When you telnet to a router the who command or the show user command will show whether someone else is also telnetted into that router. I would think that this is a better solution.
But if you really want to limit the router to 1 telnet session you certainly can do it. The exact syntax will depend on how many vty ports are supported on the router. If the router has the traditional 5 vty ports you would configure this:
line vty 1 4
no exec
If the router has more vty ports than 5 adjust the syntax so that the last parameter in the line command is the number of the maxumum vty.
If you configure this the first person who telnets will get vty 0. When anyone else attempts to telnet while vty 0 is active they will not be able to login. I would be very cautious about limiting the router this way. But if you want to do it, it certainly can be done.
HTH
Rick
HTH
Rick
