How to Override DNS

How to Override DNS

Overview

If the gateway cannot connect to services via domain names, such as RCMS connection and NTP time synchronization failures (see the logs below), but the SIM card is registered and can ping the public IP address, troubleshooting can be done by looking for DNS issues.

Troubleshooting

NTP Log
Jan  1 00:11:47 router daemon.err ntpdate[2451]: Can't find host pool.ntp.org: Name or service not known (-2)
Jan  1 00:11:47 router daemon.err ntpdate[2451]: Can't find host pool.ntp.org: Name or service not known (-2)

NTP log shows domain name pool.ntp.org resolve failed.
RCMS Log
Jan  1 00:11:07 router user.debug rcms[2006]: url:https://rcms-cloud.robustel.net:443/link/device/activate
Jan  1 00:11:07 router user.debug rcms[2006]: POST payload : { "sn": "0xxxxxxx42", "timestamp": 1483229467, "mac": "34:xx:xx:xx:xx:2A", "imei": "5xxxxxxxxxx7", "deviceModel": "R3000-L4L", "token": "xxxxx", "version": 1 }
Jan  1 00:11:09 router user.err rcms[2006]: curl_easy_perform() failed: Error
Jan  1 00:11:09 router user.err rcms[2006]: curl_easy_getinfo() failed: No error
Jan  1 00:11:09 router user.err rcms[2006]: Device IOT HUB try register failed!!
Jan  1 00:11:09 router user.debug rcms[2006]: Active failed, Try in 180s...
RCMS Log shows Time is not updated and server connection failed.

However, the Internet connection is normal, device can reach public IP 8.8.8.8. So the Internet connection issues have been ruled out
Ping Detection Log
Jan  1 00:00:39 router user.debug rping[1152]: --- 8.8.8.8 ping statistics ---
Jan  1 00:00:39 router user.debug rping[1152]: 1 packets transmitted, 1 packets received, 0% packet loss
Jan  1 00:00:39 router user.debug rping[1152]: round-trip min/avg/max = 33.554/33.554/33.554 ms
Jan  1 00:00:39 router user.debug link_manager[732]: recv action ping_success from rping
Jan  1 00:00:39 router user.debug link_manager[732]: target link WWAN1, state Connected
Jan  1 00:00:39 router user.info link_manager[732]: WWAN1 ping test success 
This problem often occurs when using a SIM card for Internet connectivity, as the DNS server address is provided by the ISP, which can sometimes be unavailable. In this case, you can configure a working DNS server for the gateway to use.

Steps

Navigatge to WEBGUI -> Interface -> Link Manager -> WWAN -> Advanced Settings -> Override DNS, set a working DNS server address, for example Google DNS 8.8.8.8


Validation

After DNS setup, the active link DNS would be changed to corresponding IP

Check if DNS is working.


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