The command that encrypts all plaintext passwords

B

The correct answer is B. Router(config)# service password-encryption.

Explanation:

In Cisco devices, passwords are stored in plaintext format by default. If an unauthorized person gains access to the device, they can easily view these passwords, which can lead to security breaches. The service password-encryption command encrypts all plaintext passwords, making them more secure.

To use the service password-encryption command, you need to access the global configuration mode of the Cisco device. This can be done by entering the "configure terminal" command in the device's command-line interface (CLI).

Once in global configuration mode, you can use the "service password-encryption" command to enable password encryption. This command will encrypt all plaintext passwords, including those used for remote authentication, Telnet, and console access.

Note that this command does not encrypt passwords that are already configured on the device. To encrypt existing passwords, you need to delete and re-enter them.

Option A, Router# service password-encryption, is an incorrect command. The correct syntax requires access to the global configuration mode, and the "#" symbol indicates privileged EXEC mode.

Option C, Router(config)# password-encryption, is an incorrect command. This command will encrypt only the enable secret password and not all plaintext passwords.

Option D, Router# password-encryption, is an incorrect command. This command does not exist in Cisco devices. The correct syntax requires access to the global configuration mode, and the "#" symbol indicates privileged EXEC mode.