[ntp:questions] Re: ntpd transmit timestamp precision

Brian Utterback brian.utterback at sun.removeme.com
Mon Feb 13 16:11:41 UTC 2006

Damion de Soto wrote:
> Hi,
> I was wondering if anyone knew if ntpd contained code to do this (from 
> RFC2030):
>       It is advisable to fill the non-significant low order bits of the
>       timestamp with a random, unbiased bitstring, both to avoid
>       systematic roundoff errors and as a means of loop detection and
>       replay detection (see below). One way of doing this is to generate
>       a random bitstring in a 64-bit word, then perform an arithmetic
>       right shift a number of bits equal to the number of significant
>       bits of the timestamp, then add the result to the original
>       timestamp.
> The ntp packets from my platform all have the same fractional seconds, 
> so I'm guessing it does not.  Is there any reason why not?
> It seems a fairly trivial change in a couple of places in ntpd/ntp_proto.c

Yes and no. If your system supports either clock_gettime or getclock,
then the code does not bother with the random bitstring, since there
are only two unused bits to set. Not worth the trouble.


Quidquid latine dictum sit, altum sonatur.
Brian Utterback - OP/N1 RPE, Sun Microsystems, Inc.
Ph:877-259-7345, Em:brian.utterback-at-ess-you-enn-dot-kom

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