Authentication for the Controller and NTP/SNTP Server
We highly recommend that controllers synchronize their time with an external NTP/SNTP server. We also recommend that you authenticate this connection to the NTP/SNTP server, as a best practice. By default, an MD5 checksum is used in this scenario.
Each NTP/SNTP server IP address is added to the controller database. The respective controller then attempts to poll an NTP/SNTP server from this database in the index order. The controller then obtains and synchronizes the current time at each user-defined polling interval, as well as following a reboot event. By default, the NTP polling interval is 600 seconds.
Guidelines and Restrictions on NTP
When the time difference between the NTP server and the controller exceeds 1000s, the ntpd process exits and adds a panic message to the system log. In this situation, set the time on the controller manually.
As a part of the federal certification requirements, controller supports NTPv4 protocol which is a standard Open Source Code.
Controllers support both the versions—NTPv3 and NTPv4 versions. However you can use either one of the two versions and not both at the same time.
NTPv4 supports both IPv4 and IPv6 servers, and supports SHA1 authentication for NTP messages.