[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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