# WHATPORT(1021)

## NAME

port 1021 — exp1 — RFC 3692-style experiment — One of the two port numbers RFC 4727 set aside for experiments, so nothing shipped should ever be here.

Protocol: TCP  
IANA: exp1

## DESCRIPTION

RFC 4727 reserves values across several IANA registries for RFC 3692-style experimentation, and 1021 (exp1) with 1022 (exp2) are that pair in the port registry — registered for TCP, UDP, SCTP and DCCP alike. They exist so a lab or an in-progress protocol can be tested without squatting on someone else's assignment, and the RFC is explicit that these values are not for deployed services. In practice 1021 is rarely found open, which suggests the rule is mostly respected.

## EXPOSURE

**Expose with care.** Nothing production is supposed to live on an experimental port. If something does, that is a configuration decision to revisit, and it should be identified before it is reachable off the host.

## CHECK

```sh
sudo lsof -nP -iTCP:1021 -sTCP:LISTEN
```

## SEE ALSO

- spec — [RFC 4727 — Experimental Values in IPv4, IPv6, ICMP, UDP, TCP headers](https://www.rfc-editor.org/rfc/rfc4727.html) (rfc-editor.org)
- iana — [IANA port registry — 1021](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=1021) (iana.org)

---

HTML: <https://whatport.net/1021/> · JSON: <https://whatport.net/1021.json> · full dataset: <https://whatport.net/ports.json>