IPv6 ULA Generator - Unique Local Address Prefix (RFC 4193) & EUI-64
IPv6 ULA Generator
Create a private fd00::/8 prefix for your network, and work out EUI-64 addresses
A Private Prefix
Get a fdxx:xxxx:xxxx::/48 prefix with a Global ID chosen so it is very unlikely to clash with anyone else's.
Ready-Made Subnets
See the first 16, 64 or 256 of the 65,536 /64 subnets in your /48 and copy the list.
EUI-64 and SLAAC
Turn a MAC address into its interface ID, link-local address and the address it would autoconfigure in a /64.
Full Privacy
Prefixes are generated in your browser and never leave it.
What a ULA Is For
IPv6 Unique Local Addresses, in fc00::/7 and in practice fd00::/8, are the IPv6 counterpart of private IPv4 ranges: addresses for use inside a site or between a few sites that are not routed on the public Internet. Unlike 10.0.0.0/8, every network is meant to pick its own random 40-bit Global ID, so two networks that later join or connect by VPN are very unlikely to have overlapping addresses.
A ULA prefix is a /48, which leaves 16 bits for 65,536 /64 subnets, the size IPv6 hosts expect. RFC 4193 suggests deriving the Global ID by hashing the time and a MAC-based identifier, and offers that method here, but a cryptographically random ID is just as good and is the default. Keep ULA prefixes out of public DNS and do not route them to the Internet.
Key Takeaways
- Two methods: A secure random Global ID, or the RFC 4193 SHA-1 method from a MAC and the current time.
- Checked against RFC 4291: The EUI-64 conversion reproduces the RFC's worked example, 34-56-78-9A-BC-DE to 3656:78ff:fe9a:bcde.
- Related tools: See also the IPv6 Subnet Calculator and the MAC Address Formatter.