# WHATPORT(5911)

## NAME

port 5911 — ats-acars (IANA) / VNC display :11 — Registered to an aeronautical ACARS service you will never meet; in practice it is VNC display :11.

Protocol: TCP  
IANA registry

## DESCRIPTION

IANA assigns TCP/UDP 5911 to `ats-acars`, "Air Traffic Services applications using ACARS" (the SCTP side of the same number is `cpdlc`, Controller Pilot Data Link Communication). Those are ICAO datalink registrations for aviation ground/air networks and they do not appear on the public internet. What actually answers here is a VNC server: RFB maps display :N to port 5900+N, so 5911 is display :11, handed out by QEMU/KVM, VirtualBox VRDE, or a multi-user Linux host running one Xvnc per user.

## EXPOSURE

**Do not expose.** If it is VNC it inherits VNC's problems — a plaintext RFB version banner before auth, and a legacy DES challenge-response capped at 8 password characters. Reach it over SSH or a VPN, not directly.

## CHECK

```sh
nc -w 3 TARGET 5911 | head -c 12; echo
```

## SEE ALSO

- iana — [IANA port registry — 5911 (ats-acars, cpdlc)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=5911) (iana.org)
- spec — [RFC 6143 — The Remote Framebuffer Protocol](https://datatracker.ietf.org/doc/html/rfc6143) (datatracker.ietf.org)
- source — [TigerVNC/tigervnc](https://github.com/TigerVNC/tigervnc) (github.com)

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HTML: <https://whatport.net/5911/> · JSON: <https://whatport.net/5911.json> · full dataset: <https://whatport.net/ports.json>