Connection between ADSL Modem Router (Bridge Mode) to VPN Router
Recently, I applied for ADSL 1 Fixed IP having a free ADSL Modem Router (Billion BIPAC 5102) with 4 port 10/100 Mpbs. But I need to connect my internal network from the outside, so I bought VPN Router (Linksys RV042). Knowing that I have to turn "Billion" Router to Bridge mode and make "Linksys" as a router instead. So my current network diagram is as follows (still I cannot access to internet):
Internet<==>WAN (Bridge Mode)- "Billion Model: BIPAC 5102 Modem" - LAN Port 192.168.1.1<==> WAN Port 192.168.1.50 "Linksys Model: RV042" LAN Port 192.168.1.100 <==>Switch at my local network (192.168.1.xxx)
(Remark: <==> means connect to...)
I have a bit knowledge on VPN. My understanding is that I should replace 192.168.1.50 at Linksys WAN's side with 1 Fixed public IP that I received from my ISP. But doing so, it will definitely cannot connect to Billion BIPAC' LAN Side which is 192.168.1.1.
What should I do to make internet connection and can use VPN Service from this Linksys router? (I could not ask for more Public IPs from my ISP)