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Subnetting in Computer Networks

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Prerita Agarwal
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23 Jul, 2024 @ 01:30 PM


A subnet is a portion of a larger network that has been partitioned and separated to form a smaller network. It allows for better management and organisation of network resources and provides improved security and control over network traffic by restricting access between subnets. 


This article will discuss Subnetting in Computer Networks. Let’s get started with what is subnetting!

What is Subnetting?

Subnetting is the process of dividing a single, large network into smaller subnetworks, or subnets. Each subnet is a separate network that can contain multiple devices, such as computers, printers, and servers. Subnetting is important because it helps to optimise network performance, enhance network security, and manage IP address allocation more effectively.

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What is a Subnet Mask?

A subnet mask is a 32-bit integer that is generated by setting all host bits to 0s and all network bits to 1s. The subnet mask divides the IP address into network and host addresses in this manner.  The value "255" is always assigned to a broadcast address, while the address "0" is always assigned to a network address. Both cannot be assigned to hosts because they are only used for these specific purposes.

Subnetting separates the host element of an IP address further into a subnet when an organization requires further subnetworking. Subnet masks serve only to enable the subnetting procedure. Because the subnet mask effectively uses its own 32-bit value to disguise the IP address, the term "mask" is used.

Uses of Subnetting

The uses of subnetting are as follows:

  • When a network is divided into subnets, each subnet has its unique network address, which is used to identify the subnet and its devices.
  • By dividing the network into subnets, the network administrator can allocate IP addresses more efficiently and improve network performance.
  • A subnet can be utilised to maintain quality and order for specific workforce structures by keeping IP addresses geographically grouped.
  • It makes it easier to extend significant geographic distances.
  • Users can apply network security settings using subnetting.
  • It minimises transmission traffic and collision and improves overall network efficiency.

How Does Subnetting Work?

To subnet a network, the network administrator must choose a subnet mask that divides the IP address range into smaller subnets. The subnet mask is a 32-bit number, typically expressed in dotted decimal notation, that identifies the network and host portions of the IP address.

For example, a subnet mask of would divide the IP address range into 256 subnets, each containing up to 254 devices. It won’t be 256. It is because the first address will be reserved for the network address and the last for the broadcasting. 

The first three octets of the IP address would identify the network portion, while the fourth octet would identify the host portion. 

Subnetting Working

When a device sends data to another device on a different subnet, the data must be routed through a router. The router uses its routing table to determine the most efficient path for the data to take to reach its destination.

Examples of Subnetting

Let's say you have been given a network address of, which means you have 256 IP addresses available for use (since the subnet mask is This is a classless representation of IP addresses. Here /24 means the first 24 bits represent the network id part. 

However, you need to create three smaller networks with the following number of hosts:

  • Network 1: 25 hosts.
  • Network 2: 50 hosts.
  • Network 3: 100 hosts.

You would need to subnet the original network address into smaller subnets to do this. Here's how you can do it:

Step 1. Determine the number of bits needed for each subnet:

  • Network 1: 5 bits (since 2^5 = 32, and you need at least 25 hosts).
  • Network 2: 6 bits (since 2^6 = 64, and you need at least 50 hosts).
  • Network 3: 7 bits (since 2^7 = 128, and you need at least 100 hosts).

Step 2. Add the number of bits needed for each subnet to the original subnet mask:

  • Network 1: (since you added 5 bits to the original subnet mask).
  • Network 2: (since you added 6 bits to the original subnet mask).
  • Network 3: (since you added 7 bits to the original subnet mask).

Step 3. Determine the new subnet addresses for each network:

  • Network 1: (since you added 5 bits, which gives you 32 subnets).
  • Network 2: (since you added 6 bits, which gives you 64 subnets).
  • Network 3: (since you added 7 bits, which gives you 128 subnets).

Now you have three subnets with the required number of hosts. Network 1 can support up to 30 hosts (since the broadcast address takes one address, and the network address takes another). Network 2 can support up to 62 hosts, and Network 3 can support up to 126 hosts. The remaining addresses in each subnet can be used for future expansion.

Advantages of Subnetting

The key responsibility of a network administrator is to design and implement an efficient IP addressing scheme for the network. This involves dividing the network into appropriate subnets and allocating IP addresses to devices on those subnets.

To make network administration more efficient and effective, subnetting can be used to:

  1. Improve network performance: By dividing the network into smaller subnets, network traffic can be better managed, resulting in faster and more efficient network performance.
  2. Increase security: By implementing subnetting, access to different parts of the network can be restricted, improving security and reducing the risk of unauthorised access.
  3. Optimise resource allocation: By segmenting the network into different subnets, network resources can be more efficiently allocated, resulting in better performance and reduced downtime.
  4. Simplify network management: By dividing the network into smaller, more manageable subnets, network administrators can monitor and manage the network more easily.

Disadvantages of Subnetting

While subnetting has many advantages, there are also some potential disadvantages to consider:

  1. Complexity: Subnetting can add complexity to network design and management. It requires careful planning to ensure that subnets are properly designed and configured, which can be time-consuming and require additional resources.
  2. Increased administrative overhead: Managing multiple subnets can be more complex than managing a single network. Additional administrative overhead may be required to manage each subnet's IP addresses, routing, and security policies.
  3. Potential performance issues: In some cases, subnetting can create additional traffic and reduce performance. This can occur when devices on different subnets need to communicate with each other, which can cause additional routing and delays.
  4. Security risks: Subnetting can potentially increase the risk of security breaches. If subnets are not properly configured or managed, they can be vulnerable to attacks or unauthorised access.

Frequently Asked Questions

What is subnetting and its types?

Subnetting is a technique for partitioning a single physical network into logical sub-networks (subnets). Subnetting enables a company to expand its network without having to obtain a new network number from its Internet service provider. Subnetting is classified into two types: static and variable length.

What is 255.255 255.0 subnetting?

This implies the use of 254 valid IP addresses within the defined network. To access the internet, one can connect up to 254 internet-enabled devices like as phones, PCs, IoT devices, and others to the home network.

What is subnetting with example?

Subnetting is a method of partitioning an IP network by separating a block of addresses into smaller groups. To understand what is going on, look at some minor integers rather than the entire IP address. Consider the range of 'addresses' 100 to 129.

What is CIDR and subnetting?

CIDR (Classless Inter-Domain Routing) is an IP addressing method that allows for flexible subnetting by describing networks using a prefix notation, hence improving address allocation and routing in computer networks. Subnetting is a method of separating a big IP network into smaller subnetworks in computer networks to improve resource management and routing performance.


This article discussed Subnetting in Computer Networks in a detailed manner. We covered all aspects of subnetting, starting from what is subnet to the advantages and disadvantages of subnetting.

We hope this article has helped you understand what is subnetting and all about it. 

You can check our other articles for further reading:

Happy Learning!

Topics covered
What is Subnetting?
What is a Subnet Mask?
Uses of Subnetting
How Does Subnetting Work?
Examples of Subnetting
Advantages of Subnetting
Disadvantages of Subnetting
Frequently Asked Questions
What is subnetting and its types?
What is 255.255 255.0 subnetting?
What is subnetting with example?
What is CIDR and subnetting?