Sunday, January 18, 2009

IE Vol 1 Multiple Candidate RPs Complete

In this lab, two candidate RPs are created, which only advertise a portion of the multicast addresses. This requires the group-list option of the ip pim send-rp-announce command. Not much to it, just configure the access list to only allow the multicast groups that the router wants to be an RP for.

There is one thing to keep in mind on this command. Typically, whenever creating a multicast access-list, you want to use the destination address, since a multicast group can only be a destination, and not a source. But we are not filtering here, we are telling the RP which groups to advertise. Therefore, the groups to be advertised are configred as the source of the access-list. Perhaps more easily, a standard ip access-list can be used.

On a minor irritating note, the lab specifies a /4 address, when it should have used a /5. /1 is a class A, /2 is a class B, /3 is a class C, therefore /4 would be the entire class D. To split a class D down the middle, a /5 is required.

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