As I explain in "Exchange 2000 SP2's DSAccess Component," DSAccess performs automatic topology detection to build a list of domain controllers (DCs) and Global Catalogs (GCs) that are suitable to provide directory services. However, at times you might want to select a specific DC or GC—for example, you might want to direct all network traffic to a particular server. With Exchange 2000 Server Service Pack 2 (SP2), you can define a list of preferred GCs or DCs for DSAccess to use.
To specify such a list, you need to modify the registry. (Remember that you modify the registry at your own risk; introducing errors in the registry can make your system unusable.) Open the registry and navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess\Profiles\Default subkey. For each DC or GC you want to put into the list, create a unique subkey and name the subkey using the format UserDCx or UserGCx, respectively. For example, name the subkey for your first DC UserDC1; name the subkey for your first GC UserGC1. For each new key, add the set of values that Table A shows.
You can also change the size and timeout of the DSAccess cache values by modifying the registry. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeDSAccess and add a new key called Instance0, then add the values that Table B shows.