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// Other services

Port 1983: Loophole Test Protocol

Port 1983 is assigned by IANA to lhtp (Loophole Test Protocol).

1983

How lhtp works

Other services
client:1983lhtpresponse client:1983lhtpresponse

The client sends a request to port 1983 and the lhtp 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 1983 dangerous?

We have no specific security note for port 1983. 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 1983

ServicePortTransportDescriptionReferenceUpdated
lhtp 1983 TCP, UDP Loophole Test Protocol - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1983, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1983'      # process listening on 1983
sudo lsof -nP -i :1983

macOS

sudo lsof -nP -i :1983

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1983 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1983
netstat -ano | findstr :1983

From another machine

nmap -p 1983 -sV <host>
sudo nmap -sU -p 1983 <host>
nc -zv <host> 1983

Block it in the firewall

sudo ufw deny 1983/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1983" -Direction Inbound -LocalPort 1983 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1983 used for?

Port 1983 is assigned by IANA to lhtp (Loophole Test Protocol).

Is port 1983 TCP or UDP?

Port 1983 is registered for TCP and UDP.

Is it safe to open port 1983?

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 1983 is open?

On Linux run "ss -ltnup 'sport = :1983'", on macOS "lsof -nP -i :1983", and on Windows "netstat -ano | findstr :1983" to see the local process. From another machine, "nmap -p 1983 <host>" shows whether it is reachable.

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