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:
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