Final answer:
The 'service password-encryption' command on a Cisco router encrypts all current and future plaintext passwords in the configuration except for those protected by stronger methods like the 'enable secret' command.
Step-by-step explanation:
The command service password-encryption on a Cisco router is used to encrypt all current and future passwords that are not already encrypted by stronger methods. This includes passwords such as those used for console access, VTY access, and enable passwords configured with the password command. Passwords set with the enable secret command are already encrypted with a stronger encryption algorithm and are not affected by this command.
When this command is issued, all passwords configured on the router will be encrypted, regardless of how they were configured.
The correct answer to the question 'An administrator issues the service password-encryption command on a Cisco router. Which of the following passwords will be encrypted on the router?' would be option d: passwords configured by any means along with any passwords configured in the future. This is because the command applies encryption to all plaintext passwords throughout the router’s configuration.