Understanding Network Segmentation and Subnetting

Why It Matters#

Whether you’re working in IT support, system administration, or cybersecurity, having a solid grasp of network segmentation and subnetting is essential. These concepts form the backbone of modern network design and are critical for building secure, scalable, and high-performance environments.

Knowing how to segment a network properly allows you to:

• Control and limit access between departments (e.g., finance and HR)
• Isolate sensitive devices or servers from the rest of the network
• Reduce the spread of malware or unauthorized traffic in case of a breach
• Optimize network performance by minimizing unnecessary broadcast traffic

You’ll often apply this knowledge in real-world scenarios such as:

• Designing network infrastructures for offices or data centers
• Managing VLANs and IP allocation in corporate environments
• Implementing security policies based on Zero Trust architecture
• Troubleshooting communication issues between different subnets

Understanding how IP addresses, subnets, and masks work under the hood equips you to confidently navigate and shape the

What Is Network Segmentation?#

Network segmentation is the process of dividing a computer network into smaller parts called subnetworks or subnets. These logical divisions help control the flow of traffic and improve security by isolating different parts of the network.

By segmenting a network, you can:

• Apply different security rules to different zones
• Reduce the impact of internal threats
• Improve performance and organization

In the past, IT teams focused mainly on perimeter security, thinking external threats were the most dangerous. Today, with Zero Trust principles, internal traffic is also closely monitored to prevent breaches within the network itself.

What Is a Subnet?#

A subnet (short for subnetwork) is a smaller, logical section of a larger network. Subnets are identified by a specific IP address range, and they allow devices in the same subnet to communicate directly. If two devices are on different subnets, they need a router to talk to each other.

What Is an IP Address?#

An IP (Internet Protocol) address is a unique identifier for a device on a network — like a street address for your computer. Every device on a network has its own IP address.

There are two main versions:

• IPv4: The most common. It’s a 32-bit number written as four decimal numbers separated by dots (e.g., 192.168.1.1).
• IPv6: A newer version using 128 bits, designed to support more devices in the future.

Each part of an IPv4 address is called an octet, and it can have a value between 0 and 255.

What Are IP Address Classes?#

IPv4 addresses are divided into classes (A, B, and C) based on how many networks and hosts they support.

Each class defines how the IP address is split between the Network ID and the Host ID:

• Network ID: Identifies the subnet
• Host ID: Identifies a specific device within that subnet

What Is a Subnet Mask?#

A subnet mask is a 32-bit number that defines how much of the IP address represents the network portion versus the host portion.

Here’s a simple example:

IP Address : 172.18.2.11 → 10101100.00010010.00000010.00001011 Subnet Mask : 255.255.0.0 → 11111111.11111111.00000000.00000000 Binary AND : → 10101100.00010010.00000000.00000000 Network ID : 172.18.0.0

The AND operation shows how the subnet mask helps extract the Network ID from an IP address. This is how devices determine whether another host is in the same subnet or not.

Why Is Subnetting Important?#

Subnetting helps:

• Improve network performance
• Add security boundaries
• Organize devices in a scalable and efficient way
• Reduce broadcast traffic

Understanding how subnetting works is a fundamental part of managing and securing networks — whether you’re working in IT support, system administration, or cybersecurity.

📘 For more details, check the official Microsoft guide:
IP Addressing and Subnetting