Re: [Ntp] Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts

Harlan Stenn <stenn@nwtime.org> Mon, 02 September 2019 10:47 UTC

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From: Harlan Stenn <stenn@nwtime.org>
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Date: Mon, 2 Sep 2019 03:47:12 -0700
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Subject: Re: [Ntp] Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts
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On 8/28/2019 4:30 AM, Magnus Danielson wrote:
> I agree. If someone knocks on the door with v5 packets, reply in v5
> form, if someone knocks on the door with v4 packets, reply in v4 form.
> As people migrate to v5, they can start using all the benefits from it.

So what's the value and purpose of the version field in the packet if we
decide it no longer identifies the structure/content of the fields in
the packet?

An implementation that speaks "version N" MUST understand version N
packet formats, and SHOULD understand versions <N.

If there is a blanket requirement that if we understand version N and we
get a packet that is version >N, then if we respond with that same
version instead of responding with a version N packet, then we are
effectively saying we MUST NOT ever change the layout and meaning of the
content of the base packet.

What I'm seeing in this thread is that folks disagree with the above,
and in that case I'm wondering if folks understand what they think
they're advocating for.

Please see Heiko's last comment below, and understand it in this context.

> For loop-protection, keeping a list of nodes from the source is a very
> easy base condition to avoid routing loops, since as an announcement
> comes in, if none of the nodes in the list is oneself, you may use it,
> where as if any of the nodes is oneself, a loop is for sure detected.

The recipient has NO KNOWLEDGE of what the incoming refid means.

It's SOLE PURPOSE in this is degree-one loop detection, and that happens
at the "top" of the local tree.

> While the trace loop detection mechanism is sufficient in theory, it
> does not completely solve all loop problems, as transient loops may
> occur, but it at least avoids problems in the long term.

I don't believe there is any current way to communicate this knowledge,
so larger trace loop detection seems impossible without a way to
communicate this information.  It also begs the question of *where* this
detection should happen.

I think Heiko mentioned a loop they saw and I would be very interested
in seeing the details there, as such a loop should break as soon as any of:

- the stratum in the loop devolves to 16
- the root distance grows
- possibly something else

The point being that the important thing is that if a loop happens there
is an automatic recovery path.  If we never get a loop that's better,
but it won't be fatal to a properly configured setup if a loop happens
and the loop is then broken.

> If I only had time to describe all the things I would do to enhance NTP,
> it has a number of built-in assumptions which is not useful or correct.

How about a list of at least some of the built-in assumptions that you
think are not useful or correct?

H
--
> Cheers,
> Magnus
> 
> On 2019-08-28 13:23, Heiko Gerstung wrote:
>> Why not define a method in v5 that not only protects against degree 1 loops but maybe also against degree 2,3 or n? 
>>
>> This is what I meant when trying to explain that we should not stick to the existing packet format with its shortcomings.
>>
>> Regards,
>>    Heiko
>>
> 
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-- 
Harlan Stenn, Network Time Foundation
http://nwtime.org - be a Member!