Replication Topology Generation
One of the keys to understanding AD DS replication is understanding how the replication topology is created. By default, the process of creating the replication topology is handled automatically by AD DS. Although the replication topology can be manually configured, in most cases the default configuration by the system is the best option.
In order for the replication topology to be successfully created, the following components must be in place:
Routable IP infrastructure. In order to configure intersite replication, you need to configure AD DS sites and map the sites to IP subnet address ranges. Domain controllers and client computers use this IP subnet to site mapping when locating domain controllers.
DNS. AD DS ...