Distantance Vector and Link State


Interior Gateway Protocols (IGPs) can be classified as two types:
Distance vector routing protocols
Link-state routing protocols

Distance Vector Routing Protocol Operation

Distance vector means that routes are advertised as vectors of distance and direction. Distance is defined in terms of a metric such as hop count and direction is simply the next-hop router or exit interface. Distance vector protocols typically use the Bellman-Ford algorithm for the best path route determination.
Some distance vector protocols periodically send complete routing tables to all connected neighbors. In large networks, these routing updates can become enormous, causing significant traffic on the links.
Distance vector protocols work best in situations where:
The network is simple and flat and does not require a special hierarchical design.
The administrators do not have enough knowledge to configure and troubleshoot link-state protocols.
Specific types of networks, such as hub-and-spoke networks, are being implemented.
Worst-case convergence times in a network are not a concern.
Distance vector routing protocol functions and operations will be explained in the next chapter. You will also learn about the operations and configuration of the distance vector routing protocols RIP and EIGRP.

Link-state Protocol Operation

In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a "complete view" or topology of the network by gathering information from all of the other routers. To continue our analogy of sign posts, using a link-state routing protocol is like having a complete map of the network topology. The sign posts along the way from source to destination are not necessary, because all link-state routers are using an identical "map" of the network. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology.
Link-state protocols work best in situations where:
The network design is hierarchical, usually occurring in large networks.
The administrators have a good knowledge of the implemented link-state routing protocol.
Fast convergence of the network is crucial.
Link-state routing protocol functions and operations will be explained in later chapters. You will also learn about the operations and configuration of the link-state routing protocol OSPF.

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