13.1 About NAT
Normally, network address translation is used to interconnect local networks with external networks. This technology has been developed as a solution to the need for more IPv4 addresses. Also, the demand for technologies such as NAT had been increasing because a specific range of IP addresses (see RFC 1918) had been designated for internal use only (routing on the Internet is not supported).
NAT translates IP header information. It translates the internal addresses of IP packets that need to pass through public networks into external addresses. NAT uses static and dynamic external addresses to translate internal addresses to external addresses.