3Com Switch 8800 Advanced Software V5 Configuration Guide

IPv6 PIM Overview 679
prefix: The prefix of the embedded RP unicast address extracted from the IPv6
multicast address. The number of bits extracted is determined by the plen field of
the IPv6 multicast address.
zero: These bits are zeroed.
RIID: The RIID field of the IPv6 multicast address is extracted as the interface ID of
the IPv6 unicast address of the RP.
For example, if an IPv6 multicast address with an embedded RP address is
FF77:0630:2001:DB8:BEEF::/80, the IPv6 unicast address of the RP is
2001:DB8:BEEF::6/48.
RPT building
Figure 207 Building an RPT in IPv6 PIM-SM
As shown in Figure 207, the process of building an RPT is as follows:
1 When a receiver joins an IPv6 multicast group G, it uses an MLD report message to
inform the directly connected DR.
2 Upon getting the IPv6 multicast group G’s receiver information, the DR sends a
join message, which is hop by hop forwarded to the RP corresponding 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 * means any
IPv6 multicast source. The RP is the root, while 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. Upon receiving the prune message, the
Source
Server
Host A
Host B
Host C
Receiver
Receiver
IPv6 multicast packets
RPT
Join message
RP DR
DR