Advanced DMZ Hosting is a feature that places the device outside the firewall and also assigns the WAN IP address to the device (so the modem and device both have the same WAN IP address).
This is done using the MAC address instead of the IP address. The problem the EU was experiencing was that once he put in the MAC address for his server, the server would not get the WAN IP. In the case of a Windows box, it had a self-assigned IP address, and on a Linux box, it had no IP address. In the case of the Linux box, it also did not show the MAC address in the Select Device drop-down menu. After talking to Bill Ge regarding this issue, we learned a little more and Jake recreated the setup using both Windows and Linux. In both cases, he was able to select the device from the drop-down or manually enter the MAC address. In both cases the Advanced DMZ Hosting worked as it should, assigning the WAN IP address to the device. Once the router was rebooted, the device shows on the Homepage of the GUI with the WAN IP address. After conveying our findings with the EU, he emailed me back and stated that he had the DHCP server turned off on the router and had manually configured IP addresses on the servers. Once he turned on the DHCP server and the servers obtained their IP addresses automatically, the Advanced DMZ Hosting worked as it should.