# WHATPORT(3)

## NAME

port 3 — Reserved (formerly compressnet) — Reserved at IANA — the old compressnet registration was de-assigned in 2025.

Protocol: TCP  
IANA registry

## DESCRIPTION

Port 3 carried the 'compressnet' Compression Process registration for decades, alongside port 2 for its management utility. IANA de-assigned both on 2025-02-13 and now marks them Reserved, so no service owns this number. There is no protocol here to speak of and no software in common use that binds it. If a scan shows port 3 open, the service is unidentified and you have to fingerprint it directly.

## EXPOSURE

**Expose with care.** Nothing is registered here, so an open port 3 is an unidentified listener — identify what owns the socket before deciding anything.

## CHECK

```sh
nc -vz TARGET 3
```

## 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)

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HTML: <https://whatport.net/3/> · JSON: <https://whatport.net/3.json> · full dataset: <https://whatport.net/ports.json>