TL;RD Playing with Linux network namespaces
I had a Linux server with two physical network interfaces which were separated into two network namespaces. Security was set up like two machines with single network card in each connected to different physical networks.
At one day, someone found out, that a process runs in the 'red' network namespace needs to connect to a remote machine, reachable via the physical network interface connected to the other namespace we call as host namespace. How to do so?