Port 123
ntp · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | ntp |
| Reference | RFC 5905 |
Frequently asked questions
What is port 123 used for?
Port 123 is registered with the IANA for ntp (TCP/UDP). Description: Network Time Protocol.
Is port 123 a well-known port?
Yes. Port 123 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 123 is open?
Locally on Linux with ss -tulpn | grep ':123\b', on Windows with netstat -ano | findstr :123. To test a remote host use Test-NetConnection <host> -Port 123 in PowerShell or nc -zv <host> 123 on Linux/macOS.
How do I open port 123 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 123/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=123/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 123" -Direction Inbound -Protocol TCP -LocalPort 123 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | ntp | Network Time Protocol |
| UDP | ntp | Network Time Protocol |