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Fortigate 600F 25G SFP28 mixed 1G ethernet SDWAN issue

Hello everyone,

             We have a unique issue I can't figure out. We have a new 20G ISP connection we are trying to integrate into an SD-WAN that has 1G ISP's. We are using a FortiGate 600F. They are all set as WAN roles. Anytime we plug in the 20G interface (the 25G SFP28 fiber transceiver) It takes over the WAN connections entirely and it makes it so the other 2 1G ethernet WANS don't work. When the 20G Fiber is plugged in, all traffic on the 1G ethernet WANS stop. Then the minute we unplug the 20G fiber connection, the 1G ethernet WANS work again. Anyone have any thoughts of what might be going on?

Honored Contributor


If I understand well, now your SD-WAN has 3 interfaces:

  • 2x 1G ISPs
  • 1x 20G ISP

And when you plug the 20G link, the other 2 stop working.

This can just reflect your SD-WAN configuration, having 20G as main and 2x 1G as fail-over links.

You can check in SD-WAN rules (Network > SD-WAN > SD-WAN Rules).


I looked at the SD-WAN Rules. We had removed the 20G connection from the SD-WAN completely. It still didn't allow traffic on the 1G interfaces. We had to remove the 20G Fiber from the transceiver to let traffic work on the 1G connections. When we plug the 20G Fiber connection back in, the 1G traffic stops. So it happens when the fiber 20G has an active link on it is when the 1G interfaces stop passing traffic.


Hi @solzorrohelp,


Is the 20G WAN using DHCP? If yes, please refer to


Have you confirmed that all WAN links appear in the routing table as default routes? You can run 'get router info routing-table all' to confirm. 




It is using DHCP on the 20G. I I will try this at our next test and see if it works. Thank you so much!!

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