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// Other services

Port 39: Resource Location Protocol

Port 39 is assigned by IANA to rlp (Resource Location Protocol).

39

How rlp works

Other services
client:39rlpresponse client:39rlpresponse

The client sends a request to port 39 and the rlp 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 39 dangerous?

We have no specific security note for port 39. 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 39

ServicePortTransportDescriptionReferenceUpdated
rlp 39 TCP, UDP Resource Location Protocol - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 39, and is it reachable?

Linux

sudo ss -ltnup 'sport = :39'      # process listening on 39
sudo lsof -nP -i :39

macOS

sudo lsof -nP -i :39

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 39 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 39
netstat -ano | findstr :39

From another machine

nmap -p 39 -sV <host>
sudo nmap -sU -p 39 <host>
nc -zv <host> 39

Block it in the firewall

sudo ufw deny 39/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 39" -Direction Inbound -LocalPort 39 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 39 used for?

Port 39 is assigned by IANA to rlp (Resource Location Protocol).

Is port 39 TCP or UDP?

Port 39 is registered for TCP and UDP.

Is it safe to open port 39?

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 39 is open?

On Linux run "ss -ltnup 'sport = :39'", on macOS "lsof -nP -i :39", and on Windows "netstat -ano | findstr :39" to see the local process. From another machine, "nmap -p 39 <host>" shows whether it is reachable.

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