IP Address Classification

Each IP address has two parts: Network ID part and Host ID part. The first octet part(s) or the high-order bits, represents Network ID of the IP address. Network ID part of any network remains same for all the hosts of that particular network.

The remaining octets act as host IDs of the IP address. The IP Address classes are
categorized based on the decimal number in the first octet that is based on the Network ID part.

IP address class can be classified into five categories. You may read, Types of IP Addresses for all the classification of IP address.

For learning subnets, generally Class A, Class B and Class C are required. So, based on these classes, the Address Class Summary table is presented below:

Class	Number of Subnets	Number of Hosts Per Subnet	Range of Network IDs (First Octet)
Class A	126	16,777,214	1 – 126
Class B	16,384	65,534	128 – 191
Class C	2,097,152	254	192 – 223

Each class of IP address is classified by the most significant bits. In the following table a IP class wise description of most significant bits are presented:

Class	Most Significant Bits	Binary Start	Binary End
Class A	1	00000001	01111111
Class B	10	10000000	10111111
Class C	110	11000000	11011111
Class D	1110	11100000	11101111
Class E	11110	11110000	11110111

Furthermore, if you like to classify based on the decimal value, the the classes can be classified in the following categories:

Class	First Octet
Class A	1-126
Class B	127-191
Class C	192-239
Class D	240-247
Class E	248-255