What is subnetting?

Let’s imagine that you are recently hired for a job of network engineer. Now, your major responsibility is to manage the network of your organization providing optimum performance and security. Hence, one of the things that you have to do is subnetting. But, what is subnetting?

Subnet example. Subnetting.


To be simple, subnetting is a method to sub-divide a physical network to multiple smaller logical networks. We call these smaller logical networks, the subnets. What was wrong with classful addressing? There could only be 128 class A networks each having 16,777,214 hosts. However, this is impracticable. First of all, a single network cannot handle that many hosts. Secondly, there would be an exhaustion of the addresses. With the growing number of devices, it became very important to manage the addresses. This is where the concept of subnets come to play.

For instance, Pulchowk Campus, IOE has obtained a public network of If we look into the classful addressing, then it is of class A. But, how does a public campus of Nepal get a class A network? Well, it hasn’t because there isn’t classful addressing anymore. Hence, a network provider divides a network into smaller ones.

Why do we need subnetting?

For example, Pulchowk campus has many departments. Thus, it has to divide the network (24 is the subnet mask. We will discuss subnet mask 24 in the next post.) into many networks. Since these departments are independent, they have to isolate them too. In this way, it would be easier to manage the networks and it will be efficient too. The need of subnetting can be listed as follows:

  • One network is isolated from another and there needs to be a routing mechanism between them to communicate.
  • There will be less broadcast messages. Broadcasting is a process of sending packets to multiple hosts at once. It is important in order to configure a network. However, the more the hosts, the more the broadcast messages. Compare 10 people broadcasting a message to each other with that of 100 people doing the same. Obviously, there will be more noise. Similarly, there will be more traffic in a larger network and it will be less efficient.

In the next post, we will be learning about how to do subnetting.

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