HP A8800 Configuration Manual page 133

Bidirectional RPT building
A bidirectional RPT comprises two parts: receiver-side RPT and source-side RPT. The receiver-side RPT is
rooted at the RP and takes the routers directly connected with the receivers as leaves. The source-side RPT
is also rooted at the RP but takes the routers directly connected with the sources as leaves. The processes
for building these two parts are different.
Figure 44 RPT building at the receiver side
As shown in
in PIM-SM:
1. When a receiver joins multicast group G, it uses an IGMP message to inform the directly
connected router.
2. Upon getting the receiver information, the router sends a join message, which is forwarded hop by
hop to the RP of the multicast group.
3. The routers along the path from the receiver's directly connected router to the RP form an RPT
branch, and each router on this branch adds a (*, G) entry to its forwarding table. The * means
any multicast source.
When a receiver is no longer interested in the multicast data addressed to multicast group G, the directly
connected router sends a prune message, which goes hop by hop along the reverse direction of the RPT
to the RP. Upon receiving the prune message, each upstream node deletes the interface connected with
the downstream node from the outgoing interface list and checks whether it has receivers in that multicast
group. If not, the router continues to forward the prune message to its upstream router.
Figure 44, the process for building a receiver-side RPT is similar to that for building an RPT
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