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// Other services

Port 84: Common Trace Facility

Port 84 is assigned by IANA to ctf (Common Trace Facility).

84

How ctf works

Other services
client:84ctfresponse client:84ctfresponse

The client sends a request to port 84 and the ctf 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 84 dangerous?

We have no specific security note for port 84. 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 84

ServicePortTransportDescriptionReferenceUpdated
ctf 84 TCP, UDP Common Trace Facility - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 84, and is it reachable?

Linux

sudo ss -ltnup 'sport = :84'      # process listening on 84
sudo lsof -nP -i :84

macOS

sudo lsof -nP -i :84

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 84 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 84
netstat -ano | findstr :84

From another machine

nmap -p 84 -sV <host>
sudo nmap -sU -p 84 <host>
nc -zv <host> 84

Block it in the firewall

sudo ufw deny 84/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 84" -Direction Inbound -LocalPort 84 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 84 used for?

Port 84 is assigned by IANA to ctf (Common Trace Facility).

Is port 84 TCP or UDP?

Port 84 is registered for TCP and UDP.

Is it safe to open port 84?

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 84 is open?

On Linux run "ss -ltnup 'sport = :84'", on macOS "lsof -nP -i :84", and on Windows "netstat -ano | findstr :84" to see the local process. From another machine, "nmap -p 84 <host>" shows whether it is reachable.

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