Date: Mon, 4 Nov 2013 11:09:55 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Aryeh Friedman <aryeh.friedman@gmail.com> Cc: FreeBSD Stable List <freebsd-stable@freebsd.org>, "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org> Subject: Re: how is the MAC for tap(4) computed? Message-ID: <20131104170955.GH63947@dan.emsphone.com> In-Reply-To: <CAGBxaXn27u3J6iJBoDkW_R2=_kcHzSBU=d0v5eDUvnoAsucSjw@mail.gmail.com> References: <CAGBxaXn27u3J6iJBoDkW_R2=_kcHzSBU=d0v5eDUvnoAsucSjw@mail.gmail.com>
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In the last episode (Nov 04), Aryeh Friedman said: > There seems to be a very high rate of MAC address collisions when tap is > running on different machines.... is there anyway to make the selection > of MAC more random It looks like it's generated based on the number of ticks since boot, plus the unit number of the tap device: http://fxr.watson.org/fxr/source/net/if_tap.c#L434 So if you have devices created on boot on a bunch of machines, chances are high that you'll get conflicts. Maybe instead of using the 'ticks' value, kern.hostid could be used instead? That has much better randomness than 'ticks'. -- Dan Nelson dnelson@allantgroup.com
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