Distance Vector Routing is one of the two types of routing types. (The other type is Link State Routing). Basically, Distance Vector protocols determine best path on how far the destination is, while LinkState protocols are capable of using more sophisticated methods taking into consideration link variables, such as bandwidth, delay, reliability and load. Distance Vector protocols judge best path on how far it is. Distance can be hops or a combination of metrics calculated to represent a distance value. The IP Distance Vector routing protocols still in use today are: Routing Information Protocol (RIP v1 and v2) and Interior Gateway Routing Protocol (IGRP C developed by Cisco).

A very simple distance-vector routing protocol works as follows:

1. Initially, the router makes a list of which networks it can reach, and how many hops it will cost. In the outset this will be the two or more networks to which this router is connected. The number of hops for these networks will be 1. This table is called a routing table.
2. Periodically the routing table is shared with other routers on each of the connected networks via some specified inter-router protocol. This information is only shared inbetween physically connected routers ("neighbors"), so routers on other networks are not reached by the new routing tables yet.
3. A new routing table is constructed based on the directly configured network interfaces, as before, with the addition of the new information received from other routers.
4. Bad routing paths are then purged from the new routing table. If two identical paths to the same network exists, only the one with the smallest hop-count is kept.
5. The new routing table is then communicated to all neighbors of this router. This way the routing information will spread and eventually all routers know the routing path to each network, which router it shall use to reach this network, and to which router it shall route next.

Distance-vector routing protocols are simple and efficient in small networks, and require little, if any management. However, they do not scale well, and have poor convergence properties, which has led to the development of more complex but more scalable link-state routing protocols for use in large networks.

Distance Vector Routing Protocols Key Characteristics

Related Terms: LinkState Routing, RIP, IGRP