[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
More information about the questions
mailing list