HP A6600 Configuration Manual page 310

Pruning has a similar implementation in IPv6 PIM-SM.
Graft
When a host attached to a pruned node joins an IPv6 multicast group, to reduce the join latency, IPv6
PIM-DM uses the graft mechanism to resume IPv6 multicast data forwarding to that branch. The process is
as follows:
The node that needs to receive IPv6 multicast data sends a graft message toward its upstream node,
1.
as a request to join the SPT again.
After receiving this graft message, the upstream node puts the interface on which the graft was
2.
received into the forwarding state and responds with a graft-ack message to the graft sender.
If the node that sent a graft message does not receive a graft-ack message from its upstream node, it
3.
keeps sending graft messages at a configurable interval until it receives an acknowledgment from its
upstream node.
Assert
The assert mechanism shuts off duplicate IPv6 multicast flows onto the same multi-access network, where
more than one multicast routers exists, by electing a unique IPv6 multicast forwarder on the multi-access
network.
Figure 86 Assert mechanism
As shown in
upstream node, they both forward the packet to the local subnet. As a result, the downstream node Router
C receives two identical multicast packets, and both Router A and Router B, on their own local interface,
receive a duplicate IPv6 multicast packet that the other has forwarded. 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 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. 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:
The router with a higher preference to the source wins.
•
If both routers have the same preference to the source, the router with a smaller metric to the source
•
wins.
If a tie exists in the route metric to the source, the router with a higher IPv6 link-local address wins.
•
Figure 86, after Router A and Router B receive an (S, G) IPv6 multicast packet from the
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