PAT

IPv4 address exhaustion makes public IP allocation scarce and expensive for enterprise networks. Port Address Translation (PAT), frequently referred to as NAT Overload, enables hundreds of internal hosts on private RFC 1918 subnets to share a single public IPv4 address for outbound internet access. PAT operates by tracking source port numbers on outbound Layer 4 (TCP/UDP) headers. When private traffic exits the WAN boundary interface, the router maps the private Inside Local IP and port number to the router’s public Outside Global IP and a uniquely assigned source port. ...