[TUHS] Early Internet work (Was: History of select(2))

Paul Ruizendaal pnr at planet.nl
Mon Jan 16 20:31:32 AEST 2017

On 16 Jan 2017, at 2:01 , Noel Chiappa wrote:

>> From: Paul Ruizendaal
>> I guess by April 1981 (RFC777) we reach a point where things are
>> specified to a level where implementations would interoperate with
>> today's implementations.
> Yes and no. Earlier boxes would interoperate, _if addresses on each end were
> chosen properly_. Modern handling of addresses on hosts (for the 'is this
> destination on my physical network' step of the packet-sending algorithm) did
> not come in until RFC-1122 (October 1989); prior to that, lots of host code
> probably tried to figure out if the destination was class A, B or C, etc, etc.

This is true of the Gurwitz implementation. The Wingfield implementation still uses the older form, where the first 8 bits signify the network and the remaining 24 bits the host address on that network. In terms of routing my view would be to keep it simple: traffic is either local or destined for the single interface / gateway (see below). Interop hence is just looking at TCP.

> Also, until RFC-826 (ARP, November 1982) pretty much all the network
> interfaces (and thus the code to turn the 'destination IP address' into an
> attached physical network address, for the first hop) were things like ARPANet
> that no longer exist, so you could't _actually_ fire up one of them unless you
> do something like the 'ARPANet emulation' that the various PDP-10 simulators
> use to allow old OS's running on them to talk to the current Internet.

Yes: all these old implementations have an IMP interface driver at their lowest level. What I'm doing for testing is replacing that by a SLIP driver so that I can hook up to today's network and see if it works.


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