HP MSR2003 Configuration Manual page 293

Figure 89 IPv6 multicast source registration
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
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 addressed to
the IPv6 multicast group in register messages and sends them to the RP. After receiving these register
messages, the RP decapsulates them and forwards them to the receivers-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 a switchover
to SPT when the traffic rate exceeds a specific threshold:
• The RP initiates a switchover to SPT:
The RP periodically checks the multicast packet forwarding rate. If the RP finds that the traffic rate
exceeds the specified threshold, 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
Figure 89, the IPv6 multicast source registers with the RP as follows:
283