CIDR Notation (/24, /16, /8) Explained Like You're 5

Kids using computer

2025-10-14

Imagine you have a big box of colored pencils, but you want to share them with friends in smaller groups. CIDR notation helps you split that big box of pencils, or in networks, large groups of IP addresses, into smaller, easy-to-manage groups. 

So, let’s explore CIDR notation in a fun and simple way.

What Does CIDR Mean?

First of all, CIDR stands for Classless Inter-Domain Routing. That’s a big phrase, but it simply means cutting up the big pool of IP addresses into smaller parts without worrying about old categories. Instead of big chunks, CIDR lets you be flexible, like cutting handfuls of pencils instead of only big boxes.

What Are Those Numbers After the Slash?

You often see IP addresses written like this: 192.168.1.0/24, 10.0.0.0/8, or 172.16.0.0/16. The number after the slash (/) shows how many bits are dedicated to the network part of the IP address. Bits are like tiny switches inside computers that can be ON (1) or OFF (0).

To put it simply, think of the bits like LEGO bricks. The number after the slash tells you how many bricks you use to build the base (network part) of your castle (IP address). The rest of the bricks are for decorating (host part).

Breaking Down /8, /16, and /24

  • For starters, /8 means the first 8 bits build the network part. This is a huge network, like having one big box of pencils to share with many friends. It corresponds to an old style called Class A and can hold about 16 million devices.
  • Next, /16 means 16 bits for the network part. This splits the big box into smaller boxes, making it easier to handle. This is similar to Class B, which can hold about 65,000 devices.
  • Finally, /24 means 24 bits for the network part. This is an even smaller block, like giving each friend a small pencil case. It matches Class C and holds up to 254 devices.

Why Do We Use CIDR?

Moreover, CIDR helps network owners avoid wasting IP addresses. Instead of giving every group a huge box, they give just the right-sized box. Thanks to CIDR, the internet doesn’t run out of IP addresses quickly, making it efficient and organized.

Visualizing CIDR with a Simple Drawing

Imagine, for example, a street with many houses. The network part tells you the street name. The host part tells you the house number. Printing “123 Maple Street /24” means the network is Maple Street, and the houses (hosts) are numbered individually.

With /24, the network part covers most of the IP address, so you have fewer houses but many streets. Whereas with /8, you have a big street with many houses.

How Does This Affect You?

When your home or company network is created, CIDR notation helps decide how many devices can connect. If you get a /24 IP range, that means you can have around 254 devices connected, which is perfect for most small businesses.

The Magic Number: 32 Bits in Total

Remember, each IP address has 32 bits. CIDR notation tells how many bits form the network. The leftover bits identify the hosts. For example:

  • /8 uses 8 bits for network, 24 bits for hosts.
  • /16 uses 16 bits for network, 16 bits for hosts.
  • /24 uses 24 bits for network, 8 bits for hosts.

In essence, the more bits for the network, the fewer hosts you can have, and vice versa.

Conclusion

To sum up, CIDR notation is like a map legend for the internet. It tells computers how to split a massive neighborhood of IP addresses into usable blocks. Even if it sounds technical, thinking of it as sharing pencils or houses on a street makes it easy to understand.

Once you know that /8, /16, and /24 simply show how big or small your network is, understanding CIDR becomes child's play. So, try to remember: the number after the slash counts your network bits, helping you organize your digital space better.

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