IPv4 Subnetting CLI

Note: This project is available on GitHub.

Why I built this

I'm studying for the CCNA, and Subnetting is a HUGE part of the exam. Knowing how to figure out network boundaries, valid host ranges, and broadcast/network addresses is essential if you want to pass. With this project, I put the formulas for those calculations into code so that I can run this script anytime to double check my work. It's also a proof-of-concept for my ability to write Python scripts and my understanding of subnetting math.

What I built

I developed a command-line utility in Python that displays the network topology details for a given IPv4 address and CIDR notation. The script returns:

• Detected IP Class (A-E or classless)
• The Subnet Mask in dotted decimal format (e.g., 255.255.255.192).
• The Network Address and Broadcast Address.
• The usable IP range for hosts, and total number of available hosts.
• The number of available subnets given the class.

It acts as a lightweight, fast capacity planning tool that can be run from any terminal, which is exactly the kind of automation script a systems administrator would use on a daily basis.

How I did it

The easy way to build this in Python would be to just import the built-in ipaddress module, which does all the heavy lifting automatically. However, since the goal was to learn, I intentionally chose not to use it. Instead, I built the logic from scratch using bitwise operations. At a high level, it's similar to how I do the math by hand.

The source code is available on GitHub.

What I learned

This project solidified my understanding of IPv4 architecture. Using bitwise logic to calculate the network and broadcast addresses helped me understand how subnet masks actually work at a low-level.