Firstly, you'll need to go to: Start>All Programs>Accessories>Windows Command Processor. Or Start>Search Programs and Files>Cmd.
Then you'll need to open cmd and type "ipconfig" (without the quotation marks) and press enter.
When you've done that scroll to the top and find your "Default gateway", Open a new tab or window and type that in.
Then you'll need to check that your UpNp (Universal plug and play) is enabled. If it is not enabled you must enable it by going to "toolbox" or something like that.
When your UpNp is enabled go back to cmd and find your "IVP4" address, and write it down.
Then you can close cmd (and the tab that you opened to enable UpNp if you haven't already) and open your "network" located in your library's section, and find your network infrastructure.
When you have found that Right-click and press "Properties", there should be 2 tabs named: General and Network device.
Go onto the tab named "General" and press "Settings".
It will open a new window and it will have 3 options on the bottom left-hand corner, "Add", "Edit" and "Delete".
Press "Add" and Call it something like "Cod mw3 and bo2", Then type your "IVP4" address, and in both internal and external ports type "3074" (without the quotation marks). Make sure that it is UDP not TCP.
Then press "Ok" and "Ok" again.
Then play mw3 or black ops 2 and check to see if your nat is open . If it isn't then you did something wrong .
Please note that sometimes if your nat goes from open to strict then repeat what you just did.