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DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
DVMRP Settings
To configure DVMRP for an IP interface:
Click the DVMRP Settings link on the IP Multicasting menu:
Figure 7-44. DVMRP Interface Configuration window
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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