Port Forwarding
---------------

From VirtualBox Manual:

VBoxManage modifyvm "VM name" --natpf1 "guestssh,tcp,,2222,,22"

With the above example, all TCP traffic arriving on port 2222 on any
host interface will be forwarded to port 22 in the guest. The protocol
name tcp is a mandatory attribute defining which protocol should be used
for forwarding (udp could also be used). The name guestssh is purely
descriptive and will be auto-generated if omitted. The number after
--natpf denotes the network card, like in other parts of VBoxManage.

See http://www.virtualbox.org/manual/ch06.html#natforward for
complete details.