Distance Vector Multicast Routing Protocol
The Distance Vector Multicast Routing Protocol (DVMRP), defined in RFC 1075, is a routing protocol used to share information between routers to facilitate the transportation of IP multicast packets among networks. It formed the basis of the Internet's historic multicast backbone, Mbone.
Operation
[edit]The protocol is based on the Routing Information Protocol (RIP).[1] The router generates a routing table with the multicast group of which it has knowledge with corresponding distances (i.e. number of devices/routers between the router and the destination). When a multicast packet is received by a router, it is forwarded by the router's interfaces specified in the routing table.
DVMRP operates via a reverse path flooding technique, sending a copy of a received packet (specifically IGMP messages for exchanging routing information with other routers) out through each interface except the one at which the packet arrived. If a router (i.e. a LAN which it borders) does not wish to be part of a particular multicast group, it sends a "prune message" along the source path of the multicast.
Criticisms
[edit]Being a naïve distance-vector protocol, DVMRP has difficulties with network scaling in some topologies,[2] primarily due to the periodic reflooding necessary to detect new hosts. This was more prevalent in early versions of the protocol, prior to the implementation of pruning.[3] DVMRP's flat unicast routing mechanism, which is used to determine the source interface of a data stream, also affects its ability to scale.