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Path: utzoo!watmath!clyde!akgua!mcnc!decvax!ucbvax!ulysses!smb
From: smb@ulysses.UUCP (Steven Bellovin)
Newsgroups: net.lan
Subject: Re: Ethernet addressing
Message-ID: <848@ulysses.UUCP>
Date: Tue, 15-May-84 09:36:34 EDT
Article-I.D.: ulysses.848
Posted: Tue May 15 09:36:34 1984
Date-Received: Wed, 16-May-84 07:35:34 EDT
References: <967@hao.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 10

All Ethernet devices have a unique address.  The high-order 24 bits
(well, 23, really; one's the multicast bit) are assigned by Xerox
to a manufacturer, in payment for a "nominal" administrative fee.
The low-order 24 bits are assigned by the manufacturer to each
unit, typically by means of a PROM.  These are guaranteed to be unique.
In fact, at least for some manufacturers (and maybe all; I don't have
my copy of the spec handy) once you buy a board with some particular
address, that address is yours forevermore -- if you send the board
back for repair/replacement, you may receive a new address, but they'll
typically send you back your old PROM so you can use either.