What algorithm does Secure Password Administrator (SPA) use to determine the nearest domain controll (NETIQKB42535)

What algorithm does Secure Password Administrator (SPA) use to determine the nearest domain controller to the IP address of the client?

How does Secure Password Administrator (SPA) determine the closest domain controller (DC) to the client machine?

Secure Password Administrator makes a call to the system function DsGetDcName using the client's IP address.  See the following link for more information on DsGetDcName:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ad/ad/dsgetdcname.asp

Notice the comments about the SiteName parameter:

If this parameter is NULL, DsGetDcName attempts to return a domain controller in the site closest to the site of the computer specified by ComputerName.  This parameter should be NULL, by default.

Formerly known as NETIQKB42535