This article was previously published under Q326040
Important This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows registry
This step-by-step article describes how to improve authentication throughput on a computer that is running Microsoft Internet Security and Acceleration (ISA) Server.
If the computer uses NTLM or Basic authentication for many Web clients, you may experience poor performance. This problem does not occur when authentication is turned off.
You can improve the authentication throughput by increasing the number of concurrent authentication calls that are in progress at one time between the ISA Server computer and the domain controller.
Add a registry key
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.
Follow these steps to increase the number of concurrent authentication calls in progress at one time between the ISA Server computer and the domain controller.
Start Registry Editor. To do this, click Start, click Run, type Regedt32.exe, and then click OK.
On the Edit menu, click Add Value, and then add the following registry information (where 10 represents the heaviest loads):
Value Name: MaxConcurrentApi Data Type: REG_DWORD Value: between 0 and 10
Restart the NETLOGON service.
Note When you increase the value of the MaxConcurrentApi entry to a value that is greater than 5, make sure that you monitor the number of requests that are sent to the domain controller. To do this, install the update that is described in the following Knowledge Base article on the servers:
928576 New performance counters for Windows Server 2003 let you monitor the performance of Netlogon authentication
This update enables you to track the use of the Netlogon calls.
If you have a computer that is running Microsoft Windows 2000 Advanced Server, you can use the Network Load Balancing component (previously known as WLBS) of Windows 2000 Advanced Server to distribute incoming access requests among multiple IAS servers. This helps the server perform better when network traffic is high.
To load balance the Web requests and authentication and to increase performance, you can also use more ISA Server computers in an array.
For more information about a similar problem that is experienced on an Internet Authentication Server (IAS) computer, click the following article number to view the article in the Microsoft Knowledge Base:
246118 How to configure your IAS server for a very large number of authentication requests
Microsoft Forefront Threat Management Gateway, Medium Business Edition, Microsoft Windows 2000 Server, Microsoft Windows 2000 Advanced Server, Microsoft Internet Security and Acceleration Server 2000 Service Pack 1, Microsoft Internet Security and Acceleration Server 2000 Standard Edition, Microsoft Windows Server 2003, Standard Edition (32-bit x86), Microsoft Internet Security and Acceleration Server 2004 Standard Edition, Microsoft Internet Security and Acceleration Server 2006 Standard Edition