I changed the firewall DMZ IP to be the same as the firewall WAN IP like the PDF I posted earlier in this thread suggested and it worked fine, without any problems. After this IP change I moved my mail server behind the DMZ hoping to not experience the latency issue I reported here, since I changed the IP of the DMZ to be the same as the WAN. The same latency issue occurred. It appears that even when the DMZ and WAN IP addresses are the same, moving a server from the WAN to the DMZ has the latency ARP issue.
I powered off/on my Cisco Router that is my gateway to the internet and the latency problem was resolved.
The issue is the ARP tables in the Cisco router that handles all the data going in and out of my network from the internet is the issue, and since this hardware is supplied by my carrier I do not have admin access and cannot clear the ARP. A simple power off/on is the fix here.
My setup to the question:
I've setup a D-Link DFL-700 Firewall LAN/DMZ/WAN config behind a Cisco broadband router/gateway that connects with my carrier.
We'll say my Cisco broadband gateway IP is 22.214.171.124 and is part of a class-C block (126.96.36.199/24).
I set my WAN (static) to 188.8.131.52 and set the ARP to public.
I set my LAN to 192.168.1.1 (private) and also setup the DHCP server to use 192.168.1.1 as a range 192.168.1.0/24.
I set my DMZ to 184.108.40.206 and set the ARP to public with a single IP 220.127.116.11/32.
Could I/Should I set my DMZ to the same IP as my WAN?
Note: Anytime I move a server on my 18.104.22.168 network behind the DMZ using the same IP there is a delay of many hours before the outside world can find the route despite clearing the ARP cache and DNS cache of the server that was moved.
When I read support notes from DLink I see two different scenarios. The FAQ suggests that the DMZ has a unique IP, and if NO NAT as in my case I would configure the way I've outlined here.
However, according to this link to a PDF diagram, the Dlink techs in the UK seem to suggest that the DMZ uses the same IP as the WAN.