What does PAT stand for?
PAT stands for Port Address Translation. The form of NAT most home routers use: many internal hosts share one public IP, and the router tells return traffic apart by the source port it rewrote on the way out. Also called NAT overload or many-to-one NAT.
PAT lets many devices with private addresses share a single public IP address. When a device opens a connection, the router replaces the private source address with the public one and assigns a unique source port, then records the pair in a translation table. Replies arrive at that port and are sent back to the right device. It is what a home router does, and it is why thousands of connections can leave through one address at the same time.
PAT in practice: an example
Two phones on the same Wi-Fi open the same website. The router sends both requests from its one public address, one from source port 50001 and one from 50002. The site's replies come back to those two ports and the router delivers each to the phone that asked.
What PAT is confused with
PAT vs NAT: what is the difference?
NAT is the general idea of rewriting addresses. PAT is the many-to-one form that also rewrites ports; it is also called NAT overload, and RFC 2663 calls it NAPT. Static NAT maps one private address to one public address without touching ports. What NAT stands for
PAT vs port forwarding: what is the difference?
PAT handles connections that start inside. Port forwarding is a fixed rule for connections that start outside: traffic arriving on a chosen public port is sent to one internal host.
Which exams cover PAT?
PAT is on the official CompTIA acronym list for one of the four exams covered here.
- Network+ N10-009: 2.0 (Network Implementation).
Each number is a CompTIA exam objective and the name in brackets is its domain. The exam puts the term in a scenario; it does not ask you to recite the expansion.
Check yourself: two practice questions
Written by CertSprint for this page. They are not taken from any exam.
1. A router's translation table shows many inside addresses mapped to the same outside address with different port numbers. What is configured?
- Port address translation
- Static NAT
- A DHCP reservation
- A VLAN trunk
Show the answer
A. Port address translation. One public address shared by many hosts and told apart by port number is the definition of PAT.
2. Users behind PAT can browse the web, but an outside partner cannot start a connection to an internal server. Why?
- PAT only creates table entries for connections started from inside
- The server has too little memory
- DNS is using TCP
- The switch is in the wrong VLAN
Show the answer
A. PAT only creates table entries for connections started from inside. A translation exists only after an inside host opens a connection. Unsolicited inbound traffic matches no entry, so a static mapping or port-forwarding rule is needed.
Sources: RFC 2663: IP Network Address Translator (NAT) Terminology and Considerations; RFC 3022: Traditional IP Network Address Translator (Traditional NAT); NIST glossary: port address translation. The acronym and its expansion come from CompTIA's official acronym lists, linked from each exam glossary above. The explanation, example and questions are CertSprint's own, checked against these sources on 11 November 2026.