What is a Subnet and How Do ISPs Use Them?

September 12, 2022

Author: Timothy


internet subnet

Subnets are a way to optimize and preserve the usage of Internet Protocol (IP) addresses. They  come with a wide variety of benefits such as improved performance, security, better address space management, so an ISP subnet is a common occurrence.

They are employed in both IPv4 and IPv6 addresses. What may come as a surprise is that an ISP actually assigns only a single IP address to a household, even if you have many devices. These become the foundation of subnets, which allow users to get more addresses later on.

What is an internet subnet?

A subnet (or subnetwork) is a subdivision of a network. In other words, it’s a collection of devices that are connected to the internet, all of which are usually in a single physical or geographical location.

These devices get their own addresses from a combination of an ISP-assigned IP address and a subnet mask. In essence, the ISP assigns an address space to a router, which can then be used to assign an IP address to each new device.

In IPv4, the last three digits of an IP address are used for the aforementioned devices. For example, an IP address could be 192.168.1.XXX, where XXX is any number ranging from 0 to 255. Devices, however, cannot be assigned addresses that end with 255 or 0 as these are reserved for other purposes.

Addresses ending with 255 are called the default gateway. They are used for several purposes such as address resolution and dynamic host configuration. A default gateway cannot be overridden as it’s the exit point for all packets leaving a network (or subnet).

An IP address ending with 0 are the ones actually assigned by the ISP. This is the network address that points to the subnet.

In IPv6, the foundation remains the same (a default gateway, an IP address space, and a subnet mask), but there’s a subnet address added. On an IP address of 2001:4e1:abcd:0012:0000:0000:0000:0000

  • Network address - 2001:db8:abcd 
  • Subnet address - 0012
  • Device address - 0000:0000:0000:0000

The newer version of the Internet Protocol comes with an improved way to handle IP address management. Primarily, the goal has been to create a significantly larger IP address space, which is clearly visible through the greater allocation of bytes for both the device and network address.

How do ISPs use subnets?

An ISP, as mentioned, assigns a single IP address and a subnet mask to a network. Notably, it is not a static IP address as there are now methods to automatically change assignments without much intervention.

Once an IP address and subnet mask is assigned, the router then takes care of the process by using the provided space to connect devices to the internet. An ISP can then easily manage and communicate with the entire network without having to establish a connection with each device and IP address separately.

Additionally, since all traffic moves through the network address, they have an easier time understanding usage of the internet. Instead of having to manage hundreds of devices that each send separate requests, ISPs can look at the single network address to understand what’s going on in a much simpler fashion.

Finally, ISPs use subnets to ease IP address management. IPv4 addresses have already technically ran out and are being reused. With subnets, however, ISPs have greater control over the IP address space than if each device was assigned one separately.

What are ISP proxies with subnets?

Regular proxies are simply devices that allow connections from third parties, which then send connection requests as if they were their own. In simple terms, a user can connect to a proxy and have that device relay all requests to a website or application without revealing the true source.

ISP proxies are ones that are created by an Internet Service Provider, but that are hosted on a data center instead of a household device and are intended for sale. They get all the benefits of business-grade speeds while retaining the legitimacy of a residential proxy (one created in a regular household device).

These proxies are fairly popular with botters and sneakerheads as they have immense benefits in areas where speed and legitimacy are required. Sneaker copping is a great example as vendors carefully track each user, making legitimacy a key success factor.

Since the competition in sneaker copping, however, is so fierce, speed is another success factor. ISP proxies are the only way to get both, making them popular for such use cases.

There is, however, a remaining issue. Most proxy providers sell a small IP address pool, which are part of some subnet. If someone else misuses their assigned IP address, the entire network can potentially get banned. 

Getting banned is a fairly common occurrence, so some users opt to purchase entire subnets with the associated IP address space. As the user then has control over the entire IP address pool, they are the only one responsible for a potential ban, if one were to come.


Subnets are widely used by Internet Service Providers to optimize network management processes. They make IP address assignment simpler, reduce the amount of overhead required to understand traffic, and improve overall performance.

While, most commonly, subnets are created for the purpose of creating a home network, some ISPs can repackage them into proxies. These can then be used as an IP address pool for various use cases such as sneaker copping.