The Internet Protocol (IP) uses a 32-bit, two-part address field.
The 32 bits are divided into four octets as in the following:
01111101 00001101 01001001 00001111
These binary numbers translate into:
125 13 73
The two parts of an Internet address are the network address portion and the host address portion. This allows a remote host to specify both the remote network and the host on the remote network when sending information. By convention, a host number of 0 is used to refer to the network itself.
TCP/IP supports three classes of Internet addresses: Class A, Class B, and Class C. The different classes of Internet addresses are designated by how the 32 bits of the address are allocated. The particular address class a network is assigned depends on the size of the network.