Date: Mon, 4 Nov 2013 16:08:33 -0500 From: "illoai@gmail.com" <illoai@gmail.com> To: Dan Nelson <dnelson@allantgroup.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: <CAHHBGkpwWSbRxPxhvGwwzTB5SU-dNi9PfeCuOBUB82thspHEtQ@mail.gmail.com> In-Reply-To: <20131104170955.GH63947@dan.emsphone.com> References: <CAGBxaXn27u3J6iJBoDkW_R2=_kcHzSBU=d0v5eDUvnoAsucSjw@mail.gmail.com> <20131104170955.GH63947@dan.emsphone.com>
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On 4 November 2013 12:09, Dan Nelson <dnelson@allantgroup.com> wrote: > 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'. With physical interfaces you can use something like ifconfig ath0 ether 00:2d:44:88:ff:00 (assuming the device & the driver support changing MAC addresses) I've never tried it with a virtual interface, but it should work if the device supports it. -- --
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