virtualbox

Go to VirtualBox Preferences and under "Network", add host-only network. This will add a new vboxnet0 interface, which comes up as "192.168.56.1/24"

In the Guest Settings, add the "Host-only" to a second "Network Adapter"

Once Guest boots up, assign a static IP to the second adapter.

For Debian based servers, edit /etc/network/interfaces and add the below, which should bring up the network upon reboot:

You should now be able to ping and ssh to the guest via the host server on the second interface.