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

Harlan Stenn <stenn@nwtime.org> Thu, 11 August 2022 12:00 UTC

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To: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Martin Burnicki <martin.burnicki=40meinberg.de@dmarc.ietf.org>, "ntp@ietf.org" <ntp@ietf.org>, Hal Murray <halmurray@sonic.net>
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Subject: Re: [Ntp] Antw: [EXT] Re: Quick review of WGLC for status change for draft‑ietf‑ntp‑update‑registries
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On 8/11/2022 3:57 AM, Miroslav Lichvar wrote:
> On Thu, Aug 11, 2022 at 03:16:05AM -0700, Harlan Stenn wrote:
>> On 8/9/2022 3:36 AM, Miroslav Lichvar wrote:
>>> The proposed NTPv5 header is not compatible with NTPv4. Servers can
>>> support multiple versions. If they support NTPv5, they should respond
>>> with NTPv5. If they don't support NTPv5, they shouldn't respond with
>>> anything.
>>
>> We disagree.  That's not a problem.  What's wrong with that choice being a
>> local policy choice on the part of either the implementation or the
>> responding system?
> 
> You don't see a problem with sending messages marked as being in one
> version, but conforming to another version?
> 
> All servers that currently respond to NTPv5 requests are broken. There
> is no NTPv5 specified yet. Unfortunately there is a large number of
> them, so we need to make sure NTPv5 clients will not accept these
> responses.

That is true if the design rules we've been following for decades are 
changed.

It is not true if the design rules are followed.

>>> There should be no ambiguity with extension fields. NTPv5 is expected
>>> to be compatible with NTPv4 extension fields. The main use case will
>>> be NTS. Autokey is insecure and should not be used.
>>
>> I don't understand.  Are you saying that if a v4 client sends an NTS packet
>> to a v5 server and that packet "passes the checks" then the v5 server should
>> respond with a v4 response?
> 
> If the v5 server supports v4, then yes. If it supports v5 only, it
> should not respond.

How do I reconcile what you just said in the previous line with what you 
said in the preceding quoted section?

>> I think that's what you're saying, and in that
>> case the issue of compatibility is moot - the v5 server is not responding
>> with v5 EFs.
> 
> The compatibility I mentioned makes it easier for existing NTS
> implementations to support NTPv5 in addition to NTPv4. I don't expect
> there to be any NTPv5-exclusive implementations, at least in near
> future.

What you are describing is still not clear to me.  That's OK with me.

-- 
Harlan Stenn <stenn@nwtime.org>
http://networktimefoundation.org - be a member!

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