Re: The tale of a single MAC

[Jethro R Binks <jethro.binks () strath ac uk>]

On Sun, 2 Jan 2011, Steven Bellovin wrote:

> > 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
>
> Yup.
> > 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. 
> 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.

And I'm sure many will remember that Suns of a certain vintage with 
multiple ethernet interfaces would use that same "host" MAC address on all 
those interfaces, unless you weaved some magic in the eeprom to use the 
(presumably) burned-in MAC address of the interface itself.  I have long 
forgotten precisely what the incantation was now ...

Jethro.

.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .
Jethro R Binks, Network Manager,
Information Services Directorate, University Of Strathclyde, Glasgow, UK

The University of Strathclyde is a charitable body, registered in
Scotland, number SC015263.