Port 666
doom and mdqs · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | doom and mdqs |
Frequently asked questions
What is port 666 used for?
Port 666 is registered with the IANA for doom and mdqs (TCP/UDP). Description: ; doom Id Software.
Is port 666 a well-known port?
Yes. Port 666 is in the range 0–1023 (system or well-known ports). On Linux and macOS only privileged processes may bind to these ports.
How do I check whether port 666 is open?
Locally on Linux with ss -tulpn | grep ':666\b', on Windows with netstat -ano | findstr :666. To test a remote host use Test-NetConnection <host> -Port 666 in PowerShell or nc -zv <host> 666 on Linux/macOS.
How do I open port 666 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 666/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=666/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 666" -Direction Inbound -Protocol TCP -LocalPort 666 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | mdqs | |
| UDP | mdqs | |
| TCP | doom | doom Id Software |
| UDP | doom | doom Id Software |