Replication topology is the set of connections by which domain controllers in a forest synchronize the directory partition replicas that they have in common. Replication topology is created on the basis of information stored in Active Directory.
The Knowledge Consistency Checker (KCC) is a built-in process that runs on all domain controllers and creates the replication topology for the forest. By default, the KCC runs at 15-minute intervals and designates the replication routes between domain controllers on the basis of the most favorable connections that are available at the time. The KCC creates replication connections between domain controllers in the same site automatically. When you have more than one site, you configure links between the sites; the KCC can then create the connections automatically between the sites as well.