#1 Let me give to you an example what happens with my router running tomato firmware.
With loop back in my router set to
Off, if I am behind my router and if I enter in my public IP: I can't connect to anything.
With loop back in my router set to
All, if I am behind my router and if I enter in my public IP I can connect to the router's UI as if remote control of the router is turned on.
With loop back in my router set to
Forward Only, if I am behind my router, if I enter in my public IP and I have a web server running on port 80: I am able to connect to my web server on port 80.
With loop back in my router set to
Forward Only, if I am behind my router, if I enter in my public IP and I do not have a web server running on port 80: I can't connect to anything.
**
#2 Based upon the above info, I have say if your router has loopback support, it set to
Off.
#3 I also have to say that:
a) Not all routers will allow users to adjust the loop back feature.
b) OR if they let the user adjust the loop back feature, they can only turn it off and on.
#4 As how to test for loop back (reverse nat), I point you to
http://www.pcwintech.com/test-for-reverse-nat
