Enterprises with multiple WAN links often have asymmetric routing policies, which seem to require that an inline appliance be in two places at once. Virtual inline mode solves the asymmetric routing problem by using the router configuration to send all WAN traffic through the appliance, regardless of the WAN link used. The below figure shows a simple multiple-WAN link deployment example.
The two local-side routers redirect traffic to the local appliance. The FE 0/0 ports for both routers are in the same broadcast domain as the appliance. The local appliance must use the default virtual inline configuration (Return to Ethernet Sender).