In active-passive WAN optimization you add an active WAN optimization policy to the client-side FortiGate unit and you add a WAN optimization tunnel policy and a passive WAN optimization policy to the server-side FortiGate unit.

The active policy accepts the traffic to be optimized and sends it down the WAN optimization tunnel to the server-side FortiGate unit. The active policy can also apply security profiles and other features to traffic before it exits the client-side FortiGate unit.

A tunnel explicit proxy policy on the sever-side FortiGate unit allows the server-side FortiGate unit to form a WAN optimization tunnel with the client-side FortiGate unit. The passive WAN optimization policy is required because of the active policy on the client-side FortiGate unit. You can also use the passive policy to apply WAN optimization transparent mode and features such as security profiles, logging, traffic shaping and web caching to the traffic before it exits the server-side FortiGate unit.