Before a DR can forward encapsulated packets for a specific multicast group to an RP, it must know which router in the domain is the elected RP for that multicast group. The BSR function enables this operation by doing the following:

  1. Learns the group-to-RP mappings on the C-RPs in the domain by reading the periodic advertisements each one sends to the BSR.
  2. Distributes the aggregate C-RP information as an RP-set to the PIM-SM routers in the domain. This is followed by an election to assign a specific multicast group or range of groups to the C-RPs in the domain. (The software supports assignment of up to four multicast addresses and/or ranges of multicast addresses to a C-RP.)

The BSR periodically sends bootstrap messages to the other PIM-SM routers in the domain to maintain and update the RP-set data throughout the domain, and to maintain its status as the elected BSR.


Where static RPs are configured in the domain to support the same multicast group(s) as one or more (dynamic) C-RPs, then the RP-set data has the precedence for assigning RPs for these groups unless the static RPs have been configured with the


option and if the multicast group mask for the static RP equals or exceeds the same mask for the applicable C-RP(s.)