Multicast PIM with multiple RPs
In a Multicast topology, when Multicast PIM sparse mode is implemented, we use what are known as rendezvous points (RPs). These RPs are either statically configured or are automatically elected using mechanisms such as Auto-RP and BSR.
There may be more than one RP configured in a single multicast topology, and each RP may be responsible for different multicast groups.
When a source router sends a registration request, it sends it to the RP that corresponds to the specific multicast group in question. When there are multiple RPs, each multicast router maintains a group-to-RP mapping where the groups correspond to the appropriate RPs. Using the
show ip pim rp mapping command, you can see these mappings. The Auto-RP and BSR mechanisms maintain this mapping that is used in the event that there are multiple RPs.
Note that in a topology where Auto-RP is used, there may also be multiple mapping agents as well.