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Re: [Ntp] Comments on draft-langer-ntp-nts-for-ptp

Miroslav Lichvar <mlichvar@redhat.com> Mon, 08 March 2021 11:38 UTC

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Date: Mon, 08 Mar 2021 12:38:05 +0100
From: Miroslav Lichvar <mlichvar@redhat.com>
To: "Langer, Martin" <mart.langer@ostfalia.de>
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Subject: Re: [Ntp] Comments on draft-langer-ntp-nts-for-ptp
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On Mon, Mar 08, 2021 at 11:09:49AM +0000, Langer, Martin wrote:
> The multicast connections are not comparable to the broadcast connections in NTP.

I think they are pretty much the same if you assume the NTP client is
making periodic measurements of the delay and not just once on start.

> In NTP, TESLA-secured communication could be broken, because delay attacks are not
> detectable. However, in PTP we have two-way communication (Delay Request/Response)
> during multicast, which can be used to register runtime changes (RTT). However, a formal
> analysis is indeed not available.

The delay measurement has a request and response, but the offset
measurement (using sync messages) does not. Delay messages can be much
less frequent than sync messages. That's quite different from the NTP
client-server mode, where each request has an immediate response.

-- 
Miroslav Lichvar

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