ExplanationExplanationTo configure an NTP enabled router to require authentication when other devices connect to it, use thefollowing commands:NTP_Server(config)#ntp authentication-key 2 md5 securitytutNTP_Server(config)#ntp authenticateNTP_Server(config)#ntp trusted-key 2Then you must configure the same authentication-key on the client router:NTP_Client(config)#ntp authentication-key 2 md5 securitytutNTP_Client(config)#ntp authenticateNTP_Client(config)#ntp trusted-key 2NTP_Client(config)#ntp server 10.10.10.1 key 2Note: To configure a Cisco device as a NTP client, use the command ntp server <IP address>. For example:Router(config)#ntp server 10.10.10.1. This command will instruct the router to query 10.10.10.1 for the time.