What Are Routing Protocols? (With Classifications and Types)

By Indeed Editorial Team

Published June 6, 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

If you work with computers, you may come across routing protocols. Computer networks of any size use these protocols to communicate and securely transfer data. If you work in a tech career, learning more about these protocols and the different types that exist can help you choose one that best suits your needs.

In this article, we explain what a routing protocol is, discuss three common routing protocol categories, and tell you about seven different types of these protocols.

What are routing protocols?

Routing protocols are rules that routers in a computer network use to communicate and distribute information. They tell routers the design of a network so that the routers can direct the traffic efficiently. There are seven common protocols, and each of these fits in a standard category or pairing. You can classify each of the protocols using the following three related categories:

1. Classful and classless protocols

Classful protocols perform routing updates without including subnet mask information, such as an identification number for devices with similar internet protocol (IP) network information. These protocols typically exclude subnet mask information because their focus is identifying entire networks rather than individual IP addresses. Classful protocols require greater bandwidth than classless protocols because they perform routing updates at regular intervals. Because this classification supports fewer protocol types, it's becoming less common.

Classless protocols include subnet mask information during routing updates. They can also communicate with devices in separate networks. These protocols typically focus on transferring more detailed data at a higher level of complexity. Including the subnet mask information might help produce more accurate routes for data efficiency. Classless protocols perform updates only when there are changes to the data.

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2. Interior and exterior gateway protocols

Interior Gateway Protocols (IGPs) usually exchange information with other routers within single autonomous systems. These systems can include one routing network or a group of networks operating under the same control. This allows for simpler information changes within the same internal network, without the interference of outside routers.

Exterior Gateway Protocols (EGPs) communicate information between routing networks in different autonomous systems. Because the information is in different systems, this process is typically more complex. The extra complexity can come from the need for computer networks to communicate outside of their default systems. This might make EGPs less common than other protocols that communicate within the same systems.

3. Distance-vector and link-state protocols

Distance-vector protocols can measure the distance, or hops, it takes data to arrive at its destination within a system or application. The number of hops refers to the specific number of routers the data may run through before reaching its ultimate destination. Typically, these protocols send information to other nearby devices, which might require large bandwidths for support. By sending this information, the protocols determine the most efficient routing paths.

Like distance-vector protocols, link-state protocols also find the best routing path and share information with nearby routers. Unlike distance-vector protocols, they calculate the speed and cost of the resources of each potential path. For example, if a route is longer, it may cost more to copy the data additional times. To solve this, link-state protocols apply algorithms and alert other routers when pathways have changed. They can also create and share different tables. These tables include:

  • Neighbour tables: These tables store information and details from other close routers.

  • Topology tables: These tables store information about the organization of entire networks.

  • Routing tables: These tables store information about the most efficient data routes.

The information from these tables can help link-state protocols determine and compare the data's journey speed and its components with the costs to get it there.

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7 types of routing protocols

Once you know how to categorize these protocols, you can learn more about the seven different types of routing protocols. Here's more information about each one:

1. Immediate system to immediate system (IS-IS) protocols

IS-IS protocols help routers determine the best route to take to transfer IP routing information through a computer network. It's an interior gateway and classless protocol that administrative domains or networks typically use. They help routers share information with their nearest neighbours, allowing each router to understand what the network looks like. Having this map enables routers to calculate the best route to take when exchanging information. IS-IS protocols often function best in small networks, as it can be too time-consuming to determine this route if you add too many routers to the network.

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2. Border gateway protocol (BGP)

The BGP is an EGP that allows the internet and autonomous systems to exchange information. BGPs consider all the available paths data can take to reach a specific router to determine the best one. This path is typically complicated since data may go through several autonomous systems before reaching its destination. To choose the best route, the BGP may consider factors like neighbour IP addresses, origin type, router identification, and path length.

3. Exterior gateway protocol (EGP)

BGPs and EGPs are very similar, and ultimately BGPs replaced EGPs in the mid-1990s. Both protocols exchange data and information between the internet and autonomous systems by finding the best route for the information to take. EGPs exchange routing table information, such as recognized routers, network addresses of nearby devices, and route costs. EGPs only support network topologies that have up, down, and horizontal relationships, which limits their uses. The second version of BGPs removed this limitation, so it became a more popular choice of protocol.

4. Open shortest path first (OSPF) protocol

OSPF protocols classify as link-state, interior gateway, and classless protocols. They use the shortest path first (SPF) algorithm to ensure the efficient transmission of data. Internally, this type maintains multiple databases with topology tables and information about its entire network. Typically, the information comes from link-state advertisements sent by individual routers. The advertisements, which are like reports, share detailed descriptions of the path's distance and how many resources it may require.

OSPF protocols use an algorithm called Dijkstra to recalculate pathways when topology changes occur. They also use authentication practices to ensure data is secure throughout changes or network breaches. Small and large network organizations may benefit from using OSPF protocols because of their scalability features.

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5. Interior gateway routing protocol (IGRP)

Cisco, an international technology company, created the IGRP. It uses many of RIP's foundational functions but increases the maximum amount of supported hops to 100. As a result, it may work better for larger networks. IGRPs are distance-vector and classful protocols. To function, IGRPs include metrics like network capacity, reliability, and load to compare. These protocols automatically update when changes, like route adjustments, occur. This helps to prevent routing loops, which are errors that create an endless circle of data transfer.

6. Enhanced interior gateway routing protocol (EIGRP)

Cisco also developed the EIGRP, which allows for 255 hops. The EIGRP classifies as a distance-vector, interior gateway, and classless protocol. It uses the reliable transport protocol and the diffusing update algorithm to speed up the data convergence process, which maximizes efficiency. When in use, a router can take information from other routers' tables and record them as references. If a change occurs, each router notifies its neighbour to help ensure they all know which data routes are in use. This helps prevent potential miscommunications between routers.

7. Routing information protocol (RIP)

The RIP, an IGP, is one of the first protocols created. You can use it with local area networks (LANs), which are linked computers in a small range, or wide area networks (WANs), which are telecommunications networks that cover a greater distance. There are two different versions of this protocol type, which are the RIPv1 and the RIPv2.

The RIPv1, the original version, is a classful protocol that examines and evaluates network paths based on the hops to the pre-determined destination. Typically, it communicates with other networks by broadcasting its IP address. The newer version, RIPv2, shares its routing table through a multicast address, which identifies the main computer network. This version, which is a classless protocol, also features advanced security measures, like authentication, to protect data. The RIPv2 is often most beneficial for smaller networks because it can only support router journeys of 15 hops or fewer.

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