what about 48 bits?

Mon Apr 5 01:10:57 UTC 2010

On Sun, 04 Apr 2010 11:17:28 -0400
John Peach <john-nanog at johnpeach.com> wrote:

> On Sun, 4 Apr 2010 11:10:56 -0400
> David Andersen <dga at cs.cmu.edu> wrote:
> 
> > There are some classical cases of assigning the same MAC address to every machine in a batch, resetting the counter used to number them, etc.;  unless shown otherwise, these are likely to be errors, not accidental collisions.
> > 
> >   -Dave
> > 
> > On Apr 4, 2010, at 10:57 AM, jim deleskie wrote:
> > 
> > > I've seen duplicate addresses in the wild in the past, I assume there
> > > is some amount of reuse, even though they are suppose to be unique.
> > > 
> > > -jim
> > > 
> > > On Sun, Apr 4, 2010 at 11:53 AM, A.B. Jr. <skandor at gmail.com> wrote:
> > >> Hi,
> > >> 
> > >> Lots of traffic recently about 64 bits being too short or too long.
> > >> 
> > >> What about mac addresses? Aren't they close to exhaustion? Should be. Or it
> > >> is assumed that mac addresses are being widely reused throughout the world?
> > >> All those low cost switches and wifi adapters DO use unique mac addresses?
> > >> 
> Sun, for one, used to assign the same MAC address to every NIC in the
> same box.
> 

That actually follows the original MAC addressing model -

"48-bit Absolute Internet and Ethernet Host Numbers"
http://ethernethistory.typepad.com/papers/HostNumbers.pdf

As add-in cards needed their own address, because they couldn't be sure
the host had one, and most likely didn't, I think that has evolved into
unique MAC addresses per-interface rather than per-host.

Regards,
Mark.