A common scenario is the coupling of two company networks that internally use the same address range (e.g. 10.0.0.x). This usually happens when a company needs access to one (or more) server(s) at the other site:
In this example, the networks of the companies A and B contain servers that want to access the other network via a VPN tunnel. All stations in the LAN should have access to the servers in the remote network. Because both networks use the same address range, it is initially not possible to access the other network with this configuration. If a station in the network of company A wants to access server 1 of company B, the addressee (with an address on the 10.0.0.x network) is searched for on its own local network. The request does not even reach the gateway.
The N:N mapping translates all addresses within the LAN into a new range of addresses for communication with the remote network. Company A's network is translated, for example, to the range 192.168.1.x, while company B's network is translated to 192.168.2.x. Each LAN is now accessible by the other at these new addresses. The station from the network of company A addresses the server 1 of company B under the address 192.168.2.1. The device being addressed is not located in the local network, so the request is forwarded to the gateway and routed to the remote network, as desired.
