Doing VPN is like creating a private path from one site to another so that you can transfer data between each other off the untrust network. In order to get VPN tunnel established, IP address of each end must be known. There should be three different cases for VPN setup.
Few weeks back I have chance to configure IPSec VPN for one of our customers. It’s Juniper SRX at one side and Cisco IOS at another. Make sure you understand what VPN is then you are good to go with the example configuration below. The Sample Network Diagram Here is