From owner-freebsd-net@freebsd.org  Wed Apr 21 07:55:54 2021
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Date: Wed, 21 Apr 2021 09:55:44 +0200
From: Kurt Jaeger <pi@freebsd.org>
To: Kyle Evans <kevans@freebsd.org>
Cc: FreeBSD Net <net@freebsd.org>
Subject: Re: source of ether address for tap0 ?
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Hi!

> > does anyone know how the system selects the MAC/ether adress of a
> > newly-created tap0 device ?
> >
> > ifconfig tap0 create
[...]
> > How is that selected ?

> > We had a case where two devices selected the same ether/MAC...
> 
> tap MACs are derived from the hostid (/etc/hostid) -- you generally
> end up with the same MAC in one of two scenarios:

Thanks! I've submitted two PRs to help others find this info in
the future.

augment if_tuntap man page on source of autogenerated MAC (/etc/hostid)
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255294

man page for /etc/hostid and pointer in sethostid/gethostid(3) to /etc/hostid
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255293

If I find the time, I'll try to submit the necessary patches.

-- 
pi@FreeBSD.org         +49 171 3101372                  Now what ?