FreeBSD has a MAC address prefix set aside for its use. Details are available here: https://macaddress.io/statistics/company/17619 I am not sure what would be the best place to document this.
FTR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275228 bhyve manpage is missing this information as well that the MAC address has to start with this prefix or bust.
>> FreeBSD has a (undocumented) MAC address prefix > bhyve manpage May I?
(In reply to Alexander Ziaee from comment #2) Except, i think the appropriate place to document freebsd vnet mac address is vnet(9).