Distance Vector Routing Explained

Routers use the routing table to make forwarding decisions. If multiple paths to the same destination network exist, they compare all paths, select the best, and add it to the routing table. Different routing protocols use different approaches to select the best path. This tutorial explains how distance vector routing protocols choose the best path.

Distance vector routing protocols use the number of routers between the source and destination devices to calculate and select the best and shortest path from all available paths. The number of routers corresponds to the term 'Distance'. The term 'Vector' indicates the direction to the remote network. On a path, each router is a hop. For example, if a path has five routers, you can say it has five hops.

Distance vector routing selects the path with the fewest routers. For example, if a router has three paths to reach a destination network with 2, 3, and 4 hops (routers), it will select the path with 2 hops (routers).

RIP, RIPv2, IGRP, and EIGRP are distance-vector routing protocols. Distance-vector routing protocols explore all network paths, select the path with the fewest hops to each destination, and add it to the routing table.

In distance-vector routing, a router periodically advertises its distance to other routers and receives similar advertisements from them. It uses the received advertisements to populate its routing table. In the next advertisement cycle, it advertises updated information from its routing table. This process continues until the routing tables of all routers have information about all available subnets in the network.

Advantages of Distance Vector routing

Distance vector routing is simple and straightforward. You can easily configure it on any router. Since it uses a simple hop-based algorithm, managing and troubleshooting it is also easier.

Disadvantages of Distance Vector routing

It uses a hop-based algorithm. A hop-based algorithm always selects the shortest path. In many cases, the shortest path can be slower than the longest. For example, in the following network, router A has two paths to reach the destination. Path A has only one hop. Path B has two hops.

Although path A has fewer hops than path B, it is not faster. Path B is faster than Path A. But if you use a traditional distance vector routing protocol (such as RIP or RIPv2) in this network, router A will always take path A to reach the destination.

A traditional distance vector routing protocol can not measure the bandwidth of the path it has. To overcome this issue, advanced distance-vector routing protocols, known as hybrid routing protocols, were developed. Distance vector routing creates more traffic than other routing methods. It broadcasts routing updates at a fixed interval, even if there are no changes in the network topology. It consumes a lot of network bandwidth, causing congestion.

Key points:-

• It is distributive. All nodes receive information only from their directly connected nodes, process it, and distribute it back to only directly connected nodes.
• It is repetitive. All routers periodically broadcast their routing tables.
• It is asynchronous. It does not require all routers to simultaneously broadcast and receive routing updates. Routers can follow their own periodic update time interval.
• Routers do not share partial information. They share their entire routing table at periodic intervals.
• Routers share information only with the routers directly connected to them.

Conclusion

Distance vector routing protocols offer a straightforward approach to network routing. They are easy to configure and manage. However, they rely on hop counts for path selection and frequently broadcast routing updates, resulting in inefficiencies and increased network traffic. Understanding both the advantages and limitations of distance vector routing helps you choose the best protocol for your network environment and implement appropriate optimizations where necessary.