Multicast - PIM Bootstrap (BSR)

Multicast PIM Bootstrap (BSR) is a protocol that is used to automatically find the Rendezvous Point (RP) in a multicast PIM sparse mode network. It is similar to Cisco's proprietary AutoRP, but is an open standard.

BSR is used to automate the distribution of multicast group-to-RP mappings within a PIM domain. Here's a brief overview of how it works:

  1. Election of BSR: The BSR is a router elected by the PIM routers in the network. It is responsible for coordinating multicast group information. PIM routers use a priority value and the highest IP address to elect the BSR.
  2. RP Announcements: RPs are routers that act as a meeting point for sources and receivers of multicast traffic. RPs send their information to the BSR.
  3. BSR Messages: The BSR distributes the RP information throughout the PIM domain using Bootstrap messages. These messages contain the RP set, which lists the RPs and the multicast groups they serve.
  4. RP-Set Propagation: Other PIM routers in the network receive the Bootstrap messages and learn about the available RPs and their associated multicast groups. This knowledge is used to direct multicast traffic efficiently.
  5. Dynamically Adjusting to Network Changes: The BSR mechanism is dynamic. As routers join or leave the network, or as RPs change, the BSR updates the RP-set and redistributes it, ensuring that multicast routing is optimized and up-to-date.

The BSR mechanism simplifies the management of multicast routing by automatically distributing RP information, reducing the need for manual configuration and allowing the multicast routing infrastructure to scale and adapt as the network changes.