Distance vector means that routes are advertised by providing two characteristics:
- Distance - Identifies how far it is to the destination network and is based on a metric such as the hop count, cost, bandwidth, delay, and more.
- Vector - Specifies the direction of the next-hop router or exit interface to reach the destination.
For example, in the figure, R1 knows that the distance to reach network 172.16.3.0/24 is one hop and that the direction is out of the interface S0/0/0 toward R2.
A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. Distance vector protocols use routers as sign posts along the path to the final destination. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Distance vector routing protocols do not have an actual map of the network topology.
There are four distance vector IPv4 IGPs:
- RIPv1 - First generation legacy protocol
- RIPv2 - Simple distance vector routing protocol
- IGRP - First generation Cisco proprietary protocol (obsolete and replaced by EIGRP)
- EIGRP - Advanced version of distance vector routing