4.6. PIM Assert Messages

PIM Assert messages resolve duplicate packet forwarding when multiple routers forward to the same LAN.

Assert Process:

1. Duplicate Detection: Router detects duplicate multicast packets on LAN
2. Assert Sent: Router sends Assert with its metric to source/RP
3. Metric Comparison: Routers compare metrics to elect forwarder
4. Winner Selection: Router with best metric becomes designated forwarder
5. Losers Prune: Assert losers prune their forwarding state for that interface

Metric Comparison Criteria (in order):

1. Prefer (S,G) state over (*,G) state
2. Prefer lower administrative distance
3. Prefer better metric to source or RP
4. Prefer higher IP address (tiebreaker)

Assert State:

• NoInfo: No Assert state
• I am Assert Winner: This router won Assert election
• I am Assert Loser: This router lost Assert election

note

For Assert message format, metric encoding, and state machine details, see Section 4.6 of RFC 7761.