# WHATPORT(555)

## NAME

port 555 — dsf — Registered as dsf with no description and no known implementation — an open 555 is unidentified software.

Protocol: TCP  
IANA registry

## DESCRIPTION

IANA lists TCP and UDP 555 under the service name "dsf" and gives no description, no assignee note, and no reference document; macOS ships the same bare entry in /etc/services. No maintained software is known to implement it. The number appears in circulated lists of trojan ports from the late 1990s, but those lists are unsourced folklore rather than documentation, so the only defensible statement is that anything listening on 555 has to be identified by fingerprinting it directly.

## EXPOSURE

**Do not expose.** An unexplained listener on a registered-but-unused system port is a finding to chase down, not a service to expose.

## CHECK

```sh
nc -vz -w 3 TARGET 555
```

## SEE ALSO

- iana — [IANA Service Name and Transport Protocol Port Number Registry — 555](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=555) (iana.org)

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HTML: <https://whatport.net/555/> · JSON: <https://whatport.net/555.json> · full dataset: <https://whatport.net/ports.json>