![]() ![]() ![]() For more information on time services in Windows, check out Microsoft's article How Windows Time Service Works. While using UTC time may make it easier when comparing logs from two machines in different time zones, it would render things such as calendar functions useless. Microsoft could have made things simple and just had all computers report the UTC time and be done with it, but they decided to make it user-friendly and built a utility to convert UTC to "local time" based on the time zone selected. So, even though a client computer in Atlanta says it's 16:00 and a server in the network in Seattle says it's 13:00 (adjusted for time zone), the UTC on both is 21:00. Regardless of what the time in the Notification Area says, the computer knows the UTC. ![]() Bottom line, all computers use UTC to synchronize clocks. When the UK goes on "summer time", or DST, BST is changed by an hour - it does not affect GMT. However, don't confuse GMT with British Standard Time. It is generally considered synonymous with GMT (Greenwich Mean Time). UTC is a standard time that everyone agrees on, regardless of time zones. In order to eliminate the confusion caused by the many time zones in the world, (such as those shown in Figure 2), NTP uses Coordinated Universal Time (UTC) as the standard. In order to synchronize all clocks on the network, NTP needs a "reference clock" as a reliable time source. NTP is much more accurate than the Simple Network Time Protocol (SMTP) used in Windows 2000 (though SMTP is still available in Windows 2003). Windows 2003 relies on the NTP (Network Time Protocol) to synchronize clocks across a network. To better understand this issue, let's review some basics on Windows Time Services. But does it really affect domain controllers if the DST is incorrect? Further more, if you have DCs in Atlanta, Seattle, Sydney and London, all in different time zones with various DST settings, how can they all stay within five minutes of each other? How Windows time service works However, the burning question for administrators is, "Can this also affect domain operations such as Active Directory replication and network authentication?" After all, Kerberos requires any two computers authenticating over the network to be within five minutes of each other, though it is configurable in Group Policy. and Canada that changes, Microsoft provides a way to modify these parameters for your particular time zone in KB914387. If you are in a time zone outside the U.S. Microsoft has released KB 928388, a DST hotfix to address this issue. The table here shows the previous dates for DST changes (2006) and what the new changes, starting in 2007, will be. ![]() This new legislation changes the dates for DST implementation. The biggest concern for Active Directory administrators is whether the DST change can also affect domain operations such as AD replication and network authentication. This year, though, daylight-saving time will have negative effects on Microsoft Outlook functions such as email time stamping, calendar items and other issues noted by Microsoft in Prepare calendar items for daylight saving time in 2007. For example, computers - from laptops to domain controllers - probably have the "Automatically adjust clock for daylight-saving changes" box checked that automatically advances or pushes back the time on the appointed date. ![]()
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