Introduction to Subnetting

Devices in computer networks use IP addresses to identify each other. An IP address consists of two addresses: the network address and the host address. Devices having the same network address can communicate directly.

What is Subnetting?

A subnet is a group of devices that have the same network address. If required, you can break a subnet into smaller subnets. Breaking a subnet into smaller subnets is called subnetting. Subnetting does not create new subnets; it breaks existing subnets into smaller subnets. You can use subnetting to convert a large network into many small, manageable networks. For example, if your network has 1000 devices, you can divide it into two networks with 500 devices in each or four networks with 250 devices in each.

Subnetting components

IP addresses, network addresses, host addresses, IP classes, and default IP subnets are the essential components of subnetting. The following section describes these terms.

IP address

An IP address is the numeric identity of a device on a computer network. You can write and use it in binary, decimal, and hexadecimal formats. Devices use IP addresses only in binary. Binary is complex. It uses only two numbers (0 and 1) to express all numbers, letters, and symbols.

Humans use decimal numbers. Decimal numbers are easy to use and remember. For example, 911 is a phone number used to contact emergency services in the USA. In binary, this number will be 1110001111.

If authorities ask you to choose and use this number in one format, which will you pick? Will you select the number 911 or 1110001111?

You will definitely select 911. It is much easier to remember and use.

No matter which format you select, devices always process this number in binary. If you choose decimal format, devices will convert it into binary before use.

The same thing applies to IP addresses. You write and use them in decimal, but computers and other networking devices process them in binary. They convert them into binary before use. An IP address consists of 32 binary bits. It organizes binary bits into four sections. It keeps 8 bits in each. It uses a dot as a separator. The 8 bits make up 1 byte. An IP address has four bytes separated by dots.

From 8 binary bits, the maximum number you can make in decimal is 256. Computers start counting from 0. Because of this, each section of an IP address can have a decimal value from 0 to 255.

IP classes

There are five IP classes. The decimal number in the first section indicates the IP class.

Network address and host address

An IP address consists of two parts: the network address and the host address. Network addresses create IP subnets. Host addresses provide identities to devices.

You can use only the IP addresses of classes A, B, and C to create IP networks. You cannot use the IP addresses of classes D and E, as they are reserved for various network services and research functions, respectively.

Classes A, B, and C allocate default sections for network and host addresses.

In class A, the first section is the network address. The remaining three sections are the host address.

In class B, the first and second sections are the network address. The third and fourth sections are the host address.

In class C, the first three sections are the network address. The fourth section is the host address.

Default IP subnets

Default allocation creates default IP subnets in each class. The following table lists default IP subnets.

Since classes D and E are not available for network addressing, you cannot use these classes for subnetting.

Why is Subnetting necessary?

The major problem with default IP subnets is that they are not well-optimized. They provide more IP addresses than a network needs. For example, a class A subnet provides 16777216 IP addresses. In practice, a network cannot have 16777216 devices. If you use this subnet to build a network, you will waste all the unused IP addresses.

Subnetting solves this problem. It allows you to create subnets according to your requirements. For example, you can break a class A subnet into 65536 subnets, each with 256 IP addresses.

Key points:-

• Computers and networking devices use IP addresses to identify each other on a computer network.
• There are five IP classes.
• You can use only three classes (A, B, and C) for network addressing.
• An IP address consists of two parts: the network address and the host address.
• Network addresses create IP subnets. An IP subnet is a group of devices having the same network address.
• Host addresses provide a unique identity to each device within an IP subnet.
• Default IP subnets provide more IP addresses than a typical network needs.
• Subnetting allows you to split a default IP subnet into smaller subnets.
• Subnetting does not create new subnets. It breaks the existing subnet into smaller subnets.

Conclusion

Subnetting is a crucial technique in network management that enables you to divide large, inefficient networks into smaller, more manageable segments. By understanding IP addresses, address classes, and subnetting principles, you can optimize the use of available IP addresses, reduce waste, and improve network performance and security. Mastery of subnetting ensures scalable, flexible, and efficient network design.