# WHATPORT(20221)

## NAME

port 20221 — Unassigned — The last number in an unassigned IANA block, sitting directly below the registered 20222.

Protocol: TCP/UDP  
IANA registry

## DESCRIPTION

IANA's unassigned range 20203-20221 ends here, and the very next port, 20222, is registered as iPulse-ICS — so 20221 is often scanned as the low half of a presumed pair even though nothing is assigned to it. Nmap carries it as 'unknown' on both TCP and UDP with a small open-frequency, which is enough to put it in the default top-1000 scan. There is no documented protocol for this number.

## EXPOSURE

**Expose with care.** Nothing standard listens here, so an open port is an unknown application. Fingerprint it and judge that, not the number.

## CHECK

```sh
nmap -Pn -sV -p 20221 --reason TARGET
```

## SEE ALSO

- 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)
- source — [Nmap nmap-services frequency table](https://github.com/nmap/nmap/blob/master/nmap-services) (github.com)

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HTML: <https://whatport.net/20221/> · JSON: <https://whatport.net/20221.json> · full dataset: <https://whatport.net/ports.json>