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IPv4 Subnet Calculator

Enter an IPv4 address and CIDR prefix. Calculations stay in this tab; nothing is sent or saved.

Address and prefix

Four decimal octets, 0–255. Leading zeros are not accepted.

0–32, with an optional slash: 24 or /24.

Subnet practice challenge

Work out the network, broadcast, usable range and usable host count. The timer starts when a challenge appears. Your aggregate score stays in this browser only.

Your answer

Elapsed time appears after you check your answer.

/31 treats both addresses as point-to-point endpoints; /32 identifies one address. For other prefixes, the usable count excludes the network and broadcast boundaries. At /0, special-purpose addresses still fall inside the arithmetic range.

How to read the range

For /0–/30, the range excludes the network and broadcast boundaries. /31 uses point-to-point semantics; /32 represents one address. This calculator does not check reserved or special-purpose addresses, routing, device support or whether an address can be assigned on your network.

References: RFC 3021: /31 point-to-point links and RFC 4632: CIDR prefixes.