RFC 4193
Calculate a Unique Local IPv6 Prefix
Generate a locally assigned Unique Local IPv6 Unicast prefix from your MAC address using the pseudo-random Global ID method described in RFC 4193.
Local IPv6 addressing
Enter your MAC address
RFC 4193 uses the current time together with an EUI-64 system identifier, which can be created from a 48-bit MAC address. The resulting SHA-1 digest supplies the 40-bit Global ID.
How it works
RFC 4193 does not simply hash the MAC address.
The RFC specifies: current time in 64-bit NTP format + an EUI-64 identifier → SHA-1 digest → least significant 40 bits → Global ID. That Global ID is combined with FC00::/7 and the local-assignment L bit to produce the ULA /48.
Read RFC 4193 →Important
Unique does not mean mathematically guaranteed.
RFC 4193 describes these prefixes as having a very high probability of uniqueness. Collisions are possible, so organizations should still verify that a generated ULA prefix does not conflict with an existing network before deployment.