Also called the Bellman-Ford algorithm, a routing algorithm in which every router maintains a database with one entry for each possible destination on the network.
The Routing Information Protocol (RIP), which is supported by Microsoft Windows NT and Windows 2000, is one example of a dynamic routing protocol that uses the distance vector routing algorithm.
When this algorithm is used by a routing protocol, each router advertises its routing table to its adjacent neighbors. Each advertisement contains the following information about each route in that routing table:
These advertisements are performed independently by all routers (that is, no synchronization exists between advertisements made by different routers). In addition, routers receiving advertisements do not generate acknowledgments, which reduces the overhead of routing protocol traffic.
Routers select the route with the lowest cost to each possible destination and add this to their own routing tables. These neighbors propagate the information to their neighbors hop by hop until information from all routers has spread throughout the entire internetwork.
Distance vector routing protocols (that is, protocols based on the distance vector routing algorithm) are simpler to understand and easier to configure than link state routing algorithm protocols. The main disadvantage of the distance vector routing algorithm is that changes are propagated very slowly throughout a large internetwork because all routing tables must be recalculated. This is called the Slow Convergence Problem. Other disadvantages are that routing tables can become extremely large, making distance vector routing protocols unsuitable for large internetworks, and that route advertising generates a large amount of traffic overhead.
The following table shows correspondence between routable network protocols and distance vector routing protocols.
|Network Protocol||Distance Vector Routing Protocol|
RIP or Interior Gateway Routing Protocol (IGRP)
Windows NT Server version 4 supports RIP version 1 for Internet Protocol (IP), RIP for Internetwork Packet Exchange (IPX), and Routing Table Maintenance Protocol (RTMP) for AppleTalk. Windows NT Server version 4 with Microsoft’s Routing and Remote Access Service (RRAS) installed supports RIP version 2 for IP.