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4.4. PIM Register Messages

PIM Register messages are used to deliver multicast data from a source's DR to the RP when no source-specific tree exists yet.

Key Concepts:

  • Register Encapsulation: Source DR encapsulates multicast data packets in unicast Register messages to RP
  • Register-Stop: RP sends Register-Stop when native traffic arrives or no receivers exist
  • Null-Register: Periodic probe to check if Register-Stop is still in effect
  • Register Suppression: Timer-based mechanism to prevent unnecessary encapsulation

Register Process:

  1. Source sends multicast data
  2. Source DR encapsulates packets in Register messages
  3. Register messages unicast to RP
  4. RP decapsulates and forwards on shared tree
  5. RP joins source tree (S,G) for native forwarding
  6. RP sends Register-Stop to source DR
note

For Register message format, Register-Stop conditions, and state machine details, see Section 4.4 of RFC 7761.

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