Routing
protocols can be classified into different groups according to their
characteristics. Specifically, routing protocols can be classified by
their:
Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)
Operation: Distance vector protocol, link-state protocol, or path-vector protocol
Behavior: Classful (legacy) or classless protocol
For example, IPv4 routing protocols are classified as follows:
RIPv1 (legacy): IGP, distance vector, classful protocol
IGRP (legacy): IGP, distance vector, classful protocol developed by Cisco (deprecated from 12.2 IOS and later)
RIPv2: IGP, distance vector, classless protocol
EIGRP: IGP, distance vector, classless protocol developed by Cisco
OSPF: IGP, link-state, classless protocol
IS-IS: IGP, link-state, classless protocol
BGP: EGP, path-vector, classless protocol
The
classful routing protocols, RIPv1 and IGRP, are legacy protocols and
are only used in older networks. These routing protocols have evolved
into the classless routing protocols, RIPv2 and EIGRP, respectively.
Link-state routing protocols are classless by nature.