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Re: [Ntp] CLOCK_TAI (was NTPv5: big picture)

Martin Burnicki <martin.burnicki@meinberg.de> Wed, 06 January 2021 14:29 UTC

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To: FUSTE Emmanuel <emmanuel.fuste@thalesgroup.com>, "ntp@ietf.org" <ntp@ietf.org>
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From: Martin Burnicki <martin.burnicki@meinberg.de>
Organization: Meinberg Funkuhren GmbH & Co. KG, Bad Pyrmont, Germany
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Date: Wed, 06 Jan 2021 15:29:06 +0100
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Subject: Re: [Ntp] CLOCK_TAI (was NTPv5: big picture)
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FUSTE Emmanuel wrote:
> Le 06/01/2021 à 11:58, Martin Burnicki a écrit :
>>
>> Or you would have to provide (and maintain) an NTP server implementation
>> that supports both v4 and v5, depending on the version of the request.
> As the vast majority of today ones which still support v1/v2/v3/v4, 
> being based on ntpd,  and v3/v4 for most of the others.

I don't thing NTPv1 and v2 are really supported by current
implementations, maybe except for a v2 version code in the mode 6 packets.

If I remember correctly, NTPv2 wasn't even widespread, but some fields
of the packet were changed in v3. When that happened, NTPv2 wasn't very
widespread, either.

The only thing a v4 server has to do to when it receives a v3 request is
to copy the v3 version code into the reply packet instead of the native
v4 code. That's it.

In a compatible approach you could set up the reply packet as usually,
and only append extension fields with more detailed information if the
protocol version sent by the client is v5.

A possible approach could be that

- a v5 client could send an initial v5 request

- when the server sees v5 it replies with a base packet and one or more
extension fields indicating its features/capabilities

- the client could send further requests with extension fields
requesting for additional information

- a v4 client would simply send and receive a v4 packet without the
extensions


Martin
-- 
Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: martin.burnicki@meinberg.de
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