[ih] The invention of what we now call NAT

[Brian E Carpenter]

Before 1990, running out of address space wasn't a theoretical matter; that's why DEC invented "hidden areas" for DECnet Phase IV, which sort of did NAT at the subnet ("area") level. That was in widespread use in the late 1980s. Anyone who had to work with hidden areas hated it, and it was the main motivation for migrating large DECnets to Phase V.

There was also IBM's US patent #5371852 in 1994 (filed October 14, 1992): Method and Apparatus for Making a Cluster of Computers Appear as a Single Host on a Network.

Regards
    Brian Carpenter

On 23-Apr-25 07:47, touch--- via Internet-history wrote:
> 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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