The network element must use two or more NTP servers to synchronize time.

From Firewall Security Technical Implementation Guide - Cisco

Part of Two NTP servers are not used to synchronize time.

SV-41499r1_rule The network element must use two or more NTP servers to synchronize time.

Vulnerability discussion

Without synchronized time, accurately correlating information between devices becomes difficult, if not impossible. If you cannot successfully compare logs between each of your routers, switches, and firewalls, it will be very difficult to determine the exact events that resulted in a network breach incident. NTP provides an efficient and scalable method for network elements to synchronize to an accurate time source.

Check content

Review the firewall configurations and verify that two or more NTP servers have been defined similar to the following example: ntp server 10.1.0.5 key 1 source mgmt ntp server 10.1.0.8 key 1 source mgmt ntp authenticate ntp authentication-key 1 md5 ******** ntp trusted-key 1

Fix text

Configure the device to use two separate NTP servers.

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