Hi BlackPR. NAT Loopback is not an application that is supported by Comcast on the Business Gateways. However, Static Routing under the LAN Tab does allow for customer specific configurations.
BlackPR and John,
I have posted for similar issue as follows.
Have you solved your issue by using "Static Routing" that John suggested??
Not sure you are still looking for suggestions on this or not but your trouble is with NAT reflection. Many router/firewalls cannot do it properly. I haven't used the Netgear device, I have an older Comcast router. What we do is disable all firewalling on the Comcast device and use a software firewall called pfsense. It can be installed on a PC that has a couple of network cards in it. You can then set it up with the Comcast public IP's you have so long as the Netgear will support that. pfsense has NAT reflection built in so you can access your public IP's from inside the local network. pfsense also has some great features like bandwidth limiting by IP or protocol, IPS add-ons, lots of other cool stuff. Check out pfsense at pfsense.org.