Non-GPS derived timing sources (was Re: NTp sources that work in a datacenter)

Sean Donelan sean at
Mon Jun 2 21:55:45 UTC 2003

On Mon, 2 Jun 2003, Leo Bicknell wrote:
> Could it be that providers actually have multiple sources, but for
> some reason GPS is always picked as the primary source for the
> public facing function?  At least a few providers keep their actual
> sources (the receivers themselves) "hidden", and provide a unix box
> syncing to all of them as the front end.  From my limited knowledge,
> that front end box will only show the one source it has picked as
> "best".

Like all answers, it depends.

A relatively small number of providers have blocked access to their
"master" NTP servers. So you can't see the current source from the next
stratum down.  You get a domain name, like ntp-1.ispdom.ain, for the

But a large number permit queries to their NTP servers. They will report
all the stratum 0 sources available, including the current sync'd source.
Almost no providers use more than one stratum 0 source per NTP server.
The people with lots of stratum 0 sources are almost never network service
providers. Generally NSPs have 1 stratum 0 source, a two or three stratum
1 peers, and lots of stratum 2s.  Most providers don't have a dedicated NTP
infrastructure, so their tickers are running on routers and general
purpose servers.

Due to the way NTP works, it is a self-directed hierarchy.  A stratum 1
chimer is only at the top while its synced to a stratum 0 source.

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