What Is CIDR? And Its Importance in the Networking Domain

With the increase in networking devices, either for professional or personal use, they need access to the internet to perform to the best of their capabilities. 

The process of having an IP address assigned and then being routed through the network model to connect to the internet is performed by Classless Inter-domain Routing (CIDR). 

In this article on ‘What Is CIDR?’, we will look into various aspects of the network topic. 

Cybersecurity Expert Master's Program

Master the Skills of a Cybersecurity ProfessionalView Course
Cybersecurity Expert Master's Program

What Is CIDR?

The CIDR or Classless Inter-Domain Routing is a network concept designed to oversee the assignment of IP addresses to a system to replace the outdated way of a classful addressing system.

This addressing scheme was introduced in the year 1993 by the Internet Engineering Task Force (IETF) to prevent the wastage of IPv4 addresses and to prevent the complexity of routing tables.

Now let’s look into some properties of the CIDR addressing.

Attributes of CIDR Addressing

The addressing of CIDR requires some rules to be assigned:

  1. The IP addresses in a CIDR block are to be continuous, as the ISP will provide them in a sequence of numbers, to minimize the wastage of IP addresses.
  2. The size of the CIDR Block should be of power 2, and to identify the number of addresses assigned, check the subnet mask of the IP address.

Let’s move on to the next part, the working idea of CIDR, in the article ‘What Is CIDR?’.

Working of CIDR

The CIDR uses variable-length subnet masking (VSLM) as the basis of its working, i.e., it acts as a numerical masking sequence that breaks conventional IP addresses into smaller subnets of varying sizes.


Parts of the CIDR IP addresses are mentioned as follows:

Network prefix - This part refers to the binary configuration of the IP network address.

Suffix - This part indicates the number of bits assigned to each CIDR address.

E.g.,, In this IP address,  corresponds to the network prefix.

         /12 refers to the Suffix.

FREE Course: Introduction to Cyber Security

Learn and master the basics of cybersecurityStart Learning
FREE Course: Introduction to Cyber Security

CIDR Notation

By applying the addressing method discussed in the previous section, ‘Working of CIDR,’ the addressing of an IP address for a host is done without using the standard id classes like Class A, B, and C.


In this CIDR method, we can directly assign and count the number of bits in the network id. For example, in this IP address,, bits after the ‘/’ symbol are used by the Network ID, and the host ID uses the remaining, i.e., (32-10) = 22 bits.

Moving on with the article, let’s look at some disadvantages of applying CIDR.

Disadvantages of CIDR

Applying CIDR addressing provides the network with many advantages, but the disadvantages that arise due to CIDR are as follows:

  1. To minimize the involvement of the routing table in the network, it becomes difficult to determine the route for the network data.
  2. It increases the complexity of the network address, which is one of the benefits of classful addressing.
Gain experience via a remote internship opportunity and obtain an internship certificate by choosing our unique Advanced Executive Program in Cybersecurity. Grab your seat now and enhance your resume in just 6 months. Contact our team today!


In this article on ‘What Is CIDR?’, we looked into some brief explanations about the CIDR, along with information on its properties and working idea, in the network model and its effect on assigning an IP address.

If you want to gain more insights and information about the topic and its various counterparts, you can refer to Simplilearn’s Cyber Security Expert course. After completing this professional course, you will become well versed in working with network security and network-related topics.

If you have any questions about this article on ‘What Is CIDR?’. Feel free to mention them in the comment section at the bottom of this page. Our expert team will help you solve your queries at the earliest.

About the Author

Anmol KapoorAnmol Kapoor

Anmol is a Research Analyst who aims to become a Data Scientist one day. He enjoys Data Management systems and analysis. You will find him reading a book when he is not working.

View More
  • Disclaimer
  • PMP, PMI, PMBOK, CAPM, PgMP, PfMP, ACP, PBA, RMP, SP, and OPM3 are registered marks of the Project Management Institute, Inc.
  • *According to Simplilearn survey conducted and subject to terms & conditions with Ernst & Young LLP (EY) as Process Advisors