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Monday, August 21 2017 @ 04:36 PM BST

PC MW3 - What is NAT, Port forwarding and UPnP ?

CoD Modern Warfare 3

NAT is the ability for your router to handle internet traffic and send it to the correct computer in your network. It is also a very important security layer between you and the internet. It ensures that people from the outside cannot access your computer without your permission.

Port forwarding redirects incoming connections to the computer in the network that needs it.

UPnP is an extension to port forwarding so that your computer can tell the router when to forward and when to stop forwarding.

UPnP also makes it possible that a game can setup the port forwarding automatically

Modern Warfare 3 and NAT types

For MW3 Multi Player the hosting player has to be able to receive all those incoming connections. Normally changing your NAT type from strict to open will allow you to be host.

First, make sure that UPnP is turned on on your router. Navigate to the webpage of your router and look for the option. It's recommend that you enable UPnP but disable extended security, since that will normally only cause extra latencies.

You can download a little tool that tests your UPnP status: UPnPTest. This tool will diagnose some things on your computer and router related to UPnP.

Please complete the following checklist: Test 1, 6, 7 and 8 say "PASSED". If you are on Windows XP, ensure that tests 2, 3, 4 and 5 also say "PASSED". If one of the tests failed, click the "Help Me Fix These Problems" button and follow the steps there. There is only 1 adapter listed at test 7. If this is not the case, go to your network settings (Windows 7: Control Panel -> Network and Sharing Center -> Change adapter settings) and disable all adapters you don't use. This is very important.

It is possible that you are behind a double router. This can happen if you have a modem with routing features and a router that also routes. You must disable the router features of either your modem or your router, so that there's only one router left.


There's no real definition of what a moderate NAT is.

It generally means that the port was forwarded (via UPnP or manually) but not all connections are allowed to go through.

A few causes why this can happen :

- Router firewalls. It may surprise you but your computer is not the only device with a firewall. Your router can be filtering traffic that look like attacks on it. And it can be a router sees MW3 is an attack.

- Computer firewalls. This is very unlikely, but your own computer could be filtering the traffic! Turn off all firewalls and test it.

- Bad routers. Not all routers are advanced enough to completely integrate UPnP. Some routers only integrate a small part of it and end up causing issues like a moderate NAT rather than simply keeping it strict.

Flushing your DNS cache can help with conection issues.


Stuck in MW3 while connecting to the "online services" NAT is unrelated.

If you have a very bad internet connection, don't open your NAT. You will end up worsening the gameplay instead of improving it.


Solutions for Modern Warfare 3 errors, freezes, crashes and install problems.