NTP question

Harlan Stenn stenn at nwtime.org
Thu May 2 01:45:35 UTC 2019


On 5/1/19 5:39 PM, William Herrin wrote:
> On Wed, May 1, 2019 at 12:23 PM Mehmet Akcin <mehmet at akcin.net> wrote:
> 
>> I am trying to buy a GPS based NTP server like this one
>>
>> https://timemachinescorp.com/product/gps-time-server-tm1000a/
>>
>> but I will be placing this inside a data center, do these need an actual
>> view of a sky to be able to get signal or will they work fine inside a data
>> center building? if you have any other hardware requirements to be able to
>> provide stable time service for hundreds of customers, please let me know.
>>
> 
> You buy a powered GPS antenna for it. Which antenna depends on the cable
> length and type. The amplifier in the antenna amplifies the signal just
> enough to overcome the cable loss between the antenna and the receiver.
> Nice thick cables lose less signal. Dinky thin ones are easier to work with.
> 
> You sure you need a GPS NTP server? You understand that if you do, you need
> two for reliability right, and probably at geographically diverse
> locations? If you're not on an air-gapped network, consider syncing a
> couple head-end NTP servers against tick and tock (.usno.navy.mil, the
> naval observatory) and not worrying about it. One less piece of equipment
> to manage, update, secure, etc.

Two is not a great number.  If they disagree, there is no majority
clique to be found.

Also, there is something to be said for using different models/vendors
for the time sources.  If you only have the same model from one vendor
and there is a bug, you can lose all your time sources at once.   The
GPS week rollover happens every ~19.7 years, and when that problem hits
is a function of the firmware and a manufacturing date put in the firmware.

These problems can be mitigated if you have "enough" time sources for
your internal NTP servers and you peer with enough other, possibly your,
servers.

> Regards,
> Bill Herrin

-- 
Harlan Stenn <stenn at nwtime.org>
http://networktimefoundation.org - be a member!



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