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Date:      Fri, 11 Nov 2016 12:53:13 +0100
From:      "John W. Kitz" <John.Kitz@xs4all.nl>
To:        <freebsd-arm@freebsd.org>
Subject:   RE: How to change MAC address on RPI-B?
Message-ID:  <000601d23c12$2fa70ac0$8ef52040$@Kitz@xs4all.nl>
In-Reply-To: <eb8b3f7b-ad42-9983-fa7a-bb181910db18@t-online.de>
References:  <000001d23a85$47646970$d62d3c50$@Kitz@xs4all.nl> <fbcb7639-40d6-53ca-565e-5f216c9d571a@t-online.de> <000001d23ad6$fce27e80$f6a77b80$@Kitz@xs4all.nl> <eb8b3f7b-ad42-9983-fa7a-bb181910db18@t-online.de>

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Reiner,

I've tried both, but not at the same time. To override the burned-in MAC at
bootime doesn't work on FreeBSD. It works on Linux, but only the promiscuous
mode works as aspected with the FreeBSD RPi build.

> JKi: Doesn't that depend on the sequence of events at boot time?

I don't think so. The serial number is hard-coded on the RPi. As I know, you
could change it, but with a parameter in CONFIG.TXT it doesn't work. That's
also the reason, why I like to change it. I have used a RPI with a faulty
power connector and suddenly the MAC address was changing after reboot (this
happens only once).

JKi: Again since I don't have a Pi at my disposal and since I don't have any
prior experience with one, I'm not in a position to argue this. But are you
implying that if one has two or more Pi's attached to one network(segment)
there is a, albeit slim, chance that a situation would occur in which two or
more of these Pi's would end up having the same MAC address resulting in
duplicate MAC addresses on the same LAN?

Obviously Pi's are a cheap platform, not designed for professional use, but
this would seem very awkward and unlikely to me.

In addition you mentioned in one of your emails that the Organizationally
Unique Identifier (OUI) or in short vendor portion of the MAC address used
by a Pi is b8:27:eb providing for MAC addresses ranging from
b8-27-eb-00-00-00 up to and including b8-27-eb-FF-FF-FF. Yet you mention, or
at least that is my understanding of what you wrote, that Pi's use some
algorithm to determine the last portion of the MAC address based on the Pi's
serial number, which doesn't always yield the same result on one and the
same Pi?

> JKi: I'm curious, are you just in the process of confirming that it 
> can be done or do you actually have some purpose for this and if yes, what
is it?

I've look into the FDT file with dtc and found the following string:

mac-address = [00 00 00 00 00 00];

So, I guess it should be possible to change it. I tried it and the the auto
configuration of the MAC remains. Maybe I've done something wrong.

https://wiki.freebsd.org/FlattenedDeviceTree#How_to_convert_a_platform_to_FD
T

JKi: As mentioned before I don't have a Pi at my disposal and I don't have
any prior experience with one, so I have nothing to add to this last portion
of your post.

Regards, Jk.




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