VNC FAQ-o-Matic : VNC and Firewalls : What do I need to know about routers?
Routers are essential to the operation of the Internet and to the networks that connect to them. For most Internet activity, like web-browsing and emailing, you don’t need to worry about them at all. But for a remote-control application like VNC, it’s important to have a basic understanding of what they do. A router (doesn’t matter whether it’s a “software based” router like the ICS program for Windows, or a “hardware based” router like a LinkSys or NetGear box) simply acts as a “translator” between one network and another. These two networks (e.g., a LAN and the Internet) can be distinguished by the IP address range each side uses. When a device on one side of the router needs to exchange data with a device on the other side of the router, the router automatically performs a real-time translation back-and-forth between two IP address. So if you have a PC on a LAN, think of it as having both an “internal” IP address as well as an “external” one that your router conceals from you. When
