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What is a subnet and how does it work?

Researched by
Shubham ArgawalContributing Writer
Headshot of Michal Ash
Reviewed by
Michal AshManaging Editor
Updated 5/16/23

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A subnet and a subnet mask play a key role in getting you online. They’re two of the several building blocks of your internet connection and keep the network traffic from getting congested. Without them, the modern internet wouldn’t be as ubiquitous as it is now.

As its name suggests, a subnet is short for a subnetwork. Though most people never have to configure it themselves, it’s the backbone of each internet network you connect to and ensures it is efficient and secure. So what exactly are a subnet as well as a subnet mask, and how do they work?

What is a subnet?

You can think of a subnet as a network within a network. In a way, it acts like a relay between you and the server storing the information, such as a website you want to access. It slices large networks into smaller ones so that it’s more streamlined to deliver packets of data to their rightful devices.

The reason such an intermediary exists is because, at any given time, millions of people can be connected to a network, and if a single host is tasked with reaching each of their devices, the packet of data will have to travel a long distance without losing or compromising its content. This can be inefficient, especially since our internet requests sometimes travel hundreds of thousands of miles.

Imagine instead of local post offices, there’s one in the center of a country that takes care of all incoming and outgoing mail. Not only would it be slow, but post office workers would need to take long, arduous trips to addresses in places with which they’re not even familiar. The packages are likely to be misplaced, delivered to incorrect destinations, and even lost in transit.

Similarly, it’s cumbersome for a network to route data to the final destinations on its own. So, like a local post office, a network is divided into numerous subnets that are closer to the end devices. The packages are sent to the subnets that, in turn, forward them to your phone or laptop. This prevents requests from piling up on the network’s main channel, and with each subnet handling a limited number of devices, it’s better equipped to reach the correct address.

What is a subnet mask?

The subnet mask is what makes a subnetwork work. In technical terms, it’s an internal code—a series of four numbers separated by periods—that peripheral devices like routers rely on to figure out to which device a packet of data is headed.

Each connected gadget, such as your phone or even smart TV, has a unique identity. In networking terms, this is called the IP address. If you’ve ever experienced the process of setting up a new router in your home, you have probably come across this address. Like the subnet mask, it also comprises four numbers separated by three periods (​​

When a server dispatches a piece of information, it identifies the receiver with its IP address and uses it to send it to the right channels. The bits in an IP address contain two locations: the network the receiver is on and the receiver itself. But which of the four numbers is the former and which correspond to the latter is not universal. So, based on the IP address alone, the router can’t determine where it should forward an incoming packet.

The subnet mask allows the router to tell which parts of an IP address belong to the network and which ones belong to the host. Networking equipment, like a router or switch, will perform a mathematical calculation between the IP address and the subnet mask to identify their network and host components. Once it does so, the router knows the packet’s next destination, whether it’s the final device or another subnet.

When and where are subnets used?

Since the concept of subnets was invented decades ago, their application has become standard practice across all modern networks. For widescale networks (like the internet itself), subnets are vital to prevent overload on any one channel, and more importantly, restrict potential security risks within a subset of the connected devices.

Subnets are especially handy in enterprises and offices, where IT administrators have to monitor closely what flows in their networks to ward off any potential security risks and leaks. Thanks to subnets, administrators can monitor and exercise control over a smaller number of connections in a network as opposed to impacting all the hundreds or thousands of them in a go.

On the personal devices we own like routers and laptops, subnets are activated, and configured by default. For internet service providers, each customer’s Wi-Fi network is a subnet of its own, with many devices under it such as tablets, televisions, laptops, phones, and more.

How does a subnet affect your internet experience?

Without the subnet, the internet wouldn’t be as widespread as it is today. Back in the 1980s, network managers realized that, as the web expanded, the IP address nomenclature would fall short and that there wouldn’t be enough unique ones for new connections. There are only a certain amount of numbers the IP address can contain. The subnet solved this by letting people create networks within another network, each with its own dedicated series of IP addresses that are tracked via the subnet mask.

