hello everyone. i have a router flashed with openwrt firmware. now i have two different network. one is connected to the internet(network A) and the another one is a private network that's isolated from the internet(network B).

The router is connected to the network A via ethernet cable that's plugged in the WAN port. and it's connected to the network B via WLAN ( the router acts as a client and connect to the network B's SSID)

The problem is that i use the router as my file sharing server(a usb stick is mounted), so the router plays just like a computer, it does not have any DHCP services and nothing is connected to the router's LAN port. the WAN port is connected to another router(call MAIN router here) and get a IP address from the MAIN router.My computer is connected to the MAIN router via Wi-Fi, and now i set up a VPN service on the router. It works fine, i could connect to the PPTP vpn server and get a ip from that,but if it's possible to "connect the vpn " to the Network B?

In another word, when my computer is connected to the vpn , all network traffic are sent to the network B, so i could access something in the private network?

Thanks. A figure is attached if it helps..