DNS failed or the gateway is enabled with authentication interception

Hi , I already call the ISP to change a new Modem , and also change a new router and the issue still persist on and off , i also configure the local dns to 8.8.8.8. I have no idea where is the problem, can any expert help on this ?

dear sir,
In response to your question DNS failed or the gateway is enabled with authentication interception.

First, you can check to see if you can ping the gateway with this router.If the ping succeeds, the communication to the gateway is normal.If the ping fails, the communication to the gateway is blocked.
Second, you can check to see if you can ping the 8.8.8.8 with this router.If the ping succeeds, there is no problem accessing the Internet, If ping different access to the Internet is problematic.

Then, you can do tracert 8.8.8.8 to see where the path is disconnected, can you negotiate with the ISP to check.

Finally, check whether there is a firewall on the upper layer of the router, and if so, unblock the IP address of the router.

I hope my answer can help you.

best wishes
Jack