What Is a Subnet Mask

What Is a Subnet Mask? A Complete Guide

A subnet mask is a numerical value used in computer networking to distinguish the IP address parts and determine the network components of an IP address. Subnet Mask divides a larger IP address space into more manageable, smaller subnetworks, enabling effective device organization and routing.

Helping with IP address allocation, routing, and security improves network effectiveness. Subnetting improves the management and performance of a network by reducing broadcast traffic and enabling better resource organization

This article will focus on how they contribute to secure networks, effective IP address distribution, and optimized routing. We’ll look at how subnetting can improve resource management and network performance, making it an essential concept for network administrators and consumers to understand.

What Does a Subnet Mask Do?

A subnet mask is a 32-bit address that separates an IP address into network and host parts. It is commonly expressed in decimal form (for example, It determines how many bits in an IP address are reserved for host addresses and how many are allocated to the network ID.

What is a Subnet Mask?

Let’s take an example to make you better understand the concept. Consider two devices with IP addresses and, each using a subnet mask The network parts of Device A’s IP address (192.168.1) and Device B’s IP address (192.168.1) are compared when Device A wishes to connect with Device B.

Device A can interact directly with Device B without the use of a router because these network segments match, indicating that the two devices are connected to the same network.

How Does a Subnet Mask Work?

A subnet mask distinguishes an IP’s network and host address, dividing it into two parts. The first part identifies the host (computer), while the second part specifies the network to which it belongs. To understand this concept better, let’s break down the critical components of a subnet mask:

a. Network Address Part

A device’s specific network connection is determined by the network part of its IP address. The subnet mask determines it and comprises the IP address’s leftmost bits. For instance, the first 24 bits of the subnet mask are set aside for the network part.

b. Host Address Part

The host part identifies A specific network device. The IP address’s remaining bits are what determine what it is. For example, in the subnet mask, the first 24 bits are allocated to the network portion.

Subnet masks function by drawing a line separating the network and host parts of an IP address. When communicating data to another device on the same network, a device uses the subnet mask to determine whether the destination IP address is on the same network.

Benefits of Subnet Mask

What is a subnet mask used for

Thanks to subnetting, network administrators have more control over their computer networks’ traffic, data packets, subnets, and routers.

It improves the network’s security and ensures that IP addresses are utilized effectively.

Let’s examine some of the critical benefits of subnetting in more detail:

i.Network Segmentation

 Subnet masks are essential for segmenting enormous networks into smaller, easier-to-manage subnetworks. This segmentation makes the network more secure, makes troubleshooting more manageable, and enables more effective use of the network’s resources.

ii. IP Address Assignment

Subnet masks facilitate the efficient distribution of IP addresses. Network administrators might reserve a specific range of IP addresses for devices inside a given subnet to maximize the use of IP address space.

iii. Traffic Routing

Subnet masks are essential factors in routing decisions. Routers use them to decide whether data packets should be transmitted to another network or forwarded inside the same subnet.

iv. Security

Subnet masks improve security by isolating different network parts. They restrict the broadcast domain, lowering the potential impact of security lapses and making it more difficult for unauthorized devices to access vulnerable network areas.

v. Resource Allocation

Subnets make it possible to use resources more effectively. Administrators can more efficiently distribute resources like bandwidth, servers, and network hardware to fulfil the needs of different segments by segmenting an extensive network into smaller subnets.

vi. Troubleshooting

Subnet masks help resolve network problems. They facilitate the diagnosis process by making it easier to determine whether issues are isolated to a particular subnet or impact the entire network.

vii. Expansion

As a network expands, subnets make it simpler to scale it. New subnets can be introduced without affecting the entire network to accommodate more devices or increase network capacity.

viii.Vast Connectivity

Subnetting is necessary for linking numerous sites inside an organization, known as multisite connectivity. Each site may have its subnet, allowing for effective management and communication between locations.

ix. VLAN Configuration

To divide a physical network into logical segments, virtual LANs (VLANs) frequently use subnetting. Network security, flexibility, and traffic control are all improved by VLANs.

X. Private and Public IP Address Management

Subnet masks are essential for controlling private and public IP address spaces, ensuring each address fulfils its intended function while upholding network security.

Are Subnets And Subnet Masks the Same Thing?

No, subnets and subnet masks are not the same thing. A subnet refers to a logically segmented portion of a more extensive network created by dividing the network into smaller, isolated segments to improve organization and control.

Subnet masks, conversely, are numerical configurations (typically expressed as 32-bit addresses or prefix notation) used to determine the boundaries between the network and host portions of an IP address.

Subnet masks are crucial for defining the size and range of subnets within a network. In summary, subnets are the segmented networks, while subnet masks are the tools used to define and configure these segments.

Difference Between Subnet Mask vs Default Gateway

Networking terms Subnet Mask and Default Gateway are different from one another, and each has a specific function.

Feature Subnet Mask Default Gateway
Helps with network segmentation, IP address distribution, and routing decisions by dividing an IP address into network and host components.
Acts as a point of entry and exit for data traveling between local networks and external networks, such as the Internet.
Identifies the host and network components of an IP address.
Carries out traffic routing between internal and external networks.
Numeric value (e.g., or prefix notation (e.g., /24).
IP address assigned to a networking device or router.
Defines the organization and network structure within a local network.
Forwards data packets to enable connectivity beyond the local subnet.
Where is the Subnet Mask
Set on individual devices within a local network.
Assigned to a particular router or networking device on the local network.
Network Division
Essential for organizing and managing a network's subnets.
Although not directly connected to network segmentation, communication between subnets and external networks is possible.
Increases network security by restricting access and isolating specific areas.
Controls traffic between the local network and external networks to provide secure communication.
Subnet Mask: or /24.
Default Gateway:

Even though both Subnet Mask and Default Gateway are essential networking elements, they fulfil various purposes within a network infrastructure. Subnet masks determine a local network’s IP address structure, and the default gateway facilitates connectivity with other networks.

