The Bootstrap Router (BSR) protocol is a dynamic mechanism used in Protocol Independent Multicast - Sparse Mode (PIM-SM) for distributing Rendezvous Point (RP) information. Multiple routers can be configured as candidate-BSRs (C-BSRs), but they undergo an election process. Each C-BSR advertises its priority, and the candidate with the highest priority is elected as the single BSR for the entire PIM domain. If priorities are equal, the highest IP address serves as a tie-breaker. This election ensures that there is only one active BSR at any time, providing a single, consistent source of RP-set information to all routers in the domain.

A. A router can be configured as a static RP for specific multicast groups while also being configured as a BSR candidate for dynamic RP discovery for other groups.

B. A single router can be configured to function as both a candidate-RP (C-RP) and a candidate-BSR (C-BSR) simultaneously. This is a common network design choice.

C. A PIM domain is designed to support multiple active RPs. The BSR mechanism distributes a set of available RPs, and routers map different multicast groups to different RPs.

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Multicast Routing Protocols Guide, Release 21.10.R1

For Correct Answer (D): In the "PIM" chapter, section "Bootstrap Router (BSR)", it states: "Each C-BSR collects BSMs and elects a single BSR for the PIM domain using an election algorithm. The C-BSR with the highest priority is elected as the BSR. If all C-BSRs have the same priority, the C-BSR with the highest IP address is elected as the BSR." (This confirms the election of a single BSR).

For Incorrect Answer (C): In the "PIM" chapter, section "Rendezvous Point (RP)", it describes the RP-Set: "The elected BSR builds a set of C-RPs, called the RP-Set, and includes the RP-Set in the BSMs that it periodically originates." (This confirms the existence of a set of multiple RPs).

For Incorrect Answer (B): The configuration examples within the "PIM" chapter demonstrate that the bootstrap-candidate and rp-candidate commands can be configured under the same configure>router>pim context, indicating a single router can perform both roles.

2. RFC 5059: Bootstrap Router (BSR) Mechanism for PIM

For Correct Answer (D): Section 3.1, "BSR Election," details the process where all BSR candidates in a domain elect a single BSR. It specifies, "The BSR election procedure is simple: a candidate BSR includes its own priority and address in the Bootstrap messages it originates. A C-BSR which hears about a BSR with a higher priority value... ceases to send Bootstrap messages... This ensures that eventually only one BSR is left active in the domain."