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Classless Inter-Domain Routing


Classless inter-domain routing (CIDR) is a method for allocating IP addresses and IP routing


It is defined in RFC (Request for comments) 1518 and RFC 4632


It is an address block allocation


CIDR block This block contains IP addresses. This block consists of 3 basic rules.

The 3 basic rules mentioned below:

Rule 1: In the CIDR block, the IP addresses which are allocated to the hosts should be continuous.

Rule 2: The size of the block should be of power 2 and should be equal to the total number of IP addresses.

Rule 3: The size of the block must be divisible by the first IP address of the block.


The general way of representation of the CIDR IP address is

a.b.c.d / n


Example #1

The CIDR representation is Find the IP addresses of the CIDR block?

24 represents the number of bits used for the identification of the network.

The 5 bits are used for the identification of hosts.

The CIDR address is

The first IP address is

The last IP address is

The total cost is 256.

Netmask is


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