1. A method, comprising: receiving a forward packet originating from a client; identifying a service engine selected from among a group of service engines by identifying an entry in a flow table that relates the selected service engine to the client, wherein the selected service engine is configured to select a first server to process the forward packet; receiving a reverse packet directed to an identifier of the group of service engines and destined for the client; modifying the reverse packet before it reaches the group of the service engines by: applying to the reverse packet an identifier of the selected service engine for replacing the identifier of the group of service engines; and transmitting to the selected service engine the reverse packet having the identifier of the selected service engine.