Dell EMC SmartFabric OS10 User Guide Release 10.5.0

You can configure a subset of PIM routers within the domain as candidate BSRs (C-BSRs). The C-BSRs exchange bootstrap messages (BSM) to elect the BSR. The BSR informs its status to all the routers.

Every PIM router within a domain must map a particular multicast group address to the same RP. With BSR, group-to-RP mapping is dynamic. You can configure a subset of routers within a domain as C-RPs. Each PIM router selects an RP for a multicast group from the list of group-to-RP mappings learnt from the BSR messages.

The RP election process is:

1. The C-BSRs announce their candidacy throughout the domain in BSMs. Each BSM contains a BSR priority. The C-BSR with the highest priority becomes the BSR.
2. Each C-RP unicasts periodic candidate RP advertisements to the BSR. Each message contains an RP priority value and the multicast group ranges for which the router is a C-RP.
3. The BSR determines the most efficient and stable group-to-RP mapping, which is called the RP-set formation.
4. The BSR sends the group-to-RP mapping sets to all the multicast routers. To select an RP from a set of RPs, multicast routers use the algorithm that is specified in RFC 4601.
5. The BSR sends the group range-to-RP mappings to all the routers in the domain.