New Mobo - Change MAC Address

Kuba Ober kuba at
Wed Feb 28 09:44:28 CST 2007

On Wednesday 28 February 2007, Duncan Hill wrote:
> On Wed, February 28, 2007 15:22, Tom Brown wrote:
> > Hi
> >
> >
> > We have an app thats tied to the MAC of the NIC but we are having a mobo
> > swapped out tonight. Is there anyway to change the MAC of the onboard
> > NIC's on an 1850? If we have to relicense the app this will be major
> > issues for us.
> MACs are essentially burned into the 'memory' of the NIC.

In most cases, the NIC chipset will read a serial EEPROM and set up its 
internal MAC register, along with PCI descriptors and other configuration 
data. The runtime MAC register is typically read-write and can be altered at 
will. Some NICs have functionality that allows the EEPROM to be reprogrammed 
in-situ so that the MAC change becomes more permanent. I can't imagine a NIC 
that doesn't have the MAC in a register that can be accessed along with other 
control registers. Some cost-optimized NICs may integrate the EEPROM on the 
same die, or in the same package as the one and only chip that they comprise 
of. I can't think right away of any commonplace NIC that'd have OTP memory 
(EPROM) or masked MAC and no alterable runtime MAC register. Maybe some cards 
from 10Base-5/AUI era would be that braindead, but I wouldn't know that.

Driver support for that is another story -- I can only vouch for the cards 
that I use, and they IIRC all worked OK in that respect. If one has chip(set) 
documentation, it's easy to add the necessary functionality to the driver, it 
should be a maybe 20 line patch.

Cheers, Kuba

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