I have a DrayTek 2926ac router which has an Ethernet feed as it's primary WAN and a 4G router (factory default settings + APN) as the Failover WAN.
When I disable the primary WAN, the failover WAN activates and internet is restored. However the port forwarding I have setup fails.
This is where it gets complicated (at least for me that is).
I have a dyndns host which on either port 80 or 443 will redirect to my NAS and show an empty page and the HTTP status is 200.
The dyndns host has a TTL of 60 seconds. From the Dynamic DNS section on the Draytek Vigor 2926ac router I can see the IP address is immediately updated. So, I expect that after 60 seconds I should be able to access the hosts successfully.
When I ping the host, I can see the IP address has been updated, but it times out in the browser.
To avoid confusion with browser cache, etc. I have used a 3rd party site: https://downforeveryoneorjustme.com/ and they also reported it was not working. When the primary WAN service is restored, everything is returned to normal.
As you can see from the image below showing the setup of the NAT>>Port Redirection setup that the WAN interface is set to 'ALL'.
