NTP behaviour when server is not synchronized

Hello,

NTP configuration:

Client: ntpd version 4.2.21.1532 running on Windows
XP
Servers: 2 identical stratum 1 servers with GPS antennas
directly
connected

I want comments on the following observations.
Unfortunately, the
system is currently not available, hence I cannot supply
ntpq
diagnostics. I know that 2 servers is the worst possible
configuration, it is not necessary to comment that.

For some reason one NTP server lost its GPS synch. It
switched to
internal clock started reporting stratum 12 when this
happened. The
other server was perfectly synchronized and reported stratum
1.
Problem: ntpd rejects both servers and considers itself not
synchronized.

Questions:

1. Does the NTP server behave correctly when changing its
stratum to
12? Should it perform different/other actions when it
considers itself
not synchronized?

2. Does ntpd behave correctly? Is a server's stratum used in
any way
in ntpd's clock selection process?

Thank you in advance for your support.

Best regards
Geir Guldstein

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

>>> In article <1183138077.657644.124300n2g2000hse.googlegroups.com>, Geir G
<geir.guldsteinstart.no> writes:

Geir> Hello, NTP configuration:

Geir> Client: ntpd version 4.2.21.1532 running on Windows
XP Servers: 2
Geir> identical stratum 1 servers with GPS antennas
directly connected

Are these 2 servers peering with each other?  They should
be.

Geir> I want comments on the following observations.
Unfortunately, the
Geir> system is currently not available, hence I cannot
supply ntpq
Geir> diagnostics. I know that 2 servers is the worst
possible
Geir> configuration, it is not necessary to comment
that.

Geir> For some reason one NTP server lost its GPS synch.
It switched to
Geir> internal clock started reporting stratum 12 when
this happened. The
Geir> other server was perfectly synchronized and
reported stratum 1.
Geir> Problem: ntpd rejects both servers and considers
itself not
Geir> synchronized.

This tells me it was not peering with the other S1 server. 
If it was, it
would report S2 and follow the time of the other S1 server.

Geir> Questions:

Geir> 1. Does the NTP server behave correctly when
changing its stratum to
Geir> 12? Should it perform different/other actions when
it considers itself
Geir> not synchronized?

If it is reporting S12 then you must have it configured to
use its local
clock as a refclock.  ntpd is correctly reporting that it is
sync'd to its
local refclock.

ntpd is behaving as designed.  It may be that your
configuration is
incorrect.

Geir> 2. Does ntpd behave correctly? Is a server's
stratum used in any way
Geir> in ntpd's clock selection process?

Yes.

Have you visited http://
support.ntp.org/Support/ConfiguringNTP ?

H

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

On 29 Jun, 20:07, Harlan Stenn <s...ntp.isc.org> wrote:
> >>> In article
<1183138077.657644.124...n2g2000hse.googlegroups.com>, Geir G
<geir.guldst...start.no> writes:
>
> Geir> Hello, NTP configuration:
>
> Geir> Client: ntpd version 4...1.1532
running on Windows XP Servers: 2
> Geir> identical stratum 1 servers with GPS antennas
directly connected
>
> Are these 2 servers peering with each other?  They
should be.

Please note that the servers are embedded devices and (at
least to my
knowledge) don't run the NTP reference implementation. I
don't think
they support peering.

>
> Geir> I want comments on the following observations.
Unfortunately, the
> Geir> system is currently not available, hence I
cannot supply ntpq
> Geir> diagnostics. I know that 2 servers is the
worst possible
> Geir> configuration, it is not necessary to comment
that.
>
> Geir> For some reason one NTP server lost its GPS
synch. It switched to
> Geir> internal clock started reporting stratum 12
when this happened. The
> Geir> other server was perfectly synchronized and
reported stratum 1.
> Geir> Problem: ntpd rejects both servers and
considers itself not
> Geir> synchronized.
>
> This tells me it was not peering with the other S1
server.  If it was, it
> would report S2 and follow the time of the other S1
server.

OK, you are correct.

