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Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Cesium clocks are extremely stable and are unaffected by factors such as temperature, pressure, or humidity, but are also very expensive. A GPS receiver is much less expensive to operate and is also an accurate reference clock. GPS receivers obtain their time from satellites that obtain their time from a cesium clock.
Without the use of an independent time provider, Windows time servers can acquire their time by connecting to an external NTP server, which is connected to a hardware device by means of a telephone or the Internet.
Organizations such as the United States Naval Observatory provide NTP servers that are connected to extremely reliable reference clocks. You can configure your AD DS forest to synchronize time from these external hardware devices only if they are also acting as NTP servers on your network. To do so, configure the domain controller functioning as the primary domain controller PDC emulator in your forest root to synchronize with the NTP server provided by the GPS device.
The primary difference between the two is that SNTP does not have the error management and complex filtering systems that NTP provides. The time service in Windows NT Server 4. For example, if your domain is configured to synchronize time by using the domain hierarchy-based method of synchronization and you want computers in the domain hierarchy to synchronize time with a Windows NT 4.
Windows NT 4. Therefore, to ensure accurate time synchronization across your network, it is recommended that you upgrade any Windows NT 4. The Windows Time service is designed to synchronize the clocks of computers on a network. The network time synchronization process, also called time convergence, occurs throughout a network as each computer accesses time from a more accurate time server. Time convergence involves a process by which an authoritative server provides the current time to client computers in the form of NTP packets.
The information provided within a packet indicates whether an adjustment needs to be made to the computer's current clock time so that it is synchronized with the more accurate server. As part of the time convergence process, domain members attempt to synchronize time with any domain controller located in the same domain. If the computer is a domain controller, it attempts to synchronize with a more authoritative domain controller.
Computers running Windows XP Home Edition or computers that are not joined to a domain do not attempt to synchronize with the domain hierarchy, but are configured by default to obtain time from time. To establish a computer running Windows Server as authoritative, the computer must be configured to be a reliable time source. By default, the first domain controller that is installed on a Windows Server domain is automatically configured to be a reliable time source.
Because it is the authoritative computer for the domain, it must be configured to synchronize with an external time source rather than with the domain hierarchy. Also by default, all other Windows Server domain members are configured to synchronize with the domain hierarchy. After you have established a Windows Server network, you can configure the Windows Time service to use one of the following options for synchronization:.
Synchronization that is based on a domain hierarchy uses the AD DS domain hierarchy to find a reliable source with which to synchronize time. Based on domain hierarchy, the Windows Time service determines the accuracy of each time server. In a Windows Server forest, the computer that holds the primary domain controller PDC emulator operations master role, located in the forest root domain, holds the position of best time source, unless another reliable time source has been configured.
The following figure illustrates a path of time synchronization between computers in a domain hierarchy. A computer that is configured to be a reliable time source is identified as the root of the time service.
The root of the time service is the authoritative server for the domain and typically is configured to retrieve time from an external NTP server or hardware device. A time server can be configured as a reliable time source to optimize how time is transferred throughout the domain hierarchy. If a domain controller is configured to be a reliable time source, Net Logon service announces that domain controller as a reliable time source when it logs on to the network.
When other domain controllers look for a time source to synchronize with, they choose a reliable source first if one is available. A cycle in the synchronization network occurs when time remains consistent between a group of domain controllers and the same time is shared between them continuously without a resynchronization with another reliable time source.
The Windows Time service's time source selection algorithm is designed to protect against these types of problems. If the computer is not a member of a domain, it must be configured to synchronize with a specified time source.
If the computer is a member server or workstation within a domain, by default, it follows the AD DS hierarchy and synchronizes its time with a domain controller in its local domain that is currently running the Windows Time service. If the computer is a domain controller, it makes up to six queries to locate another domain controller to synchronize with. Each query is designed to identify a time source with certain attributes, such as a type of domain controller, a particular location, and whether or not it is a reliable time source.
The time source must also adhere to the following constraints:. A PDC emulator can synchronize with a reliable time source in its own domain or any domain controller in the parent domain. If the domain controller is not able to synchronize with the type of domain controller that it is querying, the query is not made.
The domain controller knows which type of computer it can obtain time from before it makes the query. For example, a local PDC emulator does not attempt to query numbers three or six because a domain controller does not attempt to synchronize with itself. The following table lists the queries that a domain controller makes to find a time source and the order in which the queries are made. A domain controller does not attempt to synchronize with itself.
Each query returns a list of domain controllers that can be used as a time source. Windows Time assigns each domain controller that is queried a score based on the reliability and location of the domain controller. The following table lists the scores assigned by Windows Time to each type of domain controller.
When the Windows Time service determines that it has identified the domain controller with the best possible score, no more queries are made. The scores assigned by the time service are cumulative, which means that a PDC emulator located in the same site receives a score of nine. If the root of the time service is not configured to synchronize with an external source, the internal hardware clock of the computer governs the time.
Manually-specified synchronization enables you to designate a single peer or list of peers from which a computer obtains time. If the computer is not a member of a domain, it must be manually configured to synchronize with a specified time source.
A computer that is a member of a domain is configured by default to synchronize from the domain hierarchy, manually-specified synchronization is most useful for the forest root of the domain or for computers that are not joined to a domain. Manually specifying an external NTP server to synchronize with the authoritative computer for your domain provides reliable time.
However, configuring the authoritative computer for your domain to synchronize with a hardware clock is actually a better solution for providing the most accurate, secure time to your domain. Manually-specified time sources are not authenticated unless a specific time provider is written for them, and they are therefore vulnerable to attackers.
Also, if a computer synchronizes with a manually-specified source rather than its authenticating domain controller, the two computers might be out of synchronization, causing Kerberos authentication to fail. This might cause other actions requiring network authentication to fail, such as printing or file sharing. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Please rate your experience Yes No. Any additional feedback?
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