Using RUT240 to Add 4G to a Fortigate


I have a RUT240 to add 4G internet access to a Fortigate firewall.

The basic idea is Forti-WAN1 —> RUT240-WAN —> RUT240-mob1s1a1 —> internet

I have the Forti and RUT240’s WAN interfaces in the same subnet, but I’m not sure what else I need to do on the RUT240 in terms of the firewall and routing.

Can someone please offer some insight as to how I get this working?


If you will not be utilizing any of the RUT240 software features, then we have two modes that most likely suit your needs the best:

  • Bridge - relays the DHCP lease and all traffic to a LAN client;

  • Passthrough - Same as bridge, but also uses the same WAN address for access to the internet, so services like RMS and ping reboot will still work.

These modes can be set by navigating to Network → Interfaces → General, editing the mob1s1a1 interface, and instead of NAT mode choosing Bridge or Passthrough. Make sure the Fortigate WAN interface is using DHCP to obtain the IP address from the carrier.
It should be noted, that the only way to reach the RUT240 after the bridge/passthrough mode is configured, is by setting a static IP address on your PC to be in the same network as the previous LAN network of the RUT240 (e.g. if LAN was, your PC should be set to and the RUT240 will be reachable on

Hope this helps!

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Hi Daumantas

That’s exactly what I’m looking for. I can still connect to the RUT240 via its wifi for maintenance, etc.

Thank you very much!

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