IPv4 addresses

IPv4 addresses consist of 32 bits. These 32 bits are divided into four sections of 8 bits, each called an octet. Addresses are typically represented in dotted-decimal notation. For example: 10.200.34.201
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 public and private 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 Class E addresses also are defined. The Class D address space has the first 4 bits set to 1110 and has a first octet of 224 to 247.These addresses are used for IP multicast.

Class E addresses have the first 4 bits set to 1111 and have a first octet of 248 to 255. These addresses are reserved for experimental use.