CCIE PIM AUTO RP

CCIE PIM AUTO RP
Re. www.cisco.com

I would like to talk about Auto-RP, how the Auto-RP works and what tools do we have to troubleshoot when we encounter with problems. Well we should all know that we have today 3 basic operation modes of PIM

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Sparse Mode - also called source tree and it is mostly used today Multicast Networks using a Pull Technology meaning if you do not ask I will not send it

Dense Mode - also called shared tree using Push Technology meaning I will always send and if you say you do not need it I will Prune (hold) back and strat to countdown a timeout counter before I will start again sending.

Sparse-Dense Mode - commonly people think that it is a new and better mode but it is actually an implementation meaning that I will use Sparse mode if I have an RP (Rendezvous Point) for that group but if I don't have an RP then I will use Dense Mode.

When we enable PIM Sparse Mode we must have a RP for the group we use, and all the traffic will pass trough the RP (By default) unless indicated otherwise

To set an RP in a Sparse Group we have 3 basic methods:
a) Static
b) Auto-RP Cisco proprietary
c) BSR the industry standard

Auto RP:
First Step before we start with any multicast config we need to make sure that all our unicast routing is working so that is step 1 before we even think on Multicast.

Why?! Because Multicast is relaying on our Unicast for the RPF (Reverse Path Forwarding) check is done based on the Unicast routing Table and the RPF is basic check of backwards Path between the Sources of the Traffic to the Destination, with that said each time a new group is announced it must go trough the RPF check.

To Enable Auto RP we must specify an RP-Candidate and RP-Mapping

RP-Candidate is to announce your self as an RP, you can also announce one Router to be RP for certain groups and different Router to be RP for different groups.

RP-Mapping the Mapping agent can be the same Router as the Candidate but it also can be a different Router the mapping agent is telling all the routers in the Multicast Domain where is the RP for each group.

When you enable the RP Candidate you Join a Group 224.0.1.39 and all other routers in the multicast join Group 224.0.1.40 listening to the Mapping agent.