[ntp:questions] NTP v3 server, v4 client can't synch

Romain at ntp.org Romain at ntp.org
Wed Sep 9 01:11:01 UTC 2009


Greetings,

I write with a concern from my day job, working on APM (application
performance monitoring) devices for OPNET Technologies, Inc.  I'm
attempting to help a customer who is using an NTP v3 server running
under a VMware virtual machine.  The APM device (FreeBSD) polls the
server, but appears to give it no credence, prefering to wander off
on its own until its own time is several minutes off.  Rebooting
our device gives us a step correction with "ntpdate -b", so the v3
server is apparently good enough for that purpose.

As might be imagined, this is the sort of site where we have no
choice except to try working with the existing plant.  There are
about 10 APM devices running FreeBSD (ntpd 4.2.0-a) and none of
them are able to peer with the designated server.  Yet the customer
reports that they don't have trouble getting other NTP clients
within their network to sync.

The constraints imposed by the installation seem tight.  In
addition to the NTPv3 service, the ntpq outputs below show high
jitter, not surprising when a VM doesn't have any execution latency
assurances.  The server reports stratum=7, which makes me wonder
if the whole works are actually unsynchronized, but ntptrace times
out while trying to discover more.

- Continual, automatic step corrections are undersirable because they
  will cause bogus measurements in the APM device.

- Specifying NTP version 3 in the "server" line had no benefit.

- Given that there's no synch with root, we're guessing
  that attempting to peer the APM devices is probably futile.

- Specifying a lower minpoll seems like it could magnify the effect
  of the server jitter.

Perhaps we want to clear out ntp.drift and set high minpoll/maxpoll?
(E.g., minpoll 10 / maxpoll 14).

Might the huff-'n-puff filter help negate the server jitter?

Any other suggestions?

Thanks!

Sample ntpq outputs follow...

ntpq> peers
   remote           refid       st t when poll reach   delay   offset  jitter
=============================================================================
 172.20.18.68   aaa.bbb.ccc.ddd  7 u  844 1024   377   1.025  581084. 598.644
*LOCAL(0)       LOCAL(0)        10 l   40   64   377   0.000    0.000   0.001

ntpq> assoc
ind assID status  conf reach auth condition  last_event cnt
===========================================================
  1 9692   b014   yes   yes  none    reject   reachable   1
  2 9693   9614   yes   yes  none  sys.peer   reachable   1

ntpq> pstatus 9692

status=b014 reach, conf, 1 event, event_reach,
srcadr=172.20.16.33, srcport=123, dstadr=172.20.18.68,
dstport=123, leap=00, stratum=7, precision=-6, rootdelay=31.250,
rootdispersion=905.106, refid=aaa.bbb.ccc.ddd, reach=377, unreach=0,
hmode=3, pmode=4, hpoll=10, ppoll=10, flash=00 ok, keyid=0, ttl=0,
offset=581084.301, delay=1.025, dispersion=30.385, jitter=598.644,
reftime=ce002d00.39e3722a Thu, Jul 9 2009 3:46:56.226,
org=ce007490.f9e3722a Thu, Jul 9 2009 8:52:16.976,
rec=ce00724b.e47048df Thu, Jul 9 2009 8:42:35.892,
xmt=ce00724b.e42d1b9b Thu, Jul 9 2009 8:42:35.891,
filtdelay=     1.03    1.00    0.99    1.40    1.25    0.86    1.39    1.29,
filtoffset=  581084. 580485. 579932. 579333. 578734. 578134. 577550. 576967.,
filtdisp=     15.63   30.99   46.33   61.72   77.08   92.44   107.80 123.16

ntpq> pstatus 9693
status=9614 reach, conf, sel_sys.peer, 1 event, event_reach,
srcadr=LOCAL(0), srcport=123, dstadr=127.0.0.1, dstport=123, leap=00,
stratum=10, precision=-20, rootdelay=0.000, rootdispersion=10.000,
refid=LOCAL(0), reach=377, unreach=0, hmode=3, pmode=4, hpoll=6,
ppoll=6, flash=00 ok, keyid=0, ttl=0, offset=0.000, delay=0.000,
dispersion=0.917, jitter=0.001,
reftime=ce0075ee.e3fcb8eb Thu, Jul 9 2009 8:58:06.890,
org=ce0075ee.e3fcb8eb Thu, Jul 9 2009 8:58:06.890,
rec=ce0075ee.e3fcde66 Thu, Jul 9 2009 8:58:06.890,
xmt=ce0075ee.e3fc9370 Thu, Jul 9 2009 8:58:06.890,
filtdelay=     0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00,
filtoffset=    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00,
filtdisp=      0.00    0.95    1.89    2.84    3.83    4.79    5.75    6.72

It's not an apples-to-apples comparison, but here are a few
ntpq outputs from an equivalent device running in our lab:

ntpq> rv
status=06f4 leap_none, sync_ntp, 15 events, event_peer/strat_chg,
version="ntpd 4.2.0-a Tue Jan 15 23:21:10 UTC 2008 (1)",
processor="amd64", system="FreeBSD/6.3-RELEASE", leap=00, stratum=3,
precision=-20, rootdelay=12.202, rootdispersion=94.765, peer=23700,
refid=10.21.1.21,
reftime=ce51690f.a3bebb04  Tue, Sep  8 2009 16:36:47.639, poll=7,
clock=ce516b6b.7f4501f0  Tue, Sep  8 2009 16:46:51.497, state=4,
offset=-1.532, frequency=52.385, jitter=0.477, stability=0.060

ntpq> peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*scout.fractal.n 204.152.184.72   2 u   90  128  377    0.257   -1.170   0.111
 LOCAL(0)        LOCAL(0)        10 l   32   64  377    0.000    0.000   0.001

ntpq> as
ind assID status  conf reach auth condition  last_event cnt
===========================================================
  1 23700  b614   yes   yes  none  sys.peer   reachable  1
  2 23701  9014   yes   yes  none    reject   reachable  1

ntpq> pstatus 23700
status=b614 reach, conf, sel_sys.peer, 1 event, event_reach,
srcadr=scout.fractal.networkphysics.com, srcport=123, dstadr=10.22.4.16,
dstport=123, leap=00, stratum=2, precision=-20, rootdelay=11.948,
rootdispersion=75.531, refid=204.152.184.72, reach=377, unreach=0,
hmode=3, pmode=4, hpoll=7, ppoll=7, flash=00 ok, keyid=0, ttl=0,
offset=-1.170, delay=0.257, dispersion=8.670, jitter=0.114,
reftime=ce516bdb.8e3ad18d  Tue, Sep  8 2009 16:48:43.555,
org=ce516c15.a382a12f  Tue, Sep  8 2009 16:49:41.638,
rec=ce516c15.a3d11774  Tue, Sep  8 2009 16:49:41.639,
xmt=ce516c15.a3b7f3ea  Tue, Sep  8 2009 16:49:41.639,
filtdelay=     0.35    0.28    0.27    0.34    0.27    0.28    0.26    0.30,
filtoffset=   -1.02   -1.01   -1.03   -1.08   -1.10   -1.13   -1.17   -1.25,
filtdisp=      0.00    1.95    3.90    5.82    7.73    9.68   11.61   13.52

--
Romain Kang         Neither KZSU 90.1 FM Radio nor Stanford University assume
rkang at opnet.com             no responsibility for the content of this message.
romain at kzsu.stanford.edu




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