Subnetting – Ultimate Guide – Definition, How & Why?

By Staff Contributor on December 18, 2023

In computer networking, understanding the concept of subnets and subnetting is crucial for managing and troubleshooting network issues. So, in this ultimate guide, we will explain everything you need to know about subnets, subnet masks, and subnet calculators. Additionally, we will introduce you to popular subnetting tools.

What Is a Subnet?

What Is a Classful Address?

What Is an IP Address?

Why Do We Use Subnetting?

What Is a Subnet Mask and How Do You Perform Subnet Masking?

What Is a Subnet Calculator?

3 Best Subnetting Tools

1. SolarWinds IP Address Manager (Free Trial)

2. Advanced Subnet Calculator (Free Tool)

3. Spiceworks Subnet Calculator

Let’s begin by defining a subnet and its related concepts.  

What Is a Subnet?

A subnet, or subnetwork, represents a smaller division within a larger IP network. This division results from the process of partitioning the IP network into multiple, more manageable segments.

Each subnet functions as a separate, logical network segment with its range of IP addresses. This configuration allows devices within the same subnet to communicate more efficiently. By dividing a network into smaller subnets, administrators can isolate different departments, zones, or types of devices. This approach ensures that local traffic remains confined within individual subnets. Devices within a subnet can communicate directly without passing through routers or other networking equipment.

Some use cases for subnets are intranets (internal networks), secured staging servers, and environment separation.  

What Is an IP Address?

An IP address is a unique numerical identifier for devices in a network. It enables communication and data exchange between devices. IP addresses are fundamental to the internet’s infrastructure.

Two main IP address versions exist: IPv4 and IPv6.

IPv4 addresses are 32 bits long or 4 bytes. They consist of four decimal numbers (0-255) separated by periods. For example,

IPv6 addresses were introduced to overcome IPv4 limitations. They are 128 bits long or 16 bytes. IPv6 addresses have eight groups of four hexadecimal digits separated by colons. For example, 2001:0db8:85a3:0000:0000:8a2e:0370:7334.  

What Is a Classful Address?

In the early days of IP addressing, addresses were divided into classes (Class A, B, and C) based on the size of the network and the number of hosts they could support. This classification system is known as classful addressing.

Each class has a different default subnet mask, distinguishing the IP address’s network portion from the host portion. However, classful addressing has been phased out by the more flexible CIDR (Classless Inter-Domain Routing) system, allowing for more efficient IP address space use.  

Why Do We Use Subnetting?

Subnetting plays a crucial role in the design and management of computer networks, as it serves multiple purposes, including:

  1. Improved Network Management: By dividing an extensive network into smaller subnets, administrators can more easily manage, monitor, and troubleshoot network issues and apply specific security policies.
  2. Reduced Network Congestion: Subnetting helps reduce network congestion by isolating local traffic within individual subnets, allowing for more efficient use of available bandwidth.
  3. Enhanced Security: Subnets provide isolation between different network segments, making it more difficult for attackers to access sensitive information or propagate malware across the entire network. Additionally, it allows access controls to different areas of the network, further strengthening overall security.
  4. Address Space Conservation: Subnetting allows for more efficient use of IP address space by breaking down large address blocks into smaller, more usable segments.

What Is a Subnet Mask and How Do You Perform Subnet Masking?

Subnet masking divides IP address spaces into smaller subnets, using a 32-bit (IPv4) or 128-bit (IPv6) subnet mask. This mask, combined with an IP address, determines network and host portions, aiding routers and devices in identifying addresses within the same subnet for efficient data routing. The subnet mask consists of consecutive 1’s (network portion) followed by consecutive 0’s (host portion). For example, an IPv4 subnet mask of represents a 24-bit network portion and an 8-bit host portion.

To determine the network address of a given IP address, you perform a bitwise AND operation between the IP address and the subnet mask. For example, let’s say you have an IP address of and a subnet mask of In binary form:

IP: 11000000.10101000.00000001.00000101

Subnet: 11111111.11111111.11111111.00000000

Performing the bitwise AND operation:

Network: 11000000.10101000.00000001.00000000

Converting back to decimal, the network address is All devices with IP addresses that share this network portion (192.168.1.x, where x ranges from 0 to 255) belong to the same subnet.

Other Notations

CIDR (Classless Inter-Domain Routing) or “slash” notation is an alternative to subnet mask notation, expressing a subnet’s network address and prefix length more compactly. It consists of an IP address followed by a forward slash (/) and a decimal number representing the network portion’s size in consecutive 1’s.

For example, for an IPv4 address:

CIDR notation:

Subnet mask:

In this example, the /24 indicates that the first 24 bits (3 bytes) of the IP address represent the network portion. This corresponds to a subnet mask of The host portion of the IP address consists of the remaining 8 bits (1 byte).

CIDR notation can be used with both IPv4 and IPv6 addresses. For example, for an IPv6 address:

CIDR notation: 2001:db8::/32

Subnet mask: FFFF:FFFF:0000:0000:0000:0000:0000:0000

Here the /32 indicates that the first 32 bits (4 bytes) of the IPv6 address represent the network portion. This corresponds to a subnet mask of FFFF:FFFF:0000:0000:0000:0000:0000:0000. The host portion of the IP address consists of the remaining 96 bits (12 bytes).  

What Is a Subnet Calculator?

A subnet calculator is a tool that simplifies the process of subnetting by automating subnet mask calculations. By inputting the IP address and the desired number of subnets or hosts, a subnet calculator can quickly generate information such as the subnet mask, network address, broadcast address, and the range of usable IP addresses for each subnet.  

