|  | 11.8 | Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP)
| 11.8.8 | Example of dynamic routing

Adaptive, or dynamic, routing occurs when routers send periodic routing update messages to each other. Each time a router receives a message containing new information, it recalculates the new best route, and sends the new updated information to other routers. By using dynamic routing, routers can adjust to changing network conditions.

Before the advent of dynamic updating of routing tables, most vendors had to maintain router tables for their clients. This meant that vendors had to manually enter network numbers, their associated distances, and port numbers into the router tables of all the equipment they sold or leased. As networks grew larger, this became an increasingly cumbersome, time-consuming, and expensive task. Dynamic routing eliminates the need for network administrators or vendors to manually enter information into routing tables. It works best when bandwidth and large amounts of network traffic are not issues. RIP, IGRP, EIGRP, and OSPF are all examples of dynamic routing protocols because they allow this process to occur. Without dynamic routing protocols, the Internet would be impossible.