Computer Networking

Transport Layer

Examples of Classless IP Addressing

Example: Consider a classless IP address is / 28. Find out the range of IP Addresses in the CIDR block or classless block.


  • 28 bits are used for network identification.
  • Remaining 4 bits are used for host’s identification in the classless

Given CIDR IP Address may be represented as

00010101.00001011.00101000.00100011 / 28


  • First IP Address = 00010100.00001010.00011110.00100000=
  • Last IP Address = 00010100.00001010.00011110.00101111=

Put all Host bits to zero for first IP, and put all host bits to “1” for Last IP of Network.

Note: Direct broadcast IP address of a network is always the last IP of that Network.

Thus, Range of IP Addresses = [ ,]

Now Check all Three rules of CIRD block

  • Rule 01: As all IP’s are contiguous ( to So Rule 1 is satisfied.
  • Rule 02: Range ( to contains 16 IP’s which is the Power of 2. So Rule 2 is satisfied.
  • Rule 03: According to third rule, First IP must be divisible by network size. As the Network Size is 24 and last 4 bits of first IP are Zero. So, it is divisible. Hence, Rule 3 is also satisfied.

As all 3 rules are valid, so, Classless block with 16 IP’s is Valid.


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