What are the classifications of classful IP addresses?

IP addresses are generally represented by a 32-bit unsigned binary value. It is represented in a dotted decimal format. For example, 9.250.7.5 is a valid IP address.

The IP address consists of a pair of numbers −

IP address = <network number><host number>

Class-based IP addresses

The first bits of the IP address specify how the rest of the address should be separated into its network and host part. This IP address consists of network ID and Host ID.

Classes of IP address

There are 5 classes of IP address in computer network, which are as follows −

• Class A
• Class B
• Class C
• Class D
• Class E

The numbers of IP addresses possible in a network of classes are as follows −

• Class A= 2³¹
• Class B= 2³⁰
• Class C= 2²⁹
• Class D= 2²⁸

The representation of IP address = Binary notation, Dotted decimal notation( 4 octets).

The binary format of the IP address is: 10000000 00000010 00000111 00001001

The dotted decimal format: 192.169.175.8

               {each octet is 8-bit representation total 32 bit representation of IP address}

Generally,

• Class A= start with ‘0’
• Class B= start with ‘10’
• Class C= start with ‘110’
• Class D= start with ‘1110’
• Class E= start with ‘1111’

Now let’s try to understand each class in detail −

Class A

The number of possible networks of class A= 2⁷ =128

Size of each network = 2²⁴ = 16M.

Number of Hosts = (2²⁴ -2)

In Class A, we don’t use the starting address for all 0’s and the last address for all 1’s.

Therefore, practically number of network’s in Class A= 128-2 = 126

Range= 0-126

That is, Class A addresses use 7 bits for the <network> and 24 bits for the <host> portion of the IP address.

This allows for 2⁷ -2 (126), networks each with 2²⁴-2 (16777214) hosts – a total of more than 2 billion addresses.

Class B

The number of IP Addresses= 2³⁰

Number of networks for class B= 2¹⁴ =16K

Size of each network = 2¹⁶

 Number of Hosts= 2¹⁶-2

<------------2³⁰---------------🡪

16 bits                     16 bits

Starts with 10- - - - - - - -
   10 0 0 0 0 0 0 =128
   10 0 0 0 0 0 1 =
    .  
    .
   10 1 1 1 1 1 1 = 191

Therefore, Range= 128-191

That is, the Class B addresses use 14 bits for the <network> and 16 bits for the <host> portion of the IP address. This allows for 2¹⁴-2 (16382) networks each with 2¹⁶-2 (65534) hosts – a total of more than 1 billion addresses.

Class C

Number of IP Addresses= 2²⁹

Number of networks of Class C = 2²¹ networks= 2 million

Size of each network= 2⁸ IP addresses are in one network of Class C.

<------------2²⁹---------------🡪

  21 bits                                        8 bits

Starts with 1 1 0- - - - - - - -
   1 1 0 0 0 0 0 0 =192
   1 1 0 0 0 0 0 1 = 193
   .
   .
   1 1 0 1 1 1 1 1 = 223 => number of Hosts

Therefore, range= 192-223

That is, Class C addresses use 21 bits for the <network> and 8 bits for the <host> portion of the IP address. That allows for 2²¹-2 (2097150) networks each with 2⁸ -2 (254) hosts – total of more than half a billion addresses.

Class D

Class D addresses are reserved for multicasting (a sort of broadcasting, but in a limited area, and only to hosts using the same Class D address). There is nothing Called as network ID and Host ID in Class D.

Class D starts with ‘1110…’
   1 1 1 0 0 0 0 0 =224
   .
   .
   .
   1 1 1 0 1 1 1 1 = 239

Therefore, Range= 224-239

This class is used for Multicasting and group emailing and group based broadcasting.

Class E

These addresses are reserved for future or experimental use.

There is nothing called network ID and Host ID in Class E.

Class E starts with ‘1111…….’
   1 1 1 1 0 0 0 0=240
   .
   .
   .
   1 1 1 1 1 1 1 1 = 255

Therefore, Range= 240-255

It is used for Military applications.