Routing - Distance Vector Routing Protocols

A Distance Vector Routing Protocol is a type of dynamic routing protocol used in packet-switched networks for router-to-router data packet transfers. It determines the best path for data packets based on distance. The "distance" is calculated as the number of hops (the number of passes through intermediate routers) or based on a metric that measures delay, bandwidth, or other factors influencing the path quality. Each router maintains a table, known as a distance vector, that contains the distance between itself and all possible destination nodes within the network.

Distance vector routing protocols typically fall under the grouping of Interior Gateway Protocols (IGPs)

The basic principles of distance vector routing protocols include:

  1. Periodic Updates: Routers periodically share their distance vectors with their immediate neighbors. These updates help in maintaining up-to-date routing information and adapting to network topology changes.

  2. Routing by Rumor: Information about the entire network topology is not known to each router. Instead, each router builds its routing table based on the information received from its neighbors, hence the concept of "routing by rumor."

  3. Metric for Path Selection: The protocols use various metrics (like hop count, delay, bandwidth) to determine the best path. For example, in the Routing Information Protocol (RIP), the metric is the hop count, with a maximum number of hops allowed being 15, beyond which the destination is considered unreachable.

  4. Distance Vector Algorithm: The Bellman-Ford algorithm is commonly used in distance vector protocols to calculate the best paths and update routing tables.

  5. Count to Infinity Problem: One of the limitations of distance vector protocols is the "count to infinity" problem, where updates about changes in network topology (e.g., a failed link) can take a long time to propagate throughout the network, causing routing loops and inefficiencies.

Examples of distance vector routing protocols include the Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP). These protocols are simpler and consume less bandwidth for updates compared to link-state routing protocols, but they are generally considered slower to converge and less scalable.

Enhanced Interior Gateway Routing Protocol (EIGRP) is also a distance vector routing protocol, but it is considered highly efficient and quick compared to other protocols of the same category. For this reason, it is often referred to as an advanced distance vector routing protocol or a hybrid routing protocol because it incorporates features of both distance-vector and link-state protocols.