[ntp:questions] Re: Asymmetric lines

Richard B. Gilbert rgilbert88 at comcast.net
Sat Feb 5 02:07:40 UTC 2005


John Pettitt wrote:

>
> Hi all
>    I just put up a stratum 1 server (FreeBSD using the GPS18 with PPS) 
> on the end of a very asymmetric line (6000 kbps down 608 kbps up).   
> When I look on the local machine (gatekeeper.no-such-agency.net) I see 
> this:
>
> ntpq> pe
>     remote           refid      st t when poll reach   delay   offset  
> jitter
> ============================================================================== 
>
> *GPS_NMEA(0)     .GPS.            0 l    8   16  377    0.000    
> 0.003   0.002
> LOCAL(0)        73.78.73.84      5 l    1   64  377    0.000    
> 0.000   0.002
> +[stratum1-a]    .GPS.            1 u   29   64  377   21.147    
> 2.068   9.112
> +[stratum2-b]    .CDMA.           1 u   51   64  377   17.442    
> 2.019   6.896
> +time.sr.sonic.n 63.192.96.10     2 u   37   64  377   10.896    
> 0.891   0.579
>
>
> note: names of the stratum 1 servers edited
>
> However when I look from one of my other boxes 
> (eschelon.no-such-agency.net in a server farm connected by multiple 
> OC12's) I see
>
> ntpq> pe
>     remote           refid      st t when poll reach   delay   offset  
> jitter
> ============================================================================== 
>
> LOCAL(0)        73.78.73.84      5 l   57   64  377    0.000    
> 0.000   0.002
> *gatekeeper.no-s .GPS.            1 u  777 1024  377   21.392   
> -1.933   0.098  <- my S1 server
> +[stratum1-a]    .GPS.            1 u  791 1024  377    7.456   
> -1.524   0.421
> +[stratum1-b]    .CDMA.           1 u  789 1024  377    3.446   
> -1.171   0.216
>
>
> Again the names of the stratum 1's edited but they are the same 
> servers as above.
>
> So I'm seeing a 2ms offset on the box itself and about 600ms from the 
> outside world.     I probably wouldn't care about this except that the 
> offset seems to be stopping ntpd on my S1 from backing off it's poll 
> intervals (it's been stuck at 64 for 12 hours).
>
> I seem to recall an asymmetric fudge patch being discussed but I can't 
> find it.  Does anybody have a copy?  (or other suggestions for 
> tweaking the setup)
>
> John
> P.S. both gatekeeper and eschelon are part of pool.ntp.org

I don't see the 600ms!   Gatekeeper differs from its reference clock by 
3 microseconds and from its upstream network servers by  1 -- 2 
milliseconds.   Eschelon is seeing a -1.9 millisecond offset from 
gatekeeper and -1 to -1.5 millisecond offsets from its upstream networks 
servers.   What am I missing?




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