Configuring Cached Dfs Referral Expiration Time in Dfs 4.1

ID: Q222604

The information in this article applies to:

Microsoft Windows NT Server versions 4.0 SP3, 4.0 SP4

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

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 that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific 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 on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

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: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

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.

WORKAROUND

To work around this problem, restart the Dfs clients.

STATUS

Microsoft has confirmed this to be a problem in Windows NT 4.0.

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 : kbbug4.00 kbfix4.00
Version : winnt:4.0 SP3,4.0 SP4
Platform : winnt
Issue type : kbbug