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SESK: Stuff Everyone Should Know · sesk.info/aplus-ntp-port

Which port does Network Time Protocol (NTP) use to keep clocks in sync?

Port 123 is for NTP.

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  1. 53
  2. 25
  3. 123 ✔

Why: NTP is registered to port 123. Hosts use it to agree on the time. Port 53 is DNS and 25 is SMTP.

Huh, didn't know that: The IANA entry for port 123 points to RFC 5905 for NTP.

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References

Answer: 123. NTP is registered to port 123. Hosts use it to agree on the time. Port 53 is DNS and 25 is SMTP.

  1. IANA Service Name and Transport Protocol Port Number Registry CSV www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv
    ntp,123,udp,Network Time Protocol
    Checked 2026-10-11.

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