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As shown in
, the process of building an RPT is as follows:
1.
When a receiver joins the 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 the 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 examines 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 is to inform the RP about the existence of the IPv6
multicast source.
Figure 87
IPv6 multicast source registration
As shown in
, the IPv6 multicast source registers with the RP as follows:
1.
The IPv6 multicast source S sends the first IPv6 multicast packet to IPv6 multicast group G.
2.
After receiving the multicast packet, the DR that directly connects to the multicast source
encapsulates the packet in a register message, and then sends the message to the corresponding
RP by unicast.
3.
When the RP receives the register message, it does the following
a.
Extracts the multicast packet from the register message.
b.
Forwards the multicast IPv6 multicast packet down the RPT.
