I have a RUT955 with two SIMs configured to failover on ping fail. Each SIM has it's own public static IP address. I need to connect an external service (TCP to specific port) to the router automatically which will use whichever SIM is active.
I think it is pretty clear there needs to be an intermediate device deciding which SIM IP to route traffic to but I am struggling to find a solution. I know the router supports HSRP (Hot Standby Router Protocol) which I think is ideal but it only seems to work with two routers on the LAN side only, not one router on the WAN side? Another option is to initiate a GRE tunnel from the router to the intermediate device and route traffic to the endpoint of this tunnel. Any other ideas?