Microsoft KB Archive/222604

= Configuring Cached Dfs Referral Expiration Time in Dfs 4.1 =

PSS ID Number: 222604

Article Last Modified on 10/16/2002

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The information in this article applies to:


 * Microsoft Windows NT Server 4.0 SP3
 * Microsoft Windows NT Server 4.0 SP4

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This article was previously published under Q222604



IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry



SYMPTOMS
If the target directory of a Dfs volume is modified, clients do not become aware of the change for a whole week, unless they are restarted.

It takes a week because the Cached Dfs Referral Expiration time is one week. In some versions of Dfs, this value is hard-coded.



CAUSE
As documented in the release notes of Dfs 4.1, the "Cached Dfs referral expiration has been extended from 5 minutes to 1 week, to improve response times and reduce load on the root server." This value is hard-coded, and cannot be modified by the user in the base release of Dfs 4.1.

In Dfs 4.0, the cached Dfs referral expiration time was hard-coded to five minutes. This ensures that changes are communicated promptly to clients, but it can generate significant amounts of Dfs-related network traffic.

In Dfs 4.1, the cached Dfs referral expiration time was changed to a hard-coded value of one week. This minimizes the amount of Dfs-related network traffic, but changes to Dfs referrals will not be communicated to clients for one week, unless the Dfs clients are restarted.

In networks where Dfs references are changed on a regular basis, the new expiration time of one week is too long for clients to efficiently reflect the changes.



RESOLUTION
A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Windows NT 4.0 service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. 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;EN-US;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 typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English-language version of this fix should have the following file attributes or later:   Date      Time                 Size    File name     Platform -  98/10/28  21:33                 62,096 Dfs.sys       (x86) 98/10/28 21:34                106,576 Dfs.sys       (Alpha)

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

After applying the fix and before restarting the computer, add the following value to the registry to specify the value for the cached Dfs referral expiration time:

 Start Registry Editor (Regedt32.exe). Locate the following key in the registry: 

HKEY_LOCAL_MACHINE\Software\Microsoft\DfsHost\volumes

NOTE: The above registry key is one path; it has been wrapped for readability. On the Edit menu, click Add Value, and then add the following registry value:

Value Name: TimeToLiveInSecs

Data Type: REG_DWORD

Value: cached Dfs referral expiration time in seconds

Default: 604800 seconds (one week)

 Quit Registry Editor.

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WORKAROUND
To work around this problem, restart the Dfs clients.

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STATUS
Microsoft has confirmed that this is a problem in Windows NT 4.0.

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MORE INFORMATION
You should choose a value for TimeToLiveInSecs that is appropriate for your network.

If your Dfs configuration is stable, a large value is recommended to reduce the amount of Dfs-related traffic to a minimum. In such static Dfs networks, the default value of one week may be perfectly appropriate.

You should only need to consider configuring a smaller value if your Dfs configuration is so volatile that the frequency of workstation restarts required to access the correct locations through Dfs becomes disruptive to normal production work.

The amount of Dfs-related network traffic is directly proportional to the number of Dfs clients on your network -- doubling the number of clients will double the traffic.

Furthermore, the amount of Dfs-related network traffic is inversely proportional to the value chosen for TimeToLiveInSecs -- halving this value will double the traffic.

These points should be considered carefully before you modify TimeToLiveInSecs.

It is also recommended that you monitor network traffic volumes after reducing the value of TimeToLiveInSecs, using Network Monitor for example, to ensure that the amount of Dfs-related traffic is not excessive, and is not impacting network performance and throughput.

Additional query words: 4.00

Keywords: kbbug kbQFE KB222604

Technology: kbWinNT400search kbWinNTS400search kbWinNTS400sp3 kbWinNTS400sp4 kbWinNTsearch kbWinNTSsearch

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