How to configure an ISA Server computer for a very large number of authentication requests

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.

1. Start Registry Editor. To do this, click Start, click Run, type Regedt32.exe, and then click OK.
2. Locate the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters
3. 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
4. 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: 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: