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| author | Gary E. Miller <gem@rellim.com> | 2016-05-30 14:08:19 -0700 |
|---|---|---|
| committer | Gary E. Miller <gem@rellim.com> | 2016-05-30 14:08:19 -0700 |
| commit | 59f0734c707a627ee0989f94c19d3b96a6df972c (patch) | |
| tree | f4719243e839c25dbb1655f8d66aa5152605ad64 /www | |
| parent | 88a9a169a5ccbb217817e5af89c85b31997212b1 (diff) | |
| download | gpsd-59f0734c707a627ee0989f94c19d3b96a6df972c.tar.gz | |
Add info on ARP problems, only need to bump rev every month/release.
Many thanks to Dan Drown for the pointer to ARP issues.
Diffstat (limited to 'www')
| -rw-r--r-- | www/gpsd-time-service-howto.txt | 23 |
1 files changed, 18 insertions, 5 deletions
diff --git a/www/gpsd-time-service-howto.txt b/www/gpsd-time-service-howto.txt index a611c528..d328b985 100644 --- a/www/gpsd-time-service-howto.txt +++ b/www/gpsd-time-service-howto.txt @@ -944,7 +944,7 @@ After you have verified with cgps that your GPS receiver has a good 3D lock you can check that gpsd is outputing good time by running ntpshmmon. ----------------------------------------------------------------------------- -# ntpshmmon +# ntpshmmon ntpshmmon version 1 # Name Seen@ Clock Real L Prec sample NTP0 1461537438.593729271 1461537438.593633306 1461537438.703999996 0 -1 @@ -1060,6 +1060,21 @@ you reboot, expect it to converge to a new/different drift value and that may take a while depending on how different the basic calibration factors are. +=== ARP is the sound of your server choking === + +By default ntpd and chronyd poll remote servers every 64 seconds. This +is an unfortuneate choice. Linux by default only keeps an ARP table +entry for 60 seconds, anytime thereafter it may be flushed. + +If the ARP table has flushed the entry for a remote peer or server then +when the NTP server sends a request to the remote server an entire ARP +cycle will be added to the NTP packet round trip time (RTT). This will +throw off the time measurements to servers on the local lan. + +The colution is the same for both ntpd and chronyd, add the "minpoll 5" +command to any 'server" or "peer directive. This will cause the maximum +polling period to be 32 seconds, well under the 60 second ARP timeout. + == NTP tuning and performance details == This section deals specifically with ntpd. It discusses algorithms @@ -1743,9 +1758,7 @@ by Jaap Winius <jwinius@rjsystems.nl>. 2.6 May 2016:: New section on GPS time. Note the existence of the GR801-W. - -2.7 May 2016:: Describe the special timeserver build of GPSD. Recommend NTPsec. - -2.8 May 2016:: Add Macx-1 link. + Add section on ARP problems + |