Understanding Operations Master Roles

As I mentioned earlier, all domain controllers are nearly equal in Active Directory—that is, any one of them can be updated and can replicate changes to the others. This decentralization is in direct contrast to Windows NT 4.0-style domains, which had only one PDC that accepted directory object modifications and any number of BDCs that held read-only copies of the accounts database. BDCs could authenticate users, but any changes to any attributes of domain accounts had to take place in direct communication with the PDC. Because the PDC pushed out copies of the accounts database, known as the SAM database, to the BDCs for a domain, this sort of replication was known as single-master replication because one master computer communicated changes to slaved, less-capable computers.

Enter Active Directory onto the scene, where there are effectively no distinctions between domain controllers in most operations. Unless your domain is functioning at the NT interim functional level (more on that in the migration section later in this chapter), all domain controllers for a domain can accept changes for data in their domain, and domain controllers have peers to which they replicate changes to those objects. This sort of setup typically is called multimaster replication because each domain controller acts as a master, passing changes to other domain controllers until those changes are replicated fully.

Replication is covered in detail in the next ...

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