H3C Technologies H3C S12500 Series Switches - Manual (Page 393)

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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.
Figure 105 IPv6 multicast source registration
As shown in Figure 105 , the IPv6 multicast source registers with the RP as follows:
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, after 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 source-side DR is the root, and 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 a switchover to SPT 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
In an IPv6 PIM-SM domain, an IPv6 multicast group corresponds to one RP and one RPT. Before the
switchover to SPT occurs, 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. After receiving these
register messages, the RP extracts the multicast data and sends the multicast data down the RPT to the