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Subnet calculator

Type an IPv4 or IPv6 address or range to see its network, masks, usable addresses and reverse DNS zones. Then split it, check addresses against it, or tidy up a list of ranges.

Calculator

CIDR like 10.0.0.0/8 or 2001:db8::/32, an address and netmask like 172.16.0.1 255.255.240.0 (or 0xfffff000), or one address. Results update as you type.

Split into subnets

Split by

Splits the range from the calculator above.

Is an address in this range?

Checked against the range from the calculator above. Separate several with spaces or commas.

Summarise a list of ranges

CIDR blocks, single addresses or start–end ranges, IPv4 and IPv6 mixed. Overlapping and neighbouring ranges are merged into the fewest blocks that cover exactly the same addresses. Text after # is ignored.

Range to CIDR

Turns any run of addresses into the smallest list of CIDR blocks that covers it exactly.