Increase the Number of NPS Concurrent Authentications

Updated: February 29, 2012

Applies To: Windows Server 2008, Windows Server 2008 R2, Windows Server 2012

You can use this procedure to increase the number of concurrent authentications between NPS and domain controllers when NPS is not installed on a domain controller.

If the NPS server is on a computer other than a domain controller and it is receiving a very large number of authentication requests per second, you can improve performance by increasing the number of concurrent authentications between the NPS server and the domain controller.

Incorrectly editing the registry can severely damage your system. Before making changes to the registry, you should back up any valued data on the computer.

Administrative Credentials

To complete this procedure, you must be a member of the Administrators group.

  1. Click Start, click Run, type regedit, and then press ENTER. Registry Editor opens.

  2. In Registry Editor, browse to the following key:


  3. Right-click Parameters, point to New, and then click DWORD (32-bit) Value.

  4. Replace the default text for the new key by typing the text MaxConcurrentApi, and then press ENTER.

  5. Right-click MaxConcurrentApi, and then click Modify. The Edit DWORD (32-bit) Value dialog box opens.

  6. In Value data, type a value between 2 and 5. Do not enter a value higher than 5, or NPS might place an excessive load on the domain controller. Click OK.

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