CIDR Subnetting
Software Engineer path · lesson 67 of 99An interactive calculator that demonstrates how Classless Inter-Domain Routing breaks IP spaces into subnets.
Biggest block first
Order these CIDR blocks from the most addresses to the fewest.
Tap a piece, then tap where it goes — or drag it. Tap the tray to take one back.
- 1Drop a step here
- 2Drop a step here
- 3Drop a step here
- 4Drop a step here
- 5Drop a step here
Test your knowledge
If you have a /24 network and you divide it into two equal /25 subnets, how many total USABLE host IPs do you have across both subnets?
The short version
CIDR is like cutting a cake. A /24 network is a whole cake (256 slices). If you want to serve two different parties in separate rooms, you cut it in half (/25), giving each room 128 slices. The larger the slash number, the smaller the slice of cake.
In more depth
CIDR (Classless Inter-Domain Routing)
CIDR is a method for allocating IP addresses and IP routing. It replaced the old Class A/B/C system.
How it Works
An IPv4 address has 32 bits. The number after the slash indicates how many bits are fixed for the "Network" portion. The remaining bits are used for "Hosts" (devices).
As the CIDR number increases, the number of available IPs decreases by half.
Interview Questions
References & Further Reading
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