FortiGate SDWAN rule failover

[nwensley]

I have a FortiGate SDWAN rule configured to select the outgoing WAN interface by Best Quality as the result of Performance SLA measurements.

What happens if bandwidth of the selected outgoing WAN interface is saturated?

Does excess traffic begin to use the next most preferred outgoing WAN interface from the Best Quality Performance SLA measurement results?

Or will the WAN interface with Best Quality from Performance SLA measurement results continue to be used?

[spoojary]

When the bandwidth of the selected outgoing WAN interface is saturated in a FortiGate SD-WAN rule configured with the Best Quality strategy based on performance SLA measurements, the excess traffic will not automatically start using the next most preferred outgoing WAN interface. The WAN interface with the best quality from the performance SLA measurement results will continue to be used until the bandwidth saturation issue is resolved. The SD-WAN rules do not automatically switch to the next interface based on bandwidth saturation; they rely on the initial performance SLA measurements to determine the best quality interface for traffic routing.

[nwensley]

Thank you for the fast and helpful information.

In order to validate the trustworthiness of your comment (aside from your forum profile), can I confirm please you are an employee of Fortinet?

I have not tested this theory, but if the bandwidth of a WAN interface selected as Best Quality becomes saturated, the Performance SLA measurements should degrade as a result. For example due to packet loss or latency. The next Best Quality WAN interface might then be selected.

Perhaps then the WAN interface will no longer be selected as Best Quality until bandwidth reduces and Performance SLA measurements improve?

[spoojary · Accepted solution]

Yes i am employee.

https://docs.fortinet.com/document/fortigate/7.4.3/administration-guide/22371/best-quality-strategy

he WAN interface that was previously selected as the best quality may not be chosen again until its bandwidth reduces and the performance SLA measurements improve. The SD-WAN system dynamically adjusts based on real-time conditions to ensure optimal performance and reliability.

[nwensley]

Thank you once again for your fast and helpful answers sir.

I like Best Quality as a method to select outgoing interface. But I did have concern this was a safe strategy in the situation of bandwidth saturation and possible lack of failover. It requires some operational experience and testing on my part to see the behaviour.