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RPT establishment
Figure 96 RPT establishment in an IPv6 PIM-SM domain
As shown in Figure 96, the process of building an RPT is as follows:
1. When a receiver joins IPv6 multicast group G, it uses an MLD report message to inform the directly
connected DR.
2. After getting the IPv6 multicast group G's receiver information, the DR sends a join message, which
is forwarded hop by hop to the RP that corresponds to the multicast group.
3. The routers along the path from the DR to the RP form an RPT branch. Each router on this branch
generates a (*, G) entry in its forwarding table. The asterisk means any IPv6 multicast source. The
RP is the root of the RPT, and the DRs are the leaves of the RPT.
The IPv6 multicast data addressed to the IPv6 multicast group G flows through the RP, reaches the
corresponding DR along the established RPT, and finally is delivered to the receiver.
When a receiver is no longer interested in the IPv6 multicast data addressed to a multicast group G, the
directly connected DR sends a prune message, which goes hop by hop along the RPT to the RP. After
receiving the prune message, the upstream node deletes the interface connected with this downstream
node from the outgoing interface list and determines whether it has receivers for that IPv6 multicast group.
If not, the router continues to forward the prune message to its upstream router.
Multicast source registration
The purpose of IPv6 multicast source registration will inform the RP about the existence of the IPv6
multicast source.
Source
Server
Host A
Host B
Host C
Receiver
Receiver
IPv6 multicast packets
RPT
Join message
RP DR
DR
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