3Com 10014298 manual Assert Mechanism Diagram

Configuring PIM-DM 131

as a redundancy packet without the multicast 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.

■Assert mechanism

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 32 Assert Mechanism Diagram

Multicast packets forwarded by the upstream node

Router A Router B

Receiver

Router C

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

■Graft

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.

Configuring PIM-DM is described in the following sections:

■Configuring PIM-DM

■Example: PIM-DM Configuration

Configuring PIM-DMBasic PIM-DM configuration includes:

■Enabling Multicast

■Enabling PIM-DM

■Entering PIM View

Advanced PIM-DM configuration includes:

■Configuring the Interface Hello Message Interval

■Configuring the Filtering of Multicast Source/Group

■Configuring the Filtering of PIM Neighbors