The port 23/TCP is historically associated with Telnet To open a Terminal-mode format, the use of the remote control device should be exceptional and limited to controlled equipment or environments when secure protocols such as SSH are not available.
What is Port 23 used for?
The port 23/TCP is associated with Telnet, a terminal protocol that is still encountered on some old equipment, network consoles or embedded systems. Telnet exchanges do not provide native encryption: identifiers, commands and data can therefore be read on the network path.
A Telnet card should be interpreted as a need for an legacy compatibility, not as the default choice to administer modern equipment.
Transport Protocol
TCP
Safety precautions
Should we open this port in the firewall?
Avoid, expose Telnet to the Internet and limit it to strictly necessary d-sections. When the equipment allows, SSH is preferable because it protects the authentication and session. If an device requires Telnet, compensate by segmentation, source filtering and access via VPN or bastion.
How do I check this port?
To distinguish a network problem from a Telnet problem, check first that the service is listening to the destination. From Windows, Test-NetConnection SERVER -Port 23 test the establishment tactile; under Linux, nc -vz SERVER 23 can provide the same connectivity control.
- To train the to listen to the service on equipment.
- Test the path of the TITLE from the expected a administration network.
- If the session opens, then closes, check the service’s authentication and restrictions.
- Control the ACL
FAQ — port 23 / Telnet
Does Telnet encrypt the password?
No, Telnet does not provide native encryption for the session. That is the main reason why SSH is preferable.
Does an open port mean that Telnet is usable?
It only confirms that, a tactile connection can be established. The service can then refuse the session according to the authentication, or the ACLs.
When to store Telnet?
Mostly when old equipment does not propose a safer protocol d administration, the flow must be isolated and restricted.