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# Distance Vector Routing Algorithm

Last Updated on April 17, 2023 by Prepbytes

Routing algorithms are crucial in the field of computer networking, where a number of devices communicate with each other to share information. The distance vector algorithm is one such algorithm used in routing data across networks. In this article, we will discuss the distance vector routing algorithm, We will understand how distance vector routing protocol works with the help of an example, and what are some advantages and disadvantages of using this distance vector algorithm.

## What is a Distance Vector Routing Algorithm?

Distance vector routing algorithm is a type of routing algorithm that is used to determine the best path for data packets to travel through a network. This algorithm is also known as Bellman-Ford Algorithm, named after its creators Richard Bellman and Lester Ford Jr.

The distance vector routing algorithm works by each router in a network maintaining a table of the distances to all other routers in the network. This table is called the distance vector. The distance vector contains the distance to all the other routers in the network as well as the next hop router that the data packet should be sent to in order to reach its destination.

The distance vector routing algorithm uses the Bellman-Ford equation to calculate the distance vector table. The Bellman-Ford equation takes into account the cost of the link between the current router and its neighbors, as well as the distance vector of the neighboring routers. The algorithm then selects the shortest path to the destination router based on the information in the distance vector table.

One of the main advantages of the distance vector routing algorithm is its simplicity. It is easy to implement and understand, making it a popular choice for small networks. However, it is not as efficient as other routing algorithms such as Link State Routing Algorithm, and it is more prone to routing loops.

A routing loop is when a packet is sent in a loop between routers because the router’s distance vector table is not updated correctly. To prevent this from happening, the Distance Vector Routing Algorithm uses a technique called split horizon.

Split horizon is a technique that prevents a router from sending its distance vector information back to the router from which it received it. This prevents a loop from forming and ensures that the distance vector table is updated correctly.

In conclusion, the distance vector routing algorithm is a widely used routing algorithm that is simple to implement and understand. It works by each router maintaining a table of the distances to all other routers in the network and using the Bellman-Ford equation to calculate the shortest path to the destination router. However, it is not as efficient as other routing algorithms and is more prone to routing loops. Thus it is used in small networks and not in large networks.

## Features of Distance Vector Routing Protocol

The Distance vector routing protocol includes the following features:

1. It is distributed in nature, meaning that each node takes information from one or more of its directly connected neighbors, does the calculation, and then distributes the result to its neighbors.
2. It is an iterative process in which information is exchanged between neighbors until no more information is available.
3. It is asynchronous because it does not require all of its nodes to work in unison.
4. It is mostly utilized in RIP and ARPANET.
5. Each router keeps a distance table called Vector.
6. Data sharing is only available between adjacent nodes.
7. The routers communicate the entire autonomous framework’s knowledge (or concept).

## How Distance Vector Routing Protocol Works

The Distance Vector Routing protocol follows these basic steps:

1. Initialization: Each router in the network is configured with its own distance vector table, which lists the distance (in terms of hop count or other metrics) to every other network in the inter-network.
2. Sending distance vectors: Each router sends its distance vector table to its immediate neighbors.
3. Updating distance vectors: Upon receiving a distance vector from a neighbor, a router updates its own table by comparing the distance to a network via its neighbor with the distance currently listed in its own table. If the new distance is shorter, the router updates its table with the new information.
4. Calculating best path: Using the information in its distance vector table, each router calculates the best path to each network and updates its routing table accordingly.
5. Periodic updates: The sending and updating distance vectors are repeated periodically, typically every 30 seconds. This allows the network to adapt to changes in topology quickly.
6. Convergence: The process of sending and updating distance vectors continues until all routers in the network have the most up-to-date information and have converged on the best path to each network.

### Example of Distance Vector Routing

In the network shown below, there are three routers, A, C, and D, with the following weights − AC =8, CD =4, and DA =3.

Step 1 − Each router in this DVR(Distance Vector Routing) network shares its routing table with every neighbor. For example, A will share its routing table with neighbors C and D, and neighbors C and D will share their routing table with A.

Step 2 − If the path via a neighbor is less expensive, the router adjusts its local table to send packets to the neighbor. In this table, the router updates the lower cost for A and C by updating the new weight from 8 to 7 in router A and from 8 to 7 in router C.

