D-Link DES-3326 manual Dvmrp, 140

DES-3326 Layer 3 Fast Ethernet Switch User’s Guide

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DVMRP

To configure DVMRP for an IP interface, highlight DVMRP Interface Configuration from the Setup IP Multicast menu and press Enter.

Figure 6-58. DVMRP Interface Configuration screen

This menu allows the Distance-Vector Multicast Routing Protocol to be configured for each IP interface defined on the switch.

The Distance Vector Multicast Routing Protocol (DVMRP) is a hop-based method of building multicast delivery trees from multicast sources to all nodes of a network. Because the delivery trees are ‘pruned’ and ‘shortest path’, DVMRP is relatively efficient. Because multicast group membership information is forwarded by a distance-vector algorithm, propagation is slow. DVMRP is optimized for high delay (high latency) relatively low bandwidth networks, and can be considered as a ‘best-effort’ multicasting protocol.

DVMRP resembles the Routing Information Protocol (RIP), but is extended for multicast delivery. It relies upon RIP hop counts to calculate ‘shortest paths’ back to the source of a multicast message, but defines a ‘route cost’ to calculate which branches of a multicast delivery tree should be ‘pruned’ – once the delivery tree is established.

When a sender initiates a multicast, DVMRP initially assumes that all users on the network will want to receive the multicast message. When an adjacent router receives the message, it checks its unicast routing table to determine the interface that gives the shortest path (lowest cost) back to the source. If the multicast was received over the shortest path, then the adjacent router enters the information into its tables and forwards the message. If the message is not received on the shortest path back to the source, the message is dropped.

Route cost is a relative number that is used by DVMRP to calculate which branches of a multicast delivery tree should be ‘pruned’. The ‘cost’ is relative to other costs assigned to other DVMRP routes throughout the network.

The higher the route cost, the lower the probability that the current route will be chosen to be an active branch of the multicast delivery tree (not ‘pruned’) – if there is an alternative route.

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