If you want to Forward Ports to VirtualBox or Virtual Machine and use it like a server, follow instructions for VirtuaBox Port forwarding.

The only other machine talking on br2 is my pfSense VM. It has a virtual NIC which talks to br2, and gets my internet addressable IP address from the cable modem. Everything works, all is happiness.

Boxes is a great way to spin up virtual machines on Linux. Jack Wallen shows you how it's done.