HP A6600 Configuration Manual page 318

Bidirectional RPT building
A bidirectional RPT comprises a receiver-side RPT and a 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 IPv6 multicast sources as leaves. The
processes for building these two parts are different.
Figure 92 RPT building at the receiver side
Receiver
Host A
Source
Server A
Join message
Receiver-side RPT
IPv6 Multicast packets
As shown in Figure
IPv6 PIM-SM:
When a receiver joins IPv6 multicast group G, it uses an MLD message to inform the directly
1.
connected router.
After getting the receiver information, the router sends a join message, which is forwarded hop by
2.
hop to the RP of the IPv6 multicast group.
The routers along the path from the receiver's directly connected router to the RP form an RPT
3.
branch, and each router on this branch adds a (*, G) entry to its forwarding table. The * means any
IPv6 multicast source.
When a receiver is no longer interested in the multicast data addressed to IPv6 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. After 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 IPv6
multicast group. If not, the router continues to forward the prune message to its upstream router.
RP
92, the process for building a receiver-side RPT is similar to that for building an RPT in
Source
Host C
307
Server B
Receiver
Host B
Receiver