[ntp:questions] ntp & adsl

Folkert van Heusden folkert at vanheusden.com
Mon Jan 30 21:30:59 UTC 2006


Hi,

I've heard that NTP acts funny when it tries to sync over an ADSL line.
That seems to be the case indeed:
0 root at muur:/home/folkert/www$ ntpq -c pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 GENERIC(0)      .DCFa.           0 l   23   64    3    0.000  -17.386  26.356  <- dcf77 receiver
-keetweej.intran 130.149.17.8     2 u  810 1024  376    0.735    2.724   0.084  <- other server on my lan
 thegateap.intra .STEP.          16 u    - 1024    0    0.000    0.000 4000.00  <- other server on my lan
+auth1.xs4all.nl 131.188.3.220    2 u  973 1024  377    8.421    1.179   0.024  <- ntp server of my ISP
-ntp1.nl.uu.net  .GPS.            1 u  943 1024  377   19.800    4.600   2.127
+ntp3-rz.rrze.un .DCFp.           1 u  837 1024  377   29.495    0.022   0.091
*sombrero.cs.tu- .PPS.            1 u  856 1024  377   30.856    1.031   0.530
+chime1.surfnet. .GPS.            1 u  757 1024  377   13.889    2.078   0.005
 chime2.surfnet. .STEP.          16 u    - 1024    0    0.000    0.000 4000.00

And there it is: 20ms offset. From what I've heard this is caused by
ADSL being asymetric.
Now I was wondering, can't this be fixed by telling the NTP daemon how
much asynchronous the line is? I mean: it can be easily measured what
the down- and upload bandwidth is.


Folkert van Heusden

www.vanheusden.com/multitail - multitail is tail on steroids. multiple
               windows, filtering, coloring, anything you can think of
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Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com



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