IPv6 Unique Local Addressing

Sort of but not quite equivalent to RFC 1918.

• Any site can generate a ULA and start using it
• Not meant to go over the global v6 Internet

Terms

ULA — Unique Local Address

• Globally unique via randomness
• Take the form, fdxx:xxxx:xxxx::/48
• Five bytes or 40 bits of entropy

Site prefixes

\( 2^{40} = 1{,}099{,}511{,}627{,}776 \)

Approximately 1 trillion unique site prefixes.

Site prefix generation

Each site should generate a unique ULA using a RNG.

Random.org - Five Random Bytes

fdxx:xxxx:xxxx::/48

Examples

Don’t copy my examples … ☹️

• fd1a:b22c:c764::/48
• fd39:42fb:f7a7::/48
• fdb1:bf6c:f270::/48

References

RFC 4193: Unique Local IPv6 Unicast Addresses | RFC Editor