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// Other services

Port 639: MSDP

Port 639 is assigned by IANA to msdp (MSDP).

639

How msdp works

Other services
client:639msdpresponse client:639msdpresponse

The client sends a request to port 639 and the msdp 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 639 dangerous?

We have no specific security note for port 639. 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 639

ServicePortTransportDescriptionReferenceUpdated
msdp 639 TCP, UDP MSDP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 639, and is it reachable?

Linux

sudo ss -ltnup 'sport = :639'      # process listening on 639
sudo lsof -nP -i :639

macOS

sudo lsof -nP -i :639

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 639 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 639
netstat -ano | findstr :639

From another machine

nmap -p 639 -sV <host>
sudo nmap -sU -p 639 <host>
nc -zv <host> 639

Block it in the firewall

sudo ufw deny 639/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 639" -Direction Inbound -LocalPort 639 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 639 used for?

Port 639 is assigned by IANA to msdp (MSDP).

Is port 639 TCP or UDP?

Port 639 is registered for TCP and UDP.

Is it safe to open port 639?

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 639 is open?

On Linux run "ss -ltnup 'sport = :639'", on macOS "lsof -nP -i :639", and on Windows "netstat -ano | findstr :639" to see the local process. From another machine, "nmap -p 639 <host>" shows whether it is reachable.

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