CyberHunter
Local dataset, no network
// Other services

Port 543:

Port 543 is assigned by IANA to klogin ().

543

How klogin works

Other services
client:543kloginresponse client:543kloginresponse

The client sends a request to port 543 and the klogin service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 543 dangerous?

We have no specific security note for port 543. 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 543

ServicePortTransportDescriptionReferenceUpdated
klogin 543 TCP, UDP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 543, and is it reachable?

Linux

sudo ss -ltnup 'sport = :543'      # process listening on 543
sudo lsof -nP -i :543

macOS

sudo lsof -nP -i :543

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 543 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 543
netstat -ano | findstr :543

From another machine

nmap -p 543 -sV <host>
sudo nmap -sU -p 543 <host>
nc -zv <host> 543

Block it in the firewall

sudo ufw deny 543/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 543" -Direction Inbound -LocalPort 543 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 543 used for?

Port 543 is assigned by IANA to klogin ().

Is port 543 TCP or UDP?

Port 543 is registered for TCP and UDP.

Is it safe to open port 543?

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 543 is open?

On Linux run "ss -ltnup 'sport = :543'", on macOS "lsof -nP -i :543", and on Windows "netstat -ano | findstr :543" to see the local process. From another machine, "nmap -p 543 <host>" shows whether it is reachable.

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