what about 48 bits?

Kevin Oberman oberman at es.net
Mon Apr 5 00:26:52 CDT 2010


> Date: Sun, 04 Apr 2010 23:30:42 -0500
> From: Larry Sheldon <LarrySheldon at 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.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751




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