What is KCC and Global Catalog
KCC is an acronym for Knowledge Consistency Checker. The KCC is responsible for the replication process in our forest. KCC is a built-in process that is able to dynamically adjust itself to the topology of our digital forest in order to most efficiently contain the data provided by new domain controllers. These connections between domain controllers always arrange themselves as two-way circuits, meaning, obviously, that the replication process goes two ways. By default the replication is performed every 900 seconds (15 Minutes). – However, it is possible to change it.
Here’s the process visualized:
In short, the Global Catalog contains all forest data. With Global Catalog we are performing a quick login to our machine and we are retrieving information from the active directory quickly. Now, you might be asking yourself, why? What’s the point of using Global Catalogue? Well, to demonstrate the usefulness of the Global Catalog in a real life example let’s say we have 2 DC on our site,
DC01 = Global Catalog is enabled
DC02= Global Catalog is not allowed.
Once we try to query AD by conducting a search using “Meir P” the process will be performed directly to DC01, because only on DC01 is the Global Catalog enabled. Now let’s enable the global catalog in DC02, once we try to perform a search the query performs against two DC’s the outputs will be quicker.
Highlights & Conclusions: There is no disadvantage to allowing Global Catalog. The Global Catalog contains all object data, such as attributes and classes. Also, I hope you didn’t forget – the replication between Globe Catalog is performed using KCC, so make sure you have GB enabled on all your sites!