Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!XEROX.COM!JLarson.pa
From: JLarson.pa@XEROX.COM
Newsgroups: comp.protocols.tcp-ip
Subject: Mobile Toasters (was ToasterNet..)
Message-ID: <881212-182513-5931@Xerox>
Date: 13 Dec 88 02:25:02 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 18

Re: What was the rationale for 48-bit Ethernet addresses?  They are never
	used beyond the "Local" Area Network; 

Machines may move from one "Local" Area Network to another (and even
between non-local networks).  Unique 48-bit Ethernet addresses eliminates a
layer of a network administration that would be required otherwise.  

Also, unique host numbers are useful in large distributed systems  (for
generating unique identifiers).  It just happens to be a nice optimization
that a unique 48-bit XNS host number and a 48-bit Ethernet address are the
same.  

There is some danger though for a distributed system algorithm which
absolutely depend son a unique ID.  We have seen cases in the Xerox
Internet where 48-bit host numbers were not unique as intended.
(Apparently PROM burners can get stuck on the same number once in a while.)

John Larson
Xerox PARC