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Configure the Time Source for the Forest

Updated: October 15, 2008

Applies To: Windows Server 2008, Windows Server 2008 R2

You can use these procedures to configure the Windows Time service (W32time) on the domain controller that holds the primary domain controller (PDC) emulator operations master role in the forest root domain to synchronize time from an external time server or a reliable time source. When you deploy a new forest root domain or when you move the role of the PDC emulator in the forest root domain to a new domain controller, you must configure the PDC emulator role holder in the forest root domain to synchronize time for the forest from an external time source on the Internet or from a hardware clock on the internal network. If you do not configure the PDC emulator to synchronize time from an external or internal time source, the PDC emulator uses its internal clock and is itself the reliable time source for the forest.

As an alternative to configuring the PDC emulator, you can configure a different domain controller in the forest root domain to synchronize time from a reliable time source. If there is such a domain controller in the forest root domain, the PDC emulator no longer advertises as a reliable time source.

The procedures in this topic configure the PDC emulator (or other domain controller) to connect to an external Network Time Protocol (NTP) time server for time synchronization. To configure the PDC emulator to synchronize time from a hardware clock device on the internal network, consult the instructions for the hardware clock device.

If you move the role of the PDC emulator to a new domain controller, you must also change the configuration of the Windows Time service on the previous PDC emulator. For more information, see Change the Windows Time Service Configuration on the PDC Emulator in the Forest Root Domain.

Before you configure the Windows Time service on the PDC emulator, you can determine the time difference between it and the time source as a means to test basic NTP communication.

If you have not selected a set of external NTP servers, use the following sites to create your list of time servers. This list is referred to in the procedure as the “manual peer list.”

After you configure the Windows Time service on the PDC emulator, be sure to monitor the System log in Event Viewer for W32time errors.

noteNote
The following procedures use the w32tm command-line tool. For more information about the w32tm command, type w32tm /? at a command prompt or see Windows Time Service Tools and Settings (http://go.microsoft.com/fwlink/?LinkId=112116).

Membership in the local Administrators group, or equivalent, is the minimum required to complete this procedure locally. Membership in Domain Admins, or equivalent, is the minimum required to complete this procedure remotely. Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (http://go.microsoft.com/fwlink/?LinkId=83477).

  1. Open a Command Prompt as an administrator: On the Start menu, right-click Command Prompt, and then click Run as administrator. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Continue.

  2. To display the time difference between the local computer and the target time source and to check NTP communication, at the command prompt, type the following command, and then press ENTER:

    w32tm /stripchart /computer:<target> /samples:<n> /dataonly
    

     

    Parameter Description

    W32tm /stripchart

    Displays a strip chart of the offset between synchronizing computers. A strip chart plots two-dimensional data—in this case, the local time and the offset.

    /computer:<target>

    Specifies the Domain Name System (DNS) name or IP address of the NTP server that you are comparing the local computer's time against, such as time.windows.com or time-nw.nist.gov.

    /samples:<n>

    Specifies the number of time samples that will be returned from the target computer to test basic NTP communication.

    /dataonly

    Specifies that results show only data, not graphics.

    If this procedure fails, check the System event log for Time-Service errors and follow any resolution steps that are provided in the More Info link in the error. It is possible that a perimeter firewall is blocking access to the Internet time server. NTP port 123 must be open for outbound and inbound traffic on all routers and firewalls between the PDC emulator and the Internet. If necessary, enable debug logging for W32time, as described in Enable Windows Time Service Debug Logging. Resolve any NTP connection issues before you proceed to step 3.

  3. To configure the PDC emulator to use an NTP time source, at the command prompt, type the following command, and then press ENTER:

    w32tm /config /manualpeerlist:<peers> /syncfromflags:manual /reliable:yes /update
    

     

    Parameter Description

    w32tm /config /update

    Configures the computer to synchronize time.

    /manualpeerlist:<peers>

    Specifies the list of DNS names or IP addresses for the NTP time source with which the PDC emulator synchronizes. (This list is referred to as the manual peer list.) For example, you can specify time.windows.com as the NTP time server. When you specify multiple peers, use a space as the delimiter and enclose the names of the peers in quotation marks.

    /syncfromflags:manual

    Specifies that time will be synchronized with peers in the manual peer list.

    /reliable:yes

    Specifies that the computer is a reliable time source.

noteNote
When you specify a peer in the manual peer list, do not specify a computer that uses the forest root domain controller as its source for time, such as another domain controller in the forest. The time service does not operate correctly if there are cycles in the time source configuration. Peers should be external to the domain hierarchy.

After you configure the PDC emulator as the time source for the forest, log on to a client computer in the forest root domain and perform steps 1 and 2 in the preceding procedure to check Windows Time service performance on the PDC emulator. Use the DNS name of the PDC emulator for the computer target in the command.

If you receive error messages, the User Datagram Protocol (UDP) ports on the PDC emulator might be disabled or blocked. You can use the following procedure to check the port status on the PDC emulator, if necessary.

Membership in the local Administrators group, or equivalent, is the minimum required to complete this procedure locally. Membership in Domain Admins, or equivalent, is the minimum required to complete this procedure remotely. Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (http://go.microsoft.com/fwlink/?LinkId=83477).

  1. To check inbound UDP port 123 status on the domain controller that is the PDC emulator, click Start, point to Administrative Tools, and then click Windows Firewall with Advanced Security.

  2. Click Inbound Rules. Check that Active Directory Domain Controller - W32Time (NTP-UDP-In) has a status of enabled (green) and is not blocked:

    • If this rule is disabled (dimmed), right-click the rule, and then click Enable.

    • If the rule is blocked, right-click the rule, and then click Properties. Under Action, click Allow the connections, and then click OK.

  3. To check outbound UDP port status on the domain controller, click Outbound Rules.

  4. Check that Active Directory Domain Controller (UDP-Out) has a status of enabled and is not blocked:

    • If the rule is disabled (dimmed), right-click the rule, and then click Enable.

    • If the rule is blocked, right-click the rule, and then click Properties. Under Action, click Allow the connections, and then click OK.

    Or

    To open only outbound UDP port 123, create a separate outbound rule for the specific port, as follows:

    1. In Windows Firewall with Advanced Security, right-click Outbound Rules, and then click New.

    2. In the New Outbound Rule Wizard, click Port, and then click Next.

    3. Click UDP, click Specific local ports, type 123, and then click Next.

    4. Follow the directions in the wizard to configure the security settings and name the rule, and then click Finish.

  5. To ensure that the PDC emulator responds, on an NTP client, repeat the test in step 2 of the procedure “To configure the Windows Time service on the PDC emulator” earlier in this topic.

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