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Commonly confused · Networking Fundamentals

NAT vs PAT: What's the Difference?

Basic NAT maps private IP addresses to public IP addresses, usually one-to-one. PAT (also called NAT overload) maps many private addresses to a single public address by tracking unique source port numbers for each session.

Network Address Translation (NAT)

Full definition
vs

Port Address Translation (PAT)

Full definition
Network Address TranslationPort Address Translation
MappingOne-to-one (static) or pool-based (dynamic)Many-to-one using port numbers
Public addresses neededOne per simultaneous inside hostOften just one
Translation keyIP addressIP address plus Layer 4 port
Cisco keywordip nat inside source static, or a poolip nat inside source list ... overload
Inbound accessStatic NAT allows unsolicited inbound connections to a hostInbound requires port forwarding
Common usePublishing an internal serverHome and office Internet access
Remember it

PAT is NAT that overloads one public IP by juggling port numbers.

Exam tip

If a question says many users share one public IP, the answer is PAT or NAT overload. If it says an internal server must be reachable at a fixed public address, the answer is static NAT.

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