Now that you have your own NTP servers up and running (such as some Raspberry Pis with external DCF77 or GPS times sources) you should monitor them appropriately, that is: at least their offset, jitter, and reach. From an operational/security perspective it is always good to have some historical graphs that show how any service behaves under normal circumstances to easily get an idea about a problem in case one occurs. With this post I am showing how to monitor your NTP servers for offset, jitter, reach, and traffic aka “NTP packets sent/received”.
This post shows how to use a GPS receiver with a Raspberry Pi to build a stratum 1 NTP server. I am showing how to solder and use the GPS module (especially with its PPS pin) and listing all Linux commands to set up and check the receiver and its NTP part, which is IPv6-only in my case. Some more hints to increase the performance of the server round things off. In summary this is a nice “do it yourself” project with a working stratum 1 NTP server at really low costs. Great. However, keep in mind that you should not rely on such projects in enterprise environments that are more focused on reliability and availability (which is not the case on self soldered modules and many config file edits).