Failed to telnet to s series switch

For S series switches (except S1700 switches), if you fail to log in to the Telnet server through Telnet, troubleshoot the failure as follows:
1. Check whether the number of login users reaches the upper limit.
Log in to the switch 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 a switch.

2. Check whether an ACL is configured in the VTY user interface view. (Telnet IPv4 is used as an example.)
Run the user-interface vty command on the Telnet server to enter the user interface view. 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.
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, then run the related command to permit the IP address of the client in the ACL.

3. Check whether the access protocol is correctly configured in the VTY user interface view.
Note that by default, the switch uses Telnet in V200R006 and earlier versions, so you do not need to configure protocol inbound telnet; the switch uses SSH in V200R007 and later versions, so you must configure protocol inbound telnet if you want to log in through Telnet.
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 inbound is set to telnet or all. (By default, the system supports the SSH protocol.) If protocol inbound is not set to telnet or all, run the protocol inbound { telnet | all } command to allow Telnet users to connect to the switch.

4. Check whether an authentication mode is set for login users in the user interface view.
- If password authentication is configured using the authentication-mode password command, you must enter the password upon login.
- If AAA authentication is configured using the authentication-mode aaa command, you must run the local-user command to create a local AAA user.

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