Method and system in an IP network for using a network address translation (NAT) with any type of application

The present invention is based on a dual dynamic Network Address Translation (NAT): one Network Address Translation (NAT) is executed close to the client stations of customers (to NAT), and one Network Address Translation (NAT) is executed close to the application server (to un-NAT). The networks between the client stations and the application server, only see registerd addresses (public IP addresses), while the application only sees the real private IP address. The present invention is based on a method for "NATting" and "un-NATting" the IP addresses without having to pre configure the "NATting" devices (the devices executing the operations of translating the network addresses).