High CPU usage occurs for six seconds on a Windows Server 2003-based computer that has multiple network adapters

You have a Windows Server 2003-based computer that has multiple network adapters. On this computer, CPU usage increases to 100 percent for about six seconds when the system tries to resolve NetBIOS names by using the LmHosts file. On a multi-core or multiprocessor system, the CPU usage on one CPU increases to 100 percent for about six seconds, and the CPU usage on other CPUs is also abnormally high. This situation usually occurs when many concurrent accesses occur to some shared resources and may occur repeatedly.

This problem occurs because of a race condition. An endless loop may occur in the following scenario:

• Multiple network name resolutions are performed on each adapter.
• Some name resolutions are canceled after one of them succeeds.
• A lookup into the LmHosts file is performed.

In this scenario, the lookup enters a dead loop that can only be ended by a time-out. This time-out is configured in a registry entry. By default, this time-out is set to six seconds.

Note A computer that has multiple network adapters is also known as a multi-homed computer. This problem is seen when one of the adapters on a multi-homed computer was a "Microsoft Loopback Adapter." This configuration may be one reason for the race condition that is mentioned in the Cause section.

To verify that you are experiencing this problem, we recommend that you disable LmHosts lookup as a troubleshooting test. If this problem no longer occurs after you disable LmHosts lookup, you can be certain that you are experiencing this problem.

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 2003 Service Pack 1 or Windows Server 2003 Service Pack 2 installed on the computer. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Restart requirement

You have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

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 2003 with Service Pack 1, x86-based versions

Windows Server 2003 with Service Pack 2, x86-based versions

Windows Server 2003 with Service Pack 1, Itanium-based versions

Windows Server 2003 with Service Pack 2, Itanium-based versions

Windows Server 2003 with Service Pack 1, x64-based versions

Windows Server 2003 with Service Pack 2, x64-based versions

Windows XP Professional x64 Edition with Service Pack 1

Windows XP Professional x64 Edition with Service Pack 2

Workaround 1

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: To reduce the effect of this problem, you can use an LmhostsTimeout registry entry to set the time-out for the NetBIOS name resolution. To do this, follow these steps:

1. Click Start, click Run, type regedit, and then press ENTER.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\netbt\parameters
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type LmhostsTimeout, and then press ENTER.
5. Right-click LmhostsTimeout, and then click Modify.
6. Click Decimal under Base.
7. In the Value data box, type an appropriate value, and then click OK.
8. Exit Registry Editor.

The value that you specify for this registry entry represents the time-out value in milliseconds. The minimum for this value is 1000 (1 second). You can set the time-out to a shorter period to reduce the duration of the CPU upsurge.

For more information about this registry setting, click the following article number to view the article in the Microsoft Knowledge Base:

Workaround 2

You can also disable LmHosts resolution to work around this problem. To do this, follow these steps:

1. Open Network Connections in Control Panel. To do this, click Start, click Settings, click Control Panel, and then double-click Network Connections.
2. Right-click the appropriate network connection, and then click Properties.
3. Select Internet Protocol (TCP/IP), and then click Properties.
4. Click Advanced.
5. On the WINS tab, click to clear the Enable LMHOSTS lookup check box.
6. Click OK three times.

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

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

Technical support for x64-based versions of Microsoft Windows

If your hardware came with a Microsoft Windows x64 edition already installed, your hardware manufacturer provides technical support and assistance for the Windows x64 edition. In this case, your hardware manufacturer provides support because a Windows x64 edition was included with your hardware. Your hardware manufacturer might have customized the Windows x64 edition installation by using unique components. Unique components might include specific device drivers or might include optional settings to maximize the performance of the hardware. Microsoft will provide reasonable-effort assistance if you must have technical help with a Windows x64 edition. However, you might have to contact your manufacturer directly. Your manufacturer is best qualified to support the software that your manufacturer installed on the hardware. If you purchased a Windows x64 edition such as a Windows Server 2003 x64 edition separately, contact Microsoft for technical support.

For product information about Windows XP Professional x64 Edition, visit the following Microsoft Web site: For product information about x64-based versions of Windows Server 2003, visit the following Microsoft Web site: