About this tool
What is a ULA?
Unique Local Addresses (fc00::/7): the IPv6 equivalent of private IPv4 space — globally unique yet unroutable on the public internet, per RFC 4193, for internal networks that still want stable, non-colliding addresses.
How to use it
- Generate a random /48 ULA prefix.
- Subnet it per site/VLAN like public space.
- Document it alongside your public allocations.
Examples
- Lab networks that must never collide after mergers.
- Home labs with stable internal addressing.
- ULA + public dual-stack for controlled egress.
Important limitations
- Randomness quality matters: use proper generation (like this tool), not hand-picked prefixes.
- ULA is not a security boundary — firewall it like any internal space.
- Some software assumes global addresses; test ULA-only paths.
Privacy
Generated locally with secure randomness. Prefixes stay on your device.
Frequently asked questions
ULA vs link-local (fe80)?
ULA routes across your organization; link-local never leaves one link.
Why random, not sequential?
Random /48s make collisions after mergers vanishingly unlikely.
Do I still need public IPv6?
For internet services yes — ULA complements, not replaces.
Related tools
IPv4 subnet calculator · MAC address generator · Random port generator