Ipv6 Pim-Sm Overview - HP MSR2003 Configuration Manual

1. The node that needs to receive the IPv6 multicast data sends a graft message to its upstream node,
telling it to rejoin the SPT.
2. After receiving this graft message, the upstream node adds the receiving interface to the outgoing
interface list of the (S, G) entry for the IPv6 multicast group. It also sends a graft-ack message to the
graft sender.
3. If the graft sender receives a graft-ack message, the graft process finishes. Otherwise, the graft
sender continues to send graft messages at a configurable interval until it receives an
acknowledgment from its upstream node.
Assert
On a subnet with more than one multicast router, the assert mechanism shuts off duplicate multicast flows
to the network. It does this by electing a unique multicast forwarder for the subnet.
Figure 84 Assert mechanism
As shown in
both forward the packet to the local subnet. As a result, the downstream node Router C receives two
identical multicast packets. Router A and Router B, on their own downstream interfaces, receive a
duplicate packet forwarded by the other. After detecting this condition, both routers send an assert
message to all IPv6 PIM routers on the local subnet through the interface that received the packet. The
assert message contains the IPv6 multicast source address (S), the IPv6 multicast group address (G), and
the metric preference and metric of the IPv6 unicast route/MBGP route/static multicast route to the IPv6
multicast source. By comparing these parameters, either Router A or Router B becomes the unique
forwarder of the subsequent (S, G) packets on the subnet. The comparison process is as follows:
1. The router with a higher metric preference to the IPv6 multicast source wins.
2. If both routers have the same metric preference to the IPv6 multicast source, the router with a
smaller metric to the IPv6 multicast source wins.
3. If both routers have the same metric, 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 cycles to build SPTs for IPv6 multicast data forwarding. Although
an SPT has the shortest paths from the IPv6 multicast source to the receivers, it is built with a low efficiency.
Therefore, IPv6 PIM-DM is not suitable for large and medium-sized networks.
IPv6 PIM-SM uses the pull mode for IPv6 multicast forwarding, and it is suitable for large-sized and
medium-sized networks with sparsely and widely distributed IPv6 multicast group members.
Figure 84, after Router A and Router B receive an (S, G) packet from the upstream node, they
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