PAT / NAT Overload

PAT, or Port Address Translation, also called NAT Overload, is the most common form of NAT used in home and enterprise networks. It allows many devices with private IP addresses to share a single public IP address simultaneously by tracking each connection using a unique combination of the public IP address and a port number. When a device on the internal network initiates a connection, the router assigns it a unique source port number and records the mapping in a translation table, using that mapping to correctly deliver return traffic back to the right internal device. This is what allows an entire office or household to access the Internet through a single public IP address.