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Figure 37 RPT building at the receiver side
As shown in Figure 37, the process for building a receiver-side RPT is the same as the process for building
an RPT in PIM-SM:
1. When a receiver wants to join the multicast group G, it uses an IGMP message to inform the
directly connected router.
2. After receiving the message, the router sends a join message, which is forwarded hop by hop to
the RP for the multicast group.
3. The routers along the path from the receiver's directly connected router to the RP form an RPT
branch. Each router on this branch adds a (*, G) entry to its forwarding table.
After a receiver leaves the multicast group G, the directly connected router sends a prune message. The
prune message goes hop by hop along the reverse direction of the RPT to the RP. After receiving the prune
message, an upstream node removes the interface that connects to the downstream node from the
outgoing interface list. It also checks whether it has receivers for that multicast group. If not, the router
continues to forward the prune message to its upstream router.
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