[ntp:questions] TimeStamp

Greg Dowd GDowd at symmetricom.com
Tue Oct 30 23:23:43 UTC 2007


Are you sure the clock wasn't set in between?  Is this a one-time or a
consistent state?  What mode packet is this, mode 3 or 4?  And why do
you say they are only a few seconds apart?  The receive timestamp is the
time the request was received by the server if in a mode 4 packet.  In a
mode 3, it should be 0.  If this was a server response, the
receive/transmit timestamps should be a lot closer than a couple of
seconds.  It should be micro or milliseconds unless you have a
breakpoint or something.

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Message: 7
Date: Tue, 30 Oct 2007 14:42:17 -0700
From: Aggie <c.kevin.lam at gmail.com>
Subject: [ntp:questions] TimeStamp
To: questions at lists.ntp.org
Message-ID: <1193780537.398219.254570 at z24g2000prh.googlegroups.com>
Content-Type: text/plain; charset="iso-8859-1"

Dear all,
I'm very confused on how ntp do the timestamp. I'm running ntpd on
vxworks. It seems to me that the receive timestamp and the Transmit
timestamp are using two different clocks, because when I use ethereal/
wireshark to look up the information of the ntp packet, the Recevie Time
Stamp is: Jan 1, 1970 00:21:26.0827 UTC the Transmit Time Stamp is : Oct
29, 2007 15:20:30.1500 UTC

However, the actual time period between these two time stamps is only a
couple second apart. It makes me think that they are using to different
clock to stamp the packet. Am I Right???

Kevin



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Message: 8
Date: Tue, 30 Oct 2007 17:51:59 -0500
From: hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray)
Subject: Re: [ntp:questions] TimeStamp
To: questions at lists.ntp.org
Message-ID: <ydydnTEd1sESKLranZ2dnUVZ_hSdnZ2d at megapath.net>


>I'm very confused on how ntp do the timestamp. I'm running ntpd on 
>vxworks. It seems to me that the receive timestamp and the Transmit 
>timestamp are using two different clocks, because when I use ethereal/ 
>wireshark to look up the information of the ntp packet, the Recevie 
>Time Stamp is: Jan 1, 1970 00:21:26.0827 UTC the Transmit Time Stamp is

>: Oct 29, 2007 15:20:30.1500 UTC
>
>However, the actual time period between these two time stamps is only a

>couple second apart. It makes me think that they are using to different

>clock to stamp the packet. Am I Right???

It looks like a bug in the Receive timestamp code.

(That's assuming your clock is within a day or so.)

--
These are my opinions, not necessarily my employer's.  I hate spam.



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Message: 9
Date: Tue, 30 Oct 2007 23:01:29 +0000
From: david at ex.djwhome.demon.co.uk.invalid (David Woolley)
Subject: Re: [ntp:questions] Server and Client can't sync
To: questions at lists.ntp.org
Message-ID: <4727b89a$0$512$5a6aecb4 at news.aaisp.net.uk>

In article <1193698184.474071.249360 at i13g2000prf.googlegroups.com>,
Aggie <c.kevin.lam at gmail.com> wrote:

>   To have NTPD run on VxWorks and Windows. Set VxWorks as the Server

> couple minutes, the clock on Windows was changed to 5:15pm, Nov 21
> 1988. I have no idea why it happened. So I looked at the timestamp

> Reference clock update Time: Oct 29, 2007 15:17:57.08333 UTC
> Originate Time Stamp: Oct 29, 2007 15:16:42.9551 UTC
> Receive Time Stamp: Jan 1, 1970 00:21:26.0827 UTC
> Transmit Time Stamp: Oct 29, 2007 15:20:30.1500 UTC

I don't have the VxWorks knowledge (few if any on the newsgroup do) to
understand why the receive and transmit timestamps are wildly different
when you didn't change the clock between them, however, if you are
really
running ntpd on Windows, because the delay was huge and negative, it
should not have stepped the time.  If it really is ntpd, maybe there is
a bug in that it doesn't use the absolute magnitude of root distance to
decide to reject a source.  A minus eighteen years delay really
shouldn't be accepted!



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