Configuring NTP

Router(config)#clock timezone GB <+ or – from GMT>
Router(config)#ntp server <IP / hostname>
Router(config)#ntp master <stratum number>

Server Side Authentication

Router(config)#ntp authentication-key MY_KEY_NUMBER md5 MY_KEY
Router(config)#ntp peer REMOTE_PEER key MY_KEY_NUMBER

Client Side Authentication

Router(config)#ntp authentication-key MY_KEY_NUMBER md5 MY_KEY
Router(config)#ntp trusted-key MY_KEY
Router(config)#ntp server SERVER_IP