What is Computer Network | Distance Vector Routing Algorithm?

Distance Vector Routing Algorithm (DV) The Distance Vector Routing algorithm is one of the fundamental routing algorithms used in computer networks. It is employed to determine the best path for data packets to travel across a network. The algorithm relies on the principle of sharing routing information between directly connected neighbors and uses this information to calculate the shortest path to each destination in the network.

Key Concepts:

1. Routing Table: Each router maintains a table (routing table) that contains the following information:
   • The destination address.
   • The cost (distance) to reach that destination.
   • The next hop router to reach the destination.
2. Distance Metric: The metric typically used in Distance Vector algorithms is the hop count. A hop is defined as one step from a router to a directly connected router. The number of hops to reach a destination determines its “distance”.
3. Periodic Updates: Routers send their routing tables to their neighbors periodically (or when a change occurs). This exchange allows routers to update their knowledge about network topology.
4. Bellman-Ford Algorithm: The distance vector algorithm uses a variation of the Bellman-Ford algorithm. In this algorithm, a router computes the shortest path to each destination based on the information received from its neighbors.

How It Works:

1. Initialization: Each router initializes its routing table. Initially, the router will set the distance to itself as 0 and the distance to other routers as infinity (∞). The next hop for all other routers is unknown.
2. Exchange Information: Routers periodically exchange their routing tables with neighboring routers. When a router receives a table from a neighbor, it updates its own table based on the new information.
3. Update Process: If a router learns a shorter path to a destination from a neighbor, it updates its routing table. This process repeats as routers continue to exchange information.
4. Convergence: The algorithm converges when all routers have consistent and correct routing tables. This may take some time, depending on network size and topology.

Example of the Distance Vector Algorithm:

Consider three routers in a network: A, B, and C. The distance between A and B is 1, between B and C is 1, and between A and C is initially unknown.

• Router A sends its routing table to B, which contains its best-known distances to all other routers.
• Router B then updates its table using A’s information.
• Router B sends its updated table to C, and C updates its table.
• The process continues with each router sharing its updated routing information.

Advantages of Distance Vector Routing:

• Simple to Implement: The algorithm is straightforward and easy to configure.
• Suitable for Small Networks: It is effective for small networks with limited topology changes.

Disadvantages of Distance Vector Routing:

• Slow Convergence: It may take time to stabilize when there are network topology changes.
• Count to Infinity Problem: This occurs when routers incorrectly calculate the shortest path due to a failure in the network.
• Bandwidth Usage: Frequent exchange of routing tables can consume bandwidth, especially in large networks.
• Limited Scalability: In larger networks, the algorithm becomes inefficient and prone to errors.

Example Protocols Using Distance Vector Algorithm:

1. RIP (Routing Information Protocol): The most popular protocol based on the Distance Vector algorithm. It uses hop count as its metric.
2. IGRP (Interior Gateway Routing Protocol): A Cisco proprietary protocol that also follows the Distance Vector algorithm but uses a more sophisticated metric.

Conclusion:

The Distance Vector Routing Algorithm is a foundational technique in network routing, but its limitations (like slow convergence and the potential for routing loops) make it less effective in larger or more complex networks compared to more modern routing algorithms like Link-State algorithms.