Is Leap Second Impact Windows Servers and Application?

By | June 21, 2015

Is your Windows infrastructure is ready for the Leap Second change? Before start discussing the Windows Server and Application impact, Leap Second is a one second adjustment to UTC time (Coordinated Universal Time) across the globe which is added every few years to maintain alignment with solar time. The next leap second will be added at 23:59:59 on Tues 30th June 2015 by adding an additional second before 00:00:00 on 1st July 2015.

See also:Time Service in Windows (Part 1)

How Windows Time service will handle leap second?

Windows NTP Server

Leap second is not only affecting the Windows Time service, all external NTP servers will get affected or get the Leap second changes

Once an external NTP server sends a Leap Indicator that has a value of 01 to the Windows Time service NTP server, Windows NTP server sends the same value to all NTP clients

Windows Client

After the leap second change, NTP client running on Windows Time service is one second faster than the Universal Time (UTC). This time difference is updated at the next time synchronization from a NTP server, see more from MS

How Applications will handle leap second?

Most applications do not care about the leap second change, yes – applications are in minute time adjustments to the system clock, so leap seconds are not making any difference and impact

If application is coded that needs to be precise on sub-second accuracy then need to consider how the clock change will impact on leap second, however most of the applications are coded to use minute time

See also: Understanding the time zone configuration

Leap Second Vulnerability

Currently there is no Vulnerability on Windows servers, Windows Servers detect the Leap Second change and dynamically fix it and no impact at all, however watch out future changes


Normally Leap second change/update doesn’t cause any problem unless you are Windows infrastructure and application is time sensitive less than a second in duration

Windows and Applications are robust to handle leap second changes, however keep an eye on your IT environment and NTP Windows servers, and last leap second event (June 2012) didn’t affect the windows servers

Other Time Service issues


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