[ntp:questions] Syncing to nearby vs. faraway servers

Rich Wales richw at richw.org
Tue Jun 16 17:25:50 UTC 2009


Replying to Bill Unruh:

> If the Stanford machines all cluster around a time server milliseconds
> different from the rest of the world they are wrong.

Stanford's stratum-2 servers currently appear to be syncing to
grandfather.stanford.edu (171.64.7.87) -- a stratum-1 server which
is located here on the Stanford campus and is syncing to its own
TrueTime GPS clock:

ntpq> host
current host is grandfather.Stanford.EDU
ntpq> peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*TRUETIME(1)     .GPS.            0 l   50   64  377    0.000   -0.985   1.829
+bigben.cac.wash .USNO.           1 u  546 1024  377   22.287   10.470   0.654
+clock.isc.org   .GPS.            1 u  537 1024  377    5.419    3.775   0.098
ntpq> rl 0
associd=0 status=0464 leap_none, sync_uhf_radio, 6 events, freq_mode,
version="ntpd 4.2.2p4 at 1.1585-o Sun May 10 16:52:30 UTC 2009 (1)",
processor="i686", system="Linux/2.6.18-6-686", leap=00, stratum=1,
precision=-20, rootdelay=0.000, rootdispersion=4.536, peer=28528,
refid=GPS, reftime=cde24fb4.00436a6b  Tue, Jun 16 2009 10:07:00.001,
poll=10, clock=cde24fe8.c16630c8  Tue, Jun 16 2009 10:07:52.755,
state=4, offset=-0.985, frequency=91.096, jitter=1.829, noise=2.957,
stability=0.000, tai=0

As for grandfather's two stratum-1 backup servers, here's the current
info on bigben.cac.washington.edu:

ntpq> host
current host is bigben.cac.washington.edu
ntpq> peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*GPS_VME(0)      .USNO.           0 l    9   16  377    0.000   -0.014   0.058
 192.5.40.40     .INIT.          16 u    - 1024    0    0.000    0.000 4000.00
 204.34.198.40   .INIT.          16 u  26h 1024    0    0.000    0.000 4000.00
ntpq> rl 0
associd=0 status=0444 leap_none, sync_uhf_radio, 4 events, freq_mode,
version="ntpd 4.2.0 at 1.1161-r Tue Mar 23 22:34:33 UTC 2004 (19)",
processor="9000/800", system="HP-UX/B.11.11", leap=00, stratum=1,
precision=-18, rootdelay=0.000, rootdispersion=0.643, peer=25020,
refid=USNO, reftime=cde2500a.4f0dec40  Tue, Jun 16 2009 10:08:26.308,
poll=4, clock=cde2500d.8a678bfe  Tue, Jun 16 2009 10:08:29.540, state=4,
offset=-0.028, frequency=-38.586, jitter=0.043, stability=0.001,
hostname="bigben", signature="md5WithRSAEncryption", flags=0x80001,
hostkey=3279293228, refresh=3454105890

I note that both grandfather.stanford.edu and bigben.cac.washington.edu
seem to be on good terms with their respective reference clocks, and
yet Stanford is seeing a significant offset w/r/t Washington right now.

I can't get any more info on clock.isc.org; it doesn't appear to be
configured to permit outside queries.

> There may be some problem with asymmetric delays to the Stanford
> machines.

Based on the above, it does look like there *could* be significant
asymmetry between Stanford and the University of Washington.  Or,
there could be something amiss with the setup of Stanford's and/or
Washington's stratum-1 servers and/or reference clocks.  I don't
work with the group managing Stanford's campus NTP service; I can
try tracking them down and asking them questions, but I don't know
what (if anything) I'll be able to find.

As for my own paths to the Stanford campus NTP servers, my work
desktop (100BASE-TX to the campus backbone) is currently getting
delays of less than 1 msec to three campus stratum-2 servers:

ntpq> host
current host is localhost
ntpq> peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
-liberation.rich 10.0.229.53      5 u   37   64  376    6.582   -0.078   0.902
 whodunit.richw. 10.0.229.114     4 u  173  256  373    6.247    0.576   7.396
-sandals.richw.o 10.0.229.53      5 u  176  256  376   27.820  -36.280   5.879
+Argus.Stanford. 171.64.7.87      2 u   30 1024  377    0.864   -0.852   0.066
+caribou.Stanfor 171.64.7.87      2 u  869 1024  377    0.748   -0.816   0.108
*dusk.Stanford.E 171.64.7.87      2 u  221 1024  377    0.781    3.065   0.159
-198.186.191.229 64.147.116.229   2 u   90 1024  377   18.819    3.815   1.206
-14.1e.5546.stat 128.249.1.10     3 u   88 1024  377   48.191    6.928   0.643
xntp1.sscgateway 136.159.2.9      3 u  792 1024  377   63.018   98.021  16.014
-bock130.dotsour 192.53.103.108   2 u   87 1024  377  165.595    9.211  19.234
-cheddar.halon.o 193.0.0.228      2 u   33 1024  377  168.741    8.314   4.664
ntpq> rl 0
associd=0 status=06f4 leap_none, sync_ntp, 15 events, freq_mode,
version="ntpd 4.2.4p4 at 1.1520-o Wed May 13 21:05:42 UTC 2009 (1)",
processor="i686", system="Linux/2.6.28-11-generic", leap=00, stratum=3,
precision=-20, rootdelay=5.145, rootdispersion=72.180, peer=56461,
refid=171.64.7.89,
reftime=cde250e7.f1698f15  Tue, Jun 16 2009 10:12:07.943, poll=10,
clock=cde251cb.ada3d08e  Tue, Jun 16 2009 10:15:55.678, state=4,
offset=3.065, frequency=-18.528, jitter=0.159, noise=2.047,
stability=0.000, tai=0

so it doesn't seem to me that I would be suffering from asymmetric
paths locally.

-- 
Rich Wales  /  richw at richw.org  /  richw at stanford.edu




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