Browser-based tool

IPv6 Subnet Calculator

Calculate an IPv6 network, exact address count, first and last address, and child subnet count. Split a delegated prefix without enumerating its address space.

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Calculate and split a prefix

Use an IPv6 address and parent prefix, then choose the child prefix. Pasted CIDR notation overrides the parent selector.

IPv6 address or CIDRDocumentation example. Brackets, ports, and zone IDs are not accepted.

Parent prefix

Child prefixAt least as long as the parent. /64 is common for SLAAC LANs.

How to interpret the result

A /56 contains 256 distinct /64 prefixes because eight extra bits select the child networks. Each /64 contains 2⁶⁴ addresses. The first and last addresses describe the mathematical range; this tool does not allocate addresses or configure a router.

The calculator clears host bits to find the network boundary. A /128 identifies one address. Use the IPv4 calculator for subnet masks and traditional broadcast calculations.

IPv6 Subnet Calculator

Calculate and split a prefix

Exact prefix results

How to interpret the result