Port 23
telnet · TCP/UDP
| Range | System/well-known port (0–1023) |
|---|---|
| Protocol | TCP/UDP |
| Service | telnet |
| Reference | RFC 854 |
Frequently asked questions
What is port 23 used for?
Port 23 is registered with the IANA for telnet (TCP/UDP). Description: Telnet.
Is port 23 a well-known port?
Yes. Port 23 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 23 is open?
Locally on Linux with ss -tulpn | grep ':23\b', on Windows with netstat -ano | findstr :23. To test a remote host use Test-NetConnection <host> -Port 23 in PowerShell or nc -zv <host> 23 on Linux/macOS.
How do I open port 23 in the firewall?
Ubuntu/Debian (ufw): sudo ufw allow 23/tcp. Fedora/RHEL (firewalld): sudo firewall-cmd --add-port=23/tcp --permanent, then firewall-cmd --reload. Windows (PowerShell as administrator): New-NetFirewallRule -DisplayName "Port 23" -Direction Inbound -Protocol TCP -LocalPort 23 -Action Allow.
IANA registry entries
| Protocol | Service | Description (IANA) |
|---|---|---|
| TCP | telnet | Telnet |
| UDP | telnet | Telnet |