3 Best Subnetting Tools

Several subnetting tools are available to help network administrators manage IP networks more efficiently. Here, we will discuss three popular tools: SolarWinds® IP Address Manager (IPAM), Advanced Subnet Calculator, and Spiceworks Subnet Calculator.  

1. SolarWinds IP Address Manager (Free Trial)

The SolarWinds IP Address Manager (IPAM) is a robust and feature-rich IP address management solution. It streamlines the process of managing and monitoring IP address spaces and overseeing DHCP and DNS servers. The tool is particularly beneficial for network administrators who require a comprehensive and user-friendly platform for managing complex networks.

©2023 SolarWinds Worldwide, LLC. All rights reserved.

Key features of the SolarWinds IPAM include:

  1. Automated IP Address Tracking and Monitoring: IPAM automatically tracks and monitors IP address allocation and usage across the network, ensuring that administrators have an up-to-date overview of the IP address space and can identify potential issues or conflicts.
  2. IP Address Conflict Detection and Resolution: The tool helps to detect and resolve IP address conflicts, minimizing network disruptions and improving overall network stability.
  3. Detailed IP Address History and Usage Reporting: IPAM provides detailed reports on IP address history and usage, allowing administrators to analyze trends, identify potential issues, and optimize IP address allocation.
  4. Integration with DHCP and DNS Servers: SolarWinds IPAM integrates seamlessly with popular DHCP and DNS servers, such as Microsoft, Cisco, and BIND, enabling centralized management of IP address spaces, DHCP scopes, and DNS zones.
  5. Customizable Alerting and Reporting: The tool offers customizable alerting and reporting options, allowing administrators to receive notifications of critical events or potential issues and generate custom reports tailored to their specific needs.
  6. Scalability: IPAM can scale with the size of your network, making it suitable for organizations of all sizes.

Learn more       Download Free Trial

By leveraging the SolarWinds IP Address Manager, network administrators can simplify the management of IP address spaces and related resources. This ensures efficient and organized allocation of network resources. Moreover, it helps reduce the risk of IP address conflicts and other network issues.  

2. Advanced Subnet Calculator (Free Tool)

The Advanced Subnet Calculator, developed by SolarWinds, is a versatile and comprehensive subnetting tool. This tool has many features to help network administrators efficiently manage and plan their IP address spaces.

©2023 SolarWinds Worldwide, LLC. All rights reserved.

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This standalone tool boasts ease of use, and rich functionality, which includes the following key features:

  1. Support for CIDR and Classful Subnetting: The calculator accommodates both CIDR (Classless Inter-Domain Routing) and classful subnetting methods.
  2. IPv4 and IPv6 Compatibility: The Advanced Subnet Calculator supports IPv4 and IPv6 address spaces, ensuring they remain relevant and valuable as networks transition to the newer addressing standard.
  3. IP Address Range Calculation: The tool can quickly determine the range of usable IP addresses for each subnet, assisting administrators in effectively planning and allocating IP address resources.
  4. Subnet Mask Generation: The calculator generates appropriate subnet masks based on user input and determines the ideal subnet mask for a given network requirement.
  5. Network Address and Broadcast Address Calculation: The Advanced Subnet Calculator automatically calculates network addresses and broadcast addresses for each subnet, providing essential information for configuring and troubleshooting network devices.
  6. Subnet Supernetting and Aggregation: The tool can also perform supernetting and aggregation calculations, which helps consolidate multiple smaller subnets into larger ones or determine the most efficient allocation of address space.

The Advanced Subnet Calculator is an excellent choice for network administrators who require a robust and reliable tool.  

3. Spiceworks Subnet Calculator

The Spiceworks Subnet Calculator tool offers network administrators an easy-to-use and efficient solution for performing basic subnet calculations. With a focus on simplicity and user-friendliness, the Spiceworks Subnet Calculator offers several useful features to streamline the subnetting process.

© Copyright 2006 – 2023 Spiceworks Inc.

  1. Intuitive Interface: With a straightforward design, the calculator’s interface enables users to input the required information and quickly obtain subnetting results.
  2. Flexible Subnetting Options: Users can generate subnet masks based on the desired number of subnets or hosts per subnet, providing flexibility to accommodate various network requirements.
  3. CIDR Notation Support: The Spiceworks Subnet Calculator supports CIDR (Classless Inter-Domain Routing) notation.
  4. Network Address and Broadcast Address Calculation: The tool automatically calculates each subnet’s network address and broadcast address, providing essential information for network configuration and troubleshooting.
  5. IP Address Range Calculation: The calculator displays the range of usable IP addresses for each subnet, making it easier for administrators to plan and allocate IP address resources.

While the Spiceworks Subnet Calculator may offer fewer advanced features than other subnetting tools, it is still an excellent choice.  


Understanding subnets and subnetting is essential for efficient network management and troubleshooting. Consequently, this guide has provided an overview of subnets, subnet masks, and popular subnetting tools.

By leveraging these tools and concepts, network administrators can better manage IP address spaces, reduce network congestion, improve security, and conserve address resources.

This post was written by Juan Reyes. Juan is an engineer by profession and a dreamer by heart who crossed the seas to reach Japan following the promise of opportunity and challenge. While trying to find himself and build a meaningful life in the east, Juan borrows wisdom from his experiences as an entrepreneur, artist, hustler, father figure, husband, and friend to start writing about passion, meaning, self-development, leadership, relationships, and mental health. His many years of struggle and self-discovery have inspired him and drive to embark on a journey for wisdom.

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