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Distance vector routing is a simple routing protocol used in packet-switched networks that utilizes distance to decide the best packet forwarding path. Distance is typically represented by the hop count. A routing protocol is a set of rules used by routers to determine the most appropriate paths into which they should forward packets towards their intended destinations. A packet is the most fundamental unit of data transmission on the Internet and other TCP/IP (transmission control protocol/Internet protocol) networks. A router is an electronic device and/or software that connects at least two networks, such as two LANs (local area networks) or WANs (wide area networks), and forwards packets between them. A hop is the trip that a packet takes from one router to another as it traverses a network on the way to its destination. Distance vector routing protocols are simple, require little management, and are efficient for small networks. However, they have poor convergence properties and do not scale well. Convergence is the process of routers updating their routing tables (i.e., built-in databases) and agreeing with each other on optimal routes for forwarding packets. This has led to the development of more scalable, but more complex, link state routing protocols for use in large networks. In link state routing each router shares information with other routers about the reachability of other networks and the metric (i.e., value) to reach the other networks in order to determine the best path. The metric is based not only on number of hops, but also on other factors, including link speeds and traffic congestion, as determined by the network designers. Distance vector protocols date back to the ARPANET network in the early 1970s. ARPANET, a pioneering WAN created by the U.S. Defense Advanced Research Project Agency (ARPA) in 1969, was the world's first packet-switched network and the precursor to the Internet. Examples of distance vector routing protocols are RIP (routing information protocol), IGRP (interior gateway routing protocol) and EIGRP (enhanced IGRP). Created November 19, 2005. |