How to Configure an Authoritative Time Server in Windows Server

How to configure an authoritative time server in Windows Server

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INTRODUCTION

Windows includes W32Time, the Time Service tool that is required by the Kerberos

authentication protocol. The purpose of the Windows Time service is to make sure that all

computers that are running Microsoft Windows 2000 or later versions in an organization use a

common time.

To guarantee appropriate common time usage, the Windows Time service uses a hierarchical

relationship that controls authority, and the Windows Time service does not permit loops. By

default, Windows-based computers use the following hierarchy:

All client desktop computers nominate the authenticating

domain controller as their in-bound time partner.

All member servers follow the same process that client

desktop computers follow.

All domain controllers in a domain nominate the primary

domain controller (PDC) operations master as their in-

bound time partner.

All PDC operations masters follow the hierarchy of domains

in the selection of their in-bound time partner.

In this hierarchy, the PDC operations master at the root of the forest becomes authoritative for

the organization. We highly recommend that you configure the authoritative time server to gather

the time from a hardware source. When you configure the authoritative time server to sync with

an Internet time source, there is no authentication. We also recommend that you reduce your

time correction settings for your servers and stand-alone clients. These recommendations provide

more accuracy and security to your domain.

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Configuring the Windows Time service to use an internal hardware clock

http://support.microsoft.com/kb/816042#top

To have us configure the Windows Time service to use an internal hardware clock for you, go to

the "Fix it for me" section. If you prefer to fix this problem yourself, go to the "Let me fix it

myself" section.

Fix it for me

To fix this problem automatically, click the Fix it button or link. Click Run in the File

Download dialog box, and follow the steps in the Fix it wizard.

Fix this problem

Microsoft Fix it 50394

Notes

This wizard may apply to English versions only; however,

the automatic fix also works for other language versions of

Windows.

If you are not on the computer that has the problem, save the

Fix it solution to a flash drive or a CD and then run it on the

computer that has the problem.

Let me fix it myself

Important This section, method, or task contains steps that tell you how to modify the registry.

However, serious problems might occur if you modify the registry incorrectly. Therefore, make

sure that you follow these steps carefully. For added protection, back up the registry before you

modify it. Then, you can restore the registry if a problem occurs. For more information about

how to back up and restore the registry, click the following article number to view the article in

the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows

To configure the PDC master without using an external time source, change the announce flag on

the PDC master. The PDC master is the server that holds the forest root PDC master role for the

domain. This configuration forces the PDC master to announce itself as a reliable time source

and uses the built-in complementary metal oxide semiconductor (CMOS) clock. To configure the

PDC master by using an internal hardware clock, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.

2. Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\

CurrentControlSet\Services\W32Time\Config\

AnnounceFlags

3. In the right pane, right-click AnnounceFlags, and then

click Modify.

4. In Edit DWORD Value, type A in the Value data box, and

then click OK.

5. Quit Registry Editor.

6. At the command prompt, type the following command to

restart the Windows Time service, and then press ENTER:

net stop w32time && net start w32time

Note The PDC master must not be configured to synchronize with itself. For more information

about why the PDC master must not be configured to synchronize with itself, visit the following

Web site to view Request For Comment (RFC) 1305:

http://www.rfc-editor.org/

If the PDC master is configured to synchronize with itself, the following events are logged in the

System log:

Event Type: Information

Event Source: W32Time

Event Category: None

Event ID: 38

Computer: ComputerName

Description: The time provider NtpClient cannot reach or is currently receiving invalid time data

fromNTP_server_IP_Address. For more information, see Help and Support Center at

http://support.microsoft.com.

Event Type: Warning



Event ID: 47


Description: Time Provider NtpClient: No valid response has been received from manually

configured peerNTP_server_IP_Address after 8 attempts to contact it. This peer will be

discarded as a time source and NtpClient will attempt to discover a new peer with this DNS

name. For more information, see Help and Support Center at http://support.microsoft.com.

