NAT
acronymnetworking
Stands for: Network Address Translation
Rewriting IP addresses in transit, classically to let many private hosts share one public address.
Network Address Translation (RFC 2663) is why a whole home or office can sit behind a single public IP. It comes in flavours, source NAT, destination NAT, port translation, and it complicates anything that assumes the address it sees is the real one.
NAT was a workaround for address exhaustion that became permanent infrastructure. Rewriting source addresses so many hosts share one public address bought the IPv4 internet decades of extra life, and in doing so changed the architecture from end-to-end reachability to something closer to one-way visibility.
That side effect is the reason it is often mistaken for security. NAT does prevent unsolicited inbound connections, but as a consequence of having no translation entry rather than as a policy decision, and it inspects nothing. A NAT device is not a firewall, and the belief that it is has left plenty of internal networks flat behind a router that was never enforcing anything.
The cost is paid by protocols that carry addresses inside their payload or expect peers to connect back. Voice, video, and peer-to-peer applications all had to develop traversal machinery, which is why STUN, TURN, and ICE exist at all. IPv6 removes the original justification entirely by making addresses plentiful, and the persistence of NAT-like habits in IPv6 deployments is mostly cultural rather than technical.
Also known as: nat, pat, masquerade, source nat, snat, dnat