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// Other services

Port 21000: IRTrans Control

Port 21000 is assigned by IANA to irtrans (IRTrans Control).

21000

How irtrans works

Other services
client:21000irtransresponse client:21000irtransresponse

The client sends a request to port 21000 and the irtrans 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 21000 dangerous?

We have no specific security note for port 21000. 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 21000

ServicePortTransportDescriptionReferenceUpdated
irtrans 21000 TCP, UDP IRTrans Control - 2004-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 21000, and is it reachable?

Linux

sudo ss -ltnup 'sport = :21000'      # process listening on 21000
sudo lsof -nP -i :21000

macOS

sudo lsof -nP -i :21000

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21000 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 21000
netstat -ano | findstr :21000

From another machine

nmap -p 21000 -sV <host>
sudo nmap -sU -p 21000 <host>
nc -zv <host> 21000

Block it in the firewall

sudo ufw deny 21000/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 21000" -Direction Inbound -LocalPort 21000 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 21000 used for?

Port 21000 is assigned by IANA to irtrans (IRTrans Control).

Is port 21000 TCP or UDP?

Port 21000 is registered for TCP and UDP.

Is it safe to open port 21000?

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 21000 is open?

On Linux run "ss -ltnup 'sport = :21000'", on macOS "lsof -nP -i :21000", and on Windows "netstat -ano | findstr :21000" to see the local process. From another machine, "nmap -p 21000 <host>" shows whether it is reachable.

05 Related
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