WAN Link Failover not working

Hi Sandra Koehler ,

Thank you for reaching out to the community, Please refer the useful documentation below:
>  Configure gateway load balancing and failover.
>  WAN link load balancing and session persistence.
>  How to Choose The Gateway For A Firewall Rule.
>  VPN & SD-WAN Zero Downtime Failover - Best Practice Guide.

What you are referring to ( Active - Backup Gateway ) is called WLM (WAN Link Management) by Sophos.

Regarding routing decision, WLM has lowest priority. static/dynamic routing or SDwan routing all have higher priorities.

For example:

1- If you have only set a static default route 0.0.0.0/0 to specific gateway (let's say gateway A), even with gateway A failure, FW won't use the second gateway because static route has higher priority.

2- If you have a SDWAN route with only GW A as gateway and with "Route only through specified gateways" enabled, firewall won't use the second gateway.

These are just couple of examples and there could be some issues with NAT also. I recommend contacting sophos support or contacting me over private chat to do a live diagnostic check.

Thank you - I actually had a couple of migrated SD-WAN route that didn't have the backup gateway specified. No 0.0.0.0/0 statics in the configuration. I'm going to review the documentation and see if I missed anything, and then get back to you. Thank you!