Now that we have a general idea of how replication works, let's examine details of the replication transactions themselves. This information helps to diagnose replication problems. It also helps to make critical architectural decisions such as where to place specific domain controllers and how to select the proper inter-site polling frequency.
Multiple-master replication raises several challenges:
Data consistency. It is important that the replicas of each naming context match exactly on every domain controller after all updates have converged.
Redundant updates. Domain controllers should not waste time replicating updates that they have already received from the same replication partner.