3.2. Phase Two: Register-Stop

Register encapsulation is inefficient for two reasons: encapsulation/decapsulation overhead and potentially longer paths. The RP typically switches to native forwarding.

Process:

1. RP Joins Source: When RP receives Register-encapsulated packets from source S for group G, it initiates a (S,G) source-specific Join towards S
2. (S,G) Tree: Join propagates hop-by-hop towards S, instantiating (S,G) state for forwarding packets from source S to group G
3. Native Flow: Packets from S begin flowing natively towards RP along the (S,G) tree
4. Register-Stop: When RP receives native packets, it sends Register-Stop to source DR to prevent unnecessary encapsulation

At the end of Phase Two, traffic flows natively from S along the source tree to the RP, then along the shared tree to receivers. Where trees intersect, traffic may transfer from source tree to RP tree.

note

For detailed Register and Register-Stop message formats and procedures, see Section 3.2 of RFC 7761.