IPv4 range expander
Turn a start and end IP into the smallest CIDR block that contains them.
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About the ipv4 range expander
Takes a start and end address and returns both the smallest single CIDR block containing them and the exact set of blocks that covers the range with nothing spare. The exact decomposition is what firewall and routing rules need.
Frequently asked questions
Why does the containing block include extra addresses?
CIDR blocks must align to a power-of-two boundary, so an arbitrary range rarely fits one exactly. The exact block list avoids granting access to addresses outside the range you meant.
Why so many blocks for a small range?
Ranges that start or end off a natural boundary need several blocks of different sizes to tile exactly. Shifting the start to an aligned address usually collapses the list dramatically.