# WHATPORT(21571)

## NAME

port 21571 — Unassigned — Unassigned by IANA with no documented service — present in default scans on frequency alone.

Protocol: TCP  
IANA registry

## DESCRIPTION

21571 falls in IANA's unassigned range 21555-21589 and has no registration. Nmap's table names it 'unknown' with a small but nonzero open-frequency, which is the only reason it appears in the default top-1000 TCP scan. Nothing in the public record ties it to a product, protocol, or malware family. Whatever you find open here was put there by someone locally.

## EXPOSURE

**Expose with care.** No standard service means no default guidance. Identify the listener and inherit that service's exposure rules.

## CHECK

```sh
nc -vz TARGET 21571
```

## 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)

---

HTML: <https://whatport.net/21571/> · JSON: <https://whatport.net/21571.json> · full dataset: <https://whatport.net/ports.json>