Re: [chrony-users] chrony with only 2 sources

[Yan Seiner <yan@xxxxxxxxxx>]

On 02/28/2014 04:33 AM, Miroslav Lichvar wrote:
> On Thu, Feb 27, 2014 at 02:40:21PM -0800, Yan Seiner wrote:
> > My ISP, in their infinite wisdom, has decided to block port 123 as a
> > "security measure".  They do offer one time server on their network,
> > but I have no access to any other time server.
> I'm curious to know if they block the NTP port as a fix to the ntpd
> monlist amplification attacks.

Probably; they indicated they had a problem with an unspecified attack.  
They blocked the port with no notification to the subscribers.

> > MS Name/IP address         Stratum Poll Reach LastRx Last sample
> > ===============================================================================
> > #x TTY                           0   4   377    10   +360ms[ +360ms]
> > +/- 5337us
> > ^x cache01.dns.rionetworks.c     2   6   177    98  +1005us[+1005us]
> > +/-   84ms
> This shows that the two sources don't overlap (i.e. 360 +/- 5 ms is
> outside 1ms +/- 84).
>
> > refclock SHM 0 poll 4 offset 0.0 refid TTY
> > server time.rionetworks.com
> >
> > Is there anything I can do to weigh one signal more than the other?
> You can set the delay and offset options for the refclock so it
> overlaps with the other source. Try "offset 0.36 delay 0.1".
>
> However, without PPS, the timing signal from serial GPS is usually
> much worse than what is possible with NTP over internet. You can try
> adding "noselect" to the refclock and see how stable it when compared
> to the NTP source in the chronyc sourcestats output.

I'm coming to that realization.  I was hoping for better results but I 
did this on the cheap (an old wifi access point I had laying around and 
a $20 serial TTL module off ebay.)

I do have another board with full serial capabilities.  What's a good 
serial GPS module with PPS, either 5V TTL or RS232?

Thanks.

>


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