what about 48 bits?

Jonathan Lassoff jof at thejof.com
Sun Apr 4 10:46:17 CDT 2010


Excerpts from John Peach's message of Sun Apr 04 08:17:28 -0700 2010:
> 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.

I could see how that *could* work as long as each interface connected to
a different LAN.

Maybe the NICs shared a single MII/MAC sublayer somehow? I've never
borne witness to this though.


Re: MAC address exhaustion, if the the second-to-least significant bit
in the first byte is 0 (Globally Unique / Individually Assigned bit),
then the first three bytes of the MAC should correspond to the
manufacturer's "Organizationally Unique Identifier". These are
maintained by the IEEE, and they have a list of who's who here:
http://standards.ieee.org/regauth/oui/index.shtml


I haven't ever programmatically gone through the list, but it looks like
a lot of the space is assigned.

Cheers,
jof




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