VTY (Virtual Terminal Lines) are used when you wish to telnet into a router remotely. In order for the router to allow telnet connections, the VTY lines need to be configured with a password, which is not a default setting. If you were to try connect to a router with telnet and the VTY password had not been configured, you would receive the following error message “Password required, but none set”
The router by default does not care which physical interface your telnet session is coming from, and hence the Telnet lines are Virtual.
A Router by default has 5 VTY lines, numbered from 0-4. We are able to configure a different password on each line, however the router randomly selects one of the VTY lines for use when a telnet session is initiated, because of this random selection, it makes no sense to have different password on each VTY, so when configuring the lines, we will choose the same password for all 5 lines.
To configure the VTY lines, we need to be in Global Configuration mode, then type the command ‘line vty 0 4’ – this tells the router we wish to connect to the VTY lines, from 0 – 4 (all 5 at the same time). We then can issue the ‘password password’ to set the password on the lines. We then need to issue the ‘login’ command which informs the router to do password checking when someone tries to telnet into the router. Lastly, don’t forget to save your config.
Below is the live demonstration video on how to configure the VTY passwords.