Classless routing protocols carry subnet mask information in the routing updates when routing updates are advertised to connected networks. Classless routing allows VLSM (Variable Length Subnet Masking). Supports dis-contiguous networks.
Examples of classless routing protocols include RIPv2, EIGRP, OSPF, and IS-IS.
Classful routing protocols does not send subnet mask information when a route update is sent out.
Examples of classful routing protocols include RIPv1 and IGRP.