NETGEAR M4200 Software Administration Manual page 557

M4200 and m4300 series prosafe managed switches

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IP 192.168.1.1

IP 192.168.4.2

Figure 57. Configuring and Using PIM-DM

PIM-DM uses the existing unicast routing table and join, prune, and graft mechanism to build

a tree. PIM-DM creates source-based shortest-path distribution trees that use reverse path

forwarding (RPF). PIM-DM cannot be used to build a shared distribution tree, as PIM-SM

can. PIM-DM assumes that when a sender starts sending data, all downstream routers and

hosts want to receive a multicast datagram. PIM-DM initially floods multicast traffic

throughout the network. Routers that do not have any downstream neighbors prune back the

unwanted traffic. Apart from prune messages, PIM-DM uses two other types of messages:

graft messages and assert messages. Graft messages are used whenever a new host wants

to join the group. Assert messages are used to shut off duplicate flows onto the same

multi-access network.

To minimize the repeated flooding of datagrams and subsequent pruning associated with a

particular (S,G) pair, PIM-DM uses a state refresh message. This message is sent by the

routers directly connected to the source and is propagated throughout the network. When

Managed Switches

Subnet 192.168.3.0/24

Subnet 192.168.6.0/24

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