what about 48 bits?

Sun Apr 4 22:34:33 UTC 2010

On Sun, Apr 4, 2010 at 9:53 AM, A.B. Jr. <skandor at gmail.com> wrote:
> 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?

Hardware MAC-48 addresses are not assigned based on a network
topology.  The first 24 bits are used for  OUI   which is an ID number
applied for [and paid for] by a manufacturer of network devices,   the
2nd LSB of the most significant byte is reserved for  'local vs
universal  administration flag',  and the LSB of the most significant
byte is reserved for unicast/multicast flag.      The bottom 24 bits
are assigned by manufacturer.

So there are  22 bits of usable global unicast OUIs,  that is
4,194,304 possible.
and each OUI has   16,777,216   MAC address numbers.

Of the possible OUIs,  only 13,557   are currently listed as allocated
 in  the IEEE   OUI  listing.
http://standards.ieee.org/regauth/oui/index.shtml

So a theoretical maximum of   227,448,717,312 unicast  MAC addresses
could be globally assigned today (which is a vast overestimate,
assuming all presently assigned OUIs  are already completely
exhausted).   Out of  70,368,744,177,664,   that is   what, 0.3%  ?

--
-J