cisco ios: meaning of vty numbers
 

In an example in the book I'm looking at, it has a config command "line vty 0 15" followed by "password telnet" to change the login password. Could someone explain what the numbers are for (0 15)? And why 0 15 was chosen for the example instead of 0 0 or something else? I know that they refer to the "First Line range" and "Last Line range", but I'm not sure what that means.

The numbers refer to the first (0) and 16th (15) telnet or SSH connection. line vty 0 15 means "the following settings shall apply to all telnet/ssh sessions".

Thanks.