Classes of IP Addresses

There are following five classes of IP Addresses:

Class A – It is used for allocating an IP address.
Class B - It is used for allocating an IP address.
Class C – It is used for allocating an IP address.
Class D – It is used for multicasting.
Class E – It is reserved for experimental use.

Class A Network Addresses

In Class A network address, the one byte (8-bits) is assigned to the network address, and the remaining three bytes are used for host addresses.

The class A address format is as follows:

Network.Host.Host.Host

0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHH

Where –

0 = Leading bit.

It is fixed and used to identify class A network.

N = Network Address

H = Host Address

Class A network address range:

00000000 = 0

01111111 = 127

Total number of addresses in class A is 2³¹
Class A address has 1 byte (8-bits) for the network address, where 0 is fixed by default, and remaining 7 bits are used to represent network address.

Therefore, some unique network addresses in class A are 2⁷ = 128.

Class A address has 3 bytes (24-bits) for the host address.

Therefore, the number of unique Host addresses in class A 2²⁴ = = (16777216).

Number of valid Networks addresses in class A = 2⁷-2

= 128-2

= 126

Range of valid network addresses in class A are1.0.0.1 to 126.255.255.254.

Number of valid Host addresses in class A = 2²⁴-2

= 16777216-2

= 16777214

Range of valid host addresses in class A are 10.0.0.1 to 10.255.255.254.

Note: We have subtracted 2 because the first byte of network address (all 0s) is reserved for the default route, and last byte address (all 1s) is reserved for loopback and broadcast address. We cannot assign the first and last address to any user.

Class B Network Addresses

In Class B network address, the first 2 bytes (16-bits) are assigned to the network address, and the remaining 2 bytes (16-bits) are assigned to host address.

The class B address format is as follows:

Network.Network.Host.Host

10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH

Where –

10 = Leading bit

It is fixed and used to identify the class B network.

N = Network Address

H = Host Address

Class B Address Range:

10000000 = 128

10111111 = 191

Total number of addresses in class B are 2³⁰
Class B address has 2 bytes (16-bits) for the network address, where 10 is fixed by default, and remaining bits used for the network address.

Therefore, the number of unique network addresses in class B are 2¹⁴ = 16,384 .
Class B address has 2 bytes (16-bits) for the host address.

Therefore, the number of unique host addresses in class B are 2¹⁶ = 65,536.

Number of valid Network addresses in class A = 2¹⁴ -2

= 16,384-2

= 16,382

Range of valid network addresses in class B are 128.1.0.1 to 191.255.255.254.

Number of valid Host in class B= 2²⁴ -2

= 65,536-2

= 65,534

Range of valid host addresses in class B are 172.16.0.1 to 172.16.255.254.

Class C Network Addresses

In Class C network address, the first 3 bytes are assigned to the network address, and the remaining 1 byte is used for the host address.

The class C address format is as follows:

Network.Network.Network.Host

110NNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

Where –

110 = Leading bit

N = Network Address

H = Host Address

Class C Address Range

11000000 = 192

11011111 = 223

Total number of addresses in class C is 2²⁹
Class A address has 3 bytes (24-bits) for the network address, where 110 is fixed by default, and remaining bits used for the network address.

Therefore, the number of unique network addresses in class C is 2²¹ = 2,097,152.

Class C address has 1 byte (8-bits) for the host address.

Therefore, the number of unique host addresses in class C is

2⁸= 256

Number of valid Networks in class C= 2²¹ -2

= 16,384-2

= 16,382

Range of valid network addresses in class C are 192.0.1.1 to 223.255.254.254

Number of valid Host addresses in class C= 2⁸-2

= 256-2

= 254

Range of valid host addressesin class C are 192.168.100.1 to 192.168.100.254

Class D Network Addresses

Class D network address begins with binary 1110, which is fixed for identifying the Class D network.
The range of Class D network is 224 to 239.
Class D address is used for multicast addresses.

Class E Network Address

Class E network address begins with binary 1111, which is fixed for identifying the Class E network.
The range of class E network is 240 to 255.
Class E network addresses are reserved for experimental use.

Reserved IP Addresses:

There are some reserved IP addresses, which are given below:

The network address of all 0s.
The network address of all 1s.
Network 127.0.0.1
Node address of all 0s.
Node address of all 1s.
Entire IP address set to all 0s, i.e. 0.0.0.0.
Entire IP address set to all 1s, i.e., 255.255.255.255.

We can summarize all the classes of IP addresses in the below table:

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