Today article is very theoretical, dedicated to those who have not yet had contact with configuring your network, or those who have forgotten theoretical details. So’ let’s see what kinds of IP addresses we have and what are the differences between them. More of you have 192.168.x.x IP address in home network, but if you check your IP network from outside, then it will be different. Why? For a moment everything will be clear and understandable.

IP address – What is it?

IP address is an ID of computer in the network. Thanks to this others devices know where to send the data. Computers do not communicate like humans, they do not understand: open website. Computers speak in binary language using zeroes and ones. DNS servers translate names understood by us on binary addresses (IP addresses). Is IP address binary? Yes, it is. IP address is a 32 bits sequence. Let us analyze an example address: 

In binary system it looks like this:

W systemie dwójkowym będzie on wyglądał następująco (każdy oktet, czyli część adresu musimy zamienić na liczą dwójkową). Jeżeli macie z tym problem, w sieci jest wiele kalkulatorów, które to robią.

11000000 | 10101000 | 00000001 | 00000001

How does it work? We convert each octet (8 bits) to the decimal number. If you do not know how to do this, you will find in the network a lot of “calculators”.



IP address classes

Now, we will discuss what IP address classes are. It is very simple topic, you have to only remember couple things. Classes were introduced in order to allow the use of networks with different dimensions. We do not a large number of computers in our home networks (even 20 is a small number). However, in case of the world wide network it looks totally different.


A class

You have to remember that in case of this class the fist bit is always equal 0. Therefore, the first octet is from range 1 – 127. You can calculate it easily 🙂 We have 16 millions hosts in this class. However, this class is used also as loop-back (i.e. localhost address). Therefore we can not use addresses like or in any network.

B class

In this class two firsts bits are equal 10. Therefore the fist octet is from range 128 – 191. This class is used in the world wide network.

C class

This is the most liked class in the world. Why? Because it is the most often used. Class C is used for local network, firsts bits are equal 110. Therefore, the first octet is from range 192 – 223.

D class

This class is dedicated for multi-casting, i.e. sending the information to the group of recipients. Firsts bits are equal 1110, so the first octet is from range 224 – 239.

E class

These addresses are reserved by IETF for experimental purposes. The first octet is from range 240 – 255.

Network and broadcast addresses

So, we know how to identify the network. However some of addresses are reserved for specific purposes, i.e. network address (used for identification of network) and broadcast address (used for sending packets to all hosts in the same network).


Private addresses

It is very useful to know which networks are private. Here are addresses reserved for local networks:

  • – – for private networks in A class
  • – – for private networks in B class
  • – – for private networks in C class

If we want to connect our computer to the Internet, we have to translate our private addresses to the public address. This operation is called NAT and is performed by our router.