Port 0
no service name · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | no service name |
| Reference | RFC 6335 |
| Modified | 2024-12-20 |
Frequently asked questions
What is port 0 used for?
Port 0 is registered with the IANA for no service name (TCP/UDP). Description: Reserved.
Is port 0 a well-known port?
Yes. Port 0 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 0 is open?
Locally on Linux with ss -tulpn | grep ':0\b', on Windows with netstat -ano | findstr :0. To test a remote host use Test-NetConnection <host> -Port 0 in PowerShell or nc -zv <host> 0 on Linux/macOS.
How do I open port 0 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 0/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=0/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 0" -Direction Inbound -Protocol TCP -LocalPort 0 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | – | Reserved |
| UDP | – | Reserved |