Routing is the glue that binds the Internet together. Without it, TCP/IP traffic is limited to a single physical network. Routing allows traffic from your local network to reach its destination somewhere else in the worldperhaps after passing through many intermediate networks.
The important role of routing and the complex interconnection of Internet networks make the design of routing protocols a major challenge to network software developers. Consequently, most discussions of routing concern protocol design. Very little is written about the important task of properly configuring routing protocols. However, more day-to-day problems are caused by improperly configured routers than by improperly designed routing algorithms. As system administrators, we need to ensure that the routing on our systems is properly configured. This is the task we tackle in this chapter.