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I'm troubleshooting some time issues in my domain and before making any big changes I want to have a thorough understanding of what's going on. I've got a few lingering questions at the moment:

  • What sources (rtc, ntp, etc.) are queried by Windows to keep time? How does this differ in a mixed Active Directory / Novell environment?
  • What is the order that each source is queried in?
  • How does Windows decide whether to act as an NTP client, peer or server?
  • In what situations will Windows update the RTC, if ever?
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  • Whoops, not sure how my last comment got lost. I edited my question to be more specific regarding the definition of a "source". Also, added the bullet point about NTP query modes.
    – bshacklett
    Jan 28, 2011 at 16:59

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In an AD environment, all DCs will sync their time with the DC that owns the PDC Emulator FSMO role. All client machines will then sync their time with a DC in their site.

The DC that owns the PDC Emulator FSMO role is setup to not sync at all, but most admins will change this. It's common to set this DC to sync to an NTP server on the internet.

As for Novell environment and RTC, I'm not sure...Hopefully somebody smarter than me will come along.

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eDirectory servers use NTP or Novell TimeSync to synchronize to each other, you design a basic hierarchy. If the clients have the Novell client they should automatically sync to their nearest replica servers. If they don't then you have to configured time synchronization independently.

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  • The local account has to have permission to set workstation time for this to work. Starting with WinNT and higher kernels.
    – geoffc
    Jan 30, 2011 at 13:33
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- What sources are queried by Windows to keep time? How does this differ in a mixed Active Directory / Novell environment?

It depends - there are lots of options, there's no one answers but a common answer is to use an NTP source.

What is the order that each source is queried in?

Again, it entirely depends on the setup as there's a lot of options and they can be ordered in many ways too.

In what situations will Windows update the RTC, if ever?

You're not going to like me for saying this again, but it depends on implementation, certainly when using AD time sync the RTC will be updated each time a machine is updated or updates itself from the AD time, same for direct NTP too.

Perhaps you could come back with more specific questions regarding your actual existing systems? We might be able to be more help.

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  • Well, I'm looking more for what happens in a default configuration. Let's consider a new domain with two DCs and 5 client machines. Without any third-party software configured, how will the clients react? My current understanding is that they will pull time from the RTC on boot, then use NTP to query the authenticating DC, which gets its time from the PDC emulator. Are there any other potential sources? Also, how does a machine decide what NTP mode to operate in?
    – bshacklett
    Jan 28, 2011 at 16:55
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In simplified terms, as far as Windows AD clients are concerned, they sync with the PDC emulator. The PDC emulator can be configured to sync with an external time source.

Here's a good article on the subject:

http://technet.microsoft.com/en-us/library/cc773013(WS.10).aspx

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After doing a good amount of research, I've found the following. Please correct me if you see any incorrect information:

What sources (rtc, ntp, etc.) are queried by Windows to keep time? How does this differ in a mixed Active Directory / Novell environment?

  • RTC
  • A time server that is located by NT5DS
  • The NTP server specified in the W32Time service parameters key (HKLM\SYSTEM\CurrentControlSet\Services\W32Time\Parameters)

In a Novell environment, the Novell client may be configured to update the time on login. This option is configured under the Advanced Settings tab. The option is "Set Station Time (On || Off)"

What is the order that each source is queried in?

Windows queries the RTC on system startup, then the Windows Time Service takes over. If the Novell client is installed and configured with "Set Station Time" on, it will update the system's time on login.

How does Windows decide whether to act as an NTP client, peer or server?

Windows operates in NTP Symmetric mode. "...in which servers and clients are indistinguishable yet maintain a small amount of state information..."—RFC 958 - Network Time Protocol (NTP)

In what situations will Windows update the RTC, if ever?

From what I can see, Windows will not ever set the BIOS clock.

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