IP classes A, B, C, D, E

IP addresse are of different classes:

Class A (1-127):
first octet always starts with 0 and is for the network address and next three octets - for the unique hosts inside the network.

Class B (128-191):
first octet always starts with 10. First and second octets are for the network address and next two octets - for the unique hosts inside the network.

Class C (192-223):
first octet always starts with 110. First three octets are for the network address and the last octet - for the unique hosts inside the network.