On 23/06/2020 06:34 pm, R.Wieser wrote:
> Hello all,
>
> I've got a few computers in seperate subnets which I do not allow to
> communicate with each other.
> When I need to transfer data between computers in those subnets I use an USB
> stick.
>
> Somehow my thoughts went to if it would be possible to use an RPi 3B+ as a
> kind go-between.
>
> 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).  Is that at all possible (at a usable speed) ?
>
> The second would be to how to transfer data from one subnet to the other.
>
> 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).
>
> Does anyone know if such a sulution or project (and tutorial?) for such a
> thing exists ?
>
> Regards,
> Rudy Wieser
>
>

Reading through this thread it seems you're worried that adding a USB
ethernet dongle would slow traffic down. The built-in ethernet on the Pi
hangs off the USB bus; adding another dongle uses the same USB bus. So,
no extra slowdown. Two ethernet ports would normally be on two separate
LAN segments, with (on Linux anyway) no connection between them unless
forwarding is enabled - not by default.

Then look at NFS (network file system). Add nfs-kernel-server to your
Pi. Both Windows and Linux have NFS clients.

You can then export a single directory which can be mounted by clients.
Each client can then read and write (if set up like that) to that
directory as if it were a local directory.
e.g. in /etc/exports (/var/ftp/pub is on the Pi) (see also below)
this exports a public directory
/var/public 192.168.0.0/24(rw,sync) 192.168.100.0(rw,sync)

Each (linux) client has a line in /etc/fstab

server:/path/to/export localmountpoint fstype option,option,... 0 0

e.g.
raspberrypi:/var/public /home/rudy/raspberry nfs rsize=8192,wsize=8192 0 0

Options can be found in man nfs.

from man exports:
EXAMPLE
        # sample /etc/exports file
        /               master(rw) trusty(rw,no_root_squash)
        /projects       proj*.local.domain(rw)
        /usr            *.local.domain(ro) @trusted(rw)
        /home/joe       pc001(rw,all_squash,anonuid=150,anongid=100)
        /pub            *(ro,insecure,all_squash)
        /srv/www        -sync,rw server @trusted @external(ro)
        /foo            2001:db8:9:e54::/64(rw) 192.0.2.0/24(rw)
        /build          buildhost[0-9].local.domain(rw)

The first line exports the entire filesystem to machines master and
trusty. In addition to write access, all uid squashing is turned off
for host trusty.
The second and third entry show examples for wildcard hostnames and net‐
    groups (this is the entry `@trusted').
The fourth line shows the entry for the PC/NFS client discussed above.
Line  5 exports the public FTP directory to every host in the world,
executing all requests under the nobody account. The insecure option in
this entry also allows clients with NFS implementations that don't use a
reserved port for NFS.
The sixth line  exports a directory read-write to the machine 'server'
as well as the `@trusted' netgroup, and read-only to netgroup
`@external', all three mounts with the `sync' option enabled.
The seventh line  exports  a  directory  to both an IPv6 and an IPv4
subnet.
The eighth line demonstrates a character class wildcard match.



--

Chris Elvidge, England

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