What NAT is
Network Address Translation (NAT) is a method that lets a router rewrite the source and destination addresses of packets as they move between a private network and the public internet. It is the reason a home or office with dozens of devices can connect to the internet through just one public IP address.
How it works
When a device sends traffic out, the router replaces the private source address with its own public address and remembers the mapping:
- Your laptop at
192.168.1.5sends a request. - The router rewrites it to come from the public IP and notes the connection.
- The reply arrives at the public IP, and the router forwards it back to your laptop.
This form, where many private addresses share one public address using port numbers, is often called PAT or NAT overload.
Why it matters
NAT slowed the exhaustion of IPv4 addresses by letting entire networks hide behind a single public address. It also adds a basic layer of isolation, since devices on the private side are not directly reachable from the internet without a deliberate port-forwarding rule. A side effect is that many devices appear to come from the same public address, which can complicate logging. You can see the public address your network presents using the WhatIP my-ip tool.