What Is a Subnet Mask? Definition, Working, and Benefits


A subnet mask is defined as a 32-bit address that segregates an IP address into network bits that identify the network and host bits that identify the host device operating on that network. This article explains a subnet mask, how it works, and its benefits to network infrastructure.

What Is a Subnet Mask?

A subnet mask is a 32-bit address that segregates an IP address into network bits that identify the network and host bits that identify the host device operating on that network. It encapsulates a range of IP addresses that a subnet can use, wherein the subnet refers to a smaller network within a more extensive network.

Technically, subnet masks are used internally within a network. Routing devices or switches rely on subnet masks to route data packets to suitable destinations. Data packets that traverse over the internet or any network do not indicate the subnet mask but only reveal the IP address of the destination. However, the routers match this destination IP address to the data packet’s subnet mask to deliver the data packet to the right place.

Let’s consider an analogy to understand the subnet mask concept better. Suppose a user named ‘Davis’ writes a letter to his friend ‘Tom’. Davis sends this letter to Tom’s office rather than his residence. Tom’s place of employment is a large enterprise with several co-located departments. The administrative team at Tom’s office sorts the mail by department rather than by employee name to ensure that the correspondence isn’t missed and there is no confusion in the process. On receiving Davis’s letter, the team identifies that Tom works in the HR department. As a result, the letter is sent to the HR department instead of Tom. The HR department then hands the letter over to Tom.

In the above example, Tom represents an IP address while the HR department serves as a subnet mask. Since the letter was matched to Tom’s department in the initial stages, Davis’s mail was quickly sorted into a group of potential recipients. Without this initial sorting, the administrative team would have to invest more time in looking for the exact location of Tom’s desk, which could have been in any corner of the enterprise building.

Now let’s look at a real-world example. A data packet addresses the IP address, representing a class C network. Since the IP address is split into a network and host address, here, in a class C network, the network portion is represented by ‘192.0.4′. Thus, the network routers deliver the data packet to the network identified by 192.0.4.

Upon arrival at the right network, the router within the network then consults the routing table for forwarding the packet further. It uses the data packet’s subnet mask of to perform some binary mathematics, observe the device address ‘16′, and thereby calculate which subnet it should forward the data packet to. On determining the target subnet, it sends the packet to the router that is responsible for delivering data packets within that very subnet. As such, the data packet is eventually delivered to the destination IP address of

Representation of subnet masks

Subnetting is a process that logically partitions an IP network into multiple subnets. Such network subdivision allows better usage of IPv4 addresses and makes the network’s data routing more secure and efficient.

When a new device connects to a network, an IP address is assigned to. Here, the IP address (IPv4) refers to a 32-bit numeric address that has four numbers separated by periods, and each group of numbers within a block is referred to as an octet. The number in each octet ranges from 0 to 255. In such IP addresses, the network and host portions become indistinguishable without the subnet mask.

Let’s look at an example:

The IP address for a device may be:
11000000. 10101000. 01111011. 10000100

The subnet mask for the IP network above:
11111111. 11111111. 11111111. 00000000

One can represent the IP address and subnet mask as:

Subnet masks are vital to the process of subnetting. With minor adjustments in the subnet mask, you can assign the available IP addresses within a network. For example, a household home network has a standard subnet mask of This implies using 254 usable IP addresses within the defined network. In simple words, One can connect up to 254 internet-enabled devices such as phones, computers, IoT gadgets, and others to the home network to access the internet.

Moreover, when a device on a network observes the network and host bits on another device’s IP address, it can determine whether the other device is on the same home/business network or online on another network. Thus, devices rely on subnet masks to provide the necessary information to communicate with other devices on the same or outside networks.

See More: What is DHCP (Dynamic Host Configuration Protocol)? Meaning, Working, and Features

How Does Subnetting Work?

Subnetting is key to creating fast and efficient computer networks. As businesses worldwide continue to grow, efficient network organization and management are crucial for large firms that intend to expand technologically. Complex networks turn into resilient ones when the traffic has efficient routes to traverse over the network. Without adequate data paths, all network traffic would travel haphazardly over all possible routes, causing traffic congestion and bottlenecks that would degrade the network’s performance.

Subnets allow network traffic to pass through a minimum number of routers so that data packets only need to traverse a shorter distance by following mini-routes to reach the target destination within a more extensive network.

IP addresses act as an identity for the hardware devices on a network. You can locate a particular device if these IP addresses are organized logically and understandably. That’s where subnetting comes into the picture. It not only helps in localizing network equipment but also aids in maintaining efficiency and order across the network.

As computer networks have thousands of interconnected devices, the corresponding IP addresses of all such devices can, in turn, create complex routes for the network traffic to traverse. However, with subnetting, the usage of IP addresses is limited to a few devices. Network engineers can thereby sort data by creating sub-networks, ensuring that the traffic reaches the right place without touching every part of the complex network’s complex routers. As such, the task of engineers is to match each IP address to the corresponding subnet mask.

