HP A6600 Configuration Manual page 309

Neighbor discovery
In an IPv6 PIM domain, a PIM router discovers IPv6 PIM neighbors, maintains IPv6 PIM neighboring
relationships with other routers, and builds and maintains SPTs by periodically multicasting IPv6 PIM hello
messages to all other IPv6 PIM routers on the local subnet.
Every IPv6 PIM enabled interface on a router sends hello messages periodically, and thus learns the IPv6
PIM neighboring information pertinent to the interface.
SPT establishment
The process of constructing an SPT is the flood and prune process.
In an IPv6 PIM-DM domain, an IPv6 multicast source first floods IPv6 multicast packets when it sends
1.
IPv6 multicast data to IPv6 multicast group G. The packet undergoes an RPF check. If the packet
passes the RPF check, the router creates an (S, G) entry and forwards the packet to all downstream
nodes in the network. In the flooding process, an (S, G) entry is created on all the routers in the IPv6
PIM-DM domain.
The nodes without downstream receivers are pruned. A router that has no down stream receivers
2.
sends a prune message to the upstream node to notify the upstream node to delete the
corresponding interface from the outgoing interface list in the (S, G) entry and stop forwarding
subsequent packets addressed to that IPv6 multicast group down to this node.
An (S, G) entry contains the multicast source address S, IPv6 multicast group address G, outgoing
interface list, and incoming interface.
For a given IPv6 multicast stream, the interface that receives the IPv6 multicast stream is referred to as
"upstream", and the interfaces that forward the IPv6 multicast stream are referred to as "downstream".
A leaf router first initiates a prune process. As shown in
to it (the router connected with Host A, for example) sends a prune message, and this prune process
continues until only necessary branches remain in the IPv6 PIM-DM domain. These branches constitute the
SPT.
Figure 85 SPT establishment in an IPv6 PIM-DM domain
The flood-and-prune process takes place periodically. A pruned state timeout mechanism is provided. A
pruned branch restarts multicast forwarding when the pruned state times out and then is pruned again
when it no longer has any multicast receiver.
Figure 85, a router without any receiver attached
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