4.5. PIM Join/Prune Messages
PIM Join/Prune messages are used to build and maintain multicast distribution trees.
Message Types:
- (*,G) Join: Join shared tree for all sources to group G
- (S,G) Join: Join source-specific tree from source S to group G
- (S,G,rpt) Prune: Prune source S from shared tree for group G
- (*,G) Prune: Prune all sources from shared tree
Key Mechanisms:
- Periodic Refresh: Join/Prune state maintained by periodic message refresh
- Upstream Neighbors: Messages sent to RPF neighbor towards source or RP
- Aggregation: Multiple Join/Prune entries in single message for efficiency
- Holdtime: Specifies how long receiver should maintain state
State Machine: Join/Prune messages trigger state transitions in the TIB, affecting forwarding behavior.
note
For detailed Join/Prune message format, encoding, and state machine specifications, see Section 4.5 of RFC 7761.