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// Other services

Port 20810: CRTech NLM

Port 20810 is assigned by IANA to crtech-nlm (CRTech NLM).

20810

How crtech-nlm works

Other services
client:20810crtech-nlmresponse client:20810crtech-nlmresponse

The client sends a request to port 20810 and the crtech-nlm service answers.

Transport
TCP
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 20810 dangerous?

We have no specific security note for port 20810. 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 20810

ServicePortTransportDescriptionReferenceUpdated
crtech-nlm 20810 TCP CRTech NLM - 2021-06-24
-20810-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 20810, and is it reachable?

Linux

sudo ss -ltnup 'sport = :20810'      # process listening on 20810
sudo lsof -nP -i :20810

macOS

sudo lsof -nP -i :20810

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 20810 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 20810
netstat -ano | findstr :20810

From another machine

nmap -p 20810 -sV <host>
nc -zv <host> 20810

Block it in the firewall

sudo ufw deny 20810/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 20810" -Direction Inbound -LocalPort 20810 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 20810 used for?

Port 20810 is assigned by IANA to crtech-nlm (CRTech NLM).

Is port 20810 TCP or UDP?

Port 20810 is registered for TCP.

Is it safe to open port 20810?

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 20810 is open?

On Linux run "ss -ltnup 'sport = :20810'", on macOS "lsof -nP -i :20810", and on Windows "netstat -ano | findstr :20810" to see the local process. From another machine, "nmap -p 20810 <host>" shows whether it is reachable.

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