Site-to-site VPN and 4G modems

[ToniJ]

Hi,

I have two offices, both offices have Fortigate Firewalls. These primary connections have both static ip-addresses and there is site-to-site vpn connection between offices. Now we would like to do backup with 4G modems, we have supported modems and both 4G connections are with static ip-addresses. What I want to know, is how is the smartest way to backup primary line with 4G connection. So for example if office2 primary connection goes down, site-to-site vpn would use 4g connection etc.

Or is only solution to create site-to-site cross all the connections?

Regards,

Toni

[emnoc]

Dynamic routing protocol OSPF,  adjust priority-routes, or dead-gateway detect. Just make sure to reduce the priority on the backup routes