3com 8807 User Guide

C

HAPTER

 43: PIM-DM C

ONFIGURATION

forwarding. The unicast routing information as path judgment can come from any 
unicast routing protocol independent of any specified unicast routing protocol 
such as the routing information learned by RIP and OSPF

As shown in the following figure, both routers A and B on the LAN have their own 
receiving paths to multicast source S. In this case, when they receive a multicast 
packet sent from multicast source S, they will both forward the packet to the LAN. 
Multicast Router C at the downstream node will receive two copies of the same 
multicast packet.

Figure 110   Assert mechanism diagram

When they detect such a case, routers need to select a unique sender by using the 
assert mechanism. Routers will send Assert packets to select the best path. If two 
or more than two paths have the same priority and metric, the path with a higher 
IP address will be the upstream neighbor of the (S, G) entry, which is responsible 
for forwarding the (S, G) multicast packet.

n 

When the pruned downstream node needs to be restored to the forwarding state, 
the node will send a graft packet to inform the upstream node.

1 PIM-DM basic configuration includes:

■

Enabling multicast

■

Enabling PIM-DM

2 PIM-DM advanced configuration includes:

■

Configuring the time interval for ports to send Hello packets

■

Entering the PIM view

■

Configuring filtering of multicast source/group

■

Configuring filtering of PIM neighbor

Receiver

Router A

Router B

Router C

Multicast packets forwarded by the

upstream node