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Port 16003 (alfin)

IANA assigns port 16003 to alfin: Automation and Control by REGULACE.ORG.

Registered (user) port, 1024-49151 UDP

Port 16003 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

IANA assignment

Service nameProtoDescriptionAssigneeReference
alfin UDP Automation and Control by REGULACE.ORG Ing Tomas Halabala -

Registry dates for this port: registered 2010-10-06.

Check what is listening on port 16003

Linux: UDP 16003
sudo ss -ulnp 'sport = :16003'
Linux / macOS: which process owns the port
sudo lsof -nP -i :16003
Windows (Command Prompt)
netstat -ano | findstr :16003
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 16003

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 16003

Block port 16003 in the firewall

ufw
sudo ufw deny 16003/udp
iptables
sudo iptables -A INPUT -p udp --dport 16003 -j DROP
nftables
sudo nft add rule inet filter input udp dport 16003 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 16003' -Direction Inbound -Protocol UDP -LocalPort 16003 -Action Block

Related ports

16001fmsascon16002gsms16020jwpc16021jwpc-bin

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