Windows – Cannot access virtual machine via ping from the physical host machine

Turns out I forgot a step... I needed to add a route to the virtual guest telling it how to get to the external LAN my appliance is sitting on via the IP address of the vboxnet0 interface on the VirtualBox host. Once I did this, I was able to communicate with it externally.

thanks @Sirex for commenting on my question enough to make me think about it more!

Take a look at this link.

Internal networking:

This can be used to create a different kind of software-based network which is visible to selected virtual machines, but not to applications running on the host or to the outside world.

The problem you are facing is that the VM's cant reach your DHCP server. It's getting an APIPA adress (169.254.xx.xx)

Bridged networking

This is for more advanced networking needs such as network simulations and running servers in a guest. When enabled, VirtualBox connects to one of your installed network cards and exchanges network packets directly, circumventing your host operating system's network stack.

If you have a router or DHCP server on your network, configure this option to receive DHCP packets through the host machines NIC, so the VM's automatically obtain IP adresses.

Else you can configure static ip adresses op both VM's

Example:

 VM Mars:  IP 192.168.1.5, Subnetmask 255.255.255.0 
 VM Saturn: IP 192.168.1.6, Subnetmask 255.255.255.0

EDIT: If you want the host to communicate with the VM's use a bridged network for the VM's and either give the VM's a static address within the same subnet that your host is in. Or let DHCP assign IP adresses to the VM's dynamicly (to assume your host is getting an DHCP address from the same server/router )