Double NAT error on new AirPort Express

Question

I live in an apartment complex with a single network connection. The address is given to me from the complexes shared router as a DHCP address - this is where the ISP has our complex's modem. My neighbor also has an AirPort Express and I think I may be getting conflict with his... in my AirPort Utility, I can see his "horizontally" in line with mine connecting to "Internet", not vertically.

If I connect straight from my computer to my network wall jack, I can browse to my hearts content... I have a solid speed and all is well. If I plug in my AirPort Express to the jack, I get solid green on the Express as well as on the "Internet" icon in my AirPort utility (hardwire connection from my laptop). As long as my laptop's wireless radio is off, I have a solid connection. If I try to connect WiFi from my iPhone 4 or turn on my WiFi radio on my laptop, I get an intermittent wireless connection and spotty internet.

I also keep getting this DUAL NAT message on my screen.

Let me know if you think you may know.

[10/15/2012 - I will do my best to get a screenshot]

Answer 1

You're connecting a router to a router, so you will get dual NAT.

The shared router is translating the single IP from the ISP into a shared network for you all to use. If you connect a second router to this to connect multiple devices, then you are creating a second network, and network address translation (NAT) is happening twice.

I'm not sire if the airport express supports bridged mode, but you could try this to see if it will allow you to connect multiple devices over Wi-Fi with the main shared router distributing the IP addresses. If you can do this, it should solve your dual NAT problem.

Dual NAT shouldn't however cause intermittent connection, that's more likely interference from other nearby Wi-Fi devices, so I'd suggest selecting different channels (if possible) until you find one that gives you a more stable connection.