Grant,

> Is that "have not (yet)" or "will not (ever)" allow them to communicate
> with each other?

I think this is one of the few instances where a single "yes" is
appropriate. :-)

I have not ever, nor do I intend to have them ever communicate with each
other over ethernet.

> I'm guessing that the computers currently can't  communicate with each
> other via TCP/IP (et al.).

Correct.

> But are you willing to (re)configure things so that they can communicate
> with each other via TCP/IP?  Or do you want to forbid that?

Nope and yes.    Thats why I placed them on their own subnets.

> What precisely does "communicate" mean in this context?  -  Does storing a
> file in an intermediary location for the far end system to pick up count
> as "communication"?  Or are you specifically referring to something like
> end-to-end TCP/IP connections?

[quote=me]
For that I could imagine a kind of "post office" solution, where 'puters on
both subnets can leave messages for each other and ofcourse read each others
replies, but never directly talk to each other.  (both 'puters connect to a
known port on the RPi).
[/quote]

> I ask these questions because I've had client's have different answers and
> they effect the solution(s).

I think the above quote answers it.  :-)

>> The first problem would be that I would need to add another (or more)
>> ethernet connection (so the 'puters on one subnet cannot reach 'puters on
>> the other one).
>
> Now it sounds like you might be willing to allow end-to-end TCP/IP
> connections.

Nope.   I thought about that, but consider it to be too dangerous - unless I
would only allow only a very small range of ports thru, with zero
firewall-intelligence (opening other ports when the "inside" 'puter asks for
it).  But that would mean I would need to be very sure that no port in the
allowed range would be used by any of the 'puters default, or later
installed programs/services.   As I can't be I decided that the "postoffice"
way of handling stuff would be best.

>> (at a usable speed) ?
>
> It depends what you consider to be a usable speed.

I have been considering hooking up two 'puters thru a classic RS232
connection (DB9 connectors).  Alas, even on their highest speeds, 128000
bps, it islaughably slow in comparision to a LAN connection.

> I know exactly what I would use if I wanted computers on different
> networks to exchange messages / files / commands with each other without
> being able to establish end-to-end connections between them.
>
> I'd use UUCP over SSH.  (You can use UUCP over TCP or serial too.)

I don't know anything about UUCP, and have to look into it.

Though the programs are less of a problem.  I enjoy programming, and have no
problem with trying my hand at writing stuff for both the (Windows) 'puters
as well as the RPi (even though I'm a very much a novice on the latter).

The biggest issue is if the RPi allows for electrically & programmatically
seperated ethernet connections, and allows me adress the ethernet interfaces
seperatily.

> the only limitations that I see are the network speed, storage capacity,
> both of which are only an issue if you want to send some really big files
> / messages.

I'm not really considering (very) big files, but would like to be able to
move a gig or so without having to wait for the better part of a day (as I
would need to when using an RS232 connection).

Regards,
Rudy Wieser

P.s.
I just realized I should take a peek at USB-to-RS232 converters.  Those
might well have a much higher thruput than what the UART offers.

--- SoupGate-Win32 v1.05