So I got VirtualBox just for Ubuntu Server, I'm currently Running Ubuntu 12.04 as my main OS. But when I got everything set up in Ubuntu Server 12.04, including my ports forwarded and a test Minecraft server up... I realized that nobody could join my public IP I sent out, not even me! I can connect to the ipv4 address. It acts like I didn't forward my ports. But I forwarded 25565 to Input and Output and they're both TCP and UDP. Is this just a virtual box issue or am I doing something wrong? * Using Eth0 wired connection
By default, a virtual machine will be set up to NAT networking. This means that VirtualBox acts as a "virtual router" that allows the VM to access the internet, but will not allow external users to access the VM properly.
To do what you want, you need to set your VM up to use "bridged" networking. This way, on the host computer, an interface will be created that will be "bridged" to the VM's network interface. Thus, the VM will act, for all intents and purposes, as if it were hooked up to the same network as the host system (down to you needing to configure its IP address as you did for the host system).
Read here for the different VirtualBox networking modes and what each of them does. http://www.virtualbox.org/manual/ch06.html. Pay special attention to the section on "bridged networking".