Port 6668 (ircu)

IANA assigns port 6668 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 6668?

sudo ss -tlnp 'sport = :6668'

Linux / macOS: which process owns the port

sudo lsof -nP -i :6668

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':6668 '

Windows (Command Prompt)

netstat -ano | findstr :6668

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6668 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 6668

From Windows

Test-NetConnection HOST -Port 6668

ufw

sudo ufw deny 6668/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 6668 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 6668 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 6668' -Direction Inbound -Protocol TCP -LocalPort 6668 -Action Block

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