Controlling VTY (Telnet) Access
You’ll probably have a difficult time trying to stop users from telnetting to a large router because
any active interface on a router is fair game for VTY access. You could try to create an extended
IP access list that limits Telnet access to every IP address on the router. But if you did that, you’d
have to apply it inbound on every interface, and that really wouldn’t scale well to a large router
with dozens, even hundreds, of interfaces, would it? Here’s a much better solution: Use a
standard IP access list to control access to the VTY lines themselves.