Event Type: Error



Event ID: 29


Description: The time provider NtpClient is configured to acquire time from one or more time

sources, however none of the sources are currently accessible. No attempt to contact a source

will be made for 15 minutes. NtpClient has no source of accurate time. For more information,

see Help and Support Center at http://support.microsoft.com.

When the PDC master runs without using an external time source, the following event is logged

in the Application log:

Event Type: Error



Event ID: 12

Description: Time Provider NtpClient: This machine is configured to use the domain hierarchy

to determine its time source, but it is the PDC emulator for the domain at the root of the forest, so

there is no machine above it in the domain hierarchy to use as a time source. It is recommended

that you either configure a reliable time service in the root domain, or manually configure the

PDC to synchronize with an external time source. Otherwise, this machine will function as the

authoritative time source in the domain hierarchy. If an external time source is not configured or

used for this computer, you may choose to disable the NtpClient.

This text is a reminder to use an external time source, and it can be ignored.

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Configuring the Windows Time service to use an external time source

To have us help you configure an internal time server to synchronize with an external time

source, go to the "Fix it for me" section. If you prefer to fix this problem yourself, go to the "Let

me fix it myself" section.

Fix it for me


To fix this problem automatically, click the Fix it button or link. Click Run in the File

Download dialog box, and follow the steps in the Fix it wizard.

Fix this problem

Microsoft Fix it 50395

Notes

This wizard may apply to English versions only; however,

the automatic fix also works for other language versions of

Windows.

If you are not on the computer that has the problem, save the

Fix it solution to a flash drive or a CD and then run it on the

computer that has the problem.

Let me fix it myself

To configure an internal time server to synchronize with an external time source, follow these

steps:

1. Change the server type to NTP. To do this, follow these

steps:

a. Click Start, click Run, type regedit, and then

click OK.

b. Locate and then click the following registry subkey:


CurrentControlSet\Services\W32Time\

Parameters\Type

c. In the right pane, right-click Type, and then

click Modify.

d. In Edit Value, type NTP in the Value data box, and

then click OK.

2. Set

AnnounceFlags

to 5. To do this, follow these steps:

a. Locate and then click the following registry subkey:



AnnounceFlags

b. In the right pane, right-click AnnounceFlags, and

then click Modify.

c. In Edit DWORD Value, type 5 in the Value

data box, and then click OK.

Notes

If an authoritative time server that is configured

to use an AnnounceFlag value of 0x5 does not

synchronize with an upstream time server, a

client server may not correctly synchronize

with the authoritative time server when the time

synchronization between the authoritative time

server and the upstream time server resumes.

Therefore, if you have a poor network

connection or other concerns that may cause

time synchronization failure of the authoritative

server to an upstream server, set the

AnnounceFlag value to 0xA instead of to 0x5.

If an authoritative time server that is configured

to use an AnnounceFlag value of 0x5 and to

synchronize with an upstream time server at a

fixed interval that is specified in

SpecialPollInterval, a client server may not

correctly synchronize with the authoritative

time server after the authoritative time server

restarts. Therefore, if you configure your

authoritative time server to synchronize with an

upstream NTP server at a fixed interval that is

specified in SpecialPollInterval, set the

AnnounceFlag value to 0xA instead of 0x5.

3. Enable NTPServer. To do this, follow these steps:




TimeProviders\NtpServer

b. In the right pane, right-click Enabled, and then

click Modify.

c. In Edit DWORD Value, type 1 in the Value

data box, and then click OK.

4. Specify the time sources. To do this, follow these steps:



CurrentControlSet\Services\W32Time\Parameters

b. In the right pane, right-click NtpServer, and then

click Modify.

c. In Edit Value, type Peers in the Value data box, and

then click OK.

Note Peers is a placeholder for a space-delimited list

of peers from which your computer obtains time

stamps. Each DNS name that is listed must be unique.

You must append ,0x1to the end of each DNS name.

If you do not append ,0x1 to the end of each DNS

name, the changes made in step 5 will not take effect.

