For the past few days while playing MW2, my NAT Type seems to be set to strict. This has never happened before. My UPnP is set to available and my when testing the connection via PS3 The NAT type is Type 2, with again UPnP available. My ISP is Plusnet with a Thompson Gateway TG585 v8 model. Any ideas whats wrong?
This happens to me every 2 months or so, and a simple reboot of my router clears it right up, and sets it back to NAT type 2. Give it a try and let me know if it works