For PIM-SM to operate, the following elements must exist in the PIM-SM domain:
You must enable an underlying unicast routing protocol for the switch to provide routing table information to PIM-SM.
You must configure an active BSR to send bootstrap messages to all PIM-v2 configured switches and routers to enable them to learn group-to-RP mapping. If you configure several BSRs in a network, an active BSR is elected based on priority and IP address (if priority is equal, the BSR with the higher IP address is elected).
You must include an RP to perform the following tasks:
manage one or several IP multicast groups
become the root for the shared tree to these groups
accept join messages from receiver switches for groups that it manages
elect an active RP based on priority and IP address (if priority is equal, the RP with the higher IP address is elected)