Network Security Tools
Jul 10, 2026
Jul 31, 2026
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2 min read
Every network professional has done it: pulled up a notepad, sketched out binary, and manually worked through a subnet mask to figure out where one network ends and another begins. It's a foundational skill — and also exactly the kind of repetitive, detail-sensitive task that's worth automating.
That's why we built the OpenVPN Subnet Calculator: a free, no-sign-up tool that takes an IP address and a CIDR prefix or subnet mask, and instantly returns everything you need to design, document, or troubleshoot a network.
What it calculates
Enter any IPv4 or IPv6 address along with its CIDR prefix (like /24) or subnet mask (like 255.255.255.0), and the calculator returns:
- Network address — the base address identifying the subnet itself.
- Broadcast address — the address used to reach every host on the subnet.
- Usable host range — the first and last assignable addresses.
- Wildcard mask — the inverse of the subnet mask, useful for ACLs and routing configs.
It works the same way whether you're planning a home lab VLAN or documenting enterprise network segmentation for a compliance audit.
A cheat sheet built in
Below the calculator, you'll find a CIDR-to-subnet-mask cheat sheet: the handful of prefixes most people reach for day to day, plus the complete /0 through /32 table for the times you need something less common. It's designed to be the tab you keep open instead of the one you have to re-Google every few months.
Understand the numbers, not just the output
A calculator that only spits out an answer doesn't help you learn the material — or catch a mistake when something looks off. That's why the page includes plain-language explanations of what each result actually means: what a subnet is, how a subnet mask works, and how CIDR notation compresses all of it into a single, readable number. Useful whether you're new to networking, studying for a certification, or just want a quick refresher before a design review.
Who it's for
This tool is built for anyone who touches IP addressing: network administrators and engineers doing it daily; security professionals segmenting networks for zero-trust or compliance reasons; IT managers who need a fast, reliable reference; and students or certification candidates building foundational skills.
Try it now
The OpenVPN Subnet Calculator is free, requires no account, and is available whenever you need it. Plus, it's far more reliable than doing it by hand or asking an AI bot that might hallucinate.
