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Duplicate MACs [was Re: how do I disable IPv6?]

>> Although I've heard stories of duplicate MAC addresses from
>> unscrupulous vendors before.
> I have heard those stories as well, though never actually seen it,
> and I am not sure I have ever actually talked to anyone who had
> personally seen it either.

I've seen it personally, though not with anything running NetBSD.  I
used to work for a provider that, among other things, did Internet
telephony.  They sold, among other things, Linksys PAP2s (an ATA - a
device which speaks Internet telephony out one side and POTS,
traditional wired phone service, out the other).

There was one batch for which the MACs on the stickers did not match
the MACs the devices actually used, and one MAC actually used
duplicated the MAC of one we already had.  I don't know what happened,
but I speculate that somewhere in the supply chain someone bought from
a graymarket vendor and got devices that either were part of a stolen
and laundered batch or were part of an unauthorized factory run.  I
also don't know whether the "bad" MACs were deliberate duplication or
just randomly chosen, though the collision argues for the former.
(But, hm, they used the right vendor portion, so there were only 24
bits available, so the birthday paradox point was 4K devices.  I don't
think we had 4K of them, but we had enough that chance is not too
implausible an explanation.)

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