>
> Geir> Questions:
>
> Geir> 1. Does the NTP server behave correctly when
changing its stratum to
> Geir> 12? Should it perform different/other actions
when it considers itself
> Geir> not synchronized?
>
> If it is reporting S12 then you must have it configured
to use its local
> clock as a refclock.  ntpd is correctly reporting that
it is sync'd to its
> local refclock.
>
> ntpd is behaving as designed.  It may be that your
configuration is
> incorrect.

No specific configuration was done to the server to make it
use its
local clock. It seems this is the the default behavior for
the device.

>
> Geir> 2. Does ntpd behave correctly? Is a server's
stratum used in any way
> Geir> in ntpd's clock selection process?
>
> Yes.

Is that 'Yes' to both questions?

>
> Have you visitedhttp:/
/support.ntp.org/Support/ConfiguringNTP?
>
> H

Yes, I have. But sometimes it is more convenient to ask the
experts
directly. Thank you for your answers Harlan.

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

Geir G wrote:
> Hello,
> 
> NTP configuration:
> 
> Client: ntpd version 4.2.21.1532 running on Windows
XP
> Servers: 2 identical stratum 1 servers with GPS
antennas directly
> connected
> 
> I want comments on the following observations.
Unfortunately, the
> system is currently not available, hence I cannot
supply ntpq
> diagnostics. I know that 2 servers is the worst
possible
> configuration, it is not necessary to comment that.
> 
> For some reason one NTP server lost its GPS synch. It
switched to
> internal clock started reporting stratum 12 when this
happened. The
> other server was perfectly synchronized and reported
stratum 1.
> Problem: ntpd rejects both servers and considers itself
not
> synchronized.
> 
> Questions:
> 
> 1. Does the NTP server behave correctly when changing
its stratum to
> 12? 

Yes it does.  I'm assuming that the server was set up to use
its local 
clock as a "clock of last resort.

> Should it perform different/other actions when it
considers itself
> not synchronized?

What would you like it to do?  Set fire to itself?

> 
> 2. Does ntpd behave correctly? Is a server's stratum
used in any way
> in ntpd's clock selection process?

Yes it is.  Other things being equal, a stratum one server
will be 
preferred over a stratum two server or a stratum three
server.  A server 
at stratum 12 will NOT be used by any system that has a
better server 
available; this is why a stratum of 10 or 12 is conventional
for an 
unsynchronized local clock.  Note that a stratum one server
can have 
extremely poor quality of time; a server synchronized to the
WWV 
broadcast can be off by many milliseconds thanks to the
vagaries of HF 
radio propagation.

Ntpd should not have rejected the server that remained
synchronized at 
stratum 1 unless there was some other problem with it that
you have not 
described.  The log files of the clients may reveal why the
remaining 
stratum 1 server was rejected.

Situations such as you have described are the reason that a
minimum of 
four servers is recommended.  Not all of the four need a
hardware 
reference clock unless you insist on extremely accurate
time; internet 
servers at stratum 1 or 2 will serve quite well.  OTOH, GPS
timing 
receivers can be purchased for less than $100 US each so you
can easily 
have as many stratum one servers as you think you will
need.