A subnet mask is like an IP address that identifies the network and host parts within the original IP address. This identification helps establish specific routes for sending the data to a particular destination. Thus, the subnet mask serves as a tool that the network routers use to match the data packet’s IP address with the destination’s sub-network.

Significance of subnetting

Today, computer networks of different sizes are used across the IT industry. These networks are bifurcated into various categories depending on the number of hosts that have access to them. Considering this, IP addresses are divided into classes used by class A networks, class B networks, and class C networks.

Class D and E networks also exist; however, they serve other purposes. For example, class D networks are suitable for multicasting tasks, while class E networks are used in the research and development sector.

The table below reveals the different network classes, their subnet masks, address range, and the number of hosts that they support.

Class A, Class B, and Class C Ranges | SourceOpens a new window

Class A networks can handle hosts in the range of 65,536 to 16 million, class B networks can manage hosts 256 to 65,534, and class C networks can support 254 host addresses.

In general scenarios, IP addresses are sufficient for network routers to direct traffic to the correct network. However, when you consider class A networks, it involves millions of connected devices. Routing data traffic to the correct destination can become a time-intensive task as the number of devices increases. This is where subnetting proves to be beneficial. It allows only a certain range of devices within a sub-network to use specific IP addresses.

See More: Top 10 Wifi 6 Mesh Routers in 2022

Benefits of Subnetting

Subnetting gives network administrators better control over their computer networks, including traffic, data packets, subnets, and routers. It boosts the network’s overall performance, enhances its security, and ensures that IP addresses are used efficiently.

Let’s dive deeper into some of the critical benefits of subnetting:

1. Efficient data routing

Broadcast traffic causes a severe bottleneck on a more extensive network. Here, broadcasting implies that the data packets travel to every node on the network. Subnetting allows you to segregate such broadcast domains into smaller sections. This results in fewer nodes that the broadcast traffic may have to interact with, making data routing efficient and direct.

In other words, subnets enable the interaction and communication of multiple devices on different smaller networks simultaneously, thereby reducing the communication traffic over the more extensive network where different instruments interact simultaneously.

Let’s consider an analogy here. Suppose 60 people are connected over a conference call on Skype. If all 60 individuals start talking simultaneously, there would only be noise and chaos on the call, making communication inefficient. However, if you split these 60 people into 12 breakout rooms, there’s a high possibility that it may lead to a much more productive and peaceful session.

Subnet masks play an important role here as they ensure that the traffic is contained within the defined subnet. As a result, network congestion is avoided, and the network load is also considerably reduced. Moreover, as subnetting limits the distance data packets need to traverse in a network, the data routing activity is carried out effectively. This boosts overall network performance and speed.

2. Enhanced network security

For enterprises having more extensive local networks, several connected devices and a significantly high volume of data traffic exist. In such cases, subnets can be beneficial in a security context rather than safeguarding one extensive network.

Let’s say hackers attack a smaller subnet. In such a case, only that network segment gets compromised and affected. While the attackers have access only to the devices on that specific subnet, other devices on the more extensive network are not visible to them. This reduces the attack surface as intruders do not gain access to all the devices.

A network manager can use small subnets to identify and address external threats by controlling network traffic through route maps, quality of service mechanisms, and network access control lists (ACLs). Here, route map configurations refer to the routing of data packets without relying on routing tables, QoS services prioritize high-performance applications by adjusting network traffic, and ACLs control network traffic to specific subnets. Subnets are essential to such network applications as they enhance overall network security.

Subnets also help in isolating legitimate local networks. Moreover, they control access to all devices running on the entire network. As a result, specific files or processes can be secured from unwanted access, and even remote network access can be limited.

3. Prolonged usage of IPv4 addresses

With the emergence of the internet, IP addresses were easy to capture. The first version of the ‘Internet Protocol’ was IPv4, which became a standard communication model in the 1980s for internet users. According to History Computer (Nov. 2021), IPv4 accounted for around 94% of internet traffic. However, as IPv4 addresses were limited, the IP address stock began depleting over time as intelligent devices, personal computers, televisions, speakers, etc., grew in numbers. Considering this scenario, subnetting broadened the usage of a single public IP address.

Hence, rather than each device holding a unique IP address, a network can possess multiple IP addresses on one IP network. This implies each device on the network has a portion defining the IP address of the network and a part that specifies the subnet. As such, subnetting facilitated the continued use of IPv4 as an internet standard for an extended period.

See More: What Is IPv6 (Internet Protocol Version 6)? Definition, Features, and Uses


Large companies employ network administrators and network engineers to subnet their computer networks. This secures their networks from external threats, boosts routing efficiency, preserves public IPv4 addresses, and also enhances network speed and performance. Subnetting invariably makes use of subnet masks to route inbound data traffic to the desired hosts. Irrespective of the size of subnets, subnet masks ensure the smooth and reliable operation of smaller networks.

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