8 Steps to Understanding IP Subnetting

Step 3 - IP Addresses

The "IP" in IP addresses refers to the Internet Protocol, where protocol is loosely defined as "rules of communication". Imagine using a two-way radio in a police car. Your conversations would probably end with "over" to indicate you are finishing a particular part of the conversation. You might also say "over and out" when you are finished the conversation itself. These are nothing more than the rules of talking over a two-way radio - or the protocol.

So, IP addressing must be understood as part of the rules for conversations over the Internet. But it has grown so popular that it is also used on most any network connected to the Internet, making it safe to say IP addressing is relevant for most networks as well as the Internet.

So what is an IP address? Technically, it is the means whereby an entity on a network can be addressed. It is made up solely of numbers, and these numbers are conventionally written in the particular form of XXX.XXX.XXX.XXX, which is referred to as dotted decimal format.

Any one of the numbers between the dots can be between 0 and 255, so example IP addresses include:


These numbers can also be written in binary form by taking each of the decimal values separated by dots and converting to binary. So a number like could be written as:


Each of these binary components is referred to as an octet, but this term is not often used in subnetting practice. It does seem to come up in classrooms and books, so know what it is (and then forget about it).

Why is each number limited to 0 to 255? Well, IP addresses are limited to 32 bits in length and the maximum number of combinations of binary numbers you could have in an octet is 256 (mathematically calculated as 28). Hence, the largest IP address you could have would be, given that any one octet could be from 0 to 255.

There is one more aspect of an IP address that is important to understand - the concept of a class.

Each IP address belongs to a class of IP addresses depending on the number in the first octet. These classes are:

Notice that the number 127 is not included. That’s because it is used in a special, self reflecting number called a loopback address. Think of this as an address that says, “this is my address.” Note that only the first three classes - A, B and C - are used by network administrators. These are the commonly used classes. The other two, D and E, are reserved.

You define the class of an IP address by looking at its first octet value, but the structure of an IP address for any one class is different. Each IP address has a network address and a host address. The network part of the address is the common address for any one network, while the host address part is for each individual device on that network. So, if your phone number is 711-612-1234, the area code (711) would be the common, or network, component of the telephone system, while your individual phone number of (612-1234) would be your host address.

The network and host components of class IP addresses are:

The technical numbers behind class addressing are as follows:

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Written by Dale Janssen
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Dale Janssen is a co-founder of Techopedia and has been involved in the IT Industry for most of his career. He purchased his first computer in 1978 - an Ohio Scientific computer with a whopping memory size of 48K, operating a relic of an operating system called CPM. In fact, his roots go so far back in the computing biz that when he graduated from university, there was no such thing as a computer science department.