You can improve authentication throughput between an ISA Server and a domain controller by increasing the number of concurrent authentication calls that are in progress:

1. Use Regedt32.exe to navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters.

2. On the Edit menu, Add Value name MaxConcurrentApi, as a REG_DWORD data type.

3. Set the data value to a number between 2 and 5.

4. Open a CMD prompt and type:

net stop netlogon
net start netlogon