Players who don't see other players in the game.
How to do it:
Press Win + R
Type the default gateway into your browser address bar.
Now you are at the administration panel of your router.
Here come the tricky part.
Open this page: http://portforward.com/english/applications/port_forwarding/Call_of_Duty_-_Advanced_Warfare/
Search for the brand of your router and open it.
If you don't know the exact model of the router or the page doesn't list it just open pages until you see the same thing on the pictures and your router admin panel.
Navigate to the appropriate page in your router using the pictures of the other website.
Set protocol to: "all"
Start port: 25252
End port: 26252
Local ip: the "IPv4" address displayed in the previously opened command line.
If the router asks for internal ports, then write the same ports as before.
If there is an "enabled" checkbox, tick it.
Press save or equivalent.