your new stream.

Your new stream will need an RP and an RP mapping agent for that stream. It doesn't need to be the same RP as for the first stream. You could change the ACL on the RP to specifically announce the RP for the new stream:

access-list 1 permit 239.10.10.0 0.0.0.255
access-list 1 permit 239.20.20.20 0.0.0.0

or you could expand the existing range on the ACL from a /24 to include the new stream:

access-list 1 permit 239.0.0.0 0.255.255.255

or you can manually set the RP address on each router:

access-list 1 permit 239.20.20.20 0.0.0.0
ip pim rp-address <rp ip address> 1
2
  • Thanks, this was more of an academic question than anything else. So from what you're saying, if (let's say) I have an isolated L2 network with a bunch of cisco switches and a few hundred multicast streams, if I introduced a multicast router (there's none atm) here that's not setup as the RP for any of them, then the traffic would NOT go to the router until it becomes the RP for it, correct?
    – rantsh
    Jan 14 '16 at 17:07
  • If you are using PIM SM, the multicast router would need to have an RP for any stream it wants to route, else it won't route it. It is a different story with PIM DM or PIM SM/DM which will route a stream as DM to any multicast router peers.
    – Ron Maupin
    Jan 14 '16 at 17:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.