Port 203
at-3 · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | at-3 |
Frequently asked questions
What is port 203 used for?
Port 203 is registered with the IANA for at-3 (TCP/UDP). Description: AppleTalk Unused.
Is port 203 a well-known port?
Yes. Port 203 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 203 is open?
Locally on Linux with ss -tulpn | grep ':203\b', on Windows with netstat -ano | findstr :203. To test a remote host use Test-NetConnection <host> -Port 203 in PowerShell or nc -zv <host> 203 on Linux/macOS.
How do I open port 203 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 203/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=203/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 203" -Direction Inbound -Protocol TCP -LocalPort 203 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | at-3 | AppleTalk Unused |
| UDP | at-3 | AppleTalk Unused |