The example below illustrates more VPN scenarios.
Example (A) illustrates a road warrier. The IP address of the road warrior is not known nor is it's router's address.
Example (B) illustrates another workstation. This workstation, perhaps an employee working at home on a Cable or DSL link, has a static IP address.
Example (C) illustrates another VPN server. The VPN bridges the networks 10.10.10.0/24 and 10.10.20/24.
All three of these scenarios may be running at the same time.