Importance of Subnetting

By Ma Wen Jie

Subnetting can help to connect large groups of computers to one external IP address.
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Subnetting is the practice of creating smaller network chunks that use a unique series of addresses, either to keep data inside the physical network or to funnel large numbers of addresses through a router or bridge to a single external Internet Protocol (IP) address. Subnetting is a common practice in network architecture and has a number of important functions.


Subnetting is built in to the system of IP addressing. By assigning a series of computers similar IP addresses and assigning that network the appropriate network mask, computers on that network can communicate among each other easily. The formal networking standards for subnetting were established in 1985 with the networking standard RFC950.


Subnetting can help ensure network security by facilitating communication between computers on the same subnet while preventing access from computers on other subnets. In fact, your home router works as a security device under this principle. A public IP address on the provider side of the router allows for other Internet IPs to send information, but all of the computers behind the router use a different IP address. The IP address on the home side of your router uses a subnet that is not routable, meaning that its IP must be converted to the public IP of your router before the address will be transmitted through your provider’s routers.

IP Limitations

Another reason that subnetting has become important is that the number of IP addresses available on a single network is limited. There are about 3 billion IP addresses available through standard IP networking. But there are many more devices in the world that require IP addresses. By connecting collections of devices on a subnet and then presenting that subnet to the Internet via a single IP using a router (the way your home router works), far more than 3 billion devices can connect to the Internet.

Subnet Mask

Subnet masks define the number of bits that the network will use to assign IP addresses. In most cases, home networks use a mask of, which creates a 24-bit mask that allows up to 256 addresses in a subnet. For example, if your home network is set to the non-routable network address of 192.168.0.X, you would have through available for network devices. If you had more than 255 devices on your network, the 256th device would be unable to address the network.


When setting up a subnet, consider how many devices you would like to attach to your network. If you are setting up a subnet in a larger company, a 24-bit subnet mask may not be sufficient. You might be better off using a mask instead of a mask in order to allow up to 65,526 hosts on your network instead of 255.