Tools / Port checker / 23
Is port 23 open?
Port 23 is Telnet. Enter your server below to test it from Dallas, Amsterdam and London.
What port 23 is used for
Unencrypted remote terminal access from before SSH. Still found on old network equipment and some IoT devices.
Should port 23 be open?
Should not face the internet directly. Everything, including passwords, crosses the network in clear text. Disable it and use SSH.
How to open port 23
Ubuntu or Debian with ufw, allowing only your own address (replace 203.0.113.10):
sudo ufw allow from 203.0.113.10 to any port 23 proto tcp
Rocky, Alma or CentOS with firewalld:
sudo firewall-cmd --permanent --add-port=23/tcp && sudo firewall-cmd --reload
Windows Server, in PowerShell as administrator:
New-NetFirewallRule -DisplayName "Port 23" -Direction Inbound -Protocol TCP -LocalPort 23 -Action Allow
Then check that the service listens on all addresses, not only 127.0.0.1, and test again above.
Check another port
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Run your service on a PrivateByte server: a firewall you control and every port yours to open.