The IP in TCP/IP stands for Internet Protocol, and works in the network layer. IPs are probably known to most people online, but most dont know they can be put into three different classes – Class A, Class B and Class C.

All IPs are divided into 4 octets, and depending on the value of the first octets – you can determine what class an IP belongs to. Besides the difference in value, there is a practical difference between the classes. Whilst class A can have few networks and many nodes (clients), class C kan have a lot of networks and few nodes. Now I want to look at how different IPs are classified by looking at their values:

30.30.30.30 / 255.0.0.0 = This is a class A network. We can tell by looking at the octets, which will be: 00010010.00010010.00010010.00010010. All IPs that start with a 0 will be a class A network.

129.100.45.2 / 255.255.0.0 = This is a class B network. The octets are: 10000001.01100100.00101101.00000010. As you can see the first octet starts with 1 and the next with 0. That makes it a class B network.

199.20.120.37 / 255.255.255.0 = Now, here you might think that this is also class B. But it is not the second octet that determines the next “1/0” to determine if this is a class B or C network. It is in fact a class C network because when looking at the first octet, it is 199. Now, as a general rule you can divide the three classes into three value ranges (A = 0 – 127, B = 128 – 191, C = 192 – 223). Also you can look at the subnet mask, 255 is network – whilst 0 is for nodes. Class C has 3 networks (255.255.255) and one for nodes (0).

201.100.55.1 / 255.255.255.0 = This is also a class C IP address for the same reason as above.

167.100.30.66 / 255.255.255.0 = Seeing that the first octet is 10100111, and 167 is in the range of class B – this is of course a class B network. Note that the subnet mask is the same as in a class C network, which indicates that there is a limited amount of node addresses.