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4.7. PIM Bootstrap and RP Discovery

PIM uses the Bootstrap Router (BSR) mechanism for dynamic RP discovery across the domain.

Bootstrap Router (BSR) Election:

  • BSR Priority: Configurable priority value (higher wins)
  • Bootstrap Messages: BSR periodically floods Bootstrap messages
  • Election Process: Routers compare BSR priority and address to elect BSR

RP Discovery Process:

  1. Candidate-RP-Advertisement: RP candidates send C-RP-Adv messages to BSR
  2. RP-Set Distribution: BSR compiles RP set and includes in Bootstrap messages
  3. Flooding: Bootstrap messages flood hop-by-hop throughout domain
  4. Hash Function: Routers use hash function to map groups to specific RP

Hash Function Properties:

  • Order-preserving: Minimizes disruption when RP set changes
  • Deterministic: All routers select same RP for a group
  • Load distribution: Spreads groups across multiple RPs
note

For complete BSR specification, message formats, and hash algorithm, see Section 4.7 of RFC 7761 and RFC 5059.

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