Port 3
no service name · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | no service name |
| Modified | 2025-02-13 |
Frequently asked questions
What is port 3 used for?
Port 3 is registered with the IANA for no service name (TCP/UDP). Description: Reserved.
Is port 3 a well-known port?
Yes. Port 3 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 3 is open?
Locally on Linux with ss -tulpn | grep ':3\b', on Windows with netstat -ano | findstr :3. To test a remote host use Test-NetConnection <host> -Port 3 in PowerShell or nc -zv <host> 3 on Linux/macOS.
How do I open port 3 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 3/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=3/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 3" -Direction Inbound -Protocol TCP -LocalPort 3 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | – | Reserved |
| UDP | – | Reserved |