Introduction To Ipv6 Pim-Sm; How Ipv6 Pim-Sm Works - HP 4800G Series Configuration Manual

address (S), the multicast group address (G), and the preference and metric of the IPv6 unicast route to
the source. By comparing these parameters, either Router A or Router B becomes the unique forwarder
of the subsequent (S, G) IPv6 multicast packets on the multi-access subnet. The comparison process is
as follows:
1) The router with a higher IPv6 unicast route preference to the source wins;
2) If both routers have the same IPv6 unicast route preference to the source, the router with a smaller
metric to the source wins;
3) If there is a tie in the route metric to the source, the router with a higher IPv6 link-local address
wins.

Introduction to IPv6 PIM-SM

IPv6 PIM-DM uses the "flood and prune" principle to build SPTs for IPv6 multicast data distribution.
Although an SPT has the shortest path, it is built with a low efficiency. Therefore the PIM-DM mode is
not suitable for large-and medium-sized networks.
IPv6 PIM-SM is a type of sparse mode IPv6 multicast protocol. It uses the "pull mode" for IPv6 multicast
forwarding, and is suitable for large- and medium-sized networks with sparsely and widely distributed
IPv6 multicast group members.
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, 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 is to
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, 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 a register message at the RP triggers the establishment of an SPT. Then, the IPv6 multicast
source sends subsequent IPv6 multicast packets along the SPT to the RP. Upon reaching the RP,
the IPv6 multicast packet is duplicated and delivered to the receivers along the RPT.
IPv6 multicast traffic is duplicated only where the distribution tree branches, and this process
automatically repeats until the IPv6 multicast traffic reaches the receivers.

How IPv6 PIM-SM Works

The working mechanism of IPv6 PIM-SM is summarized as follows:
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