Blogs by Jay Tillu

What are Subnets in Networking?

4 min read

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Have you ever felt overwhelmed by the sheer number of people in your apartment building? Imagine if everyone tried to use the same elevator or squeeze into the laundry room at once. Networks can face a similar challenge, especially large ones. That's where subnetting comes in, offering a way to create a more organized and efficient digital neighbourhood.

What Are Subnets?

In simple terms, a subnet, short for "subnetwork," is a logical subdivision of an IP network. It's a way to divide a larger network into smaller, more manageable segments, each with its own unique range of IP addresses. Subnets enable efficient use of IP addresses, improve network performance, and enhance security by isolating different parts of the network. Devices within a subnet can easily communicate with each other, but there's limited interaction with devices on other subnets unless they need to go through a router.

How do Subnets work?

Subnetting is the subdivision of a network into logical groups called subnets. It works like a network inside a network. Subnetting divides up a network address range into smaller subnets within the network.

Subnets work by dividing a larger IP network into smaller, more manageable segments. Each subnet has its own unique range of IP addresses. These segments, known as subnets, enable efficient communication between devices within the same subnet while also facilitating communication between different subnets through routing.

The subnet mask determines the range of IP addresses that belong to the subnet. Devices within the same subnet share the same network prefix, allowing them to communicate directly with each other without the need for routing through other networks.

The process of dividing a network into subnets involves a special tool called a subnet mask. This mask defines how many bits in an IP address represent the network portion (the subnet) and how many identify individual devices (the host). By adjusting the subnet mask, you control the number and size of subnets within the larger network.

The IP Address Split

Every device on a network has a unique IP address, similar to a street address in the real world. This IP address has two parts:

  • Network address: This identifies the network itself, like the city name in an address. In Subnetting, your network bits are denoted by 1.

  • Host address: This specifies the individual device within the network, like the street number and building number. In Subnetting, your host bits are denoted by .

Subnetting comes in by borrowing some bits from the host address portion of the IP address and using them to create subnet addresses.

Benefits of Subnets

There are several advantages to using subnets:

  • Enhanced Organization: Subnets group devices logically, based on function, department, or security needs. This simplifies network management and troubleshooting.

  • Improved Efficiency: Traffic stays local. Devices on the same subnet communicate directly, reducing congestion on the main network. Imagine mail delivered directly to your neighbourhood post office instead of being sent across town first.

  • Increased Security: Subnets can be assigned different security policies. You can create isolated subnets for sensitive data or guest access, limiting the damage if a breach occurs.

What is Classless Inter-Domain Routing (CIDR)?

CIDR, which stands for Classless Inter-Domain Routing, is a method for allocating IP addresses that plays a crucial role in subnetting. It essentially replaced the older classful network addressing system. Here's a breakdown of how CIDR works:

  • Efficient Allocation: CIDR allows for a more flexible way to assign IP addresses. Unlike the classful system with fixed sizes, CIDR lets you create blocks of addresses (CIDR blocks) with varying sizes depending on your network's needs. This helps to avoid wasting a large pool of addresses when you only need a small chunk.

  • Improved Routing: CIDR simplifies routing by allowing routers to group IP addresses with a common prefix (initial sequence of bits) into single routing table entries. This reduces the size and complexity of routing tables, making data transfer more efficient.

  • Subnet Management: CIDR notation, which combines an IP address with a slash and a number (e.g.,, is fundamental for subnetting. The number after the slash specifies the subnet mask, indicating how many bits define the network portion of the IP address. This directly ties into how you can create subnets within your larger network.

In essence, CIDR provides the foundation for subnetting. It offers a way to break down large IP address blocks into manageable subnets, while also optimizing how data is routed across networks.


Subnetting is a fundamental concept in network administration. By understanding how subnets work, you can create a more efficient, secure, and organized network environment. So, the next time you navigate a large network, remember the invisible subnets working behind the scenes to keep everything running smoothly.

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