Convert an IPv4 start-end range into the smallest list of CIDR blocks.
CIDR blocks
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Start
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End
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Enter the example value or paste your own input, choose the mode when one is available, and read the first result card for the direct answer. The output area gives a copyable block for code reviews, documentation, API tests, classwork or troubleshooting notes.
What the result means
The result covers the range exactly with CIDR blocks, which is useful for firewall and allow-list planning.
What is not included
Large ranges are capped in the preview to keep the browser responsive.
Privacy note
The calculation runs in your browser. Avoid pasting production secrets, credentials, private keys, customer data or regulated personal data unless your own policy allows browser-based tools.