H3C Technologies H3C S12500-X Series Switches - Manual (Page 156)

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• Neighbor discovery
• SPT building
• Graft
• Assert
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 Figure 23 , the router interface that does not
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 44 SPT building