FortiWeb 100D Internet Access to Backend Server

We have deployed Fortiweb 100D in reverse proxy mode. We want to provide Internet access to backend servers through Foritweb. Applications that are hosted on backend servers are accessing properly using internet. But backend server has no internet connection showing via fortiweb. All virtual servers IP and also all fortinet interfaces IP's are pinging from backend server but the router gateway 192.168.11.5 is not pinging. Please help