Network interfaces for Ubuntu VirtualBox guest on Windows host
To work effectively and relatively securely on a VirtualBox guest system, the guest needs two network adapters - a NAT and a host-only adapter. The NAT interface allows talking out to the internet, and the host-only adapter allows ssh and http in from the host.
However, it seems that Ubunt/Debian only recognizes one network interface on system installation.
So to get two interfaces on the guest, I found the following to work :