[ntp:questions] Leap second bug?

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jan 2 15:55:23 UTC 2008

Spoon wrote:
> Hello everyone,
> ntpd kicked my clock forward one second on January 1 at 00:19:38 UTC.
> (My ntp.conf lists 12 servers. Delays range from 28 to 48 ms.)

Unless you have a custom version of ntpd, I believe that ten servers is 
the absolute maximum!  I believe that ntpd will ignore the extras.

Four, Five, and Seven are the magic numbers to protect against the 
failure of one, two, and three servers.  Note that "failure" can mean 
either a server failing to respond to queries or a server with a 
blatantly incorrect time.  I have not tested this but I believe that 
ntpd will always select both the server with the "one true time" and an 
"advisory committee" of three servers if there are sufficient servers 
available to do so.

I'd suggest trimming  your server list to the five or seven servers 
closest to you in net space; e.g. the ones with the lowest value of delay.

FWIW it's rare to be able to FIND ten servers that are close to you!
Ten GOOD servers ranks close to miraculous.  Again, FWIW, even most of 
the "bad" servers know what time it is but the network between you and 
the server has enough jitter to mangle the time.

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