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Re: [Ntp] Quick review of WGLC for status change for draft-ietf-ntp-update-registries

Miroslav Lichvar <mlichvar@redhat.com> Tue, 16 August 2022 06:48 UTC

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Date: Tue, 16 Aug 2022 08:48:05 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Heiko Gerstung <heiko.gerstung=40meinberg.de@dmarc.ietf.org>
Cc: Harlan Stenn <stenn@nwtime.org>, "ntp@ietf.org" <ntp@ietf.org>
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References: <b64c6a0a-ea2e-0a19-4bb9-38bfaa2e5032@nwtime.org> <656D355F-E06A-4005-B9D6-90885FA8509D@akamai.com> <1a4bae28-f0f3-e675-899a-bad597b4ee29@nwtime.org> <F74A7B5B-3D77-42AF-BD7E-1A874CCD2D66@akamai.com> <67545c9a-3291-bbe6-c876-4c762c80c710@nwtime.org> <FF22AEFE-ED61-405E-AB40-B7901D0CD588@meinberg.de> <f79cecd6-92b0-595b-e449-6b6f8944ae66@nwtime.org> <133C5633-E4D5-42AF-8215-E3FDE28C5BF9@meinberg.de> <Yvon8eNc4hlI4LbG@localhost> <83E424AA-F0B8-48C0-B05A-33296EA5A6D9@meinberg.de>
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Subject: Re: [Ntp] Quick review of WGLC for status change for draft-ietf-ntp-update-registries
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On Tue, Aug 16, 2022 at 08:30:57AM +0200, Heiko Gerstung wrote:
> One situation we have to take care of IMHO is an NTPv2/v3/v4 client trying to use a V5 server. Maybe it would be better to just state that a V5 only implementation must not respond to V2,V3,V4 requests. If it chooses to support those older protocol versions, it has to respond with the correct (requested) packet format. 

Yes, that is specified in the current NTPv5 draft.

> The second problem is an NTP V5 client sending a request to a V2/V3/V4 server. It would be possible to send a V5 NTP request in a V4 compatible format here (as a probe) and if we receive a response indicating that V5 is not supported (as far as I understood, ntpd would for example send a V4 response, others might choose not to respond at all), we can go away and look for a V5 supporting server. 

That is also specified in the NTPv5 draft. The client can send an
NTPv4 request with a specific reference timestamp and if the server
supports NTPv5, it will respond with NTPv4 and the same specific
reference timestamp, so the client will know it can switch to NTPv5.

-- 
Miroslav Lichvar

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