How to configure NAT port forwarding in VirtualBox

When using VirtualBox with a NAT network, the guest virtual machine cannot be accessed directly from the host. The NAT network isolates the guest in a private network, separate from the host machine. This limits external access to the guest VM.

To enable communication between the host and guest, port forwarding is required. This process maps a port from the host’s IP to a port on the guest’s IP. It allows you to access services running on the guest, such as SSH or RDP, through the host machine.

Configuring port forwarding in VirtualBox involves creating rules that direct traffic from a specific port on the host to the corresponding port on the guest. These rules are applied to the VM’s NAT network, ensuring proper access while keeping the network structure intact.

1. Open VirtualBox and ensure the virtual machine is powered off.
2. Right-click on the virtual machine and select Settings.
3. Go to the Network tab in the settings menu.
4. Click on Advanced at the bottom of the Network settings.
5. Select Port Forwarding.
6. Click the + icon to add a new port forwarding rule.
7. Some of fields are filled up by default.
8. Enter the desired host and guest ports.

   For example, forward TCP packets on port 2222 of the host machine to port 22 of the guest machine where 10.0.2.15 is the default IP for the guest under the NAT network.

   Leave Host IP and Guest IP fields blank to use the default settings. Leaving these fields blank will default Host IP to 127.0.0.1 and Guest IP to the assigned IP of the guest VM.

9. Confirm the rule by clicking OK.
10. Test the forwarding rule.

    user@host:~ $ ssh -p2222 user@127.0.0.1
    Warning: Permanently added '[127.0.0.1]:2222' (ECDSA) to the list of known hosts.
    user@127.0.0.1's password:
    Welcome to Ubuntu 18.04 LTS (GNU/Linux 4.15.0-20-generic x86_64)
    
     * Documentation:  https://help.ubuntu.com
     * Management:     https://landscape.canonical.com
     * Support:        https://ubuntu.com/advantage
    
      System information as of Wed Sep  5 16:52:59 +08 2018
    
      System load:  0.0               Processes:             91
      Usage of /:   18.8% of 8.80GB   Users logged in:       1
      Memory usage: 6%                IP address for enp0s3: 10.0.2.15
      Swap usage:   0%
    
    
    138 packages can be updated.
    72 updates are security updates.
    
    
    Last login: Wed Sep  5 16:47:16 2018 from 10.0.2.2
    To run a command as administrator (user "root"), use "sudo <command>".
    See "man sudo_root" for details.
    
    user@host:~$

    The above example uses SSH as an example and SSH by default runs on port 22. In this case, the host's port 2222 forwards to the guest's port 22.