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

On 29 Jun, 21:12, "Richard B. Gilbert"
<rgilber...comcast.net> wrote:
> Geir G wrote:
> > Hello,
>
> > NTP configuration:
>
> > Client: ntpd version 4...1.1532 running on Windows
XP
> > Servers: 2 identical stratum 1 servers with GPS
antennas directly
> > connected
>
> > I want comments on the following observations.
Unfortunately, the
> > system is currently not available, hence I cannot
supply ntpq
> > diagnostics. I know that 2 servers is the worst
possible
> > configuration, it is not necessary to comment
that.
>
> > For some reason one NTP server lost its GPS synch.
It switched to
> > internal clock started reporting stratum 12 when
this happened. The
> > other server was perfectly synchronized and
reported stratum 1.
> > Problem: ntpd rejects both servers and considers
itself not
> > synchronized.
>
> > Questions:
>
> > 1. Does the NTP server behave correctly when
changing its stratum to
> > 12?
>
> Yes it does.  I'm assuming that the server was set up
to use its local
> clock as a "clock of last resort.
>
> > Should it perform different/other actions when it
considers itself
> > not synchronized?
>
> What would you like it to do?  Set fire to itself?
>
>
>
> > 2. Does ntpd behave correctly? Is a server's
stratum used in any way
> > in ntpd's clock selection process?
>
> Yes it is.  Other things being equal, a stratum one
server will be
> preferred over a stratum two server or a stratum three
server.  A server
> at stratum 12 will NOT be used by any system that has a
better server
> available; this is why a stratum of 10 or 12 is
conventional for an
> unsynchronized local clock.  Note that a stratum one
server can have
> extremely poor quality of time; a server synchronized
to the WWV
> broadcast can be off by many milliseconds thanks to the
vagaries of HF
> radio propagation.
>
> Ntpd should not have rejected the server that remained
synchronized at
> stratum 1 unless there was some other problem with it
that you have not
> described.  The log files of the clients may reveal why
the remaining
> stratum 1 server was rejected.
>
> Situations such as you have described are the reason
that a minimum of
> four servers is recommended.  Not all of the four need
a hardware
> reference clock unless you insist on extremely accurate
time; internet
> servers at stratum 1 or 2 will serve quite well.  OTOH,
GPS timing
> receivers can be purchased for less than $100 US each
so you can easily
> have as many stratum one servers as you think you will
need.

We added the following line to ntp.conf, this solved the
problem (i.e.
made ntpd stay synchronized to the stratum 1 server even
when the
other server reported stratum 12). Do you understand why
this makes a
difference?

tos ceiling 2

I do understand that more detailed information (i.e. ntpq
output) is
needed to provide an accurate answer. I will check whether
is it
possible to obtain this information.

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

Wouldn't you want to use floor instead?:

tos floor 2 

h
ttp://www.ee.udel.edu/~mills/ntp/html/manyopt.html

>From what that page says:

Ceiling:
Servers with stratum at or above ceiling will be discarded
if there are at
least minclock peers remaining. This value defaults to 15,
but can be
changed to any number from 1 to 15.

vs

Floor:
Peers with strata below floor will be discarded if there are
at least
minclock peers remaining. This value defaults to 1, but can
be changed to
any number from 1 to 15. 

-----Original Message-----
From: questions-bounces+jason=extremeoverclocking.comlists.ntp.isc.org
[mailto:questions-bounces+jason=extremeoverclocking.comlists.ntp.isc.org]
On Behalf Of Geir G
Sent: Friday, June 29, 2007 3:17 PM
To: questionslists.ntp.isc.org
Subject: Re: [ntp:questions] NTP behaviour when server is
not synchronized

We added the following line to ntp.conf, this solved the
problem (i.e.
made ntpd stay synchronized to the stratum 1 server even
when the
other server reported stratum 12). Do you understand why
this makes a
difference?

tos ceiling 2

I do understand that more detailed information (i.e. ntpq
output) is
needed to provide an accurate answer. I will check whether
is it
possible to obtain this information.

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions

>>> In article <1183141707.279603.228700n2g2000hse.googlegroups.com>, Geir G
<geir.guldsteinstart.no> writes:

Geir> Please note that the servers are embedded devices
and (at least to my
Geir> knowledge) don't run the NTP reference
implementation. I don't think
Geir> they support peering.

OK.  Please tell me (in private email if you prefer) the
vendor.

Geir> 2. Does ntpd behave correctly? Is a server's
stratum used in any way
Geir> in ntpd's clock selection process?

H>  Yes.

Geir> Is that 'Yes' to both questions?

Yes.

H>  Have you visited http:/
/support.ntp.org/Support/ConfiguringNTP?

Geir> Yes, I have. But sometimes it is more convenient to
ask the experts
Geir> directly. Thank you for your answers Harlan.

OK, and since these devices may not be configurable it may
not matter.  I
didn't realize that when I first wrote that line.  And as I
gathered from
your followup post, you have found other useful information
there to help
with your clients.

H

_______________________________________________
questions mailing list
questionslists.ntp.isc.org

https://lists.ntp.isc.org/mailman/listinfo/questions