TOOL / NETWORKING
Subnet Desk.
A small IPv4 calculator for checking a range or getting a feel for subnetting. Change the prefix and watch the network boundary move.
Select a bit to set the prefix boundary. Arrow keys also work on the slider.
- Network
- Subnet mask
- Broadcast
- Usable addresses
- Usable range
What changes when you move the prefix?
An IPv4 address has 32 bits. The prefix tells you how many identify the network; the remaining bits address hosts within it. Each extra network bit halves the size of the block.
Network, broadcast, and usable addresses
For prefixes /0 through /30, the first address identifies the network and the last is the broadcast address. The calculator excludes those two when counting usable addresses. A /31 can use both addresses on a point-to-point link; a /32 identifies one host. This is address arithmetic, not a check of routing or whether a particular address is available.
About this project
I added Subnet Desk as a practical companion to the games and visual experiments here. It runs locally in your browser and does not scan a network or transmit the address you enter. The arithmetic is tested against known ranges and boundary cases.