[ih] History of duplicate address tests

[Vint Cerf]

yeah, I hate numbers like that, John... :-)))

v


On Wed, Nov 30, 2022 at 7:06 PM John Shoch via Internet-history <
internet-history at elists.isoc.org> wrote:

> The Experimental Ethernet ca. 1973 had 8-bit source and destination
> addresses.
> Depending on the machine or interface, these could have been set with DIP
> switches, in software, or otherwise.
> At this level there was no ability to recognize that two machines might
> have the same Ethernet address.
>
> The PUP Internet was built on top of this, ca, 1974, with 8 bits of network
> number, and 8 bits of host number (conveniently matching the Ethernet).
> Each source and destination PUP "port" also included a socket number, which
> (for some protocols) might have helped disentangle duplicate host numbers.
>
> This early architecture worked very well -- interconnecting thousands of
> machines, dozens of networks, etc.
>
> But this early design also highlighted some of the more complicated issues:
> --An erroneously entered Ethernet host address could produce two
> machines on the same Ethernet with the same address.
> --Even worse, moving a machine from one network to another could yield two
> machines with the same network-relative host address.
>
> When we were finally able to publish the PUP work in the1980 IEEE paper we
> already knew about the issues, and hinted at what was to be done:
>
> "One could consider revising the entire notion of a hierarchical address
> space. Under the current design, it is sometimes necessary to change the
> host number of a machine which is moved from one net to another--an
> operational annoyance. It is conceivable that every host could be given a
> unique address within a flat address space; a more sophisticated mechanism
> would then be needed to map addresses into routes, since there would no
> longer be a network number as part of the address (except perhaps as a
> hint, to improve performance)."
> Of course, this was already underway -- 48-bit unique addresses in the
> XWire/DIX/802.3 Ethernet and in the Xerox Network System (XNS) internetwork
> architecture.
> [Dalal published this at SIGCOMM in 1981.]
>
> Hard to believe this was all 40-50 years ago.....
>
> John
>
>
>
>
> > Message: 4
> > Date: Tue, 29 Nov 2022 15:19:46 -0800
> > From: John Gilmore <gnu at toad.com>
> > To: John Kristoff <jtk at dataplane.org>
> > Cc: internet-history at elists.isoc.org
> > Subject: Re: [ih] History of duplicate address tests
> > Message-ID: <1541.1669763986 at hop.toad.com>
> >
> > John Kristoff via Internet-history <internet-history at elists.isoc.org>
> > wrote:
> > > I'm curious to know about the earliest of duplicate address detection
> > > mechanisms.
> >
> > Were there any duplicate address detection methods used in the 3-megabit
> > Experimental Ethernet?  As I recall from the early 1980s on Stanford SUN
> > workstations, the 8-bit addresses used to identify nodes were configured
> > by DIP switches on the interface board, so there was a significant
> > chance of mistakenly configuring a duplicate address.
> >
> > April 1984's RFC 895 describes how IP datagrams are carried on
> > Experimental Ethernets.  It provides no duplicate detection, merely
> > suggesting (in those days of unlimited IP address space), "The easiest
> > thing to do is to use the last eight bits of host number part of the
> > Internet address as the host's address on the Experimental Ethernet.
> > This is the recommended approach."
> >
> > Perhaps PUP or other early Ethernet protocols did duplicate address
> > detection?
> >
> >         John
> >
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> Internet-history at elists.isoc.org
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>


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