HP A8800 Configuration Manual page 393

Multicast source registration
The purpose of IPv6 multicast source registration is to inform the RP about the existence of the IPv6
multicast source.
Figure 107 IPv6 multicast source registration
Source
Server
As shown in
1. When the IPv6 multicast source S sends the first IPv6 multicast packet to IPv6 multicast group G, the
DR directly connected with the multicast source, upon receiving the multicast packet, encapsulates
the packet in a register message, and sends the message to the corresponding RP by unicast.
2. When the RP receives the register message, it extracts the multicast packet from the register
message and forwards the multicast IPv6 multicast packet down the RPT, and sends an (S, G) join
message hop by hop toward the IPv6 multicast source. Thus, the routers along the path from the RP
to the IPv6 multicast source form an SPT branch. Each router on this branch generates an (S, G)
entry in its forwarding table. The DR at the IPv6 multicast source side is the root, while the RP is the
leaf, of the SPT.
3. The subsequent IPv6 multicast data from the IPv6 multicast source travels along the established SPT
to the RP, and then the RP forwards the data along the RPT to the receivers. When the IPv6 multicast
traffic arrives at the RP along the SPT, the RP sends a register-stop message to the source-side DR
by unicast to stop the source registration process.
NOTE:
The RP is configured to initiate an SPT switchover as described in this section. Otherwise, the DR at the IPv6
multicast source side keeps encapsulating multicast data in register messages and the registration process
will not stop unless no outgoing interfaces exist in the (S, G) entry on the RP.
Switchover to SPT
A router is taken as an example in this section. As compared with the SPT switchover on a router, an SPT
switchover process is implemented in a simpler way on a switch.
In an IPv6 PIM-SM domain, an IPv6 multicast group corresponds to one RP and one RPT. Before the SPT
switchover takes place, the DR at the IPv6 multicast source side encapsulates all multicast data destined
to the multicast group in register messages and sends these messages to the RP. Upon receiving these
DR RP
SPT
Join message
Register message
IPv6 multicast packets
Figure 107, the IPv6 multicast source registers with the RP as follows:
381
Host A
Receiver
Host B
Receiver
Host C