Re: [Ntp] Finding leap-seconds.list

[Martin Burnicki <[e-mail]>]

Thomas Peterson wrote:
> As was discussed at the working group meeting at IETF 103 [0], I have decided to do some research on the leap-seconds.list file that the IETF appears to be hosting at https://www.ietf.org/timezones/data/leap-seconds.list, but for some participants of this working group appear unclear about.

During the IETF NTP WG session I posted a link in the chat which points
to a PDF I wrote some time ago:
https://www.meinbergglobal.com/download/burnicki/the_ntp_leap_second_file.pdf

There are several "original" versions of that file published by the
IERS, NIST, and USNO.

One of those original files (usually the version from NIST) is used to
update the TZDB records, and the original file is also included in the
TZDB distribution/tar ball, which is then unpacked and made available at
the IETF web site.

The problem here is that first an update of the original leap second
file appears, and only whenever the next TZDB version is released after
that the file appears on the IETF web site.

So for most users it's better to pick up a file from one of the original
sites.

> Where is this referenced in an RFC or other IETF document?
> I ran a search of “leap-seconds.list” across the spread of draft and RFC documents. No RFC that I have found makes direct reference. However, the current NTP BCP draft Section 4.6 [1] contains:
> 
> ... SNIP ...
> 
> The IETF maintains a leap second list [[7]] for NTP users who are not
>    receiving leap second information through an automatic source.
> 
>    Files are also available from other sources:
> 
> ... SNIP ...
> 
> With [[7]] holding reference to the file hosted at, and a list of links to sources.
> 
> What else is www.ietf.org hosting of a similar nature?
> This file alone is not the only thing hosted under www.ietf.org, in fact https://www.ietf.org/timezones/ directory listings show that all recent versions of the tzdb (including 2018g the most recent) which suggests a human maintaining the hosting of it, or automated process. Versions only go back to 2016. These files are also available over FTP [2].
> 

Yes, and since the leap seconds file is part of the TZDB, it also
becomes available via the IETF web site.

> How long have these files been hosted on www.ietf.org?
> Internet archive's Wayback Machine [3] shows it appearing back in 2015.
> 
> Who is using the file?
> ntpd does depend on it as was discussed at the WG meeting, [4]. FreeBSD [5] holds reference to it and users have reported issues when being unable to access it in the past. In addition, at least one library [6] make use of it outside of ntpd, however I don't believe this is heavily used or cause non-developers or system administrators any pain if it went missing.

I'm sure the file *is* heavily used, but maybe not directly from the
IETF web site.

It's a good source to become aware of an upcoming leap second, and it's
a good source to be able to determine the current UTC/TAI offset, as
e.g. required when using PTP which uses TAI timestamps by default.

Anyway, I think the file is mostly used by NTP or PTP servers since for
most applications the information interesting for clients can be passed
via the individual protocols.


Regards,

Martin
-- 
Martin Burnicki

Senior Software Engineer

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