Subnet Calculator for Mac

$ brew install ipcalc
$ ipcalc 192.168.1.0/24

What it’s for

A subnet is a block of addresses, written as an address and a prefix such as 192.168.1.10/24. Subnet Calculator shows everything about the block: where it starts and ends, how many devices fit, its mask in every form, and how to split it.

Use it when

• You’re setting up a router, a VPN or a server and need the right range and mask.
• You want to know whether two addresses are on the same network.
• You’re planning a network and need to divide a block into smaller ones.

Reading the result

Type into the one field. It accepts 192.168.1.10/24, an address and a mask (10.0.0.1 255.255.0.0), a mask as ifconfig prints it (0xffffff00), a whole line pasted from ifconfig or ip addr, and IPv6 prefixes. Results update as you type.

• Network Address is the block’s first address, and Broadcast Address its last.
• First and Last Usable Host are the range devices can use, and Usable Hosts how many fit.
• Netmask, Wildcard Mask and Prefix Length are the same size, written three ways.
• Classification says whether the block is private, public, or reserved for something else.

What you might see

• Add a prefix (/24) or a netmask. An address alone doesn’t say how big its network is.
• Invalid netmask (not contiguous). A mask must be ones then zeros. 255.255.0.255 isn’t a mask.

Options worth knowing

• Neighboring Subnets lists the blocks of the same size around yours, such as the other /28s in its /24.
• Subnet Splitting divides the block into equal parts, or By Host Requirements: enter 50, 20, 10 and it finds the smallest subnet for each.
• The field’s menu offers This Mac’s network and your recent calculations. Everything is computed on your Mac.

Related

• Subnets and CIDR, how a prefix works.
• IP addresses.