Range to CIDR

Enter a start-end IP range and get the minimal set of CIDR blocks that cover it exactly,.

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Input
Output
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About range to cidr

Range to CIDR does its work in front of you rather than sending anything away to be processed. What you see is the whole of it.

Nothing here is stored between visits. Reload the page and you start from an empty box again.

You will find it under Network, alongside 17 other tools for the same sort of job.

Supports dash-separated or newline-separated ranges.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

Convert 192.168.1.0-255 range to CIDR
Get the minimal CIDR block for a full /24 range of addresses
Input
192.168.1.0 - 192.168.1.255
Output
Start IP: 192.168.1.0
End IP: 192.168.1.255
Total addresses: 256
CIDR blocks: 192.168.1.0/24
Block count: 1

Questions

Does Range to CIDR work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use Range to CIDR on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.