I've written before on noise reduction in the Windows security event log. I've also written to describe how object access auditing works. But, I still get questions on how to reduce noise from object access events. The other day I got that question, specific to Directory Service objects, on an internal discussion list so I thought I'd clean up the answer a bit and share it with the world. In general the same is true for any type of object, although there are a few more knobs to control for DS objects.
Object access audit is generated when the system access control list (SACL) on the object matches the access that was performed on ALL of the following conditions:
The specific auditing algorithm is discussed here.
So the way to reduce the number of audit events (566 on Windows Server 2003, 4662 on Windows Server 2008, or one of the new DS Change events on Windows Server 2008) is to cause one or more of those conditions to fail, except in the specific cases that you care about.
The SACL which will generate the most audit events is "Everyone:Success & Failure:All accesses" on the domain head with OI,CI (object inherit & container inherit flags) for all object types. This SACL matches all of the above conditions in all cases. (Incidentally I think that this is pretty close to the default SACL- with the exception of failures- for Windows 2000 Active Directory installations, and SACLs are not updated when DCs are upgraded from version to version. Windows Server 2003 has much more conservative SACLs for new installations of AD.)
To reduce noise, I offer the following suggestions, addressing each of the above conditions: