R3102-R3103-HP 6600/HSR6600 Routers IP Multicast Configuration Guide

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The assert message contains the multicast source address (S), the multicast group address (G), and
the preference and metric of the IPv6 unicast route/IPv6 MBGP route/IPv6 multicast static route to
the source.
3. The routers compare these parameters, and either Router A or Router B becomes the unique
forwarder of the subsequent (S, G) IPv6 multicast packets on the shared-media subnet. The
comparison process is as follows:
a. The router with a higher preference to the source wins.
b. If both routers have the same preference to the source, the router with a smaller metric to the
source wins.
c. If a tie exists in the route metric to the source, the router with a higher IPv6 link-local address on
the downstream interface wins.
IPv6 PIM-SM overview
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-sized 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-sized 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 will build and maintain
RPTs. An RPT is rooted at a router in the IPv6 PIM domain as the common node, or 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 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.
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
• DR election
• RP discovery
• Embedded RP
• RPT building
• IPv6 multicast source registration