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.
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