[ih] Overlay networks (1980s SRI Reconstitution Protocol)

[John Day]

> On Aug 21, 2025, at 16:48, Jack Haverty via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> The ICCB discussed the "reconstitution" need back in the early 1980s.  The concept was that the Internet could be used to re-establish host-host connectivity when an underlying network, e.g., the ARPANET, was partitioned.  This was thinking beyond research to operational military usage, when the underlying network, i.e., the Defense Data Network, might be partitioned due to enemy activity.

Then by definition, it wasn’t a partition.
> 
> The mechanism would require multiple paths through the Internet. That situation existed at the time in the research installations. For example, the WBNET provided connectivity between the US east and west coasts, and could serve as a backup to the ARPANET connectivity.   Similarly, SATNET provided connectivity to Europe, and the X.25 public network provided a second path.

If there are alternate paths available, there is no partition.

This was just an exercise in sloppy thinking.

Take care,
John
> 
> I don't know any details of what was actually tested but the notion was that the relevant gateways could notice that one of their underlying networks (e.g., the ARPANET) had become partitioned. They could detect that situation by their sudden inability to communicate with other gateways on a particular underlying network.
> 
> A similar procedure had been used internally within the ARPANET, to detect and route around circuit failures.  Gateways talked to each other much as IMPs did, to detect failures and route around them. But they assumed at that time that networks were either working or not working.  In the ARPANET, circuits never "partitioned", and the gateway system had used the same assumptions about its underlying "circuits", i.e., the underlying networks.  "Reconstitution" was possible in the Internet, where it wasn't in the ARPANET.
> 
> The gateways could then exchange routing information, using the paths between gateways that still were functional, to begin to treat the broken ARPANET as two separate networks.   Routing changes would then direct Internet traffic as needed to re-establish communications between host pairs on the broken network(s).
> 
> This of course required hosts to be using TCP/IP, and also a robust connectivity within the Internet, so that there were alternate paths to be used.
> 
> The underlying "broken" network was not itself patched back together.  But assuming the individual pieces of that network continued functioning, traffic through the Internet could be resumed, passing around the breaks.  The ARPANET pieces would continue to work even when partitioned.
> 
> I recall an incident in the early 1980s when an operator from the ARPANET NOC stuck his head in my office and frantically asked if the Internet could be used to get to some west-coast computer from our east-coast location, without using the ARPANET.  Couldn't happen - there was no such "reconstitution" mechanism in place at the time. Curious, I wandered down to the NOC to see what was going on.  Some combination of buggy software and possibly an errant backhoe had partitioned the ARPANET, and the operators were trying to figure out how to put it back together.  Turned out bugs and backhoes had similar effects to bombs and missilies.
> 
> "Reconstitution" was about re-establishing communications through the Internet, not fixing broken underlying networks.
> 
> /Jack Haverty
> 
> 
> On 8/21/25 12:38, John Day via Internet-history wrote:
>> This topic has come up several times here. Could someone please explain it to me.
>> 
>> My understanding is that this was a protocol to repair network partitions.
>> If there is a network partition, there are two issues:
>> 1) it can’t be known that it is a partition until it is over. From within the network, a network partition is indistinguishable from a number of hosts being down for some other reason.
>> 2) If it is a network partition, there is no communication between the partitions so how can there be a protocol to repair it?
>> 
>> Thanks,
>> John Day
>> 
>>> On Aug 21, 2025, at 15:32, John Gilmore via Internet-history<internet-history at elists.isoc.org> wrote:
>>> 
>>> Barbara, thank you for reminding us of the Network Reconstitution Protocol.
>>> 
>>> Here are two copies of their final report:
>>> 
>>>  https://apps.dtic.mil/sti/tr/pdf/ADA184755.pdf
>>>  https://archive.org/details/ADA184755/
>>> 
>>> They appear to come from the same (microfiche) source.
>>> 
>>> Also here's a brief note by Greg Skinner about this work and report:
>>> 
>>>  https://gregbo.medium.com/network-reconstitution-protocol-79bc61067f8e
>>> 
>>> 	John
>>> 
>>> PS: Due to Greg Skinner's comment at the bottom of this Computer History
>>> Museum story, I ran across this today, from back when the Internet
>>> itself was barely an overlay network:
>>> 
>>>  "Born in a Van: Happy 40th Birthday to the Internet!
>>>  40th Anniversary of the First Major TCP Internetwork Demonstration, November 22, 1977"
>>>  by Marc Weber
>>>  Nov 22, 2017
>>>  https://medium.com/chmcore/born-in-a-van-happy-40th-birthday-to-the-internet-d81287f172bf
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