Applies To: Windows Server 2008, Windows Server 2008 R2
You can use this registry setting to alter the number of concurrent authentications performed between the NPS server and a domain controller when NPS is not installed on a domain controller.
Incorrectly editing the registry might severely damage your system. Before making changes to the registry, you should back up any valued data on the computer.
If NPS is installed on a computer other than a domain controller and NPS 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.
To increase concurrent authentication
Add a new entry named MaxConcurrentApi to this registry key and assign to it a value from 2 through 5.