Classful vs Classless Routing Protocols

A routing protocol can be divided into two categories: classful routing protocol and classless routing protocol. In this post, we will explain classful vs classless routing protocols.

The following question comes in the mind of every new candidate when they start to know various routing algorithms and protocols.

Which routing algorithm or protocol should be used for a specific network?

There is no straightforward answer to use a specific routing algorithm or protocol for a specific network. The answer of the preceding question depends upon the various factors and may also vary on the case-by-case scenarios. However, if you have a clear idea about all the different routing algorithms and protocols, you can take a decision that is best suited for your network.

On the base of TCP/IP addressing scheme, the routing protocols can be categorized into the following two categories.

  • Classful routing protocol
  • Classless routing protocol

Classful Routing Protocol

The classful routing protocols are those protocols that do not carry the subnet mask information within the routing updates. In addition, classful routing protocols require that every interface and host on the network must use the same subnet mask. These routing protocols waste more address spaces. Another problem with the classful routing protocols is that they sent out periodic routing updates to all active interfaces of each router. Sending out periodic routing updates to all active interface of each router can cause congestion on the slower WAN (Wide Area Network) links. Generally, the distance-vector routing protocols are considered as classful routing protocols. The examples of classful routing protocols include RIPv1 and IGRP.

Classless Routing Protocol

Classless routing protocols are those protocols that include the subnet mask information when the routing tables or updates are exchanged. Classless routing protocols allow to use the networks with the different length of subnet masks. Hence, these routing protocols support the CIDR (Classless Inter-Domain Routing) and VLSM (Variable Length Subnet Mask). Classless routing protocols do not send the periodic updates (which means sending the routing updates at the regular intervals) like classful routing protocols. Classless routing protocols exchange the entire routing table with the neighbor routers only at the very first time. Once the network is fully converged, routing updates are sent only when there is any changes occur in the network topology. It helps to reduce the bandwidth consumption. However, classless routing protocols send Hello messages at the regular intervals to their neighbor routers (directly connected routers), regardless when changes occur in the network topology. They use the Hello packets to verify whether the neighbor routers are alive or not. The examples of classless routing protocols include OSPF and IS-IS.

Difference between Classful and Classless Routing Protocols

The following table lists the differences between classful and classless routing protocols.Classful vs Classless Routing Protocols

In this post, we have discussed the differences between classful and classless routing protocols. Hope, it helped you. We would love to hear you valuable feedback and suggestions.

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