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Port 3981 (starfish)

IANA assigns port 3981 to starfish: Starfish System Admin.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
starfish TCP Starfish System Admin Dan Razzell -
starfish UDP Starfish System Admin Dan Razzell -

Registry dates for this port: registered 2006-06.

Check what is listening on port 3981

Linux: is anything listening on TCP 3981?
sudo ss -tlnp 'sport = :3981'
Linux: UDP 3981
sudo ss -ulnp 'sport = :3981'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3981
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3981 '
Windows (Command Prompt)
netstat -ano | findstr :3981
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3981 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3981
From Windows
Test-NetConnection HOST -Port 3981
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3981

Block port 3981 in the firewall

ufw
sudo ufw deny 3981/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3981 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3981 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3981' -Direction Inbound -Protocol TCP -LocalPort 3981 -Action Block
ufw
sudo ufw deny 3981/udp
iptables
sudo iptables -A INPUT -p udp --dport 3981 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3981 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3981' -Direction Inbound -Protocol UDP -LocalPort 3981 -Action Block

Related ports

3978secure-cfg-svr3979smwan3982eis3983eisp

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.