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Re: [Ntp] Symmetric mode

Doug Arnold <doug.arnold@meinberg-usa.com> Fri, 30 September 2022 14:23 UTC

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From: Doug Arnold <doug.arnold@meinberg-usa.com>
To: Hal Murray <halmurray@sonic.net>, Miroslav Lichvar <mlichvar@redhat.com>
CC: Hal Murray <halmurray@sonic.net>, "ntp@ietf.org" <ntp@ietf.org>
Thread-Topic: [Ntp] Symmetric mode
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Date: Fri, 30 Sep 2022 14:23:22 +0000
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References: Message from Miroslav Lichvar <mlichvar@redhat.com> of "Thu, 29 Sep 2022 16:41:32 +0200." <YzWunE8uQwTh8suS@localhost> <20220930015229.B235628C1D8@107-137-68-211.lightspeed.sntcca.sbcglobal.net>
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Subject: Re: [Ntp] Symmetric mode
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Please enlighten me. I’ve been reading the discussion on symmetric ntp, and I don’t understand the purpose. An ntp server can ask other servers for time using client server ntp, and use that information to examine its own time and that of the peer it is looking at.  Why is a different over-the-wire version of the protocol needed?

Doug

From: ntp <ntp-bounces@ietf.org> on behalf of Hal Murray <halmurray@sonic.net>
Date: Thursday, September 29, 2022 at 9:52 PM
To: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Hal Murray <halmurray@sonic.net>, ntp@ietf.org <ntp@ietf.org>
Subject: Re: [Ntp] Symmetric mode

mlichvar@redhat.com said:
> You need to either add "disable auth" to ntp.conf, or configure a symmetric
> key on both hosts and add it to the peer directive.

Thanks.  That worked.  I now see the active/passive pair where the passive is
not a direct response to the active.  I assume the timing difference is the
skew in the polling clocks.


> ntpq -p (or ntpq -c peers) prints emphemeral symmetric associations, but only
> if there was a valid response (reachable).

That "only if reachable" is important.  That takes another polling interval.
Or something like that.  I got confused by not seeing it but while
investigating it appeared.


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