Port 6666 (ircu)

IANA assigns port 6666 to ircu: IRCU.

Registered (user) port, 1024-49151 TCP

IANA assignment

Service nameProtoDescriptionAssigneeReference

ircu TCP IRCU (range 6665-6669) Brian Tackett -

Linux: is anything listening on TCP 6666?

sudo ss -tlnp 'sport = :6666'

Linux / macOS: which process owns the port

sudo lsof -nP -i :6666

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':6666 '

Windows (Command Prompt)

netstat -ano | findstr :6666

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6666 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 6666

From Windows

Test-NetConnection HOST -Port 6666

ufw

sudo ufw deny 6666/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 6666 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 6666 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 6666' -Direction Inbound -Protocol TCP -LocalPort 6666 -Action Block

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