# WHATPORT(37)

## NAME

port 37 — Time — The Time Protocol — a 32-bit seconds-since-1900 count, returned as four raw bytes.

Protocol: TCP/UDP  
IANA registry

## DESCRIPTION

RFC 868 defines Time as a machine-readable counterpart to Daytime: connect, and the server returns a 32-bit big-endian count of seconds since 1 January 1900 UTC, then closes. NIST still answers on time.nist.gov and reports that only about 2% of its Internet Time Service traffic uses it, while urging users to move to NTP. The protocol has no authentication, no round-trip correction, and one-second resolution, and its 32-bit counter rolls over in 2036. It was an inetd built-in on classic UNIX and is off by default now.

## EXPOSURE

**Expose with care.** Only defensible as a deliberate public time service; the UDP form is spoofable and reflectable, and NTP replaces it for actually setting a clock.

## CHECK

```sh
nc -w 5 time.nist.gov 37 | xxd
```

## SEE ALSO

- spec — [RFC 868 — Time Protocol](https://www.rfc-editor.org/rfc/rfc868.html) (rfc-editor.org)
- docs — [NIST Internet Time Service (ITS)](https://www.nist.gov/pml/time-and-frequency-division/time-distribution/internet-time-service-its) (nist.gov)
- iana — [IANA Service Name and Transport Protocol Port Number Registry](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml) (iana.org)

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HTML: <https://whatport.net/37/> · JSON: <https://whatport.net/37.json> · full dataset: <https://whatport.net/ports.json>