IPv6 Subnet Calculator
Calculate IPv6 CIDR ranges, address counts and child subnet previews
Calculated locally with BigInt; no network request is made.
Calculate to see the normalized CIDR, range, and subnet capacity.
About this tool
IPv6 Subnet Calculator turns an IPv6 CIDR into its normalized network address, final address, exact address capacity, and child subnet count. Choose a longer prefix such as /64, enter a starting subnet index, and preview a bounded list without trying to render billions of networks. All 128-bit calculations use browser BigInt arithmetic, so large prefixes remain exact and no address data is sent to a server.
Scenario Recipes
Plan /64 networks inside an allocation
Goal: Select a stable child subnet without manually expanding hexadecimal fields
- Paste the assigned IPv6 CIDR.
- Set the target prefix to /64 and enter the allocation index.
- Copy the normalized child CIDR into the network plan.
Result: An exact /64 range with auditable first and last addresses.
Frequently Asked Questions
Does the calculator support the full IPv6 /0 to /128 range?
Yes. The parent prefix can be from /0 to /128, and the child prefix must be equal to or longer than the parent.
Why are IPv6 address counts shown as very large integers?
IPv6 uses 128-bit addresses. A /64 alone contains 18,446,744,073,709,551,616 addresses, so exact BigInt output is required.
Can I jump to a specific child subnet instead of listing from zero?
Yes. Enter a non-negative start subnet index to preview networks from that position.
Why is the subnet preview limited to 256 rows?
Large IPv6 blocks can contain trillions of child networks. A bounded preview keeps the browser responsive while preserving exact totals.
Does IPv6 have broadcast addresses?
No. The displayed last address is the mathematical end of the subnet range, not an IPv4-style broadcast address.
Are IPv6 networks sent to a server?
No. Parsing, normalization, range calculation, and subnet enumeration all run locally.
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