[ih] First ARPANET Link Put Into Service: November 21, 1969
Vint Cerf
vint at google.com
Sun Nov 23 15:16:36 PST 2025
I made heavy use of the fake hosts for generating traffic, absorbing
traffic, reflecting traffic (ping) and for tracing paths taken by packets.
v
On Sun, Nov 23, 2025 at 5:51 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:
> There was a process involved in adding an IMP to the ARPANET. It no
> doubt changed over time, so what happened with IMP #1 and #2 may be
> different. I tried asking Ben Barker, since he is mentioned in that
> 1969 log entry, but the email addresses I have sadly no longer work.
>
> IMPs had "fake hosts" which acted like real hosts but were implemented
> as software inside the IMP. Back in 2012, Ben was helping with the
> resurrection of the old IMP code and told me:
>
> "The IMP code supported a number of "fake hosts". The TTY was one. DDT
> was
> another. There may have been another 1 or 2; I had no use for them if they
> existed, and do not remember them.
>
> Each IMP had a hardware card that contained its IMP number, I believe.
>
> There was a bit in the header that specified whether the message was for a
> real host or a fake host.
>
> I believe that the TTY was fake host 1 and the DDT was fake host zero.
>
> I believe that the default was that the TTY would be set to connect to the
> same IMP's DDT."
>
>
> Part of the process of getting an IMP online was to first get the two
> IMPs talking to each other. The TTY on one IMP could connect to the TTY
> on the other IMP, so the engineers at the two sites could "talk" over
> the net. You could also connect to the remote IMP's debugger (DDT) and
> examine or modify the remote machine's memory.
>
> After all that connectivity was working and the IMPs were judged
> functional, then the actual physical hosts could test their ability to
> communicate.
>
> So it's possible that the fuzziness in the timeline was because it may
> have taken a few weeks to run tests, get all the bugs out, and then
> declare the first 2 nodes of the ARPANET, and the NCPs in their attached
> hosts, to be "in service". The stories I've heard recounted that the
> initial testing crashed with only the LO part of LOGIN successful.
>
> One of the other fake hosts in the early IMPs was the one that sent
> measurement data to UCLA. More than a decade later, when we were
> involved in getting TCP/IP deployed, we noticed that the UCLA fake host
> was still in the code. So we used it to create a "Remote Datascope" for
> DDN (of course, worked in other ARPANET clones too) that could capture
> the TCP and IP headers of host-host traffic -- invaluable for figuring
> out what TCP was doing, especially as newly-written implementations by
> big government contractors were coming online.
>
> I doubt anyone knew, in 1969, what was starting then and how important
> it would be.
>
> /Jack
>
> On 11/23/25 13:04, Steve Crocker wrote:
> > After seeing the back and forth on this thread, I now think 21 Nov 1969
> was when Larry Roberts came to UCLA. I'll try to check with Kleinrock.
> >
> > Steve
> >
> > Sent from my iPhone
> >
> >> On Nov 23, 2025, at 3:48 PM, Jack Haverty via Internet-history <
> internet-history at elists.isoc.org> wrote:
> >>
> >> Perhaps someone in the Bay Area can go to CHM and ask what actually
> happened on November 21, 1969...? /Jack
> >>
> >>> On 11/23/25 12:22, Barbara Denny via Internet-history wrote:
> >>> Here is Don Nielson's response to my inquiry. I did cut out the
> first paragraph as it only was for me. There is a typo regarding the 1972
> ICC meeting.
> >>> barbara
> >>> ----- Forwarded Message ----- From: Don Nielson <
> nielsonz at pacbell.net>To: Barbara Denny <b_a_denny at yahoo.com>Sent: Friday,
> November 21, 2025 at 10:05:40 PM PSTSubject: Re: Fw: [ih] First ARPANET
> Link Put Into Service: November 21, 1969
> >>> "*** paragraph deleted*****
> >>> I'm certain about the following:
> >>> 1. First ARPANET connection - Between Bill Duvall at SRI and
> Charlie Kline of UCLA
> >>> on what has been accepted as 29 Oct 1969. I tried my best to
> confirm the date
> >>> while this date was being pushed by Len Kleinrock of UCLA. Even
> I and Marc Weber
> >>> the CHM dug into Engelbart's dinky handwritten notebooks and
> other stuff on file at
> >>> Stanford. As far as we could tell, nothing was noted on the SRI
> end, indicating no big
> >>> deal at the time. So, what has come to be accepted derives from
> a brief jot on Charlie's
> >>> scratchpad: "22:30 Talked to SRI Host to Host". Charlie and
> Bill are still around
> >>> and have confirmed and elaborated on the incident, being quoted
> in some places.
> >>> 2. ARPANET demo at the International Computer Communication
> Conference in WDC
> >>> of NCP in Oct 19723.
> >>> 3. First 2-net demo of TCP was on 27 Aug 1976. PRNET and ARPANET.
> >>> 4. First 3-net demo of TCP was on 22 Nov 1977. PRNET, SATNET, and
> ARPANET.
> >>> All this is easily available so 21 Nov 1969 seems an aberration by
> someone.
> >>> Take good care, Don
> >>> On 11/21/25 10:14 AM, Barbara Denny wrote:
> >>> Hi Don
> >>> Hope you are doing well. This came up on the internet history
> list. I am wondering if you could shed some insight on the log.
> >>> Hope you have a good holiday.
> >>> barbara
> >>> ----- Forwarded Message ----- From: Vint Cerf via
> Internet-history <internet-history at elists.isoc.org> To: Jack Haverty <
> jack at 3kitty.org> Cc: "internet-history at elists.isoc.org" <
> internet-history at elists.isoc.org> Sent: Friday, November 21, 2025 at
> 09:50:33 AM PST Subject: Re: [ih] First ARPANET Link Put Into Service:
> November 21, 1969
> >>> crocker and I were wondering the same thing off the list.
> >>> v
> >>> On Fri, Nov 21, 2025 at 12:49 PM Jack Haverty via
> Internet-history <
> >>> internet-history at elists.isoc.org> wrote:
> >>> > Can anyone explain why the article says "What Happened on
> November 21st"
> >>> > but the image of the "First ARPANET IMP log" shows "29 OCT"? /Jack
> >>> >
> >>> > On 11/21/25 09:37, vinton cerf via Internet-history wrote:
> >>> > > there are so many milestone dates....
> >>> > >
> >>> > > v
> >>> > >
> >>> > >
> >>> > >
> >>> > > On Fri, Nov 21, 2025 at 12:03 PM Frantisek Borsik via
> Internet-history <
> >>> > > internet-history at elists.isoc.org> wrote:
> >>> > >
> >>> > >> Happy birthday to the Internet!
> >>> > >>
> >>> > >> https://www.computerhistory.org/tdih/november/21/
> >>> > >>
> >>> > >> All the best,
> >>> > >>
> >>> > >> Frank
> >>> > >>
> >>> > >> Frantisek (Frank) Borsik
> >>> > >>
> >>> > >>
> >>> > >> *In loving memory of Dave Täht: *1965-2025
> >>> > >>
> >>> > >> https://libreqos.io/2025/04/01/in-loving-memory-of-dave/
> >>>
> >>>
> >> --
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