[ntp:questions] synchronization distance

David L. Mills mills at udel.edu
Sun Dec 5 04:28:54 UTC 2010


I'm not learning anything at all in our exchange, and that is a real 
disappointment. Apparently, there are complaints NTPv4 does not play 
nicely with Microsoft. Microsoft is not about to change. NTPv4 is not 
about to change; however, there is a minor configuration option that 
makes NTPv4 work almost as well or maybe worse than SNTP. Whether this 
is good or bad corporate practice is not based on sound engineering 
principles, but on corporate convenience. I see absolutely no need to 
care about that or especially to prolong this discussion.


David Woolley wrote:

> David L. Mills wrote:
>> David,
>> I'm not making myself absolutely crystal clear and you are obscuring 
>> the point.
>> Windows has an awesome protocol that sets the time. It happens to use 
>> the NTP packet header format, but is not otherwise compliant with the 
>> NTPv4 specification, especially the 36-h poll interval limitation, 
>> which is an engineering parameter based on the expected wander of a 
>> commodity crystal oscillator. All that doesn't matter at all, other 
>> than Windows servers are compatible with Windows clients. What does 
>> matter is that Windows servers are NOT compatible with NTPv4 clients, 
>> which SHOULD NOT BE USED. Use one of the SNTP variants instead.
> To a large extent I would agree with you, but the net effect of this 
> is to say "if you work for a marketing led company (probably true of 
> most of the Fortune 500), do not use NTP as it is almost certain that 
> your IT department has a strict Microsoft policy for their core 
> systems, and are not time synchronisation experts".
>> As a diehard workaround, use the tos maxdist command to set the 
>> distance threshold to something really high, like ten seconds. There 
>> is nothing whatsoever to be gained by this, as the expected error 
>> with update intervals of a week will be as bad or worse than with SNTP..
>> Dave
>> David Woolley wrote:
>>> David L. Mills wrote:
>>>> BlackList,
>>>> I say again with considerable emphasis: this is a Microsoft 
>>>> product, not the NTPv4 distribution that leaves here. What you see 
>>>> is what you get, 
>>> But it is often NTPv4 reference version that is used as the client 
>>> and fails to synchronize because the root dispersion is too high.
>>> Corporate politics are such that it is difficult to get a Unix 
>>> system, or even Windows running the reference version, near the root 
>>> of the time distribution  tree.  People deeper in the tree then see 
>>> the effects, even if they are using the reference implementation.
>>>> warts and all. I doubt it has anything to do with root distance, or 
>>>> any other public specification, but that doesn't make any 
>>>> difference if the customer is satisfied with the performance. Just 
>>>> don't compare it with anything in the NTP distribution, 
>>>> documentation or specification.
>>>> Dave
>>>> E-Mail Sent to this address will be added to the BlackLists wrote:
>>>>> David L. Mills wrote:
>>>>>> I had no idea somebody would try to configure current
>>>>>> NTPv4 with a poll interval of a week.
>>>>>> The current maximum allowed is 36 h.
>>>>> <http://technet.microsoft.com/en-us/library/cc773263%28WS.10%29.aspx>
>>>>> <BlockQuote>
>>>>> SpecialPollInterval
>>>>> This entry specifies the special poll interval in seconds
>>>>>  for manual peers. ...
>>>>> The default value on stand-alone clients and servers is 604,800.
>>>>> </BlockQuote>
>>>>> {7 days}
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