What is the characteristic of classful routing?
Classful routing protocols do not carry subnet mask information on their routing updates. This makes them unsuitable for hierarchical addressing that require Variable Length Subnet Mask (VLSM) and discontiguous network. Classless routing protocols do carry subnet mask information on their routing updates.RIP v1 and IGRP are classful routing protocols. RIP v2, EIGRP, OSPF, and BGP are classless routing protocol.When running a classful routing protocol on a network, make sure you use the same subnet mask everywhere. Otherwise, routing black holes can occur.Classless routing protocols extend the standard Class A, B, or C IP addressing scheme by using a subnet mask or mask length to indicate how routers must interpret an IP network ID. Classless routing protocols include the subnet mask along with the IP address when advertising routing information. Subnet masks representing the network ID are not restricted to those defined by the address classes, but can contain a variable number of high-order bits. Such subnet mask flexibility enables you to group several networks as a single entry in a routing table, significantly reducing routing overhead. Classless routing protocols includes RIP v2 and OSPF, Border Gateway Protocol version 4 (BGP4) and Intermediate System to Intermediate System (IS-IS).