See
Virtualbox Networks: In Pictures
The two Virtualbox networks that have port forwarding are 'NAT' and 'NAT Network'. Both behave like house routers
A router makes a private network for your computers and has the internet on the other side. The computers can get to anything on the internet, but port forwarding is necessary when something on the internet wants to get to the computers.
For a NAT or NAT Network guest, the guest itself is the private computer, and the host, the other computers and devices on the host's network and the internet, are all accessible to the guest with no port forwarding needed. If you always start the communication to the industrial equipment from inside the guest, then you should not need to port-forward. The equipment is part of the "internet" to the NAT guest.
If the equipment needs to start communication into the guest first, that would require port forwarding on the NAT adapter that the guest has, since it is like something on the internet trying to get into your private computer.
Each NAT adapter has its own port forwarding section in the Advanced dropdown. Each NAT Network has a port-forwarding section in the main Virtualbox window's File menu, Preferences, Network, doubleclick the NAT network. The above tutorial shows what data is needed for NAT or NAT network. For NAT you need only the Host Port and Guest Port. Host Port is what port number the outside equipment tries to communicate through. Guest Port is what port the guest expects the traffic to come on.
Example 1: I have a NAT-connected Windows Pro guest with Remote Desktop (RDP) active. The Windows OS wants RDP on port 3389. So I would set the Host and Guest ports in the Port Forwarding for the guest's NAT adapter both to 3389. No other information is needed in the Port Forwarding setup. I access the guest RDP by host.ip.add.ress:3389
Example 2: Same setup as Example 1, except the host also wants to use 3389 for its RDP. I cannot distinguish which PC, host or guest, I would remote into if they both have 3389. So I set my guest's NAT Port Forwarding to Host port 3390, guest port 3389. Now RDP on 3389 goes to the host PC, and RDP on 3390 goes to the guest. No other information is needed in the Port Forwarding setup. I access the guest RDP by host.ip.add.ress:3390, and I access the host RDP by host.ip.add.ress:3389
Example 3: Same as Example 1 except the guest uses NAT Network. In addition to the Host and Guest Ports, i must also provide the IP address the guest receives from the NAT network. If NAT Network gives my guest 10.0.2.16, then I must provide Host port 3389, Guest port 3389, Guest IP address 10.0.2.16. Nothing else needed. I access the guest RDP by host.ip.add.ress:3389
Example 4: Same as Example 2, except connected through NAT network. Host Port 3390, Guest Port 3389, guest IP 10.0.2.16. Nothing else needed. I access the guest RDP by host.ip.add.ress:3390, and I access the host RDP by host.ip.add.ress:3389
An easier way to set this up without any need for port forwarding is to use Bridged for the guest. The guest then sits in the host network along with the host and equipment, and all devices can talk to each other. (If you are worried about XP trying to access the internet, you should be able to block the XP "computer" using your network router's Access Restrictions or Parental Controls page.
