> Am 05.07.2025 um 07:59 schrieb Crystal Kolipe <[email protected]>: > > On Sat, Jul 05, 2025 at 06:18:18AM +0200, Mike Fischer wrote: >> BTW: The correct prefix for ULA is fc00::/7 (RFC 4193, RFC 8190). > > Technically yes, the prefix is specified as fc00::/7, but bit 7 is supposed > to be set to 1 which effectively makes the prefix in practice fd00::/8. > > I.E. > > F C > 11111100 > ^- this is supposed to be set.
You are correct: RFC 4193 section 3.1 [1] specifies the L flag in the 7th bit. A value of 0 is currently unspecified making addresses starting with fc… fairly rare. [1] https://datatracker.ietf.org/doc/html/rfc4193#section-3.1 However both variants have the same scoping characteristics. So to ensure maximum forward compatibility it would be best to treat them the same (other than the method used to generate the prefix).
