[Top Jimmy]

You only need a single static IP from your ISP. This static IP on the internet is what allows others to be certain that they are connecting to your DD server when they are sending or receiving a delivery. Your internet usage and the server traffic can be easily handled through this one address.

Here's the easy way to do what you are doing:

Make sure you have a router that can restrict the DHCP range on the LAN and allows a LAN address to function as a DMZ host. Restrict the DHCP range to some number of IP addresses that you think you'll ever need at one time for all your network appliances. Set the DMZ address in the router to a number outside the allowed DHCP range. This LAN IP set as the DMZ host is the static IP address that you'll assign to the Digidelivery.

Configure your server with the IP that is set as the DMZ host, the gateway is the LAN IP of the router, and the DNS servers are the same ones that your ISP gave you and are used in the router.

Follow this thread for some more tips