D-Link DES-3326SR User Manual page 251

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
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
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