The smallest logical unit of replication is a suffix, also known as a naming context. The term suffix arises from the way the base DN for the naming context is a suffix for all DNs in that context. For example, the suffix dc=example,dc=com contains all directory entries in the Example.com naming context.
The replication mechanism requires one suffix to correspond to one database. The unit of replication applies to both suppliers and consumers. Therefore, two suffixes on a master replica cannot be replicated to one suffix on a consumer replica, and vice versa.