From Mexico.purplecow.org
IOS Telnet Sessions
Overview
Managing telnet administration sessions into an IOS device isn't immediately obvious, because commands like w/where look like the right one but aren't.
The question was posed - how do I kill an admin telnet session?
The Answers
Q. How do I view a list of current admin sessions? A. who
Q. How do I view a list of current VTY lines? A. show line
Q. How do I kill one? A. clear line Tty (column 1)