Routers using a distance-vector routing protocol converge on a mutual understanding of the network's topology by sharing what they know about the network. Such routers periodically pass copies of their routing tables to their immediate network neighbors. Each recipient adds its distance-vector information to the table and forwards the modified table to its immediate neighbors. This process occurs omnidirectionally between immediately neighboring routers. Figure 10-2 uses a simple IGRP internetwork to illustrate the concept of immediate neighbors.
Figure 10-2. Each IGRP node advertises the contents of its routing table to its immediate neighbors.
In Figure 10-2, there are four routers in an autonomous system. The gateway ...