Subnet Mask in The Context of ipv4

As used in IPv4, a subnet mask is a 32-bit numerical address that separates an IP address into network and host components. This segmentation is essential for a network to be organized and for data to be routed effectively. Subnet masks are essentially binary sequences of ones (1s) and zeros (0s), though they are frequently written in decimal form (for example,

The subnet mask’s 1s and 0s represent the network and host portions, respectively. Network management, security, and traffic control are made more accessible by the ability for each subnet to have its specific IP address range and configuration. Routers and networking equipment use subnet masks to decide where to route traffic. 

How Do IP Addresses and Subnet Masks Relate?

IP addresses and subnet masks are closely related in networking and cooperate to support proper communication and network segmentation. Here is how they connect.

1. IP Address Division

An IP address identifies explicitly devices on a network and comprises 32 bits (in the case of IPv4). The network section and the host portion, which comprise the entire IP address, are utilized in addition to device identification.

2. Subnet Mask Definition

The subnet mask, a 32-bit numeric setting, specifies how the IP address is split into these two sections. It employs a series of binary 1s and then 0s. The subnet mask’s 1s and 0s represent the host and network portions, respectively.

3. Bitwise AND Operation

A bitwise AND operation is carried out between the IP address and the subnet mask to determine the network address for a given IP address inside of a particular subnet. The host bits are hidden by this process, leaving only the network bits, which stand in for the network address.

4. Network Segmentation

 Subnet masks are employed in the segmentation of networks. Network managers can create smaller, isolated subnets from a more extensive network using various subnet masks. The IP address and subnet mask combination determines the network address range for each subnet. 

5. Routing

Routing decisions are made by routers and networking equipment using subnet masks. The router uses the subnet mask to validate the network component of two devices’ IP addresses when one wishes to connect. The devices are on the same subnet if they match and can directly communicate. If not, the router uses its routing database to forward the data to the proper network or subnet.

How Do IP Classes And Subnet Masks Relate?

IP classes and subnet masks are related networking concepts that influence how IP addresses are arranged and partitioned inside a network. Subnet masks are essential in establishing the particular network segments inside these IP address classes, which were initially classified according to the first few bits of IP addresses.

The widespread adoption of Classless Inter-Domain Routing (CIDR), which enables more adaptable IP address allocation, means that IP classes have lost some significance.

i. Classes of IP Addresses

A, B, C, D, and E were the first five classes assigned to IP addresses. These classes were established using the IP address’s first few bits. There was a predetermined IP address range for each class.

ii. Using Network Segmentation And Subnet Masks

On the other hand, subnet masks are employed to segment IP addresses further ranges within these classes into more compact subnetworks or subnets. By separating larger address spaces into more manageable, smaller logical pieces, subnetting enables network managers to build more effective and manageable networks.

iii. CIDR Subnet Masks

In CIDR notation, IP addresses and subnet masks are expressed simultaneously, using a slash (“/”) and a prefix length. For instance, the first 24 bits of an IP address are used for the network component, and the remaining bits are used for host addressing, as shown by the CIDR notation “”.

iv. Practical Application

Original IP classes (A, B, and C) specified the default subnet masks that went along with them. For instance, the subnet mask for Class A addresses was, Class B addresses were, and Class C addresses were

Network administrators may modify these default values using subnet masks to make subnets of different sizes within each class and maximize the use of available address space.

How to Calculate Subnet Mask?

Subnet mask calculations are crucial for network managers to organize IP address distribution and create networks. There are a few suggestions on generating subnet masks manually, which might help you through the procedure.

i. Determine Your IP Address and CIDR Prefix

Start by choosing the IP address that will serve as the foundation of your subnetting. Then, select the CIDR prefix length, establishing the number of bits allotted for the network component (e.g., /24, /25, /26, etc.).

ii. CIDR Prefix to Subnet Mask Conversion

Subtract the CIDR prefix length from 32 (the total number of bits in an IPv4 address) to convert it to a subnet mask. The subnet mask in slash notation will be the outcome.

iii. Example Calculate Subnet Mask

For a CIDR prefix of /24:/8 Subnet Mask = 32 – 24

iv. Determine the Total Number of Subnets

Decide how many subnets you want to create or require within the network.  There will be a subnet mask for each subnet.

v. Calculate Subnet Mask for Each Subnet

Choose the number of bits to allot for the network part for each subnet. How many subnets and hosts are required for each subnet will determine this. Remember that the subnet mask’s total bit count must still equal 32.

vi. Convert Subnet Masks to Decimal Form

 If necessary, convert the binary subnet mask to decimal form. Remember that each octet in the subnet mask represents 8 bits in binary.

Final Words - Subnet Mask

As the networking landscape evolves, a strong understanding of subnet masks is critical for network professionals, building on the foundations established by IP address classes and adapting them to today’s dynamic networking requirements.

Subnet masks are essential for effectively operating IP networks since they are crucial in segmenting IP addresses into network and host components. These masks make segmenting networks possible, manage IP addresses, strengthen security, and make routing decisions.

While historically, IP classes influenced default subnet masks, the introduction of CIDR brought flexibility, allowing for more accurate subnetting by adjusting subnet mask lengths.  The interaction of IP classes, subnet masks, and CIDR highlights how network addressing has evolved.


Zayne Z

Meet Zayne VoIP Blog's dedicated Content Researcher with 5+ Years Experience. Passionate about VoIP technology, he delivers accurate, engaging articles, keeping readers informed on industry trends with excellence.