Thanks for the detailed helpful information. Will try it and get back withthe result.

We have no firewall for a moment.

On the existing connection LAN 1 connects via the router to the internet. Now new VPN connection established and LAN 2 needed to access LAN 1 over the VPN connection. I have concept to implement it using sub-interface, but not have a clear idea about...

Yes, It is ISP connection. That connects HQ to branch network.