IPv6 Subnet Calculator
Calculate an IPv6 network address and capacity from address-prefix notation.
Apply an IPv6 prefix with exact 128-bit math
An IPv6 subnet is defined by masking a 128-bit address with a prefix from zero through 128. This calculator expands and validates the address, converts its hextets to a BigInt value, clears every host bit beyond the prefix, and converts the network back to compressed notation. It also reports the remaining host-bit count and exact number of addresses.
For the default 2001:db8:1234:5678::1/48 input, the network is 2001:db8:1234::/48. Eighty host bits remain, representing exactly 1208925819614629174706176 addresses. The calculation uses integer shifts rather than floating-point approximations, so the displayed capacity remains exact even at IPv6 scale.
Reading address counts at IPv6 scale
The address count is not an estimate of assignable end hosts and does not apply IPv4 network or broadcast subtraction. IPv6 deployment normally allocates structured subnets, often with operational boundaries chosen by policy rather than maximum host count. Nothing is looked up because calculation runs in your browser. Use the network result for planning, then apply routing, delegation, and interface-allocation standards from the actual environment.
Frequently Asked Questions
Does IPv6 reserve network and broadcast addresses like IPv4?
IPv6 has no broadcast address and this calculator reports the full mathematical capacity of the prefix.
Why is BigInt arithmetic used?
A 128-bit address and its capacity exceed the exact integer range of ordinary JavaScript numbers.
Can the input already use double-colon compression?
Yes. The address is expanded for calculation and compressed again for the network output.
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