[ntp:hackers] Privacy: refclock_nmea is now munging lat/long

Dave Hart davehart at gmail.com
Mon May 18 11:35:46 UTC 2009

On Sat, Apr 25, 2009 at 11:45 PM, Dave Hart <davehart at gmail.com> wrote:
> Arguing for simply reverting the change, the operator can choose to
> use the $GPZDA NMEA sentence that lacks position information,
> providing privacy with no changes to the traditional
> ntpd+refclock_nmea code.

I attempted to use this approach but discovered my GPS 18x LVC doesn't
support $GPZDA.  Disagreeing with the assertion that I should block
public ntpq queries entirely if I am seriously concerned about that
level of privacy, I added support in refclock_nmea as of 4.2.5p176 for
optionally removing the location fields from the saved timecode
visible via "ntpq -c clockvar" and recorded in clockstats.  If you use
refclock_nmea and would prefer to keep your GPS antenna's precise
location private, use

fudge 127.127.20.__ flag4 1

Which results in:

C:\ntp>ntpq -c cv davehart.net
associd=0 status=00f0 , 15 events, clk_unspec,
device="NMEA GPS Clock",
poll=14417, noreply=0, badformat=0, baddata=0, fudgetime1=-3.500,
stratum=0, refid=gPPS, flags=8


Dave Hart

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