[ntp:questions] Time server question

Jakob Bohm jb-usenet at wisemo.com.invalid
Fri Jun 21 14:48:44 UTC 2019

On 21/06/2019 15:14, Thomas Laus wrote:
> On 2019-06-21, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>> On 21/06/2019 12:26, Thomas Laus wrote:
>>> Will either isolation solution have direct access to the computer
>>> CPU?  The GPS clock will need the ability to directly adjust the
>>> frequency of the CPU to achieve expected results for a Stratum 1
>>> serve
>> I'm not aware of anything in ntpd that directly adjusts the CPU
>> frequency and there generally isn't any fine grained way of doing that.
>> ntpd normally works by adjusting how many cycles of a fixed frequency
>> represent a certain time period, and that is a software operation.
> I guess that I should have stated this reply a little differently.  I
> meant to say that ntpd will need direct access to the hardware that
> it runs on.  That means a hardware serial port for pulse per second
> and the running system clock frequency.  The ntpd program does not
> perform well when running on a virtual machine nor in a isolated
> security environment similar to a freebsd jail.  My advice to the
> original poster is to get ntpd running as a stratum 1 source and
> then connect it to the internet with the fewest number of inter-
> mediate hops in between.  I doubt that this is possible if the
> Stratum 1 time source can be connected through any buffer device
> to the internet and still serve Stratum 1 time.

The deeper problem here is that the NTP protocol doesn't clearly
distinguish between a stratum 2 server running dozens of low quality
hops from it's time sources and a stratum 2 server that sits a single
hop from a solid stratum 1 source.

On the other hand, a GPS, WWVB or other radio clock isn't really a
stratum 1, as it receives remote time over a non-NTP protocol, so that
sort of cancels out the stratum 2 reported due to the stacking.

Running the Internet-exposed ntp server in a bastion host separate
from the difficult-to-upgrade old hardware makes perfect sense, and
an ntpd server without same machine precision time sources only needs
the permissions to use port 123 and to adjust the local clock (including
it's speed) via the various privileged system calls.  Running the 
computer clocks in such a bastion host from a quality crystal rather
than a cheap ceramic oscillator would also help reduce time errors, but
this is in the hardware buying phase and not a detail typically provided
by computer vendors.

I suspect the ntp servers run by national time services and synced to
their reference Cs and maser clocks are also receiving the time via
some kind of internal network, either ntp with stratum fudge, PTP low
latency Ethernet distribution or an amplified low latency coax
distribution of the 1Hz or 10MHz reference (the latter would be most
precise and offer no data channel for a compromised server to attack the
actual clock).


Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
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