Notation by Class

Octets and Dotted-decimal Notation

The figure below shows how the 32 bits of an IP address are broken down into four octets of eight bits each. Network ID can be called as the Wire ID.

Classifying IP Addresses

Class A addresses
Class A addresses are designed for very large networks. In a Class A address, the first octet of the address is the network ID, and the remaining three octets are the host ID. Each Class A network can accommodate more than 16 million hosts.

Class B addresses
In a Class B address, the first two octets of the IP address are used as the network ID, and the second two octets are used as the host ID. Each Class B address can accommodate more than 65,000 hosts.

Class C addresses
In a Class C address, the first three octets are used for the network ID, and the fourth octet is used for the host ID. With only eight bits for the host ID, each Class C network can accommodate only 254 hosts.