NAT (network address translation)

In short: NAT translates the private addresses in a home network into the router’s single public address. That way many devices share one internet connection.

In more detail: Devices in the home network have private IP addresses like 192.168.x.x, which are not routed on the internet. When leaving, the router replaces the sender address with its public one and remembers in a table which reply belongs to which device.

In Depth

• Port translation (PAT): Several devices use the same public address with different port numbers.
• Incoming connections: Not reachable unsolicited from outside. Servers or games need port forwarding.
• Side effect: NAT acts like a simple protective layer but does not replace a firewall.
• CGNAT: Some providers share one public address among many customers. Then port forwarding is not possible.
• IPv6: Offers enough addresses for every device, so NAT is unnecessary there.

See also: IP addresses, Firewall