On June 28, 2020 15:00, R.Wieser wrote:

> Ahem,
>
>> It's not much work - set a flag on the Pi and tell the two
>> subnets that they can find each other via the Pi.

Effectively, that makes the RPi a router.

> You are quite light on information, but I'm already quite sure that that
> is *not* what I want to have happening.
>
>> Until you do that the Pi is the only thing that can see and
>> be seen on both subnets.
>
> I think I will keep it that way.

I can think of an all-ethernet way of making the RPi a drop-box service
between two unconnected networks, but it might not suit your criteria.
Nevertheless, here it is.

1) the Linux networking stack can support multiple IP addresses on a single
   physical ethernet interface. These addresses /do not/ need to belong to
   the same subnet, or even the same network.
2) the Linux networking stack can be configured to act as a "host" (rather
   than a router), ensuring that the system isolates each network so that
   packets are not exchanged between any of the connected networks.

Taken together, this means that you can connect a generic Linux system to
/both/ of your networks, and ensure that the system maintains an isolation
barrier between the networks. So, that one generic Linux system is "visable"
to each network, with it's own unique address /on each network/.

The trick, with the RPi, is to be able to physically connect it to both
networks.
1) On some RPIs, you could hardwire one network to the RPI ethernet port,
   and use the built-in wifi to connect to the other network, or
2) hardwire one network to the RPI ethernet port and use a USB-WIFI dongle
   to connect to the other network, or
3) hardwire one network to the RPI ethernet port and use a USB-ethernet
   dongle to connect to the other network, or
4) hardwire /both/ networks to the RPI ethernet port (this would require
   running both networks through a switch, or a router configured as a
   "pass-through". (Note that a switch would maintain the independance
   and isolation of each network, while allowing both networks to use
   a shared cabling infrastructure).

So, my suggestion
a) install a switch and connect it to both networks
b) connect your RPI to the switch
c) configure your RPI as a "host" (no routing between interfaces)
d) configure your RPI ethernet with two "alias" interfaces
   a) give one alias interface an address on the /first/ network,
   b) give the other alias interface an address on the /second/ network.
e) set up whatever drop-box software you need on the RPI (SAMBA, NFS, ftp,
   whatever).

f) there is no "f"

HTH
--
Lew Pitcher
"In Skills, We Trust"

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