The BSR receives RP router advertisement messages from the candidate RPs. The BSR adds the RP router with its group prefix to the RP set. Only one BSR exists for each PIM-SM domain.
The BSR periodically sends bootstrap messages containing the complete RP set to all routers in the domain. The BSR ensures that all PIM-SM routers send join, prune, and register packets.
Within a PIM-SM domain, you can configure a small set of routers as C-BSRs. The C-BSR with the highest configured priority becomes the BSR for the domain. If two C-BSRs use equal priority, the candidate with the higher IP address becomes the BSR. If you add a new C-BSR with a higher priority to the domain, it automatically becomes the new BSR.
Important
Configure C-BSRs on routers that are central to all candidate RPs.