I had issues with Strict Nat for MW3 and spent many hours looking for a soluttion! I've put this together from a few posts i have read and this sorted the problem for me! hope this helps others
this is a guide to obtain OPEN NAT in PS3 COD MW3 with Thomson TG782T Modem
Windows 7 has Telnet Client closed as default! it can be quickly re-enabled by following these steps:
Start Control Panel Programs/Programs And Features Turn Windows features on or off Check , "Telnet Client" Hit OK
After that you can start Telnet
Step 1- On your PC - click on start - In the window "search for programs and files" type "run" - In the "run" window type " cmd " this is the command window. - Copy and paste this command. telnet 10.0.0.138 (press enter)
This will open a telnet session with your modem, you will then be asked for a Username and Password.
Username: admin (press enter) Password: your modems password (usually blank by default) (press enter)
Step 2- copy and paste these 4 command lines one at a time pressing enter after each one is done.
When i did this after a while i could not connect to any games and i could not go into the internet either on my pc it said "server error", i had to reset my router every time this happened which means i had to reset every 45 minutes. Please Help.