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We're gearing up to have an argument regarding NTP stratum as an indicator of time accuracy. The statement that started the whole thing was:
Stratum 5 can be four minutes off.
My understanding is that NTP tries as hard as it can to put forward the correct time, regardless of how many hops (stratum) you are away from an authoritative clock. I understand that the higher the stratum number means you have more of a chance of a time server gone bad or a flaky network causing incorrect calculations. I understand more than just stratum (jitter, latency, etc.) should be examined to determine how accurate a clock is. I also understand that there should be 3 or 4 (or more?) upstream time servers for redundancy and statistical reliability.
Internally, several production systems are stratum 5. I cannot reach out from my stratum 5 test system to a stratum 2 to get an offset.
ntpdate -q 1.debian.pool.ntp.org
server 208.53.158.34, stratum 0, offset 0.000000, delay 0.00000
6 Jan 15:47:46 ntpdate[]: no server suitable for synchronization found
But contacting a few of my internal stratum 3 servers, that difference is about -0.007. (Or even less!)
I'm looking for arguments I can give to non-technical managers to soothe their fears. Right now I'm leaning towards something like this.
Stratum is only a measurement of the number of hops from an authoritative clock. Our internal NTP servers receive time from stratum 2 servers. This is pretty standard across the Internet. (Else the stratum 1 servers would become overloaded. Overloaded time servers report incorrect time.) The difference between our internal stratum 3 servers and the stratum 5 production systems is roughly 7 thousands of a second. Strata 3, 4, and 5 time servers are all owned by us and communicate over our network. Unless our internal stratum 3 time servers (used as the source of time for the entire company) are wildly inaccurate, we shouldn't worry about stratum as an indicator of system time accuracy.
I realize I need to get management to state what an acceptable inaccuracy is. (We are not involved in life-and-death decisions, we do not provide time services to customers, nor do we trade stock where seconds of inaccuracy expose us to large monetary liabilities. I do understand from conversations that 4 minutes does matter to some business departments. Heck, four minutes would probably make NFS go crazy!)
Can anyone point out where my reasoning and process is wrong? Are there better arguments? Are there sites/links describing (in)accuracy of time as the strata number increase that I can use as research?
I have a really good answer on the validity of my arguments and have accepted it. I'd be really interested if others can help me learn and complete this portion of the question:
Are there sites/links describing (in)accuracy of time as the strata number increase that I can use as research? – IAmJeff – 2015-01-08T19:03:26.227
I disagree that this question would solicit responses almost entirely based on opinion. I expected responses in the form of "You are (in)correct based on these criteria." The answer below is based on data and the questioner learned from the answerer. – IAmJeff – 2015-01-08T19:12:21.737