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Port 16309 (etb4j)

IANA assigns port 16309 to etb4j.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
etb4j TCP etb4j Christopher R Smith -
etb4j UDP etb4j Christopher R Smith -

Registry dates for this port: registered 2004-11.

Check what is listening on port 16309

Linux: is anything listening on TCP 16309?
sudo ss -tlnp 'sport = :16309'
Linux: UDP 16309
sudo ss -ulnp 'sport = :16309'
Linux / macOS: which process owns the port
sudo lsof -nP -i :16309
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':16309 '
Windows (Command Prompt)
netstat -ano | findstr :16309
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 16309 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 16309
From Windows
Test-NetConnection HOST -Port 16309
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 16309

Block port 16309 in the firewall

ufw
sudo ufw deny 16309/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 16309 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 16309 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 16309' -Direction Inbound -Protocol TCP -LocalPort 16309 -Action Block
ufw
sudo ufw deny 16309/udp
iptables
sudo iptables -A INPUT -p udp --dport 16309 -j DROP
nftables
sudo nft add rule inet filter input udp dport 16309 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 16309' -Direction Inbound -Protocol UDP -LocalPort 16309 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.