[ih] The invention of what we now call NAT

[touch at strayalpha.com]

There was also a project at ISI called the “tunnel” that involved a network device with stateful ports used for network access control, developed by Danny Cohen and Annette Deschon, right around that time:
https://apps.dtic.mil/sti/tr/pdf/ADA271585.pdf

There's also Jeff Mogul’s tech report from 1989 that dances around the same concept:
https://bitsavers.org/pdf/dec/tech_reports/WRL-89-4.pdf

I would hesitate to attribute it to any one person, but I do think the timeline is roughly correct.

Joe

—
Dr. Joe Touch, temporal epistemologist
www.strayalpha.com

> On Apr 22, 2025, at 12:23 PM, Craig Partridge via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> Well, and I'm working from memory for the most part, so flaws may exist.
> 
> Van Jacobson is credited as the initial thinker about NAT in RFC 1631 prior
> to January 1993, which matches my memory, which is that Van came up with
> NAT as a concept while serving on the ROAD WG (which made its report at the
> 1992 IETF in San Diego -- see minutes p. 508ff, which mention the address
> exhaustion problem but not NAT).
> 
> I have a fuzzy memory of Van talking about the idea, which required an
> enabling idea, which was how to match which TCP connection to which host
> among the hosts sharing the IP address.  And, as I recall, Van made use of
> the fact that firewalls were doing per TCP connection mappings to firewall
> rules and said "aha, that's how you do it."   Since firewalls were a new
> concept, c. 1990 by Bellovin and Cheswick, the idea of a prior invention of
> NAT prior that 1990 would be unlikely.  Also, ISPs typically didn't charge
> for IP addresses until a bit after 1990.  So the window for someone to
> separately invent NAT exists (c. 1991-1993) but is narrow.
> 
> Craig
> 
> On Tue, Apr 22, 2025 at 12:52 PM Andrew Walding via Internet-history <
> internet-history at elists.isoc.org> wrote:
> 
>> Wizards and Historians,
>> Someone please correct me if what I had heard was wrong.  Back in the BBS
>> days when those of us were considering/wanting to connect our BBS systems
>> to the TCP/IP world (which as I recall really was not successful -
>> certainly not for my BBS) one of the members of the Homebrew Computer Club
>> of Menlo Park came up with the idea to bypass the high cost of static and
>> public IP addresses by translating private address space to a single public
>> IP, therefore avoiding the cost of having multiple public IPs.  The
>> motivation for this was to avoid paying the service provider more money, of
>> course.  Every time we added a phone line and a modem, it cost more money
>> for our BBS's so we were all very sensitive about this.  Now, we used
>> tricks like "teen lines" and so forth to minimize costs, but the thought of
>> then having to pay for multiple public IP's for each line was cost
>> prohibitive for most of us along with the perhaps bigger question: why
>> would the TCP/IP network want BBS systems on it?
>> 
>> Anyway, I heard about this trick and the code to accomplish this way before
>> RFC 1631 (1994) was even a draft.  I would say this was in 1985 or so.
>> Never saw it myself so it has always been a "tall tale" in my head.
>> 
>> Anyone know anything to confirm or deny this tall tale?
>> Andy
>> 
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