Trying to make VPN connection using Linksys RV042 and BSNL DSL modem?

Scenario…

I have BSNL DSL Modem. I want to connect my RV042 router to create vpn by using dynamic dns with dyndns.org.

my bsnl modem is configured with dynamic ip and with pppoE conncetion.

When i am tryin to connect VPN router with my bsnl modem with Automatic IP settings i can connect to internet. but i am not getting the Public IP in VPN router for that reason i am not able to connect from other location. my RV042 router takes the ip released from bsnl router.

Please help me outtt…..