[Ntp] Antw: Re: Antw: [EXT] Re: Robert Wilton's Discuss on draft‑ietf‑ntp‑interleaved‑modes‑05: (with DISCUSS and COMMENT)

Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de> Thu, 22 July 2021 09:19 UTC

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Date: Thu, 22 Jul 2021 11:19:26 +0200
From: "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de>
To: <ek.ietf@gmail.com>,<mlichvar@redhat.com>
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>>> Miroslav Lichvar <mlichvar@redhat.com> schrieb am 22.07.2021 um 10:51 in
Nachricht <YPkxqtpgzD7g8Anz@localhost>:
> On Wed, Jul 21, 2021 at 12:07:47PM ‑0700, Erik Kline wrote:
>> >
>> > Of course, this doesn't change anything about compatibility with
>> > existing NTPv4 implementations. There is no clean way to detect the
>> > support.
>> >
>> 
>> <random bad idea>
>> For client mode, could the client make use of the LI field to indicate it
>> speaks interleaved?
>> </>
> 
> No, there are clients that always set it to synchronized, other
> clients set it always to unsynchronized, and other clients set it to
> their actual status.
> 
> If we are considering unclean solutions abusing unrelated fields, the
> best one would be the reference timestamp. It is 64 bits and it is
> normally ignored by the server. The NTPv5 proposal uses this field to
> detect whether an NTPv4 server supports NTPv5. Not a clean solution,
> but I don't see a better one. What would IESG think about that?
> 
> For the interleaved mode, clients could be required to set it to a
> specific value, maybe XORed with their RX and TX timestamps, to push
> the false positive rate to the 1/2**128 territory. I think this would
> truly make it the hack that same people already consider it.
> 
> My opinion still is that clients that set their origin timestamp to
> anything else than zero or the transmit timestamp from the received
> packet don't follow the NTP specification. It's not a subset of the
> protocol.

Your opinion is different from the RFC 5905:
"Origin Timestamp (org): Time at the client when the request departed
for the server, in NTP timestamp format." (page 23)

> 
> In case this argument doesn't hold, I also analyzed traffic on
> multiple public servers to confirm that there were no implementations
> unknowingly sending requests in interleaved mode. The only instance
> was the ntpsec fork of ntp, which already supported interleaved mode,
> but had the support only partially removed, and this is what I think
> actually prompted the Daniel's objection to the proposal.
> 
> Now, with many public servers having the support, it would be
> difficult to implement a new client with such a bug and not notice it.
> 
> ‑‑ 
> Miroslav Lichvar