5. Select the poll interval. To do this, follow these steps:

a. Locate and then click the following registry

subkey:



TimeProviders\NtpClient\SpecialPollInterval

b. In the right pane, right-click SpecialPollInterval, and

then click Modify.

c. In Edit DWORD Value, type TimeInSeconds in

the Value data box, and then click OK.

Note TimeInSeconds is a placeholder for the number

of seconds that you want between each poll. A

recommended value is 900 Decimal. This value

configures the Time Server to poll every 15 minutes.

6. Configure the time correction settings. To do this, follow

these steps:




MaxPosPhaseCorrection

b. In the right pane, right-

click MaxPosPhaseCorrection, and then

click Modify.

c. In Edit DWORD Value, click to select Decimal in

the Base box.

d. In Edit DWORD Value, type TimeInSeconds in


Note TimeInSeconds is a placeholder for a reasonable

value, such as 1 hour (3600) or 30 minutes (1800).

The value that you select will depend upon the poll

interval, network condition, and external time source.

e. Locate and then click the following registry subkey:



MaxNegPhaseCorrection

f. In the right pane, right-

click MaxNegPhaseCorrection, and then

click Modify.

g. In Edit DWORD Value, click to select Decimal in

the Base box.

h. In Edit DWORD Value, type TimeInSeconds in


Note TimeInSeconds is a placeholder for a reasonable

value, such as 1 hour (3600) or 30 minutes (1800).

The value that you select will depend upon the poll

interval, network condition, and external time source.

7. Quit Registry Editor.

8. At the command prompt, type the following command to

restart the Windows Time service, and then press ENTER:

net stop w32time && net start w32time

NOTE: For a list of available time servers, see Microsoft KB Article 262680 - A list of the

Simple Network Time Protocol (SNTP) time servers that are available on the Internet

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Troubleshooting

For the Windows Time service to function correctly, the networking infrastructure must function

correctly. The most common problems that affect the Windows Time service include the

following:

There is a problem with TCP/IP connectivity, such as a dead

gateway.

The Name Resolution service is not working correctly.

The network is experiencing high volume delays, especially

when synchronization occurs over high-latency wide area

network (WAN) links.

The Windows Time service is trying to synchronize with

inaccurate time sources.

We recommend that you use the Netdiag.exe utility to troubleshoot network-related issues.

Netdiag.exe is part of the Windows Server 2003 Support Tools package. See Tools Help for a

complete list of command-line parameters that you can use with Netdiag.exe. If your problem is

still not solved, you can turn on the Windows Time service debug log. Because the debug log

can contain very detailed information, we recommend that you contact Microsoft Product

Support Services when you turn on the Windows Time service debug log.

For a complete list of Microsoft Product Support Services phone numbers and information about

support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;[LN];CNTACTMS

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a

Microsoft Support Professional determines that a specific update will resolve your problem. The


usual support costs will apply to additional support questions and issues that do not qualify for

the specific update in question.

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MORE INFORMATION

NTP supports several different packet types. Typically, NTP clients and Simple Network Time

Protocol (SNTP) clients send client mode request packets to an NTP server. The NTP server

responds with a server mode packet. To configure the W32time service to send symmetric active

mode packets instead of client mode packets to an NTP server, type the following command at a

command prompt:

w32tm /config /manualpeerlist:<server>,0x4 /syncfromflags:MANUAL

Note Use the 0x8 flag to force W32time to send normal client requests instead of symmetric

active mode packets. The NTP servier replies to these normal client requests as usual.

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Reliable time source configuration

A computer that is configured to be a reliable time source is identified as the root of the

Windows Time service. The root of the Windows 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, the 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 select a reliable source first, if one is available.

