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

[Ulrich Windl <[e-mail]>]

>>> Denis Reilly <[e-mail]> schrieb am 25.10.2021 um 23:14 in
Nachricht
<[e-mail]>:
> 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.
> 
> 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. But it’s

> also valuable if the server is not smearing, because it can help coordinate

> client-side smearing in clients who are intelligent enough. (In other words,

> if all nodes updated to NTPv5 with support for this, the server could keep 
> the timestamps as RFC-compliant non-smeared UTC on the wire while telling
all 
> clients how to apply the leap smear uniformly if they need to, getting the 
> best parts of client-side and server-side smearing together, while keeping 
> the wire timestamps in UTC.)
> 
> In my opinion, we should aim preserve the most flexibility. We should make 
> it easier for operators to do client-side or server-side smearing, and we 
> should allow operators using servers outside their administrative domain to

> reject servers who apply rules they don’t like. We’re not going to get 
> everyone to agree on one behavior, the best we can do is make sure that 
> behaviors are standardized and easy to implement. To me it seems like we 
> would get a lot of benefit out of adding a few extensions. There have been 
> attempts to standardize this in the past, maybe we can get it done in V5 
> (just in time for leap seconds to be abolished).

So any future smearing server would add packet extensions to indicate:
* the smearing algorithm (required to indicate smearing is in progress)
* the offset from UTC (or the common time base being used in the NTP packets)

And I guess there will be numbers assigned to smearing algorithms.

Regards,
Ulrich
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