A Subnet Mask – The IP Address Hidden Helper

September 27th, 2011 by

If you start looking for information on subnet masks and IP addresses you can easily get confused, especially by IT terms like octets, notations and subnets. This article will explain in simple terms what a subnet mask is, and how it is used when setting up a home network or a larger network with multiple subnets.

What is a Subnet Mask?

Before we learn about subnet masks, we need to know what a subnet is. A subnet is a part of a larger network. Most commonly, large networks are divided into smaller ones. For example, if you work at an office, each floor might be a different subnet of a larger network and therefore have a different subnet mask. This is done in order to build a larger network, which can then be connected to the internet via a single connection. It also enables the administrator to control which subnets are allowed to exchange data with each other.

An IP address contains four parts, called octets, separated by full stops. An example of an IP address would be Each octet can contain a number between 0 and 255. A subnet masks is in the same format as an IP address and it determines which part of the IP address is used for the network identification (net) and which is used to determine the host. The net part of an IP address stays the same for all the computers in a given network, even if they are in different subnets.

Let’s say that our subnet mask is, which is the most commonly used one in small local home networks. When coupled with our IP address above, “192.168” becomes the net address, and 1.3 – the host address. To break it down even further, 1 is the subnet address, and 3 – the host address, which is different for each computer in the network. Subnet masks can be used by IT specialists to determine if two IP addresses are in the same subnet. Doing this requires converting all the numbers into binary form, so we won’t get concerned with that right now.

Simple things you should know about, when setting up a network

So, now we know what a subnet mask is. What subnet mask should we use when setting up our network? If you are building a small home network with only several computers, you can use the most commonly used format – 192.168.1.x for the IP addresses, where x is different for each computer, and for the subnet mask. It is important that every computer in the network has the same subnet mask, or the computers won’t be able to connect on the network.