[134269] in North American Network Operators' Group
Re: The tale of a single MAC
daemon@ATHENA.MIT.EDU (Steven Bellovin)
Sun Jan 2 08:51:03 2011
From: Steven Bellovin <smb@cs.columbia.edu>
In-Reply-To: <20110102150324.627b891c@opy.nosense.org>
Date: Sun, 2 Jan 2011 08:50:42 -0500
To: Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jan 1, 2011, at 11:33 24PM, Mark Smith wrote:
> On Sat, 01 Jan 2011 20:59:16 -0700
> Brielle Bruns <bruns@2mbit.com> wrote:
>=20
>> On 1/1/11 8:33 PM, Graham Wooden wrote:
>>> So here is the interesting part... Both servers are HP Proliant =
DL380 G4s,
>>> and both of their NIC1 and NIC2 MACs addresses are exactly the same. =
Not
>>> spoofd and the OS drivers are not mucking with them ... They=B9re =
burned-in=20
>>> I triple checked them in their respective BIOS screen. I acquired =
these two
>>> machines at different times and both were from the grey market. The =
=B3What
>>> the ...=B2 is sitting fresh in my mind ... How can this be?
>>=20
>>=20
>> =46rom the same grey market supplier?
>>=20
>> I know HP has a disc they put out which updates all the firmware/bios =
in=20
>> a specific server model, its not too far fetched that a vendor might=20=
>> have a modified version that also either purposely or accidentally=20
>> changes the MAC address. Off the top of my head, I'm not sure where =
the=20
>> MAC is stored - maybe an eeprom or a portion of the bios flash. Or, =
it=20
>> could be botched flashing that blew away the portion of memory where=20=
>> that was stored and the system defaulted to a built in value.
>>=20
>> Excellent example is, IIRC, the older sparc stuff, where the ethernet=20=
>> cards didn't have MAC addresses as part of the card, but were stored =
in=20
>> non-volatile or battery backed memory.
>=20
> This was actually the intended way to use "MAC" addresses, to used as
> host addresses rather than as individual interface addresses, =
according
> to the following paper -
>=20
> "48-bit Absolute Internet and Ethernet Host Numbers"
> Yogan K. Dalal and Robert S. Printis, July 1981
> http://ethernethistory.typepad.com/papers/HostNumbers.pdf
Yup.
>=20
> That paper also discusses why 48 bits were chosen as the size, despite
> "Ethernet systems" being limited to 1024 hosts.=20
>=20
> I think things evolved into MAC per NIC because when add-in NICs
> were invented there wasn't any appropriate non-volatile storage on the
> host to store the address.=20
>=20
On really old Sun gear, the MAC address was stored on a separate ROM =
chip; if the
motherboard was replaced, you'd just move the ROM chip to the new board.
I'm not sure what you mean, though, when you say "when add-in NICs were
invented" -- the Ethernet cards I used in 1982 plugged into Unibus slots
on our VAXen, so that goes back quite a ways...
--Steve Bellovin, http://www.cs.columbia.edu/~smb
