3com S7906E 설치 설명서

 

1-4 

 

Pruning has a similar implementation in IPv6 PIM-SM.  

 

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:  

1)  The node that needs to receive IPv6 multicast data sends a graft message toward its upstream 

node, as a request to join the SPT again.  

2)  Upon receiving this graft message, the upstream node puts the interface on which the graft was 

received into the forwarding state and responds with a graft-ack message to the graft sender.  

3)  If the node that sent a graft message does not receive a graft-ack message from its upstream node, 

it will keep sending graft messages at a configurable interval until it receives an acknowledgment 

from its upstream node.  

The assert mechanism is used to shutoff 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 1-2 Assert mechanism 

 

 

As shown in 

, after Router A and Router B receive an (S, G) IPv6 multicast packet from the 

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 forwarded by the other. Upon detecting this 

condition, both routers send an assert message to all IPv6 PIM routers through the interface on which 

the packet was received. The assert message contains the following information: the multicast source 

address (S), the multicast group address (G), and the preference and metric of the IPv6 unicast route to 

the source. By comparing these parameters, either Router A or Router B becomes the unique forwarder