The introduction of the subnet and isolating a group of devices into their own subnetworks resulted in a variety of additional perks. Because your subnet is independent from your neighbor’s, for example, any virus attacks on their devices won’t affect you as opposed to when everyone is sharing the same, common network. Since a subnet decreases network congestion and makes it simpler to locate a packet’s destination, it’s also faster and is partly responsible for the ultra-quick connections we experience nowadays.

How to set up a subnet and check your subnet mask

Unless you’re an IT administrator at a large corporation, you don’t have to worry about setting up your subnets. In devices like our home routers, subnets are established automatically by the internet service provider. Because the upsides of subnets are essential to how the world wide web functions, it’s no longer possible to live without them.

You can, however, check your Wi-Fi connection’s subnet mask ID, and confirm it’s activated. Here are ways to check this from various devices.

MacGo to System Settings > Wi-Fi and click the “Details” button next to the Wi-Fi you’re connected to. Head into the TCP/IP section from the menu on the left and you’ll find the “Subnet mask” listed.
Windows PCNavigate to Settings > Network & Internet and select the “Properties” option next to the connected network.
iPhoneVisit Settings > Wi-Fi and touch the “i” button next to your Wi-Fi’s name. Scroll down to find the subnet mask.
AndroidLook in Settings > Wireless & Networks > Wi-Fi > [Your network’s name].

The benefits of a subnet

The reason a subnet is now an essential element of our internet experience is because of its numerous benefits.

When a broadcaster breaks down its network into subnets, it can facilitate more optimal routes each time to the various destinations. Instead of overloading one channel, data requests travel shorter distances via subnets, which relay packets on to the next one to ensure the most productive journeys.

Thanks to such a tree-like structure, network operators ensure the least amount of data is lost on the way, and that it doesn’t have to travel through any routers it doesn’t need to. This boosts performance, and since each route is tasked with only a certain number of requests, the network is rarely congested. For users, the practice of subnetting, therefore, enables a consistent bandwidth and speeds up data deliveries.

In a large company, a subnet’s organizational skills equips administrators with the ability to isolate each group of devices with only the resources their users have been authorized to access. While the security engineers, for example, may have permission to look into the company’s core servers, people in the HR department won’t. And since the process of subnetting makes expansion as simple as plug and play, network admins can comfortably keep adding new subnets to their network as the workforce grows without affecting any of the existing connections or vice versa.

More importantly, it’s easier to spot and track down threats in multiple smaller networks than a single large one. When a threat does arise in a subnet, admins can quickly quarantine that compromised set of devices and make sure it doesn’t affect the rest. Once it’s addressed, admins can add the affected subnet back to the network without the need to reconfigure the systems again.

Subnets are also vital to prolonging the use of the most popular internet protocol. Called IPv4, you can think of it as the blueprint of a network—a globally accepted set of rules governing the exchange of data for decades. However, IPv4 is limited in the number of unique identities and devices it lets on one network, which is where the subnet steps in. When a network is sliced into subnetworks, each has its own fresh collection of IDs to assign; and if it runs out, the network manager can create a new subnet, and start all over again from zero.

Subnets extend how long we can use the IPv4 standard, which is crucial because the majority of traffic runs on it. Although there is a new IPv6 protocol that can house far more unique device identities, it will be a while before it becomes mainstream.


Understanding subnets is important to learn how they support the networks on which we depend every day. They make our connections faster, more efficient, and safer. At the same time, they’re only one of the internet’s building blocks. The internet is the result of a series of modules functioning in tandem to let you stream high-res videos or infinite scroll TikTok in an instant.

Subnets are also not enough to protect your devices and identity online. There’s a range of additional steps you can take to secure yourself, such as signing up for a VPN, which hides your location and IP address from snooping eyes.

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Contributing researcher
Researched by
Shubham ArgawalContributing Writer
Contributing reviewer
Headshot of Michal Ash
Reviewed by
Michal AshManaging Editor

Michal directs the Switchful content strategy and leads the editorial team. With a bachelor’s degree in Communications, she has more than a decade of experience in the world of marketing communications. Her diverse career has included public relations, brand development, digital strategies, and more; her key skillset has always been centered around strategic efforts for consumer-focused initiatives. In her free time, you can find her camping with friends, chasing waterfalls on her kayak, or searching for the best restaurants in Salt Lake City.