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

[Martin Burnicki <[e-mail]>]

Am 22.10.21 um 10:02 schrieb Ulrich Windl:
>>>> Doug Arnold <doug.arnold=[e-mail]> schrieb am
> 21.10.2021 um 15:36 in Nachricht
> <[e-mail]>
> 
>> One thing to keep in mind is that the use case for leap smearing is that it
>> happens in a private network, where all Stratum 1 servers are configured the
>> same.  I still consider it dangerous, though.

I fully agree. Smearing is just a hack to circumvent limitations of the 
underlying time synchronization, and avoid even worse problem that would 
occur without smearing.

The main problem is with applications that get confused when the system 
time (UTC, or a local time derived from it) unexpectedly steps back by 1 
second if a leap second is introduced.

In my opinion it doesn't really help if the system clock runs on TAI 
because unless applications have explicitly designed to take care of 
leap seconds would still request UTC or local time from the operating 
system, and thus would observe the same, unexpected time step back if 
the kernel clock runs TAI and adds the TAI/UTC offset in the reply to 
the query.

The only ways to avoid the problems would be to either abolish leap 
seconds, or fix all applications to work with TAI and convert to UTC or 
local time themselves, or to be aware the time steps back due to a leap 
second are a normal case that needs to be handled, similar as the local 
time step back at the end of DST.

> We could demand that a smearing server may only respond to authenticated packets (maybe even specific keys), so clients expecting leap smear would have to provide some cryptographic key to the server.
> A clients querying the server by mistake wuld not get a response then.

No. Exactly the other way round. Smearing is to hide the leap second 
from downstream nodes, even from dumb clients.

As I've tried to point out earlier, in any case it's the task of an 
administrator to ensure a proper configuration:

- If there are smearing and not-smearing servers, he has to configure 
which clients should query the time from which servers.

- If the clients should do the smearing, he had to configure each 
individual client whether to smear, or not.

- If a smearing server would only reply to authenticated requests, he 
had to configure on each client which server(s) to use, and which keys, 
and it wouldn't even be possible to hide the leap second from dumb clients.


Martin
-- 
Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: [e-mail]
Phone: [phone]
Linkedin: https://www.linkedin.com/in/martinburnicki/

Lange Wand 9, 31812 Bad Pyrmont, Germany
Amtsgericht Hannover 17HRA 100322
Geschäftsführer/Managing Directors: Günter Meinberg, Werner Meinberg, 
Andre Hartmann, Heiko Gerstung
Websites: https://www.meinberg.de  https://www.meinbergglobal.com
Training: https://www.meinberg.academy