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// Other services

Port 21847: NetSpeak Corp. Connection Services

Port 21847 is assigned by IANA to netspeak-cs (NetSpeak Corp. Connection Services).

21847

How netspeak-cs works

Other services
client:21847netspeak-csresponse client:21847netspeak-csresponse

The client sends a request to port 21847 and the netspeak-cs 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 21847 dangerous?

We have no specific security note for port 21847. 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 21847

ServicePortTransportDescriptionReferenceUpdated
netspeak-cs 21847 TCP, UDP NetSpeak Corp. Connection Services - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 21847, and is it reachable?

Linux

sudo ss -ltnup 'sport = :21847'      # process listening on 21847
sudo lsof -nP -i :21847

macOS

sudo lsof -nP -i :21847

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21847 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 21847
netstat -ano | findstr :21847

From another machine

nmap -p 21847 -sV <host>
sudo nmap -sU -p 21847 <host>
nc -zv <host> 21847

Block it in the firewall

sudo ufw deny 21847/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 21847" -Direction Inbound -LocalPort 21847 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 21847 used for?

Port 21847 is assigned by IANA to netspeak-cs (NetSpeak Corp. Connection Services).

Is port 21847 TCP or UDP?

Port 21847 is registered for TCP and UDP.

Is it safe to open port 21847?

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 21847 is open?

On Linux run "ss -ltnup 'sport = :21847'", on macOS "lsof -nP -i :21847", and on Windows "netstat -ano | findstr :21847" to see the local process. From another machine, "nmap -p 21847 <host>" shows whether it is reachable.

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