Re: [Ntp] [EXTERNAL] Re: Antw: Re: Antw: Re: Antw: [EXT] Re: New Version Notification for draft‑gruessing‑ntp‑ntpv5‑requirements‑03.txt

[Martin Burnicki <[e-mail]>]

Denis Reilly wrote:
> Leap smearing was one of the main topics of the BCP. Because we 
> understand why it’s a good idea in many cases, but also why it can be 
> perilous if handled incorrectly.
> 
> In the BCP, we arrived at a few key guidelines, aiming to preserve the 
> most flexibility to operators while still maintaining standard public 
> behavior:
> 
> - Don’t mix smearing and non-smearing servers
> 
> - Don’t smear if your timestamps are required to be in sync with UTC
> 
> - Only smear on totally private installations, do not smear on public 
> servers
> 
> In my view, these restrictions exist because there is no standardized 
> way to detect that a server is smearing in ntpv4. So we settled on the 
> notion that public interactions should use the standard timescale, while 
> operators could do whatever they wanted in the privacy of their own 
> networks.
> 
> At minimum, NTPV5 should include a standardized way for the server to 
> tell everyone else that it is smearing the timestamps on the wire, so 
> that clients can elect to not use the server. In my opinion, there is no 
> use in saying that smearing on the wire is not allowed in V5 – people 
> will do it anyway.

Absolutely true.

> I think that we should also have a way for the server to broadcast the 
> smearing algorithm in use on the network. This is, of course, valuable 
> when servers are smearing, because then a client which knows about this 
> can back-out the smearing behavior and obtain UTC time if it wants to.

Hm, I'm not sure what would be the best way to broadcast the smearing 
parameters in a future-safe way. There is the smear interval, when it 
starts and when it ends, and also the smear function: linear, cosine, 
quadratic, or whatever will be invented in the future.

Maybe it's easier and less error prone to let the server indicate *that* 
it provides smeared time, and what the current smear offset is. So 
clients can easily convert this back to UTC, if they want/need to.

Martin
-- 
Martin Burnicki

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