IPv6 Range to CIDR Converter
Convert IPv6 start and end addresses to a minimal CIDR set, or expand a CIDR range
Exact 128-bit BigInt arithmetic; no network request.
About this tool
IPv6 Range to CIDR Converter supports both directions. For a start and end address it uses exact 128-bit arithmetic to emit the smallest aligned CIDR blocks that cover every address exactly once. For a CIDR it returns the normalized network, first address, last address, and exact capacity. The range algorithm handles zero alignment and huge values with BigInt and never enumerates individual addresses. Invalid order, mixed IPv4/IPv6 input, and non-CIDR text are rejected locally.
Scenario Recipes
Summarize an allocated address interval
Goal: Produce routing prefixes without over-covering adjacent addresses
- Enter the inclusive IPv6 start and end addresses.
- Generate the minimal CIDR list and inspect the number of blocks.
- Copy the prefixes into the routing change after reviewing the exact boundaries.
Result: A minimal, gap-free IPv6 prefix set.
Frequently Asked Questions
Does the CIDR list cover every address exactly?
Yes. The aligned blocks are disjoint and cover the inclusive start-to-end range without gaps.
Can it handle the full IPv6 space?
Yes. BigInt arithmetic supports /0 through /128 without converting values to JavaScript Number.
Does it enumerate all addresses?
No. It calculates aligned block sizes and emits prefixes directly.
Can I mix IPv4 and IPv6 endpoints?
No. Both range endpoints must be valid IPv6 addresses.
What does CIDR mode show?
It shows normalized CIDR, first address, last address, and exact address count.
Is input sent to a server?
No. Parsing and conversion run locally.
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