ipcalc

ipcalc is a super handy tool that takes an IP address and netmask to calculate things like the broadcast address, network info, Cisco wildcard mask, and host range. Pretty cool, right?

Subnetting Made Easy

If you want to get into subnetting or supernetting, just throw in a second netmask! It’s designed not just for use but also as a teaching tool. You’ll see subnetting results displayed in easy-to-understand binary values.

How to Use ipcalc

To get started, you can enter your netmask(s) in CIDR notation (like /25) or in good old dotted decimals (like 255.255.255.0). And guess what? Inverse netmasks work too! If you forget to add a netmask, don’t sweat it; ipcalc will use the default one based on your network class.

Understanding Your Network Address

Take a look at the bits in your addresses: The ones before the space are for the network part, while those after are for the host part. Here’s a quick fact: In any network address, all host bits are zero; in a broadcast address, they’re all set!

Your Network Class

The class of your network is determined by its first bits. If you're working with a private internet as per RFC 1918, ipcalc will let you know that too! When you check out subnets, you'll notice that new bits in the network part of the netmask are shown in a different color.

Cisco Wildcard Masks

The wildcard is just the inverse netmask used mainly for access control lists in Cisco routers—very useful!

Get Creative with Subnets!

If splitting your network into subnets sounds fun (and it can be), simply enter your original network's address and netmask. Then play around with another netmask until it fits what you need.

Use It Right from Your Shell!

You can enjoy all this straight from your shell prompt! Though originally ipcalc wasn’t meant for creating HTML pages, it works just fine in /usr/local/bin/.