NAT (Network Address Translation)

NAT (Network Address Translation) is a technique in which a router replaces the private IP addresses of devices on a local network with its own public IP address when traffic goes out to the internet, and translates the replies back to the right device. This lets many devices in a home or office share a single public IP address.

NAT was introduced because IPv4 addresses ran short, and it also hides internal devices from direct access from outside. Port forwarding is used when an outside connection must reach a specific internal device, such as a game server or CCTV recorder. Internet providers often use carrier-grade NAT, sharing one address among many customers.