Using Telnet to Troubleshoot Connection Issues

Description

When LPS, clients and printers are not responding, but can be "pinged" and appear to be functioning you can use telnet to troubleshoot connection problems.

Explanation

A response from a ping does not necessarily mean the device or program is available. Telnet gives you the ability to confirm if ports are also configured or blocked in a given environment due to firewalls, vlan, or something else.

Requirements

Host system needs to have telnet set up and operating before attempting this type of diagnosis. This generally requires somebody with administrative privileges.

Steps to Determine Cause

Checking to see if LPS is responsive.

We can use telnet to determine if the LPS is listening to the select port (2723 by default, see the LPS Configuration Utility to view if you are using an alternate port.)

1. Open Command prompt, Start -> Run -> cmd -> OK. Note: Telnet can also be run from Unix.
2. Type "telnet [IP address of the LPS] 2723.
3. A failure of the port will come back immediately, while a failure of the IP connection will take 5-10 seconds, both will have the same error.
   
   C:\>telnet 172.16.34.13 2723    
   Connecting To 172.16.34.13...Could not open connection to the host, on port 2723: Connect failed
4. A success will look like a blank command window, with an underscore. You can hit enter, but you will only see new underscores:
   _
   _
5. To confirm a connection, you can open a second cmd window on the LPS server and run wdlog localhost in the Loftware Labeling directory.
   You will see a connection, and then 4 seconds (default) later a timeout.
   
    

Checking to see if a printer is responsive

Note: TCP/IP only.

1. Confirm the associated IP and Port settings from the Device Manager in Design32 (default port is 9100).
2. Open Command prompt, Start -> Run -> cmd -> OK.
3. Type "telnet [IP address of the printer] 9100.
4. A failure of the port will come back immediately, while a failure of the IP connection will take 5-10 seconds, both will have the same error:
   
   C:\>telnet 172.16.63.5 9100    
   Connecting To 172.16.63.5...Could not open connection to the host, on port 9100: Connect failed
5. From a Jet Direct device, this may mean that the TCP/IP traffic is being received, but the printer attached is not working (error state, off, etc.).