MAC address confusion

Saku Ytti saku+nanog at ytti.fi
Sat Feb 28 16:40:00 CST 2009


On (2009-02-28 22:38 +0100), JAKO Andras wrote:

Hey,

> > http://standards.ieee.org/regauth/oui/oui.txt
> > 02-07-01   (hex)		RACAL-DATACOM
> 
> After enabling DECnet routing, the interface MAC address turns to 
> something like this:
>   Hardware is BCM1250 Internal MAC, address is aa00.0400.0a04 (bia 000b.bffd.fc1a)
> AA-00-04   (hex)		DIGITAL EQUIPMENT CORPORATION

> in the list. I don't know what 02-07-01 is, but I guess that could be 
> something similar: The OUI belongs to a company, but they don't use the 
> addresses to burn them into interface cards.

I guess you shouldn't be able to assign 02 (or AA) to a company for ethernet
number, much in the same way you shouldn't be able to assign RFC1918.
However you are right, it seems that these are unexplained exceptions to rules:

http://www.iana.org/assignments/ethernet-numbers
'some of the known addresses do not follow the scheme (e.g., AA0003; 02xxxx)'

Would be interesting to see what are the historical reasons.Perhaps they simply
predate the scheme or some might not even co-exist in ethernet network to begin
with, in which case they might be better documented elsewhere.
  In any case, to avoid collision with history, better start with 06 which
seems cruft free, instead of 02, when choosing local MAC address prefix.

As a side note, the 40 prefix used as local MAC in IXP here, seems to be
just mistake in assuming ethernet follows tokenring in numbering scheme.
-- 
  ++ytti




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