# WHATPORT(4321)

## NAME

port 4321 — RWhois (Referral Whois) — Referral Whois — a whois variant that hands you a pointer to the server holding the real answer.

Protocol: TCP  
IANA registry

## DESCRIPTION

RWhois, specified in RFC 2167, extends the whois model with hierarchy: a query that a server cannot answer comes back as a referral to the server that can, which is how regional registries delegate detail for delegated IP blocks. Servers greet with a version banner such as %rwhois V-1.5 before any query. Most surviving deployments are ISPs and hosting providers publishing SWIP-style reassignment data for their address space.

## EXPOSURE

**Fine to expose.** It is a public directory service by design and carries no credentials; the only real concern is the contact detail you choose to publish in it.

## CHECK

```sh
nc -w 3 TARGET 4321 < /dev/null | head -1
```

## SEE ALSO

- spec — [RFC 2167 — Referral Whois (RWhois) Protocol V1.5](https://www.rfc-editor.org/rfc/rfc2167.html) (rfc-editor.org)
- iana — [IANA port registry — 4321 (rwhois)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=4321) (iana.org)

---

HTML: <https://whatport.net/4321/> · JSON: <https://whatport.net/4321.json> · full dataset: <https://whatport.net/ports.json>