Classless Inter-Domain Routing _CIDR, as the name suggests is a flexible system of creating and organising IP addresses in a way that makes it easier for devices such as your phones laptops, TV etc to connect and communicate without running out of space as opposed to the classful IP addressing system which was rigid with a predefined range and subnet mask and led to issues such as IP address exhaustion .
To simplify, an IP address is like a digital home address for your devices on the internet. Just like your house has an address so people can find it, every device connected to the internet—whether it’s a computer, smartphone, or smart TV—gets a unique IP address. This helps other devices know exactly where to send information.

Why Was CIDR Created?

Originally, the internet had a system where IP addresses were organised into a few set sizes, called "classes" (A, B, and C). This rigid system was simple, but it wasted a lot of address space. Imagine a company needing only 100 addresses but being assigned thousands—it’s like giving a small business a huge warehouse when they only need a small office. CIDR was introduced in the early 1990s to solve this, allowing us to allocate only the number of addresses we actually need, saving space and making it easier to manage networks

How CIDR Works

Instead of having fixed classes, CIDR lets us create custom-sized address groups. Here’s how it works:

1. Flexible Group Sizes: CIDR lets us create groups (or “blocks”) of IP addresses that fit our actual needs. It’s like choosing the exact number of addresses a business needs instead of giving them a “standard size.”

2. Easy Notation: CIDR uses a format called "CIDR notation," which looks like this: 192.168.1.0/24. The first part (192.168.1.0) is the starting address, and the second part (/24) tells us how many addresses are included. This makes it clear, even at a glance, how big each group of addresses is.

3. Combining Addresses for Simplicity: CIDR can group multiple addresses under a single "route," meaning it tells the internet, “all these addresses belong together.” This makes it faster and more efficient for routers to know where to send data.

Benefits of CIDR

1. Saves IP Addresses: CIDR allows us to use just the number of IP addresses we need, instead of taking more than necessary. This helps make sure we don’t run out of IP addresses.

2. Makes Networks Faster and Simpler to Manage: CIDR combines addresses into groups, so routers (which send data across the internet) have fewer addresses to track. This speeds things up and makes routing more efficient.

3. Easier to Expand Networks: CIDR makes it easy for big networks, like those of internet providers, to grow without running out of space for new addresses.

4. Custom-Sized Networks: CIDR lets networks be set up in different sizes, so companies can give smaller groups of addresses to small teams and larger groups to big departments. This makes sure IP addresses are used in the best way possible

Everyday Examples

Internet Service Providers (ISPs): When an ISP sets up internet for homes and businesses, CIDR helps them give each customer the exact number of IP addresses they need.

Corporate Networks: CIDR allows companies to organize their addresses for different departments or locations, making it easier to control and secure their networks.

Network Security: CIDR is also useful in setting up security rules. For example, a company could allow access to certain parts of its network only from specific address blocks.

Conclusion

CIDR is a flexible, efficient way of organizing internet addresses, ensuring we use only what we need. It keeps the internet organized, prevents waste, and makes it easier for data to move quickly and accurately. As our world becomes more connected, CIDR continues to be a fundamental part of managing and growing our global network.