As explained in Chapter 7, "The Mechanics of Routing Protocols," routers using a distance-vector routing protocol periodically pass copies of their routing tables to their immediate network neighbors. A router's routing table contains information about the distance between itself and known destinations. These destinations can be individual host computers, printers, or other networks.
Each recipient adds a distance vector—that is, its own distance "value"—to the table and forwards the modified table to its immediate neighbors. This process occurs in an omnidirectional manner among immediately neighboring routers. Figure 8-4 uses a simple RIP internetwork to illustrate the concept of immediate neighbors.