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.
Is it a CIDR block?
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.
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