Logical and Classful Addressing


Computer Networks

It is a collection of autonomous computers for transferring the data through communication links.


  • Communication is done with logical address
  • Logical Address are also known as IP Address
  • IP Addresses have range (0 – 255) where 0 is minimum and 255 is maximum
IP Address Types

IP Addressing is done by 3 methods

  1. Classful Addressing
  2. Subnetting
  3. Supernetting


It divides IP Addresses into 5 classes ie. A, B, C, D and E

It has 2 parts:

  1. Net Id
  2. Hosts

It supports 2-level of hierarchy

Classful Addressing Hierarchy Level

It supports 2 notations for IP addresses

  1. Binary (Consists of 0’s & 1’s)
    • Example 10010011 11111111 00000000 11111111
  2. Dotted Decimal
    • Example

Unicasting, in this one system transfers the data to another system

  • Unicasting supported by class A, B and C


In this one system sends or transfers the single same data to many systems simultaneously like group mails

It supported by Class D

Class E is for research and for future use.

Classful Addressing

Class A

It is identified by 1st bit of net id

ie) If 1st bit of net id is 0, then those IP Address belongs to Class A

Class A

IP address range is (0 – 127)

ie) Min Value -> 00000000 = 0 ( -> DHCP Client)

Max Value ->01111111 = 127 ie (Loop Back)

But class A does not use 0 and 127 because these are special IP Address. So class A have IP Address in range (1-126)

In class A, number of possible networks are (2 7 -2) ie 126

and it has (2 24 – 2) host for each network

Class B

It is identified by 2nd and 1st bit of net id. id) Net Id must start by 10(first 2 bits)

Class B

Range of class B is (128 – 191)

ie) Min Value -> 10000000 (128)

Max Value -> 10111111 (191)

No of possible networks are 214 -2 and it has 216-2 hosts for each network

Class C

It is identified by 3 bits. If starting 3 bits of net id in binary notation is 110 then IP belongs to Class C

Class C

Range of class C is (192 – 223)

ie) Min Value -> 11000000 (192)

Max Value -> 11011111 (223)

Number of possible networks are 221 and host are 28-2 for each network

Class D

It is identified by starting 4 bits 1110

Range of class D is (224 – 239)

Min Value -> 1110 0000 (224)

Max Value -> 1110 1111 (239)

Class E

It is identified by 1111 (4) bits of starting net id

Range of class E is (240 -255)

ie Min Value -> 11110000 (240)

Max Value -> 11111111 (255)

We can divide 32 bits into net id and host id for class A, B, C but can’t divide bits for class D and class E into host id and net id because of multicasting

But we can identify class E and class D by IP Address

  • Class C -> have minimum number of host for each network
  • Class A -> have maximum number of host for each network

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