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// Other services

Port 1823: Unisys Natural Language License Manager

Port 1823 is assigned by IANA to unisys-lm (Unisys Natural Language License Manager).

1823

How unisys-lm works

Other services
client:1823unisys-lmresponse client:1823unisys-lmresponse

The client sends a request to port 1823 and the unisys-lm 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 1823 dangerous?

We have no specific security note for port 1823. 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 1823

ServicePortTransportDescriptionReferenceUpdated
unisys-lm 1823 TCP, UDP Unisys Natural Language License Manager - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1823, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1823'      # process listening on 1823
sudo lsof -nP -i :1823

macOS

sudo lsof -nP -i :1823

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1823 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1823
netstat -ano | findstr :1823

From another machine

nmap -p 1823 -sV <host>
sudo nmap -sU -p 1823 <host>
nc -zv <host> 1823

Block it in the firewall

sudo ufw deny 1823/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1823" -Direction Inbound -LocalPort 1823 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1823 used for?

Port 1823 is assigned by IANA to unisys-lm (Unisys Natural Language License Manager).

Is port 1823 TCP or UDP?

Port 1823 is registered for TCP and UDP.

Is it safe to open port 1823?

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 1823 is open?

On Linux run "ss -ltnup 'sport = :1823'", on macOS "lsof -nP -i :1823", and on Windows "netstat -ano | findstr :1823" to see the local process. From another machine, "nmap -p 1823 <host>" shows whether it is reachable.

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