In computer
communication theory relating to packet-switched networks, a
distance-vector
routing protocol is
one of the two major classes of routing protocols, the other major
class
being the link-state protocol. Distance-vector routing protocols use
the Bellman–Ford algorithm, Ford–Fulkerson algorithm, or DUAL FSM
(in the case of Cisco Systems's protocols) to calculate paths.
A distance-vector
routing protocol requires that a router informs its neighbors of
topology changes periodically. Compared to link-state protocols,
which require a router to inform all the nodes in a network of
topology changes, distance-vector routing protocols have less
computational complexity and message overhead.
The term distance
vector
refers to the fact that the protocol manipulates vectors
(arrays) of distances to other nodes in the network. The vector
distance algorithm was the original ARPANET routing algorithm and was
also used in the internet under the name of RIP (Routing Information
Protocol).
Examples of
distance-vector routing protocols include RIPv1 and RIPv2 and IGRP.
Method
Routers using
distance-vector protocol do not have knowledge of the entire path to
a destination. Instead they use two methods:
- Direction in which router or exit interface a packet should be forwarded.
- Distance from its destination
Distance-vector
protocols are based on calculating the direction and distance to any
link in a network. "Direction" usually means the next hop
address and the exit interface. "Distance" is a
measure of the cost
to reach a certain node. The least cost route between any two nodes
is the route with minimum distance. Each node maintains a vector
(table) of minimum distance to every node. The cost of reaching a
destination is calculated using various route metrics. RIP uses the
hop count of the destination whereas IGRP takes into account other
information such as node delay and available bandwidth.
