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// Other services

Port 9999: distinct

Port 9999 is assigned by IANA to distinct (distinct).

9999

How distinct works

Other services
client:9999distinctresponse client:9999distinctresponse

The client sends a request to port 9999 and the distinct 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
Registered (1024-49151)
Category
Other services
01 Security

Is port 9999 dangerous?

We have no specific security note for port 9999. 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 9999

ServicePortTransportDescriptionReferenceUpdated
distinct 9999 TCP, UDP distinct - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 9999, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9999'      # process listening on 9999
sudo lsof -nP -i :9999

macOS

sudo lsof -nP -i :9999

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9999 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9999
netstat -ano | findstr :9999

From another machine

nmap -p 9999 -sV <host>
sudo nmap -sU -p 9999 <host>
nc -zv <host> 9999

Block it in the firewall

sudo ufw deny 9999/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9999" -Direction Inbound -LocalPort 9999 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9999 used for?

Port 9999 is assigned by IANA to distinct (distinct).

Is port 9999 TCP or UDP?

Port 9999 is registered for TCP and UDP.

Is it safe to open port 9999?

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 9999 is open?

On Linux run "ss -ltnup 'sport = :9999'", on macOS "lsof -nP -i :9999", and on Windows "netstat -ano | findstr :9999" to see the local process. From another machine, "nmap -p 9999 <host>" shows whether it is reachable.

05 Related
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