Distance-vector routing protocol definition
A distance-vector routing protocol is a method routers use to find the best path to send data based on the distance and the vector (or direction).
While distance-vector protocols were key in early network routing, most large modern networks now use more advanced protocols. However, their fundamental concepts are still essential for understanding how routing works.
History of distance-vector routing protocols
Distance-vector protocols have their roots in the early days of computer networking. An early example is the Routing Information Protocol (RIP), introduced in the late 1980s as part of the UNIX operating system. It was later standardized in RFC 1058 in 1988. RIP was designed for small, relatively static networks. In modern, large-scale networks, more advanced routing protocols have largely replaced RIP.
How a distance-vector routing protocol works
- Initialization. When a router is powered on, it sets up its routing table using directly connected networks.
- Advertisement. Once in a while, each router sends its entire routing table to its immediate neighbors.
- Update. If a router receives a shorter or otherwise better path from a neighbor, it updates its own table.
- Loop prevention. Techniques like “route poisoning” and “hold-down timers” stop endless loops in routing. For instance, an infinite metric may mark an unreachable path in the case of route poisoning.
- Convergence. After many exchanges between neighbors, all routers have an accurate and consistent view of the network. This state is known as convergence.
Examples of distance-vector routing protocols
- Routing Information Protocol (RIP). One of the earliest distance-vector protocols. It uses hop count as its metric, up to 15 hops.
- Interior Gateway Routing Protocol (IGRP). A proprietary protocol developed by Cisco. It uses multiple metrics like bandwidth, delay, reliability, and load.
- Enhanced Interior Gateway Routing Protocol (EIGRP). An improvement over IGRP, EIGRP is a Cisco-proprietary protocol. It incorporates features of link-state protocols but is based on distance-vector principles.
- Babel. A loop-avoiding distance-vector routing protocol designed for mobile and wireless networks.
- Destination-Sequenced Distance-Vector (DSDV). A variation of the traditional distance-vector protocol tailored for mobile ad hoc networks.