I went through a strict NAT ordeal a couple of months back. I tried literally everything. Port forwarding, static IPs, stuffing around with moden settings, contacting my provider, contacting the modem manufacturer.
I tried my 360 and its NAT was open. Then I tried a friend's One on my network, and it was open.
I exchanged my One for a new one, and sure enough its NAT is OPEN.
A faulty console was the problem.
For those wondering, I also had the following problems, which Im not sure were connected
- Couldnt activate achievements whether online or offline.
- Faulty Kinect. Kept switching off and on.
- Crap disc drive. often woulddnt recognise discs.
- Some apps wouldnt work.
- Couldnt party up.
Hopefully Ive helped someone.