Dynamic source translation
Dynamic source translation allows translating many original IP addresses to a much smaller pool of translated addresses, even a single IP address.
Dynamic source translation, sometimes referred to as hide NAT, is often used to mask the internal networks of a company behind one or a few public, routable IP addresses provided by an ISP.
This illustration shows the process for dynamic source translation. Because dynamic source translation involves multiple hosts using the same IP address (in a many-to-one or many-to-some relationship), the firewall needs more information to differentiate the connections when the reply packets arrive. For this, the firewall uses the source port.