# WHATPORT(43)

## NAME

port 43 — WHOIS — WHOIS — send a domain, IP or handle as one line of text, get a registration record back.

Protocol: TCP  
IANA registry

## DESCRIPTION

RFC 3912 describes WHOIS as about as simple as a protocol gets: the client connects, sends a single query terminated by CRLF, and the server writes a free-form text response and closes. There is no encryption, no authentication, and no defined response format, which is exactly why RDAP over HTTPS was built to replace it. Registries, RIRs and the IANA root server all still answer here, and the `whois` command-line client follows referrals between them. Rate limits, not access control, are how operators protect it.

## EXPOSURE

**Fine to expose.** Public-by-design query service; the only real concerns are bulk-harvesting rate limits and the fact that responses are cleartext and unauthenticated.

## CHECK

```sh
whois -h whois.iana.org example.com
```

## SEE ALSO

- spec — [RFC 3912 — WHOIS Protocol Specification](https://www.rfc-editor.org/rfc/rfc3912.html) (rfc-editor.org)
- docs — [IANA WHOIS Service](https://www.iana.org/whois) (iana.org)
- source — [Marco d'Itri's whois client (the Debian/Linux `whois`)](https://github.com/rfc1036/whois) (github.com)
- 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)

---

HTML: <https://whatport.net/43/> · JSON: <https://whatport.net/43.json> · full dataset: <https://whatport.net/ports.json>