IPv4 (Internet Protocol version 4), is the 4th version of Internet Protocol. We have a large number of addresses in IPv4. In this article, we will discuss various classes defined in IPv4.

History of IPv4

At the beginning of the IPv4 design, the complete address was divided into two parts. The first part was known as Network identifier and the rest of the part was known as a host identifier. But, they were quickly found to be inadequate.

ICANN is responsible for assigning IP Addresses.

In 1981, according to most-significant octet, IPv4 addresses are defined in five different classes. These classes are A, B, C, D, and E.

IPv4 Different Classes

Although, in IPv4 we have 4,294,967,296 unique addresses. But, some of these addresses are not used for communication purpose.  Also, one complete octet from Classes A, B, and C is used for Private IP addresses. Know more about Public and Private IP addresses. Below is the table which categories different address in different network classes.

Now, we will discuss each network class in details.

Class A

The range of the first octet of class A addresses are from 0 to 127. Thus, in the binary system, the first bit of the first octet set to zero. So, in the binary system it will be :

00000001 – 01111111
  1      –    127

But, the addresses from 0.0.0.0 to 0.255.255.255 are not usable in communication. Also, the addresses from 127.0.0.0 to 127.255.255.255 are reserved for loopback purpose. So, the range of usable IP addresses of class A is from 1.0.0.0 to 126.255.255.255.

The default subnet mask of Class A network is 255.0.0.0. So, there will be maximum 16,777,216 hosts which can be connected in a single network. The total number of different networks will be 126. The Binary representation of Networks and Hosts will be :

0NNNNNNN:HHHHHHHH:HHHHHHHH:HHHHHHHH

Class B

The range of the Class B address is from 128.0.0.0 to 191.255.255.255. So, the first two bit of the first octet is always set to 10. The binary representation of the first octet will be:

10000000  – 10111111
  128   –    191

The default subnet mask of class B address is 255.255.0.0. The Binary representation of Class B Networks and Hosts will be :

10NNNNNN:NNNNNNNN:HHHHHHHH:HHHHHHHH

Class C

The range of Class C address is from 192.0.0.0 to 223.255.255.255. So, the first three bit of the first octet is always set to 110. The binary representation of the first octet will be:

11000000  – 11011111
  192   –    223

The default subnet mask of class B address is 255.255.255.0. The Binary representation of Class C Networks and Hosts will be :

110NNNNN:NNNNNNNN:NNNNNNNN:HHHHHHHH

Class D

The range of Class D address is from 224.0.0.0 to 239.255.255.255. So, the first four-bit of the first octet is always set to 1110. The binary representation of the first octet will be:

11100000  – 11101111
  224   –    239

Note: The IP addresses of IPv4 Class D is used for multicasting purpose only. These IP addresses are not directly participating in computer networking. So, class D not have any subnet mask.

Class E

Class E is reserved for Research or study purposes. So, this class does not participate in the computer network. Like class D, this class also does not have any subnet mask. The range of addresses of this class starts from 240.0.0.0 to 255.255.255.0.

Summary

In this article, we discussed various classes of IPv4. We also discussed some different addresses of different IP classes and their range. Subnet Mask is used in Class A, B, and C but not in Class D and E. We also discuss the binary representation of different network classes.