What options exist for tracking Active Directory (AD) changes?

Polling-based solutions. At periodic intervals, a process connects to AD and requests all changes that have occurred since it last connected. You can find changes by checking uSNChanged attributes on objects. Microsoft provides the AD directory synchronization (DirSync) tool to perform this process for you. You can find more information on the polling approach at the following URLs:
- http://support.microsoft.com/?kbid=891995
- http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ad/ad/polling_for_changes_using_the_dirsync_control.asp?frame=true
- http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ad/ad/polling_for_changes_using_usnchanged.asp?frame=true

Real time notification solutions. With this method, a process registers itself with AD and requests to be notified as changes happen. This method offers a more up-to-date solution than polling-based methods, however the process receiving the changes must be able to keep up with the notification traffic. You can find information about real-time notification solutions at these URLs:
- http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ad/ad/change_notifications_in_active_directory.asp
- http://msdn.microsoft.com/library/default.asp?url=/library/en-us/ad/ad/example_code_for_receiving_change_notifications.asp