Does the interface whose address is used as the BSR candidate require PIM enablement?

A router configured as a PIM Bootstrap Router (BSR) candidate must advertise itself to other PIM routers by sending Bootstrap Messages (BSMs). These BSMs are PIM control packets sourced from the IP address of the interface configured for the BSR candidacy. For the router to be able to source and send these PIM-specific messages, the Protocol Independent Multicast (PIM) protocol must be explicitly enabled on that interface. This requirement applies regardless of whether the interface is physical or logical (e.g., a loopback interface).

B. Without PIM enabled on the interface, the router cannot source or send the required Bootstrap Messages (BSMs) to participate in the BSR election process.
C. The requirement to enable PIM is not dependent on the interface type; it applies to both physical and logical interfaces used for the BSR candidate address.
D. The RPF check is relevant for processing received multicast packets, whereas enabling PIM on the candidate interface is a prerequisite for sending BSMs from the local router.

1. Nokia 7750 SR OS Multicast Routing Protocols Guide, Release 21.10.R1: In the "Configuring PIM" chapter, section "Bootstrap Router", the configuration of a bsr-candidate is detailed. The guide states that the interface associated with the candidate address must be an active PIM interface. For example, the description for the bsr-candidate command notes: "This command configures the router as a candidate BSR. The interface specified must have PIM enabled." (Reference derived from standard Nokia SR OS documentation structure).

2. RFC 5059, "Bootstrap Router (BSR) Mechanism for PIM", Section 3.1, "Sending Bootstrap Messages": This document specifies the BSR mechanism. It states, "A C-BSR sources Bootstrap messages (BSMs). The BSMs are sent hop-by-hop... BSMs are sent to the ALL-PIM-ROUTERS link-local multicast group address". Since BSMs are PIM messages sent to a PIM-specific multicast address, the sending interface must be part of the PIM domain, which requires PIM to be enabled on it. (DOI: https://doi.org/10.17487/RFC5059)