The first multicast routing
protocol that was developed is called Distance Vector Multicast
Routing Protocol (DVMRP), defined in
RFC 1075. This protocol is used extensively on the
MBONE.
DVMRP assumes initially that every host on the network is part of the multicast group.
Multicast messages are transmitted over every possible router interface as they proceed across the network. This forms a
spanning tree to all possible members of the multicast group. A current image of the network topology is maintained using a distance-vector routing protocol such as the Routing Information Protocol (
RIP). RIP and DVMRP use the number of hops in the
path as the
distance metric.