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// Other services

Port 5911: Air Traffic Services applications using ACARS

Port 5911 is assigned by IANA to ats-acars (Air Traffic Services applications using ACARS), cpdlc (Controller Pilot Data Link Communication).

5911

How ats-acars works

Other services
client:5911ats-acarsresponse client:5911ats-acarsresponse

The client sends a request to port 5911 and the ats-acars service answers.

Transport
TCP · UDP · SCTP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned2 registered services
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 5911 dangerous?

We have no specific security note for port 5911. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 5911

ServicePortTransportDescriptionReferenceUpdated
ats-acars 5911 TCP, UDP Air Traffic Services applications using ACARS - 2022-08-08
cpdlc 5911 SCTP Controller Pilot Data Link Communication - 2011-05-18

// source: IANA service name and port number registry

03 Check it

Which program uses port 5911, and is it reachable?

Linux

sudo ss -ltnup 'sport = :5911'      # process listening on 5911
sudo lsof -nP -i :5911

macOS

sudo lsof -nP -i :5911

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5911 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 5911
netstat -ano | findstr :5911

From another machine

nmap -p 5911 -sV <host>
sudo nmap -sU -p 5911 <host>
nc -zv <host> 5911

Block it in the firewall

sudo ufw deny 5911/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 5911" -Direction Inbound -LocalPort 5911 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 5911 used for?

Port 5911 is assigned by IANA to ats-acars (Air Traffic Services applications using ACARS), cpdlc (Controller Pilot Data Link Communication).

Is port 5911 TCP or UDP?

Port 5911 is registered for TCP and UDP and SCTP.

Is it safe to open port 5911?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 5911 is open?

On Linux run "ss -ltnup 'sport = :5911'", on macOS "lsof -nP -i :5911", and on Windows "netstat -ano | findstr :5911" to see the local process. From another machine, "nmap -p 5911 <host>" shows whether it is reachable.

05 Related
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