CISC-ND-001150 - The Cisco router must be configured to authenticate Network Time Protocol (NTP) sources using authentication that is cryptographically based - ntp authenticate
If Network Time Protocol is not authenticated, an attacker can introduce a rogue NTP server. This rogue server can then be used to send incorrect time information to network devices, which will make log timestamps inaccurate and affect scheduled actions. NTP authentication is used to prevent this tampering by authenticating the time source.
Configure the Cisco router to authenticate NTP sources using authentication that is cryptographically based as shown in the example below. R2(config)#ntp authenticate R2(config)#ntp authentication-key 1 md5 xxxxxx R2(config)#ntp trusted-key 1 R2(config)#ntp server x.x.x.x key 1 R2(config)#ntp server y.y.y.y key 1