The
addressing scheme that is most commonly used is a logical broadcast. Routers that are
running a distance vector routing protocol send periodic updates even if no changes exist
in the network.
400 Chapter 5: WAN Connections
In a pure distance vector environment, the periodic routing update includes a complete
routing table. Upon receiving a full routing table from its neighbor, a router can verify
all known routes and make changes to the local routing table based on updated information.
This process is also known as ???routing by rumor??? because the router??™s understanding of
the network is based on the neighboring router??™s perspective of the network topology.
Figure 5-42 demonstrates how distance vector protocols operate.
Figure 5-42 Distance Vector Protocols
Example: Distance Vector Routing Protocols
Router B receives periodic routing updates from router A. Router B adds a distance vector
metric (such as the hop count) to each route learned from router A, increasing the distance
vector. Router B then passes its own routing table to its neighbor, router C. This step-bystep
process occurs in all directions between directly connected neighbor routers.
Traditionally, distance vector protocols were also classful protocols.
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