Which three commands are required to enable NTP authentication on a Cisco router? (Choose three)
To enable NTP authentication on a Cisco router, the following three commands are required:
ntp authenticate: This command is used to enable NTP authentication on the router. When this command is entered, the router will require authentication information to be included in any NTP packets it receives.
ntp trusted-key: This command is used to specify the key number(s) that are trusted for NTP authentication. A trusted key is one that is used by the router to authenticate NTP packets it receives.
ntp authentication-key: This command is used to specify the authentication key(s) that are used by the router to authenticate NTP packets it sends. The key number(s) specified with this command must match the key number(s) specified with the ntp trusted-key command.
In addition to the above commands, it is also recommended to configure other NTP-related commands such as ntp server and ntp source, which specify the NTP servers to synchronize with and the source interface for NTP packets respectively.
To summarize, the correct answers are: