Content

| 4.1 |  | RIP v2 Overview |
| 4.1.5 |  | Classless route lookups |

Module 2, Advanced IP Addressing Management, explains classful route lookups, in which a destination address is first matched to its major network address in the routing table and is then matched to a subnet of the major network. If no match is found at either of these steps, the packet is dropped.

This default behavior can be changed, even for classful routing protocols such as RIP v1 and Interior Gateway Routing Protocol (IGRP). Change the default behavior by entering the ip classless global command. When a router performs classless route lookups, it does not pay attention to the class of the destination address. Instead, it performs a bit-by-bit best match between the destination address and all its known routes. This capability can be very useful when working with default routes, as demonstrated in Module 3, Routing Overview. Classless route lookups can be very powerful when coupled with the other features of classless routing protocols.