The Distance Vector Multicast Routing Protocol (DVMRP) is used to share information between routers and transport Multicast packets among networks.

It's based in the RIP protocol to forward packets: the router generate a routing table with the Multicast group that it has knowledge with its corresponding distance (number of devices -routers- in the middle to reach it). When a Multicast packet is received by a router, it's forwarded by router's interfaces specified in the routing table.

The DVMRP protocol uses IGMP messages to exchange information with other routers.