What command is used to encrypt current and future passwords on the device?

The command that is used to encrypt current and future passwords on a Cisco device is "service password-encryption." When this command is executed in the global configuration mode, it enables the encryption of all plaintext passwords in the configuration file. This applies to existing passwords and any new passwords that are created subsequently.

It's important to note that the encryption mechanism used by this command provides a basic level of security by converting plaintext passwords into a more obscured format, which helps prevent unauthorized users from easily reading those passwords if they gain access to the device configuration. However, it's worth mentioning that this method does not offer strong security, and for even stronger protection, administrators might consider using other methods or stronger encryption schemes.

The other commands listed do not serve the purpose of encrypting both current and future passwords in the same way. For example, while “enable secret” is used to set a password for privileged EXEC mode that is stored in an encrypted form, it does not encrypt existing plaintext passwords already in the configuration. Similarly, “encrypt passwords” and “set encryption” are not valid Cisco IOS commands for password encryption.