IPv4 addresses consist of 32 bits, which are divided into four sections of 8 bits, each called an octet. Addresses are typically represented in dotted-decimal notation. For example
Subnet masks identify which portion of the address identifies a particular network and which portion identifies a host on the network.
The address classes defined for IP networks consist of the following subnet masks:
Class A 255.0.0.0 (8 bits)
Class B 255.255.0.0 (16 bits)
Class C 255.255.255.0 (24 bits)
Class A addresses begin with 0 and have a first octet in decimal of 1 to 127. Class B addresses begin with 10 and range from 128 to 191. Class C addresses begin with 110 and range from 192 to 223.
Class D and ...