This post refers to the issue that a device fails to be logged in via Telnet. Please see more details as you read further down.
Fault description
The Telnet server fails to be logged in via Telnet.
Possible causes
- The number of users who log in to the device reaches the upper limit.
- ACL limitation is configured in the VTY user interface view on the device.
- The allowed protocol in the VTY user interface view is incorrectly configured.
- The login authentication is configured in the user interface view.
Troubleshooting procedure
1. Check whether the number of login users reaches the upper limit.
a) Log in to the device through the console port and run the display users command to check whether all VTY user
interfaces are in use. By default, the maximum number of VTY user interfaces is 5. You can run the display user-interface maximum-vty command to check the maximum number of login users allowed by the device.
b) If the number of login users reaches the upper limit, run the user-interface maximum-vty 15 command to increase the maximum number of login users to 15.
2. Check whether an ACL is configured in the VTY user interface view (Telnet IPv4 is used as an example).
a) Run the user-interface vty command on the Telnet server to enter the user interface view and then run the display this command to check whether an ACL is configured in the VTY user interface view. If so, record the ACL number.
b) Run the display acl acl-number command on the Telnet server to check whether the IP address of the Telnet client is denied in the ACL. If so, run the undo rule rule-id command in the ACL view to delete the deny rule and then run the corresponding command to modify the ACL and permit the IP address of the client.
3. Check whether the access protocol is correctly configured on the VTY user interface view.
a) Run the user-interface vty command on the Telnet server to enter the user interface view and then run the display this command to check whether protocol.
b) inbound is set to telnet or all. By default, the system supports the SSH and Telnet protocol. If not, run the protocol inbound { telnet | all } command to allow the Telnet users to connect to the device.
4. Check whether an authentication mode is set for the loggin in users in the user interface view.
a) If password authentication is configured using the authentication-mode password command, you must enter the password upon login.
b) If AAA authentication is configured using the authentication-mode aaa command, you must run the local-user command to create a local AAA user.
If the fault persists, collect the error information and contact our technical support personnel.