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Manually-specified synchronization

With manually-specified synchronization, you can designate a single peer or list of peers that a

computer obtains time from. If the computer is not a member of a domain, it must be manually

configured to synchronize with a specified time source. By default, a computer that is a member

of a domain is configured 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. When you manually specify an external NTP server to synchronize with the

authoritative computer for your domain, you provide reliable time. However, to provide high

accuracy and security to your domain, we recommend that you configure the authoritative

computer for your domain to synchronize with a hardware clock.




Without a hardware time source, W32time is configured as a NTP type. You must reconfigure

the MaxPosPhaseCorrection and MaxNegPhaseCorrection registry entries. The recommended

value should be 15 minutes or even lower, depending on time source, network condition, and

security requirement. This requirement also applies to any reliable time source that is configured

as the forest root time source in the time sync subnet. For more information about these registry

entries, see the "Windows Time service registry entries" section in this article.

Note Manually-specified time sources are not authenticated unless a specific time provider is

written for them, and these time sources are therefore vulnerable to attacks. Also, if a computer

synchronizes with a manually-specified source instead of its authenticating domain controller,

the two computers might be out of synchronization. This scenario causes Kerberos authentication

to fail and could also cause other actions that require network authentication to fail, such as

printing or file sharing. If only the forest root is configured to synchronize with an external

source, all other computers within the forest remain synchronized with each other. This

configuration makes replay attacks difficult.

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All available synchronization mechanisms

The "all available synchronization mechanisms" option is the most valuable synchronization

method for users on a network. This method enables synchronization with the domain hierarchy

and may also provide an alternative time source if the domain hierarchy becomes unavailable,

depending on the configuration. If the client cannot synchronize time with the domain hierarchy,

the time source automatically falls back to the time source that is specified by

the NtpServer setting. This method of synchronization is most likely to provide accurate time to

clients.

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Windows Time service registry entries

The following registry entries are located under

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\

:

Registry Entry

MaxPosPhaseCorrection

Path HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config



Notes This entry specifies the largest positive time correction in seconds that the service makes. If the service determines that a change that is larger than this is required, the service logs an event. (0xFFFFFFFF is a special case that means always make a time correction.) The default value for domain members is 0xFFFFFFFF. The default value for stand-alone clients and servers is 54,000 or 15 hours.

Registry Entry

MaxNegPhaseCorrection


Notes This entry specifies the largest negative time correction in seconds that the service makes. If the service determines that a change that is larger than this is required, the service logs an event instead. (-1 is a special case that means always make a time correction.) The default value for domain members is 0xFFFFFFFF. The default value for stand-alone clients and servers is 54,000 or 15 hours.

Registry Entry

MaxPollInterval


Note This entry specifies the largest interval, in log seconds, that is allowed for the system polling interval. While a system must poll according to the scheduled interval, a provider can refuse to produce samples when requested. The default value for domain members is 10. The default value for stand-alone clients and servers is 15.

Registry Entry

SpecialPollInterval

Path HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient

Note This entry specifies the special poll interval in seconds for manual peers. When the SpecialInterval 0x1 flag is enabled, W32Time uses this poll interval instead of a poll interval that is determined by the operating system. The default value on domain members is 3,600. The default value on stand-alone clients and servers is 604,800.

Registry Entry

MaxAllowedPhaseOffset


Note This entry specifies the maximum offset, in seconds, for which W32Time tries to adjust the computer clock by using the clock rate. When the offset is greater than this rate, W32Time sets the computer clock directly. The default value for domain members is 300. The default value for stand-alone clients and servers is 1.

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REFERENCES

For more information about Windows Time service, click the following article numbers to view

the articles in the Microsoft Knowledge Base:

816043 How to turn on debug logging in the Windows Time service

884776 Configuring the Windows Time service against a large time offset

321708 How to use the Network Diagnostics Tool (Netdiag.exe) in Windows 2000

314054 How to configure an authoritative time server in Windows XP

216734 How to configure an authoritative time server in Windows 2000

For more information about the Windows Time service in a Windows Server 2003-based forest,

visit the following Microsoft Web site:

http://technet.microsoft.com/en-us/library/cc773061.aspx

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