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)