How to Override DNS

Overview

If your Robustel 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. This guide explains how to enter approved DNS server addresses, apply the setting and test name resolution. The practical conclusion is that custom DNS should be used only with reachable, trusted resolvers that match the deployment's domain requirements.

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)

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.

Conclusion