The Windows Server 2008 Terminal Services Session Broker service incorrectly balances the load among terminal servers after it runs for a while

Assume that you configure Windows Server 2008 Terminal Services Session Broker (TS Session Broker) by using DNS round robin. However, after some time, new sessions are redirected to only one server or to only a specific set of servers. This behavior occurs even though the load of other terminal servers on the network is low.

Additionally, after this problem occurs, events that resemble the following are logged in the session broker log (Tssdis.log):

4016: time GetMostSuitableServer: server name has too many (22) pending redirections. Devalvated for LB
4016: time GetMostSuitableServer: server name has too many (25) pending redirections. Devalvated for LB
4016: time GetMostSuitableServer: server name has too many (25) pending redirections. Devalvated for LB
3936: time GetMostSuitableServer: server name has too many (47) pending redirections. Devalvated for LB

Note The Tssdis.log file is located in the %windir%\system32\tssesdir directory.

A pending redirection occurs when a new user logs on to the farm of terminal servers, and TS Session Broker points the user to a particular terminal server before the logon process has finished. The session directory tracks the number of pending redirections for each terminal server, and then it increases the count when the TS Session Broker determines the target server. Additionally, the session directory decreases the count after the logon process is complete.

However, the TS Session Broker service incorrectly increases the count of pending redirections for disconnected terminal sessions, and it never decreases the count. Therefore, when the pending redirection count on a terminal server reaches its limit (16, by default), the TS Session Broker service no longer redirects new terminal sessions to this terminal server. Eventually, the number of available servers decreases to a small set or to only a single server.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must have Windows Server 2008 TS Session Broker installed.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

Windows Server 2008 file information notes

The MANIFEST files (.manifest) and MUM files (.mum) that are installed for each environment are listed separately. MUM and MANIFEST files, and the associated security catalog (.cat) files, are critical to maintaining the state of the updated component. The security catalog files (attributes not listed) are signed with a Microsoft digital signature.

For all supported x86-based versions of Windows Server 2008

For all supported x64-based versions of Windows Server 2008

To work around this problem, use one of the following methods.

Method 1

Restart TS Session Broker. This may temporarily resolve the problem. However, this problem recurs after several days.

Method 2

1. Click Start, click Run, type regedit in the Open box, and then press ENTER.
2. In Registry Editor, locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tssdis\Parameters
3. In the details pane, double-click LB_MaxNumberOfPendingRedirections.
   
   Note If the LB_MaxNumberOfPendingRedirections DWORD entry does not exist, you must create it. To do this, follow these steps:
   1. In Registry Editor, locate and then click the following registry subkey:
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tssdis\Parameters
   2. On the Edit menu, point to New, and then click DWORD Value.
   3. Type LB_MaxNumberOfPendingRedirections, and then press ENTER.
4. In the Value data box, type a number that is much larger than 16 (but less than 65535), and then click OK.
5. Exit Registry Editor

Important This method may have the following serious consequences:

• It may overload a terminal server with logon requests.
• It may disrupt or disable the network's load-balancing.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about TS Session Broker, visit the following Microsoft Web site:To enable TS Session Broker logging, follow these steps:

1. Stop the TS Session Broker service.
2. In Registry Editor, locate the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tssdis\Parameters
3. Create the TraceOutputMode DWORD registry entry, and then set its value to 3.
4. Start the TS Session Broker service.

Additional file information for Windows Server 2008

Additional files for all supported x86-based versions of Windows Server 2008

Additional files for all supported x64-based versions of Windows Server 2008