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// Other services

Port 3981: Starfish System Admin

Port 3981 is assigned by IANA to starfish (Starfish System Admin).

3981

How starfish works

Other services
client:3981starfishresponse client:3981starfishresponse

The client sends a request to port 3981 and the starfish 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 3981 dangerous?

We have no specific security note for port 3981. 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 3981

ServicePortTransportDescriptionReferenceUpdated
starfish 3981 TCP, UDP Starfish System Admin - 2006-06

// source: IANA service name and port number registry

03 Check it

Which program uses port 3981, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3981'      # process listening on 3981
sudo lsof -nP -i :3981

macOS

sudo lsof -nP -i :3981

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3981 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3981
netstat -ano | findstr :3981

From another machine

nmap -p 3981 -sV <host>
sudo nmap -sU -p 3981 <host>
nc -zv <host> 3981

Block it in the firewall

sudo ufw deny 3981/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3981" -Direction Inbound -LocalPort 3981 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3981 used for?

Port 3981 is assigned by IANA to starfish (Starfish System Admin).

Is port 3981 TCP or UDP?

Port 3981 is registered for TCP and UDP.

Is it safe to open port 3981?

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 3981 is open?

On Linux run "ss -ltnup 'sport = :3981'", on macOS "lsof -nP -i :3981", and on Windows "netstat -ano | findstr :3981" to see the local process. From another machine, "nmap -p 3981 <host>" shows whether it is reachable.

05 Related
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