line VTY

[Rajesh]

I mistakenly configured line vty Login local in my cisco switch without username but when i try to login the switch through telnet its asking username password tried CISCO, ADMIN but nothing works so please help what is the solution to login the switch Via telnet. 

[M02@rt37]

Hello @Rajesh  

Log with console port and modify your line vty config.

[MHM Cisco World]

try using Console 
then add 
username xxx password xxx
enable password xxxx <- this mandatory 

[liviu.gheorghe]

Hello @Rajesh  ,

if what M02@rt37 and @MHM Cisco World doesn't work in your situation, you can do a password recovery on the router. This procedure will place you in enable mode which gives you the chance to change usernames and passwords.

You can find a step by step procedure here: https://community.cisco.com/t5/networking-knowledge-base/password-recovery/ta-p/3123097

[Giuseppe Larosa]

Hello @Rajesh ,

if you haven't saved the change have someone to reboot the switch.

if you have saved the change you need to connect to the console as explained by M02@rt37 and @MHM Cisco World 

The issue is caused because no username exists

Hope to help

Giuseppe