How are IPv6 addresses formatted?

Addresses use lowercase hexadecimal, omit leading zeroes within groups and compress the longest run of two or more zero groups. Ties compress the leftmost run. Embedded IPv4 tails in custom CIDRs are accepted and rendered as hexadecimal groups. Arithmetic uses exact 128-bit integers.

Can I reproduce an address list?

Yes. Enter a whole seed from 0 to 4,294,967,295. With the same family, ranges, count and uniqueness setting, algorithm ip-fixtures-v1 returns the same ordered list using a Mulberry32 byte stream. Seeded output is predictable and intended for fixtures. JSON records the settings and algorithm version.

How does uniqueness work?

Unique mode samples without replacement within one batch. It checks the exact range capacity before starting and rejects an impossible count. Sampling uses a sparse Fisher-Yates shuffle, so even a complete small range does not require repeated collision attempts. Different batches may overlap.

Which IPv6 CIDRs can I use?

Custom CIDRs accept prefix lengths from /0 through /128. Host bits are masked to the network boundary displayed before generation. A /128 has one address; a /0 spans all 2^128 bit patterns. Brackets, ports and zone IDs are not accepted. Every value in the declared block is eligible, without a unicast or reachability filter.

What does private mode generate?

IPv4 uses 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, weighted by their address counts. IPv6 samples fd00::/8, the locally assigned ULA space. This does not perform RFC 4193 prefix allocation or guarantee uniqueness on a network.

What happens when the seed is blank?

The worker uses crypto.getRandomValues with rejection sampling to avoid modulo bias. A randomness failure, exceeded retry bound or ten-second timeout returns an error with no partial output. There is no weak-randomness fallback. You can cancel generation.

Do downloads include addresses outside the preview?

Yes. The preview shows up to 50 per page; copy, TXT, CSV and JSON include the complete batch of up to 10,000 addresses. CSV carries range and seed columns, and JSON includes full sampling metadata. Import address columns as text in spreadsheets.

Are addresses uploaded, probed or saved?

No. Generation runs locally in a browser worker. No generated address is contacted, checked for ownership or allocated to a device. Lists and seeds are not automatically saved. Download the batch before changing settings or leaving.

Random IPv6 Generator

Create compressed IPv6 address fixtures with exact 128-bit range arithmetic. Start in the documentation block 2001:db8::/32, switch to local ULA samples, or supply your own IPv6 CIDR.

Address familyAddress rangeAddress countRepeatable seed (optional)

Unique within this batch

1–10,000 samples. A fixed seed reproduces the same list with the same settings. Seeded fixtures are predictable; leave the seed blank to use browser crypto.

Declared range

2001:db8::/32

79,228,162,514,264,337,593,543,950,336 possible addresses · endpoints included

Fixtures with an explicit scope

Documentation: IPv4 uses the three TEST-NET /24 blocks (RFC 5737), with 768 total addresses. IPv6 uses 2001:db8::/32 (RFC 3849). These ranges are reserved for examples.

Private and local: IPv4 uses all three RFC 1918 ranges, weighted by their address counts. IPv6 samples the locally assigned half of the ULA space, fd00::/8. This is fixture generation, not RFC 4193 network-prefix allocation.

Custom CIDR: all bit patterns in the normalized block are eligible. There is no public-address filter, host-assignment check, route lookup or live-device check. Samples from arbitrary ranges may match actual addresses.

Uniqueness: exact sampling without replacement within one batch. It does not compare with other batches or networks. A count exceeding the pool is rejected before generation. Allow repeats to sample a small range more than once.

Reproducibility: algorithm ip-fixtures-v1 uses a 32-bit Mulberry32 seed and exact integer range sampling. The same family, ranges, count, uniqueness setting and seed reproduce the same ordered list. Blank seeds are not saved or recoverable.

Exact IPv4/IPv6 address arithmetic within the declared ranges. Generated samples do not identify devices, establish reachability or allocate addresses. No network probes are performed. Generation runs in your browser. Inputs and addresses are not uploaded or automatically saved.

Common questions

How are IPv6 addresses formatted?: Addresses use lowercase hexadecimal, omit leading zeroes within groups and compress the longest run of two or more zero groups. Ties compress the leftmost run. Embedded IPv4 tails in custom CIDRs are accepted and rendered as hexadecimal groups. Arithmetic uses exact 128-bit integers.
Can I reproduce an address list?: Yes. Enter a whole seed from 0 to 4,294,967,295. With the same family, ranges, count and uniqueness setting, algorithm ip-fixtures-v1 returns the same ordered list using a Mulberry32 byte stream. Seeded output is predictable and intended for fixtures. JSON records the settings and algorithm version.
How does uniqueness work?: Unique mode samples without replacement within one batch. It checks the exact range capacity before starting and rejects an impossible count. Sampling uses a sparse Fisher-Yates shuffle, so even a complete small range does not require repeated collision attempts. Different batches may overlap.
Which IPv6 CIDRs can I use?: Custom CIDRs accept prefix lengths from /0 through /128. Host bits are masked to the network boundary displayed before generation. A /128 has one address; a /0 spans all 2^128 bit patterns. Brackets, ports and zone IDs are not accepted. Every value in the declared block is eligible, without a unicast or reachability filter.
What does private mode generate?: IPv4 uses 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, weighted by their address counts. IPv6 samples fd00::/8, the locally assigned ULA space. This does not perform RFC 4193 prefix allocation or guarantee uniqueness on a network.
What happens when the seed is blank?: The worker uses crypto.getRandomValues with rejection sampling to avoid modulo bias. A randomness failure, exceeded retry bound or ten-second timeout returns an error with no partial output. There is no weak-randomness fallback. You can cancel generation.
Do downloads include addresses outside the preview?: Yes. The preview shows up to 50 per page; copy, TXT, CSV and JSON include the complete batch of up to 10,000 addresses. CSV carries range and seed columns, and JSON includes full sampling metadata. Import address columns as text in spreadsheets.
Are addresses uploaded, probed or saved?: No. Generation runs locally in a browser worker. No generated address is contacted, checked for ownership or allocated to a device. Lists and seeds are not automatically saved. Download the batch before changing settings or leaving.

Exact IPv4/IPv6 address arithmetic within the declared ranges. Generated samples do not identify devices, establish reachability or allocate addresses. No network probes are performed.