Let’s See CIDR In Networking:

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CIDR Full Form - GeeksforGeeks

Hello Readers… I hope you all are doing well. In this blog we are going to learn interesting topic of networking i.e CIDR. So stay tuned.


First of all CIDR stands for Classless Inter-Domain Routing (CIDR), commonly known as CIDR diagram, is used by users who operate networks and manage IP addresses. This allows you to see the number of IP addresses in each “slash notation” and the bitwise size of each “slash notation”.

Classless Inter-Domain Routing (CIDR) is a group of IP addresses that are assigned to a customer when they need a fixed number of IP addresses.

CIDR, customers are assigned only as many IP addresses as requested by them, so they don’t waste IP addresses compared to traditional addressing.

Properties of CIDR Block:

The following CIDR block are:

  • The IP addresses in a block are continuous.
  • The first address of a block should be exactly divisible by the number of addresses of a block.
  • The size of the Block should be power of 2.

Let’s take a example:

Like assume you need a ip for a minimum hosts of 300 underclass full addressing you will be given class B which will accommodate is total of more than 64 thousands hosts.

Hence CIDR came into play to resolve this issue:

  • here we divided into block.
  • No classes.
  • only block.
  • Notation x.y.z.w/n here n will represent mask number of bit represent block.

So; the best example let us take:


so; once you see 200, which class doesn’t belongs to, class is c, but basically normal class is class c but here; there are no classes. It is class less.

and also here 28 is represent 28 blocks, i,e id is 28.

And left one is host id i.e directly 32 – 28 = 4

so; host id is 4.

Therefore; no. of host = = 16

Here a one question is come; how does the mask represent???

The mask is nothing i.e 28. Mask will also be represent by 28. let’s we expand it;

11111111.11111111.11111111.11110000 =

NOW; 1000 = starting 11 number will represent the 32 bit and the last four digit is 0000

so; here we get a simply new id i.e

So; this is a CIDR working.

Advantages of CIDR:

  • CIDR provides efficient address space allocation. H. With CIDR, addresses are assigned in multiples of any binary size.
  • It eliminates class imbalances. H.
  • This allows for efficient routing entries. H. Many networks can be represented by a small number of routing entries.
  • No separate subnetting method is required.
  • It implements the concept of subnetting on the Internet itself, aggregating network descriptions into a single entry.

Disadvantages of CIDR:

Route determination using CIDR is complicated. There are separate tables in Class A, Class B, and Class C by using per-class addresses.


This is a concept of CIDR in networking.If you work on networking you should know this concept. Hope this blog will help you out.

Happy Learning.

Written by 

Mayuri Dhote is a Software Consultant at Knoldus Software. She has completed her MCA from VIT University. She has very dedicated towards her work. She has always ready to learn new things. Her practice area is Devops. When not working, you will find her writing poems and poetry.

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