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,

> Regards,
> Bill Herrin

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

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