Why Does Telnet Login to a Switch Fail?

Latest reply: Feb 29, 2016 03:34:51 1139 1 0 0
Why Does Telnet Login to a Switch Fail?
  • x
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Created Feb 29, 2016 03:34:51 Helpful(0) Helpful(0)

The possible causes are:

  • No reachable route is available between the PC and switch, so a TCP connection cannot be set up. Use the ping command to check whether the switch is reachable from the PC.
  • The number of users that have logged in to the switch reaches the maximum. By default, a switch allows a maximum of five VTY users at a time. When the number of online VTY users reaches the maximum value, other users cannot log in to the switch through Telnet. In this case, you can log in to the switch from the serial port and run the display users command to check whether all the VTY channels are in use. If all VTY channels are in use, run the user-interface maximum-vty command to increase the maximum number of VTY users allowed on the switch. This maximum number can be set to 15 at most. You can also run the free user-interface vty command to disconnect some online users so as to release VTY channels.
  • An ACL is bound in the VTY user interface view. In this case, add a rule in the ACL to allow the IP address of this client. 
  • Telnet is not configured as an allowed protocol in the VTY user interface view. For example, if the protocol inbound ssh command has been executed in the VTY user interface view, users cannot log in to this VTY channel through Telnet.
  • When Telnet protocol packets are lost due to loops or some other reasons, Telnet login to the device may fail intermittently. 
  • x
  • convention:


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