We have these Debian Linux "red-box" devices that VPN to a location 24/7.
This are dedicated Linux VPN devices that have a USB modem as back up.
We had it working fine until the new USB failover modem (with different ISP) had to be change...
We got the driver to work but not the fail-over script. Internet access yes VPN no.
The idea is to keep the VPN tunnel going if the main ISP goes down (logix, AT&T, COX, etc) this USB modem takes over in a couple of minutes or so keeping the VPN tunnel.
Attached is the script for your review
For any help many thanks!