@qubist thank you for your clear answers!
I wanted to ask you about IP addresses in the script /rw/config/rc.local of f37-m-firewall-dvm.
The IP addresses 10.139.1.1 and 10.139.1.2 are more or less clear from your answer elsewhere:
What about the following IP address? Should I adapt it according to IPs of my VMs? If yes, to which one? If no, what does it represent?