Which command is used to set the Telnet password on a Cisco router?

The command used to set the Telnet password on a Cisco router involves accessing the virtual terminal lines, which are represented by the vty lines. Specifically, the command "line vty 0 4" designates the configuration for virtual terminal lines 0 through 4 on the router. These lines are utilized for remote access to the router via Telnet or SSH.

After entering this command in the router's configuration mode, you would then typically issue the "password" command followed by the desired password to establish a Telnet password. Additionally, activating the login procedure with the "login" command is often the next step. This process effectively secures access over Telnet, ensuring that only users who know the password can initiate connections through those virtual terminal lines.

Other options focus on different line types: the auxiliary line is used for modem connections, and the console line pertains to direct access via the console port. Neither of these options is specifically tied to Telnet access which is why they do not apply in this context.