HP 6125XLG Configuration Manual page 146

Assert
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Neighbor discovery
In an IPv6 PIM domain, each interface that runs IPv6 PIM on a router periodically multicasts IPv6 PIM
hello messages to all other IPv6 PIM routers on the local subnet to discover IPv6 PIM neighbors, maintain
IPv6 PIM neighboring relationship with other routers, and build and maintain SPTs.
SPT building
The process of building an SPT is the flood-and-prune process:
1. In an IPv6 PIM-DM domain, when the IPv6 multicast source S sends IPv6 multicast data to the IPv6
multicast group G, the IPv6 multicast data is flooded throughout the domain. A router performs an
RPF check for the IPv6 multicast data. If the check succeeds, the router creates an (S, G) entry and
forwards the data to all downstream nodes in the network. In the flooding process, all the routers
in the IPv6 PIM-DM domain create the (S, G) entry.
2. The nodes without downstream receivers are pruned. A router that has no downstream receivers
sends a prune message to the upstream node to remove the interface that receives the prune
message from the (S, G) entry. In this way, the upstream stream node stops forwarding subsequent
packets addressed to that IPv6 multicast group down to this node.
NOTE:
An (S, G) entry contains an IPv6 multicast source address S, an IPv6 multicast group address G, an
outgoing interface list, and an incoming interface.
A prune process is initiated by a leaf router. As shown in
have any downstream receivers initiates a prune process by sending a prune message toward the IPv6
multicast source. This prune process goes on until only necessary branches are left in the IPv6 PIM-DM
domain, and these necessary branches constitute an SPT.
Figure 45 SPT building
Source
Server
The pruned state of a branch has a finite holdtime timer. When the timer expires, IPv6 multicast data is
again forwarded to the pruned branch. The flood-and-prune cycle takes place periodically to maintain
the forwarding branches.
SPT
Prune message
IPv6 multicast packets
Figure 45, the router interface that does not
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Host A
Receiver
Host B
Receiver
Host C