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Networking Fundamentals · Foundational

Network Address Translation (NAT)

A function that rewrites IP addresses (and often ports) in packet headers as traffic passes through a router or firewall.

Definition

NAT is most often used to let hosts with private addresses reach the Internet through one or more public addresses, conserving IPv4 space. It is defined in RFC 3022 and comes in static, dynamic and port-based (PAT) forms. NAT hides internal addressing but is not a security control by itself and complicates protocols that embed addresses, such as SIP and FTP active mode.

Example

A home router translates 192.168.1.20:51515 to its public address 198.51.100.7:40001.

Exam tip

NAT is not a firewall; stateful filtering is what blocks unsolicited inbound traffic.

Don't confuse it with

Related terms