DNS Issue with Failover between Starlink and Proximus SIM on Teltonika Router

NETWORKING SOLUTIONS
1

Hi everyone,

I’m experiencing a DNS-related issue with my Teltonika router when using failover between a Starlink connection and a Proximus SIM. Here’s the setup and problem:

  • Setup:

    • Router: RUT241 with the latest firmware.

    • WAN1: Starlink (no Starlink router present, connected directly via Ethernet to WAN port).

    • WAN2: Proximus SIM (mobile data).

    • Failover configured to switch between WAN1 and WAN2 based on ping tests (switch after 10 successful pings to 1.1.1.1 or 8.8.8.8).

  • Behavior:

    • Starlink WAN uses DHCP and assigns a public IP (e.g., 206.214.239.194/24) and a Starlink DNS server (206.214.239.195) to the WAN interface.

    • Failover works fine: it switches quickly between Starlink and Proximus when connectivity changes.

    • The router assigns itself (192.168.1.1) as the DNS server to DHCP clients, and I can’t seem to change this to a public DNS like 1.1.1.1 (no option available).

  • Problem:

    • After failover from Starlink to Proximus, DNS stops working shortly after the switch, even though the internet connection itself remains active.

    • The Starlink DNS server (206.214.239.195) isn’t reachable from Proximus, and it seems the router continues trying to use it as the upstream DNS, despite me setting 1.1.1.1 as the upstream DNS in the settings.

    • Manually setting 1.1.1.1 as the DNS server on my PC resolves hostnames fine, confirming it’s a router issue.

    • Previous tests didn’t show this immediately due to DNS caching on my device.

  • Suspicion:

    • I suspect the router keeps using the Starlink DNS server (206.214.239.195) as the upstream DNS for all connections, even after failover to Proximus, ignoring my configured 1.1.1.1. Could this be a firmware bug?

  • What I’ve tried:

    • Updated to the latest firmware – no change.

    • Set upstream DNS to 1.1.1.1 manually – doesn’t seem to override the Starlink DNS after failover.

    • Disconnected Starlink temporarily and disabled failover – this avoids the issue but isn’t a solution.

Has anyone encountered this behavior with failover and Starlink? Is there a way to force the router to use my specified upstream DNS (1.1.1.1) regardless of what DHCP provides, or to stop it from using the Starlink DNS after failover? Any suggestions or workarounds would be greatly appreciated!

Thanks in advance for your help!

4

@Roygtv Hello,

You can set custom DNS servers by editing your WAN interfaces under Network → WAN. Try adding 8.8.8.8 and 1.1.1.1 to both the WAN and Mob1s1a1 interfaces.

By default, all configured and automatically obtained DNS servers are used. While you can enforce a strict DNS order via the CLI, this is typically unnecessary.

On Teltonika Networks devices, DNS (handled by DNSmasq) functions as a DNS forwarder, meaning that the router does not resolve DNS queries itself but forwards them to the specified DNS servers. You can check which DNS servers are currently in use with the following command:

cat /tmp/resolv.conf.d/resolv.conf.auto

Additionally, you can push specific DNS servers to DHCP clients by adding DHCP option 6 under:
Network → DHCP → Server settings → Edit LAN server → Advanced settings.

I would also recommend enabling flushing on both interfaces in failover settings.

Kind Regards,