One of today's most common tasks for routers is connecting the numerous workstation computers in a LAN to the network of all networks, the Internet. Everyone should have the potential to access, for example, the WWW from his workstation and be able to fetch bang up-to-date information for his work. ´
So that not every single computer with it's IP address in known on the entire internet “IP masquerading” is used to hide all computers located in an intranet. IP masquerading demands two points from a router: On the one hand a valid IP address in the local network, on the other hand a valid and public IP address in the internet (static or assigned by the provider).
Because these two addresses are not allowed to exist in one logical net, the router must have two IP addresses:
- the intranet IP address to communicate with computers in the LAN
- the public IP address to communicate with remote stations in the Internet
The computers in the LAN use the router as a gateway but are not recognizable themselves. The router divides the intranet from the internet.