The data networks that we use in our everyday lives to learn, play, and work range from small, local networks to large, global internetworks. At home, a user may have a router and two or more computers. At work, an organization may have multiple routers and switches servicing the data communication needs of hundreds or even thousands of PCs.

Routers forward packets by using information in the routing table. Routes to remote networks can be learned by the router in two ways: static routes and dynamic routes.

In a large network with numerous networks and subnets, configuring and maintaining static routes between these networks requires a great deal of administrative and operational overhead. This operational overhead is especially cumbersome when changes to the network occur, such as a down link or implementing a new subnet. Implementing dynamic routing protocols can ease the burden of configuration and maintenance tasks and give the network scalability.

This chapter introduces dynamic routing protocols. It explores the benefits of using dynamic routing protocols, how different routing protocols are classified, and the metrics routing protocols use to determine the best path for network traffic. Other topics covered in this chapter include the characteristics of dynamic routing protocols and how the various routing protocols differ. Network professionals must understand the different routing protocols available in order to make informed decisions about when to use static or dynamic routing. They also need to know which dynamic routing protocol is most appropriate in a particular network environment.