Port 399
iso-tsap-c2 · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | iso-tsap-c2 |
Frequently asked questions
What is port 399 used for?
Port 399 is registered with the IANA for iso-tsap-c2 (TCP/UDP). Description: ISO Transport Class 2 Non-Control over TCP; ISO Transport Class 2 Non-Control over UDP.
Is port 399 a well-known port?
Yes. Port 399 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 399 is open?
Locally on Linux with ss -tulpn | grep ':399\b', on Windows with netstat -ano | findstr :399. To test a remote host use Test-NetConnection <host> -Port 399 in PowerShell or nc -zv <host> 399 on Linux/macOS.
How do I open port 399 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 399/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=399/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 399" -Direction Inbound -Protocol TCP -LocalPort 399 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | iso-tsap-c2 | ISO Transport Class 2 Non-Control over TCP |
| UDP | iso-tsap-c2 | ISO Transport Class 2 Non-Control over UDP |