Windows 2000 implements replication much differently than Windows NT 4. In Windows NT domain environments, replication was single-master, meaning that only one domain controller actually accepted updates – the PDC. In Windows 2000, the model is multi-master, meaning that any domain controller can update Active Directory. This presents some challenges in terms of tracking changes on the network and resolving conflicts that might occur, as I’ll discuss in a moment. However, along with the challenges that Windows 2000 Active Directory replication presents, it also presents an opportunity in that replication can finally be easily controlled, through the use of sites, site links, and schedules.
I could easily have devoted this entire article to only replication, since there is so much that takes place behind the scenes. Thankfully, what is most important to understand is a handful of concepts (albeit a rather large handful), most of which are rather straightforward. Lets begin by taking a look at how replication works.
In an Active Directory environment, all domain controllers do not contact one central domain controller for changes. Instead, they create relationships with one another which track which domain controllers are sources of replication changes for them. These relationships are called connection objects, and I’ll discuss how they work and how they are created shortly. Since every domain controller can accept updates, there is actually a distinction as to which domain controller made the original update. This update is called the originating update. Any update that is received on a DC as a result of replication is referred to as a replicated update.