About this tool
Turn a CIDR block into its first and last addresses, or collapse a start/end IP range into the smallest set of CIDR blocks. It runs entirely in your browser.
Frequently asked questions
Why does a range produce several CIDRs?
An arbitrary range rarely aligns to a single power-of-two block, so it is decomposed into the minimal list of aligned CIDR blocks that cover it exactly.
Does the order of start and end matter?
No — if the end is lower than the start they are swapped automatically before computing the covering blocks.