Step 3 − The final revised routing table with the reduced cost distance vector routing protocol for all routers A, C, and D is shown below-

## Advantages of Distance Vector Routing Algorithm

The distance vector routing algorithm, also known as the Shortest path routing algorithm in computer networks, has several advantages:

• Simplicity: The distance vector routing algorithm is relatively simple to implement and understand, making it easy to use in small networks or in places where resources are limited.
• Low overhead: The distance vector routing algorithm requires minimal overhead, as routers only exchange information with their immediate neighbors. This makes it efficient in terms of bandwidth and processing power.
• Flexibility: The distance vector routing algorithm is flexible and can be used with different metrics, such as hop count or delay, to determine the best path.Scalability: The Distance Vector Routing algorithm can be easily scaled to accommodate a growing network, as new routers can simply be added to the network and the distance vectors updated accordingly.
• Stability: Distance vector routing protocols are less likely to be affected by routing loops, which can be caused by changes in network topology and that can cause network instability.
• Compatibility: Distance vector routing protocols such as RIP and IGRP are widely supported by router vendors and are compatible with a variety of network devices, making them an attractive option for many organizations.

## Limitations of Distance Vector Routing Algorithm

The distance vector routing algorithm, also known as the Shortest path routing algorithm in computer networks, has several disadvantages:

• Slow convergence: Distance vector routing protocols have slow convergence time, meaning that it takes a long time for the network to adjust to changes in topology. This can cause temporary black holes or routing loops.
• Count-to-infinity problem: Distance vector routing protocols are prone to the count-to-infinity problem, where the distance between two routers can increase indefinitely if there is a broken link. This can make the network unreliable.
• Limited scalability: Distance vector routing protocols are unsuitable for large networks because they rely on every router knowing the entire routing table, which can lead to a high overhead.
• Limited accuracy: Distance vector routing protocols use only one metric, such as hop count, to determine the best path, which can lead to suboptimal routes.
• Limited security: Distance vector routing protocols do not have built-in security features, which can make them vulnerable to attacks.
• Limited feasibility in large networks: Distance vector routing protocols are not suitable for large networks as they rely on periodic updates from all routers, which can cause a high overhead and will not scale well.

Due to these limitations, the distance vector routing algorithm is primarily used in small networks or places, where resources are limited and more advanced routing protocols such as OSPF and EIGRP, are not feasible.

Summary

• Distance vector routing is a sort of dynamic protocol.
• The distance vector routing algorithm is also known as the Bellman-Ford algorithm or the shortest path routing algorithm in computer networks.
• The router distributes information to nearby nodes with a direct link.
• The router is used to determine the best path from source to destination.
• Each router in the network exchanges a topology change with an adjacent router on a regular basis.

## FAQs

Here are some frequently asked questions on the distance vector algorithm.

Q1: What is the difference between the distance vector algorithm and the link-state algorithm?
Answer: The distance vector algorithm is a decentralized algorithm that exchanges information about the distance between network nodes, while link-state algorithm is a centralized algorithm that exchanges information about the entire network topology.

Q2: What is a routing loop?
Answer: Routing loop is a problem that occurs in distance vector routing algorithm when a node receives updates from multiple paths that have the same cost, and as a result, the node sends data in a loop, continuously forwarding it between the same nodes.

Q3: What is the counting-to-infinity problem?
Answer: Counting-to-infinity problem is a problem that occurs in the distance vector routing algorithm when a node receives updates about a path that has failed, and continues to use the same path in its routing table, causing the distance to increase infinitely.

Q4: What is the Bellman-Ford algorithm?
Answer: Bellman-Ford algorithm is a distance vector routing algorithm that uses a dynamic programming approach to determine the shortest path to all other nodes in the network.

Q5: How do you prevent routing loops in the distance vector routing algorithm?
Answer: Routing loops can be prevented in distance vector routing algorithm by using techniques such as the split horizon, poison reverse, and hold-down timers.

Q6: How do you prevent a counting-to-infinity problem in a distance vector routing algorithm?
Answer: Counting-to-infinity problem can be prevented in the distance vector algorithm by using techniques such as route poisoning and triggered updates.

Q7: What is the difference between the distance vector algorithm and the path-vector algorithm?
Answer: The distance vector algorithm calculates the shortest path based on the cost metric, while the path-vector algorithm calculates the shortest path based on the path vector, which is a sequence of AS numbers.