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From: bruce@ssc-vax.UUCP (Bruce Stock)
Newsgroups: comp.dcom.lans
Subject: Ethernet Physical Address
Message-ID: <939@ssc-vax.UUCP>
Date: Thu, 13-Nov-86 15:41:03 EST
Article-I.D.: ssc-vax.939
Posted: Thu Nov 13 15:41:03 1986
Date-Received: Sun, 16-Nov-86 02:18:05 EST
Distribution: na
Organization: Boeing Aerospace Co., Seattle, WA
Lines: 21


 I have always been under the assumption that Ethernet Physical Addresses
 were virtually "cast in concrete" , ie unchangable.  I had heard that
 Xerox maintains a registry of physical addresses, and that manufacturers may
 reserve blocks of addresses for their products, thus avoiding any address
 conflicts.

 However recently I have come to understand that DECNET, for example, takes
 a DEUNA with a physical address something like 08-00-2b-03-fc-83, and
 replaces it with a physical address like aa-00-04-00-25-04, where the "25"
 corresponds to the DECNET node number.

 Digging a bit further, I note that our Interlan ethernet boards also have the 
 capability for over-riding the built-in physical address.

 Would any one care to shed some light on why this is necessary or desirable?
 Does it not tend to increase the risk of an address conflict on a large,
 multi-protocol, mult-vendor net?
				Thanks,
				Bruce E. Stock
				uw-beaver!ssc-vax!bruce