Examples

Problem-01:

Given the CIDR representation 20.10.30.35 / 27. Find the range of IP Addresses in the CIDR block.

Solution-

Given CIDR representation is 20.10.30.35 / 27.

It suggests-

• 27 bits are used for the identification of network.

• Remaining 5 bits are used for the identification of hosts in the network.

Given CIDR IP Address may be represented as-

00010100.00001010.00011110.00100011 / 27

So,

• First IP Address = 00010100.00001010.00011110.00100000 = 20.10.30.32

• Last IP Address = 00010100.00001010.00011110.00111111 = 20.10.30.63

Thus, Range of IP Addresses = [ 20.10.30.32 , 20.10.30.63]

Problem-02:

Given the CIDR representation 100.1.2.35 / 20. Find the range of IP Addresses in the CIDR block.

Solution-

Given CIDR representation is 100.1.2.35 / 20.

It suggests-

• 20 bits are used for the identification of network.

• Remaining 12 bits are used for the identification of hosts in the network.

Given CIDR IP Address may be represented as-

01100100.00000001.00000010.00100011 / 20

So,

• First IP Address = 01100100.00000001.00000000.00000000 = 100.1.0.0

• Last IP Address = 01100100.00000001.00001111.11111111 = 100.1.15.255

Thus, Range of IP Addresses = [ 100.1.0.0 , 100.1.15.255]

Problem-03:

Consider a block of IP Addresses ranging from 100.1.2.32 to 100.1.2.47.

1. Is it a CIDR block?

2. If yes, give the CIDR representation.

Solution-

For any given block to be a CIDR block, 3 rules must be satisfied-

Rule-01:

• According to Rule-01, all the IP Addresses must be contiguous.

• Clearly, all the given IP Addresses are contiguous.

• So, Rule-01 is satisfied.

Rule-02:

• According to Rule-02, size of the block must be presentable as 2n.

• Number of IP Addresses in the given block = 47 – 32 + 1 = 16.

• Size of the block = 16 which can be represented as 24.

• So, Rule-02 is satisfied.

Rule-03:

• According to Rule-03, first IP Address must be divisible by size of the block.

• So, 100.1.2.32 must be divisible by 24.

• 100.1.2.32 = 100.1.2.00100000 is divisible by 24 since its 4 least significant bits are zero.

• So, Rule-03 is satisfied.

Since all the rules are satisfied, therefore given block is a CIDR block.