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SESK: Stuff Everyone Should Know · sesk.info/tech-napt-many-to-one

How can NAPT let many private hosts share one public address?

It translates addresses and transport ports into one public address.

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  1. By assigning every host the same MAC
  2. By translating addresses and TCP or UDP ports ✔
  3. By converting every packet to DNS

Why: Network Address Port Translation rewrites both an address and a TCP or UDP port. Distinct translated port mappings let return traffic be matched to the correct internal connection.

Huh, didn't know that: This many-to-one form is often called NAPT, PAT, or NAT overload.

The dad joke
NAT throws a port party where everyone shares one address.
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References

Answer: By translating addresses and TCP or UDP ports. Network Address Port Translation rewrites both an address and a TCP or UDP port. Distinct translated port mappings let return traffic be matched to the correct internal connection.

  1. RFC 3022: Traditional IP Network Address Translator www.rfc-editor.org/rfc/rfc3022.html
    many network addresses and their TCP/UDP (Transmission Control Protocol/User Datagram Protocol) ports are translated into a single network address and its TCP/UDP ports
    Checked 2026-10-11.

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