The tale of a single MAC

bmanning at vacation.karoshi.com bmanning at vacation.karoshi.com
Sat Jan 1 22:43:10 CST 2011


i have seen dups in 3com, dell, and hp kit over the years.
the best was moving mac addresses btwn 802,3 and 802.5 cards.

--bill


On Sun, Jan 02, 2011 at 03:03:24PM +1030, Mark Smith wrote:
> On Sat, 01 Jan 2011 20:59:16 -0700
> Brielle Bruns <bruns at 2mbit.com> wrote:
> 
> > 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 ... They9re burned-in -
> > > 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 3What
> > > the ...2 is sitting fresh in my mind ...  How can this be?
> > 
> > 
> >  From the same grey market supplier?
> > 
> > I know HP has a disc they put out which updates all the firmware/bios in 
> > a specific server model, its not too far fetched that a vendor might 
> > have a modified version that also either purposely or accidentally 
> > changes the MAC address.  Off the top of my head, I'm not sure where the 
> > MAC is stored - maybe an eeprom or a portion of the bios flash.  Or, it 
> > could be botched flashing that blew away the portion of memory where 
> > that was stored and the system defaulted to a built in value.
> > 
> > Excellent example is, IIRC, the older sparc stuff, where the ethernet 
> > cards didn't have MAC addresses as part of the card, but were stored in 
> > non-volatile or battery backed memory.
> 
> 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 -
> 
> "48-bit Absolute Internet and Ethernet Host Numbers"
> Yogan K. Dalal and Robert S. Printis, July 1981
> http://ethernethistory.typepad.com/papers/HostNumbers.pdf
> 
> That paper also discusses why 48 bits were chosen as the size, despite
> "Ethernet systems" being limited to 1024 hosts. 
> 
> 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. 
> 
> Regards,
> mark.
> 




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