Chapter Four. Routing Table Maintenance
This chapter presents the details of the routing table structure in Cisco routers, essential information that you will need throughout the rest of the book. The first section describes the sources providing Cisco routers with routing information. The second section explains in detail how the routing table is constructed and updated in routers. The last section contains answers to the most frequently asked questions about routing table maintenance.
Routing Information Sources
As explained before, when a router forwards packets, it uses its routing table to find the output interface and the next-hop router address. Cisco routers construct their routing tables by using the following three types of routes: