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// Other services

Port 9909: domaintime

Port 9909 is assigned by IANA to domaintime (domaintime).

9909

How domaintime works

Other services
client:9909domaintimeresponse client:9909domaintimeresponse

The client sends a request to port 9909 and the domaintime 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 9909 dangerous?

We have no specific security note for port 9909. 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 9909

ServicePortTransportDescriptionReferenceUpdated
domaintime 9909 TCP, UDP domaintime - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 9909, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9909'      # process listening on 9909
sudo lsof -nP -i :9909

macOS

sudo lsof -nP -i :9909

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9909 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9909
netstat -ano | findstr :9909

From another machine

nmap -p 9909 -sV <host>
sudo nmap -sU -p 9909 <host>
nc -zv <host> 9909

Block it in the firewall

sudo ufw deny 9909/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9909" -Direction Inbound -LocalPort 9909 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9909 used for?

Port 9909 is assigned by IANA to domaintime (domaintime).

Is port 9909 TCP or UDP?

Port 9909 is registered for TCP and UDP.

Is it safe to open port 9909?

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 9909 is open?

On Linux run "ss -ltnup 'sport = :9909'", on macOS "lsof -nP -i :9909", and on Windows "netstat -ano | findstr :9909" to see the local process. From another machine, "nmap -p 9909 <host>" shows whether it is reachable.

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