[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.
--
blu
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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