Basic Subnetting in Computer Networks Explained

An IP subnet is a group of IP addresses. There are two types of IP subnets: default and custom. Default IP subnets are predefined and known as IP classes. Custom subnets are the subnets you create as per your requirements and network size. Subnetting creates custom subnets from default subnets. This tutorial introduces subnetting and describes its advantages and disadvantages.

Subnetting is a method of dividing a single IP network into small IP networks. Small networks are easier to manage than large ones. Let us take an example. There are two cities. The first city uses a flat design for addressing. All addresses directly belong to the city name. They contain only two things: resource name and city name.

The second city uses a hierarchical addressing system. It divides the city area into blocks and streets. Addresses contain blocks and street numbers or names. Finding an address in the second city is much easier and faster than in the first city.

If you relate this example to computer networks, the first city uses a single IP subnet, while the second city divides a single IP subnet into smaller IP subnets. Let’s take another example. Due to maintenance, a scheduled power cut is in effect.

If the city is divided into blocks, the electricity department may make a local announcement for the affected area rather than broadcast it across the entire city.

Apart from these two examples, there are many other examples where you can see that small things are easier to manage than big things. Breaking a big thing into smaller parts is known as segmentation.

Default IP classes have a large number of IP addresses per subnet. A class A IP subnet includes 16777214 IP addresses. A class B IP subnet includes 65534 IP addresses, while a class C IP subnet has 254 IP addresses. A computer needs and mostly uses one IP address. Putting too many computers on the same network can lead to performance issues, including broadcast storms, conflicts, and congestion.

Let’s take an example.

A company has four divisions: sales, production, development, and management. Each division has 50 users. The company uses a Class C IP subnet. Without subnetting, all computers work in a single large network.

Computers use broadcast messages to access and provide information in the network. A broadcast message is an announcement message in a computer network that is received by all hosts. Since all computers on the same network receive all broadcast messages, they will receive them regardless of whether they are relevant.

You can divide this network into subnets. After this, computers will receive only the broadcasts intended for them. Since the company has four divisions, it can divide its network into four subnets. The following figure shows the same network after subnetting.

Subnetting table

The following table lists IP subnets for this network.

Advantage of Subnetting

• Subnetting allows you to break a single large network into small networks. Small networks are easy to manage.
• Subnetting reduces network traffic by allowing only the broadcast traffic that is relevant to the subnet.
• By reducing unnecessary traffic, subnetting improves network performance.
• By keeping traffic within a subnet, subnetting increases the network's security.
• Subnetting reduces the requirement for a new IP range for each section.

Disadvantage of Subnetting

• Different subnets need a router to communicate with each other.
• Since each subnet uses its own network and broadcast addresses, more subnets mean more wasted IP addresses.
• Subnetting adds complexity to the network. An experienced network administrator is required to manage the subnetted network.

Conclusion

This tutorial introduced subnetting and explained how it improves network performance and security by dividing a large network into smaller networks. Later, it described the advantages and disadvantages of subnetting and how they affect the computer networks.