Classful and Classless Routing

Classful routing and classless routing are two different methods for routing IP packets between networks.

Classful routing was the original method of IP addressing and routing, developed in the early days of the Internet. It uses a fixed-length subnet mask that determines the size of the network portion and the host portion of an IP address. The IP address classes (A, B, and C) were defined as a way of indicating the size of the network portion and the number of hosts that could be connected to that network. Classful routing does not support variable-length subnet masks (VLSMs) or route summarization.

Classless routing, on the other hand, is a more flexible method of IP addressing and routing that allows for the use of VLSMs and route summarization. It does not rely on the fixed-length subnet mask of classful routing, but instead uses a subnet mask that can be adjusted to create smaller or larger networks as needed. This means that a single IP address space can be divided into multiple smaller subnets, allowing for more efficient use of IP addresses.

Classful routing protocols include Routing Information Protocol version 1 (RIP v1) and Interior Gateway Routing Protocol (IGRP). Classless routing protocols include Routing Information Protocol version 2 (RIP v2), Open Shortest Path First (OSPF), and Border Gateway Protocol (BGP). In general, classless routing is preferred over classful routing because of its flexibility and efficiency. It allows for better use of IP address space and more efficient routing, particularly in large networks.