Pim-Dm Configuration - 3Com 7700 Configuration Manual

128 C 6: M
HAPTER ULTICAST

PIM-DM Configuration

P
ROTOCOL
independent of any specified unicast routing protocol such as the routing
information learned by RIP and OSPF
Assert mechanism
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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 8 Assert Mechanism Diagram
Multicast packets forwarded
by the upstream node
Router A
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 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.
Graft
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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.
PIM-DM configuration include:
Enable PIM-DM
■
Configure the interface hello message interval
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When the router is run in the PIM-DM domain, it is best to enable PIM-DM on all
interfaces of the non-border router.
Enable Multicast
Refer to "Common Multicast Configuration ".
Enable PIM-DM
PIM-DM needs to be enabled in the configuration of all interfaces.
After PIM-DM is enabled on an interface, it will send PIM Hello messages
periodically and process protocol packets sent by PIM neighbors.
Receiver
Router C
Router B