How To: Fix the Xbox Live strict NAT type to open

Your router is automatically equipped with firewalls meant to protect your PC from intruders. However, these firewalls often misread information needed to run online video games, and block necessary files from reaching your XBox. In this tutorial, learn how to change the NAT settings of your modem to "Open" and allow these files to get through. By doing so, you will be able to take full advantage of your XBox Live account.
Note: If you do this right, you will not affect the computers in your home. Firewalls will still be in place to protect your PC but will no longer interfere with your XBox.

Step 1:
Go to dashboard on your XBox

Step 2:
Test your Live connection

Step 3:
Sign back in

Step 4:
Play!

If for some reason this method does not work, try any of these:
Alternative method 1:
Reset your router

Alternative method 2:
Check settings. Check if uPnP is enabled.

Alternative method 3:
Try "Port forwarding" Get Portforwarding