On Sun, 28 Jun 2020 11:54:16 +0200
"R.Wieser"  wrote:

> Ahem,
>
> > In that case you need to add a second ethernet to the
> > Pi - a good USB-2 ethernet should get you 100Mb/s,
>
> :-) Which is what my initial question started with.   Should I just plug
> a ethernet dongle into an USB port, or are other (and perhaps better)
> options available ?

 The only other real option is VLANs and a smart switch - USB
ethernet is simpler.

> Second, how do handle (configure) such an extra interface ? Especially as

 That depends - if both networks have DHCP servers then just
configure the new interface to use DHCP (probably default), plug it in and
watch it connect.

> I do not want either interface to be able to talk to the other without my
> say-so.

 You would have to do extra work to get packets passed between them.

> Are there (open source, sourcecode) programs available which will handle
> such (very restriced) communication ?

 Once you have them both connected you can run services listening to
either or both. You could set up samba with a share visible to both
read/write and use it like a drop box, or you could set up an ftp server,

> As I said, I'm a rather newbie in regard to both Linux as well as the
> RPi. I could do worse than to work my way thru a tutorial or get my
> (rather needed) pointers from someone elses project.

 This is pretty much off-the-shelf. In your position I'd probably go
with samba and set up a share or two.

> :-)  Although I know of the latter by way of what Windows offers (SMB), I
> have no idea what exactly the SAMBA service does or how I should/need to
> configure it.   Let alone which things I all need to disable to be sure
> no inadverted connections can be made between the interfaces.

 Samba is an open source SMB server, there's a vast amount available
on configuring it.

 You don't need to disable anything, you would need to enable
routing for there to be connections between the interfaces.

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