We have bought two Pfsense SG-4860 boxes. We have our equipment in a colocation datacenter. Our goals for this project is to have a redundant network with both routers connected to a WAN. The Colocation WAN offers us two equal costs redundant uplinks. When two WAN cables are connected, the colocation WAN uplinks are going to load balance over the two WAN uplinks. So when a package from R1 is send over Uplink1, the reply may come back at uplink2 - R2.

I'm looking for a solution to stack both boxes together so they maintain the same state tables. I already tried to setup a CARP but that is not working over load balancing WAN uplinks.