# WHATPORT(255)

## NAME

port 255 — Unassigned — Another unassigned port in the 250–255 gap, with no protocol behind the number.

Protocol: TCP  
IANA registry

## DESCRIPTION

IANA lists no assignment for 255 on either transport, and there is no historical registration to point at. Like its neighbour 254 it still carries a measurable open-rate in Nmap's frequency data, so it rides along in default scans and turns up in results as a nameless open port. Any listener is site-specific: an internal service someone parked on a low, memorable number, or a device firmware default that was never registered. There is nothing generic to say about what it does.

## EXPOSURE

**Expose with care.** Unregistered does not mean harmless — fingerprint the listener before exposing it, because low-numbered ports usually mean a root-owned process.

## CHECK

```sh
nmap -sV -p 255 TARGET
```

## SEE ALSO

- iana — [IANA Service Name and Transport Protocol Port Number Registry — 255](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=255) (iana.org)
- source — [nmap-services — the empirical port frequency list (255/tcp "unknown")](https://github.com/nmap/nmap/blob/master/nmap-services) (github.com)

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HTML: <https://whatport.net/255/> · JSON: <https://whatport.net/255.json> · full dataset: <https://whatport.net/ports.json>