Networking – How to i setup a guest-guest network connection with virtualbox

Consider configuring the machine with two interfaces instead of one.

On the first you can use the Host-only Adapter so that your host can always talk directly to the guest. Then configure a second interface as either NAT or Bridged Adapter depending on your specific needs for your application.

If your guest is running as a server then you'll want Bridged. For the interface that is running in Bridged mode it will act just like a regular interface, so if you want a static IP address you'll either need to configure your network's DHCP server to assign the same IP address to the MAC address of your virtual Bridged interface, or you'll have to set up that Bridged interface statically (not recommended if your network uses DHCP unless you coordinate it with your local network admins... in which case you're better off asking for the same IP address from the DHCP server).

Would require some testing/tweaking, but it sounds like setting up a second network adapter on your guest VM might be the answer.

This would allow you to use the primary adapter in a NAT configuration as rhubee recommended (which will provide your guest VM with internet access), while the second adapter has a static IP for an internal network that will not change between host and guest. The testing/tweaking portion would come in as you may possibly need to configure some static routes to ensure traffic for the services/ports route through to the correct interface.

Not quite the same goal, but I have run multiple guest VM's that share an internal only network between them, while having a separate adapter NAT'd so that they could both still hit the internet.