HP FlexFabric 5950 series Configuration Manual page 393

Figure 118 IPv6 multicast source registration
Source
Server
As shown in
1. The IPv6 multicast source S sends the first multicast packet to the IPv6 multicast group G.
When receiving the multicast packet, the source-side DR that directly connects to the IPv6
multicast source encapsulates the packet into a register message and unicasts the message to
the RP.
2. After the RP receives the register message, it decapsulates it and forwards it down to the RPT.
Meanwhile, it sends an (S, G) source-specific join message toward the IPv6 multicast source.
The routers along the path from the RP to the IPv6 multicast source constitute an SPT branch.
Each router on this branch creates an (S, G) entry in its forwarding table.
3. The subsequent IPv6 multicast data from the IPv6 multicast source are forwarded to the RP
along the SPT. When the IPv6 multicast data reaches the RP along the SPT, the RP forwards
the data to the receivers along the RPT. Meanwhile, it unicasts a register-stop message to the
source-side DR to prevent the DR from unnecessarily encapsulating the data.
Switchover to SPT
CAUTION:
If the switch is an RP, disabling switchover to SPT might cause multicast traffic forwarding failures
on the source-side DR. When disabling switchover to SPT, be sure you fully understand its impact
on your network.
In an IPv6 PIM-SM domain, only one RP and one RPT provide services for a specific IPv6 multicast
group. Before the switchover to SPT occurs, the source-side DR encapsulates all IPv6 multicast data
in register messages and sends them to the RP. After receiving these register messages, the RP
decapsulates them and forwards them to the receiver-side DR along the RPT.
IPv6 multicast forwarding along the RPT has the following weaknesses:
•
Encapsulation and decapsulation are complex on the source-side DR and the RP.
•
The path for an IPv6 multicast packet might not be the shortest one.
•
The RP might be overloaded by IPv6 multicast traffic bursts.
To eliminate these weaknesses, IPv6 PIM-SM allows an RP or the receiver-side DR to initiate the
switchover to SPT when the RP or DR receives IPv6 multicast traffic:
•
The RP initiates the switchover to SPT:
DR RP
SPT
Join message
Register message
IPv6 multicast packets
Figure 118, the IPv6 multicast source registers with the RP as follows:
383
Host A
Receiver
Host B
Receiver
Host C