what about 48 bits?

Date: Sun, 04 Apr 2010 23:30:42 -0500
From: Larry Sheldon <LarrySheldon@cox.net>

I keep seeing mention here of the "permanent" MAC address.

Really? Permanent?

Been a long time, but it seems like one of the fun things about having
DECNet-phase IV on the network was its propensity for changing the MAC
address to be the DECNet address.

And it seems like the HP-UX machines (among others) could write what
every they wanted to as addresses.

Almost every system can re-write the MAC address. It's in the original
802.3 and DIX (Blue Book) Ethernet standards. I have not run into a
system in some time that lacked this capability. Works on Windows,
MacOS, Linux, and BSD.

That said, all 802.3 devices are expected to have a permanent MAC
address in ROM. At initialization time, that address is always used
until software can program in the new address. Made MOP-DL booting
(DECnet equivalent of bootp) interesting.