IPv6 Range to CIDR

This page converts an arbitrary IPv6 start and end address into the smallest set of prefixes that covers the range exactly. The conversion UI and output remain unchanged, but the added context explains why the result may be one prefix in some cases and multiple prefixes in others.

That is useful when you receive address data as a raw span from a registry, spreadsheet, or incident report and need to express it in a format routers, firewalls, documentation systems, and AI summaries can understand clearly.

Inputs explained

Enter the first IPv6 address that must be included and the last IPv6 address that must be included. Either compressed or expanded notation is fine. The range does not need to begin on a prefix boundary, but the ending address must not precede the starting address.

How it works

The converter starts at the first IPv6 address, finds the largest aligned prefix that fits without crossing the end of the range, outputs that block, then repeats until the full span is covered. The result is a minimal exact cover, not an approximate summary.

IPv6 Range → Minimal CIDRs

Start IPv6

End IPv6

Result

CIDRs

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Step-by-Step Example

Imagine a range beginning at 2001:db8::1000 and ending at 2001:db8::1fff. If the boundaries align neatly, the result may collapse into a single prefix. If they do not, the converter emits several smaller prefixes that together cover the full span without expanding outside the requested addresses.

This exactness is what makes the page useful in security and routing work. A wider summary might be shorter, but it can also include addresses you never intended to match.

Use Cases

Use this tool when you need IPv6 prefixes for ACLs, route filters, address delegation reports, asset scoping, or documentation generated from raw start and end values. It is also helpful when you need to verify whether a registry supplied span can be represented cleanly by one prefix or requires a set of more specific entries.

Assumptions and limitations

The result is an exact mathematical cover of the entered range. It does not verify RPKI state, upstream acceptance, or whether the output aligns with your organizational allocation model. Review routing and ownership context separately before deploying the prefixes.

Frequently Asked Questions

What does IPv6 range to CIDR conversion do?

It converts a start IPv6 address and an end IPv6 address into the smallest list of IPv6 prefixes that exactly covers the requested range.

Why can one IPv6 range produce multiple prefixes?

A single prefix works only when the range aligns to a valid prefix boundary. If the boundaries are uneven, multiple prefixes are required to avoid including extra addresses.

Can I enter compressed IPv6 addresses?

Yes. Compressed and expanded IPv6 forms are both valid as long as the addresses are syntactically correct and the end is not lower than the start.

When is this output useful?

It is useful for routing policy, ACLs, address delegation records, cloud controls, and any workflow where a raw IPv6 span must be represented as prefixes.

Should I summarize further after conversion?

Only if a broader summary is acceptable for your policy. The generated result is the exact cover for the requested range and should not be widened without review.

What limitations apply here?

The output is a mathematical representation of the range. It does not check route origin validity, ownership, or whether the resulting prefixes align with your delegation model.