PS4 Solved: Error NW-31247-7 - A DNS Server Cannot be used/ Internet connection FAILED

This problem bugged me for two days. Where my PS4 cannot connect to internet via Wifi.
Message from Test Internet Connection function looks like below:


When do Setup Internet Connection, Error NW-31247-7 will occurred.

At the same time, all my other devices e.g. laptop and iPhones can connect to internet without issue.
Playing games via mobile hotspot works!

Action that WONT work:

1. Ask internet service provider (Unifi) to reset port 
2. Restart All PS4, Router & Modem
3. Setup Internet Connection on PS4 again
4. Change Wifi DNS to Google DNS 8.8.8.8 & 8.8.8.4

Solution:

1. Router - "restore factory setting"
2. PS4 - "initialization" --> "restore default setting"--> setup PS4 again
3. Setup PS4 involve mainly language, time zone, wifi, camera (if have) & PS sign-in.
4. All games still there. Wallpaper will be reset.

PS: I am not sure whether it is only router problem. You could try reset only router first. You can use same wifi name and password to ease your setup (so that you don't need to change password for all devices)

Cheers!