By Debmedia Technologies LLP · Kolkata, India · Updated
What Is IPv6 CIDR to Range Conversion?
IPv6 CIDR to range conversion turns a prefix such as 2001:db8::/32 into the first and last address that the prefix covers. CIDR notation is compact, but firewalls, spreadsheets and some tools want an explicit start and end. This converter gives you both, together with the size of the block.
It is useful when you read a registry record, plan a network, write an access list or check that two prefixes do not overlap.
How to Use This IPv6 CIDR to Range Tool
- Enter a prefix in CIDR form, such as 2001:db8::/32.
- Press Convert.
- Read the first and last address in short and full notation.
- Check the total number of addresses and, for prefixes of /64 or shorter, the number of /64 subnets.
How Big Is Each Prefix?
| Prefix | Addresses | Typical use |
|---|---|---|
| /32 | 2^96 | An internet provider or large organisation |
| /48 | 2^80 | One customer site |
| /56 | 2^72 | A home or small business |
| /64 | 2^64 | One network segment |
| /128 | 1 | A single host |
The size is always two to the power of (128 minus the prefix length). The notation is defined in RFC 4291, which defines IPv6 prefixes.
How the Range Is Calculated
The prefix length says how many leading bits are fixed. The converter sets all the remaining bits to zero to get the first address, and to one to get the last address. The tool uses exact big-integer arithmetic, so even huge blocks are precise.
Host bits in your input
If your input is 2001:db8::1/32, the bits after the first 32 are not zero. The tool clears them, shows the real network, 2001:db8::/32, and tells you it did so.
Address Types in the Result
- Global unicast (2000::/3): public addresses assigned by registries.
- Unique local (fc00::/7): private addresses, see the ULA prefix generator.
- Link-local (fe80::/10): valid on one link only.
- Documentation (2001:db8::/32): reserved for examples.
Related Tools
To do the reverse and build prefixes from a start and an end address, use the range to CIDR converter. For IPv4 networks, use the IPv4 subnet calculator. If you need to read the result more easily, try the IPv6 compression tool. The calculation runs in your browser.
Common Uses
You will use this conversion when writing firewall rules that need explicit start and end addresses, when you import a registry allocation into a spreadsheet or a database, and when you want to check that two prefixes do not overlap. It is also a quick sanity check after planning your own address space: confirm that the last address of one block is directly before the first address of the next.
Frequently Asked Questions
Disclaimer: results come from live requests and can change as records and servers change. We cannot guarantee that every answer matches what every visitor sees.