|  | 1.4 | Routing Protocols
| 1.4.5 | Distance vector concept
Distance vector based routing algorithms (also known as Bellman-Ford algorithms) pass periodic copies of a routing table from router to router. Periodic updates between routers communicate topology changes. A router receives each neighboring router's routing table. For example, in the graphic, router B receives information from router A. Router B adds a distance vector number (such as a number of hops) and updates its own routing table, which it later sends on to its other neighbor, router C. This same step-by-step process occurs in all directions between direct neighbor routers. In this way, the algorithm accumulates network distances so it can maintain a database of network topology information. Distance vector algorithms do not allow a router to know the exact topology of an internetwork.