H3C S5500-EI Configuration Manual page 389

The basic implementation of IPv6 PIM-SM is as follows:
IPv6 PIM-SM assumes that no hosts need to receive IPv6 multicast data. In the IPv6 PIM-SM mode,
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routers must specifically request a particular IPv6 multicast stream before the data is forwarded to
them. The core task for IPv6 PIM-SM to implement IPv6 multicast forwarding will build and maintain
rendezvous point trees (RPTs). An RPT is rooted at a router in the IPv6 PIM domain as the common
node, or rendezvous point (RP), through which the IPv6 multicast data travels along the RPT and
reaches the receivers.
When a receiver is interested in the IPv6 multicast data addressed to a specific IPv6 multicast group,
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the router connected to this receiver sends a join message to the RP corresponding to that IPv6
multicast group. The path along which the message goes hop by hop to the RP forms a branch of
the RPT.
• When an IPv6 multicast source sends IPv6 multicast streams to an IPv6 multicast group, the
source-side designated router (DR) first registers the multicast source with the RP by sending register
messages to the RP by unicast until it receives a register-stop message from the RP. The arrival of a
register message at the RP triggers the establishment of an SPT. The IPv6 multicast source sends
subsequent IPv6 multicast packets along the SPT to the RP. After reaching the RP, the IPv6 multicast
packet is duplicated and delivered to the receivers along the RPT.
NOTE:
IPv6 multicast traffic is duplicated only where the distribution tree branches, and this process automatically
repeats until the IPv6 multicast traffic reaches the receivers.
The working mechanism of IPv6 PIM-SM is summarized as follows:
Neighbor discovery
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DR election
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RP discovery
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• Embedded RP
RPT establishment
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IPv6 Multicast source registration
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Switchover to SPT
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• Assert
Neighbor discovery
IPv6 PIM-SM uses the similar neighbor discovery mechanism as IPv6 PIM-DM does. For more information,
see "Neighbor
DR election
IPv6 PIM-SM also uses hello messages to elect a DR for a multi-access network (such as a LAN). The
elected DR will be the only IPv6 multicast forwarder on this multi-access network.
discovery."
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