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Best practices for NTP configuration
8 Time configuration and synchronization across Management modules, IOMs and iDRACs |
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Best practices for NTP configuration
• Use enough time sources: NTP takes the available sources of time and submits their timing data
to intersection and clustering algorithms, looking for the best idea of the correct time. If there is
only 1 source of time, the answer is obvious. It may not be a good source of time, but it's the only
one. If there are 2 sources of time and they agree well enough, that's good. But if they don't, then
ntpd has no way to know which source to believe. This gets easier if there are 3 sources of time.
But if one of those 3 sources becomes unreachable or unusable, we're back to only having 2 time
sources.
• Use a diversity of reference clocks: If you are using reference clocks, it is recommended that you
use several different types. Having a diversity of sources means that any one issue is less likely
to cause a service interruption.
• Using pool servers
• Standardize to UTC time: Within an enterprise, standardize all systems to coordinated universal
time (UTC). Standardizing to UTC simplifies log correlation within the organization and with
external parties no matter what time zone the device being synchronized is located in.
• Consider the business need for cryptography: Many administrators try to secure their networks
with encrypted communications and encrypted authentication. I would introduce a note of caution
here because although there are cryptographic services associated with NTP for securing NTP
communications, the use of encryption introduces more sources for problems, such as requiring
key management, and it also requires a higher computational overhead.
• Remember Segal's Law. Ideally, it would work to have three or more Stratum 0 or Stratum 1
servers and use those servers as primary masters. Remember Segal's Law: having two NTP
servers makes it hard to know which one is accurate. Two Stratum 0 servers would provide a
more accurate timestamp because they are using a time source that is considered definitive.