Multicast - Bootstrap Router (BSR)

The Bootstrap Router (BSR) is a key component in multicast networking, specifically in the context of the the PIM Bootstrap protocol. Its main role is to automate and simplify the management of multicast group information within a PIM network. The BSR is elected for the purpose of discovering the Rendezvous Points (RPs) in the PIM sparse mode network.

Routers wanting to become the RP for a group will send their candidacy to the BSR. The BSR then creates a list of these RPs and sends it using bootstrap messages to the rest of the multicast routers on the network. By distributing this information, the BSR ensures that all routers in the network are aware of the available RPs and their multicast group mappings. The updating of this information is crucial for efficient and effective multicast routing.

The BSR itself does not keep track of multicast routes: its main function is RP discovery. Its job is not very resource-intensive as that of the RP. Even so, it is best practice to ensure that the BSR is generally centrally located within the multicast domain rather than on the edge of the network. This ensures a faster process since all candidate RPs will be fewer hops away.