Firstly go to “Settings > Miscellaneous” and tick “Enable upnp Forwarding”. Then, disable your Geo-Filter and restart your console. Finally, redo the NAT test. If it fails then please un-tick “Enable upnp Forwarding” and continue with the following instructions.
At this stage, go to the Device Manager on the Netduma router. If you see the blue box pictured below at the top of your page, please note down the IP address after “WAN IP”. For example, in the image below, you'd need to remember 192.168.2.223.
If you see the blue box please click “View other router interface”. Look for a section called DMZ - you may need to consult your other router's manual to find that section - it is usually located in Firewall/Security settings. Once you do, please enter the IP address you noted down before. Now your NAT should be open. If not, continue reading.
If you don't see the blue box your NAT should be open. If the games console does not report that your NAT is open, please continue reading.
Why is my NAT still not open?
Disable your geo-filter when booting up: The geo-filter can give the NAT test a false result. If you have an open NAT with the geo-filter disabled, you will also have an open NAT with it enabled - even though the console says otherwise.
Playstation reports Type 2: This is the best PlayStation NAT code it means you are open and protected.
If you still don't have an open NAT. Please go to “Settings > Port Forwarding” on the NETDUMA router and delete all entries. Then go to “Settings > UPnP” and make sure it is enabled.
Also make sure that any port forwarding rules from your primary router have been deleted.
Finally, make sure all your consoles have automatic IP setup. You can do this by going to the network settings on your console and choosing automatic. You could also try clearing the MAC address on your console before restarting it.
If you are still experiencing moderate/strict NAT you can manually port forward instead.
If you're on Xbox One you can also follow the steps from this video: