Source NAT Overview

Source NAT translates source addresses of packets.

Source NAT translates private IP addresses into public IP addresses so that users on an intranet can use public IP addresses to access the Internet. Figure 1 shows the translation process.

Figure 1 Source NAT mechanism

FW shows the source NAT process when the host accesses the web server.

1. Upon receiving the packets destined from the private network to the Internet, the FW translates the private source addresses into public source addresses.
2. Upon receiving the return packets, the FW translates the public destination addresses back to private destination addresses.

Based on whether port translation is performed during source address translation, source NAT falls into NAT involving only source address translation (NAT No-PAT) and NAT involving both source address translation and source port translation (NAPT, Smart NAT, Easy IP, and 3-tuple NAT).