Question on PIM Auto-RP and Mapping Agents

Unanswered Question
May 22nd, 2007

Hi Experts,

I have a few basic questions about PIM Auto-RP mechanism.

Please correct my understanding about these below :

Question 1 -

A router, when configured with the command 'ip pim send-rp-announce loopback0 scope 16' announces itself as RP on the multicast address 224.0.1.39. And, the Mapping Agent listens to these messages on 224.0.1.39 and sorts them as (RP,Groups) and re-announces them on 224.0.1.40.

Question 2 -

We know that RP is basically a mechanism for the sparse PIM mode wherein the routers get access to the multicast tree by reaching the RP router. If that is the case, then how do the routers actually get to know about the Auto-RP multicast group 224.0.1.39/40, in order for it to reach the actual RP for the actual multicast group it needs to join ?

Does it mean that the groups 224.0.1.40 and 224.0.1.39 always works in Dense mode fashion that it reaches all routers and is not pruned (as all routers need to disseminate the Auto-RP discovery information .. ?

Question 3 -

I am thinking of trying a multicast configuration on the routers using static-groups and join-group commands.. Would you know of some real nice useful links that have sample multicast lab examples ?

I know there will be a lot of great replies :-)

Cheers

Arav

I have this problem too.
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aravindhs Thu, 05/24/2007 - 01:25

Are my questions absurd or is something totally wrong with my post that there has not been a single reply even ?

cheers

Arav

swaroop.potdar Thu, 05/24/2007 - 12:49

A1) Yes thats correct announcement on .39 and discovery on .40

A2) For auto-RP to work sparse-dense mode has to be configured. Announcement and discovery happens in dense fashion and when S,G mapping are available it goes the sparse way.There are workarounds to make it work with sparse only, but its better to skip that when deploying in a live environment.

A3) You may not find anything on a link for Multicast Lab as such, but you can try to setup 5 to 8 routers to have a meaningful experimentation with multicast where you can designate 1 end always as source and 1 end as receiver and then play with the core using sparse, dense and sparse-dense, using single RP, multiple RP's.

HTH-Cheers,

Swaroop

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Posted May 22, 2007 at 9:11 AM
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