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NTP Skew or Smear Sources

I promote redundancy at every chance. Having extra DNS servers or extra DHCP servers is always grand. One issue that I noticed recently was NTP Skew or Smear. This is a method of slowly adjusting the clocks on systems to compensate for leap seconds which happen from time to time. The process is well thought out and well documented however the implementation is not perfect. While discussing redundancy a network engineer was explaining the current solution and future plans. I was asked about the NTP setup and advised them to diversify vendors of hardware solutions. After a deeper dive I found they were using cloud provider vendor NTP services from a directive up the command chain. The issue came when I saw they were configuring multiple providers NTP servers as sources. The issue here is that NTP sources might use a different smear method and the inclusion of non-smeared sources would mean the NTP calculation would favor the lowest latency source as the various vendors smear drifted apart from atomic time.

Mixing algorithms is tricky https://developers.google.com/time/smear


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