GTA02 MAC addresses

Harald Welte laforge at
Mon Jan 14 21:17:03 CET 2008

On Mon, Jan 14, 2008 at 06:18:18AM -0300, Werner Almesberger wrote:
> OpenMoko has recently obtained its own OUI, so we can now (finally :-)
> assign proper MAC addresses. In GTA02, the following items needs one:
> - BlueTooth
> - WLAN
> - Ethernet over USB. Two of them, one for the device and one for the host:
> WLAN hardware brings its own MAC address, so we can just use that one.
> BT comes with a set of MAC addresses from the vendor (en bloc, so we'd
> still have to handle the assignment of individual addresses ourselves),
> but we can choose to ignore them. (Well, politely return them.)
> Now I'd like to get a sanity check for the assignment plan:
> I was thinking of assigning three MAC addresses to each device. Can
> anyone think of any other popular protocol sitting on top of something
> else that would expect to get its own MAC address, like EoUSB does ?
> Now, how do we assign them ? There are 24 bits to play with. I was
> thinking of making allocations in blocks from which the factory then
> picks addresses randomly. I think a block size around 16-18 bits
> should do nicely.
> Does anyone see a problem with using consecutive addresses for the same
> device ? E.g., BT = base, EoUSB.device = base+1, = base+2

No,  I cannot think of any problems with that.  In fact, this is what
multi-port ethernet cards seem to do, too.

Now sure, people can determine that a neo1973 is used by looking at the
OUI prefix, and then if they have the Wifi MAC, they can predict the
bluetooth or ethernet-over-usb MAC.  The latter is of no use since it's
only private to the pc-neo USB link anyway.

I have very little knowledge of the bluetooth security world.  I don't
think any of it relies on unpredictable mac addresses, though.  As soon
as a device talks, you would see its mac address anyway.

Marcel: Do you see any problems if the Bluetooth MAC address can be
predicted if somebody has seen the WiFI MAC Address (or vice versa)?

- Harald Welte <laforge at>         
Software for the world's first truly open Free Software mobile phone

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