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Port 1901: Fujitsu ICL Terminal Emulator Program A

Port 1901 is assigned by IANA to fjicl-tep-a (Fujitsu ICL Terminal Emulator Program A).

1901

How fjicl-tep-a works

Other services
client:1901fjicl-tep-aresponse client:1901fjicl-tep-aresponse

The client sends a request to port 1901 and the fjicl-tep-a 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 1901 dangerous?

We have no specific security note for port 1901. 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 1901

ServicePortTransportDescriptionReferenceUpdated
fjicl-tep-a 1901 TCP, UDP Fujitsu ICL Terminal Emulator Program A - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1901, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1901'      # process listening on 1901
sudo lsof -nP -i :1901

macOS

sudo lsof -nP -i :1901

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1901 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1901
netstat -ano | findstr :1901

From another machine

nmap -p 1901 -sV <host>
sudo nmap -sU -p 1901 <host>
nc -zv <host> 1901

Block it in the firewall

sudo ufw deny 1901/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1901" -Direction Inbound -LocalPort 1901 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1901 used for?

Port 1901 is assigned by IANA to fjicl-tep-a (Fujitsu ICL Terminal Emulator Program A).

Is port 1901 TCP or UDP?

Port 1901 is registered for TCP and UDP.

Is it safe to open port 1901?

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 1901 is open?

On Linux run "ss -ltnup 'sport = :1901'", on macOS "lsof -nP -i :1901", and on Windows "netstat -ano | findstr :1901" to see the local process. From another machine, "nmap -p 1901 <host>" shows whether it is reachable.

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