3com S7906E 설치 설명서

 

1-3 

The process of constructing an SPT is the “flood and prune” process.  

1)  In an IPv6 PIM-DM domain, an IPv6 multicast source first floods IPv6 multicast packets when it 

sends IPv6 multicast data to IPv6 multicast group G: The packet is subject to 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.  

2)  Then, nodes without downstream receivers are pruned: A router having no down stream receivers 

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.  

 

z 

An (S, G) entry contains the multicast source address S, IPv6 multicast group address G, outgoing 

interface list, and incoming interface. 

z 

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 prune process is first initiated by a leaf router. As shown in 

, a router without any receiver 

attached to it (the router connected with Host A, for example) sends a prune message, and this prune 

process goes on until only necessary branches are left in the IPv6 PIM-DM domain. These branches 

constitute the SPT.  

Figure 1-1 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.