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Port 4166 (joost)

IANA assigns port 4166 to joost: Joost Peer to Peer Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
joost TCP Joost Peer to Peer Protocol Colm MacCarthaigh -
joost UDP Joost Peer to Peer Protocol Colm MacCarthaigh -

Registry dates for this port: registered 2007-04.

Check what is listening on port 4166

Linux: is anything listening on TCP 4166?
sudo ss -tlnp 'sport = :4166'
Linux: UDP 4166
sudo ss -ulnp 'sport = :4166'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4166
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4166 '
Windows (Command Prompt)
netstat -ano | findstr :4166
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4166 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4166
From Windows
Test-NetConnection HOST -Port 4166
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4166

Block port 4166 in the firewall

ufw
sudo ufw deny 4166/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4166 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4166 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4166' -Direction Inbound -Protocol TCP -LocalPort 4166 -Action Block
ufw
sudo ufw deny 4166/udp
iptables
sudo iptables -A INPUT -p udp --dport 4166 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4166 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4166' -Direction Inbound -Protocol UDP -LocalPort 4166 -Action Block

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