TechNet Articles

AD Replication Status Tool has 2 built-in buttons and tabs to switch within the tool to two TechNet articles containing information on Active Directory replication.

1. What is Replication Topology?

"What Is Active Directory Replication Topology?" explains what AD Replication Topology is. Topics covered are:

• Replication Within and Between Sites.
  • Discusses replication within a site and replication between sites.

• Technologies Related to Active Directory Replication Topology.
  • Discusses the technologies that interact with Active Directory replication.

• Active Directory Replication Topology Dependencies
  • Discusses dependencies that AD Replication Topology has.

2. How Replication Topology Works

"How Active Directory Replication Topology Works" explains in detail how AD Replication Topology and the different components that are part of Replication Topology work.

Topics covered are:

• Active Directory KCC Architecture and Processes
  • Discusses the Knowledge Consistency Checker (KCC) which generates the replication topology. 
  • KCC Architecture, Processes and components.
• Performance Limits for Replication Topology Generation
  • Discusses Active Directory topology generation performance limitations.   
• Goals of Replication Topology
  • Discusses the goals that are achieved by the KCC:
    • Connect every directory partition replica that must be replicated.
    • Control replication latency and cost.
    • Route replication between sites.
    • Effect client affinity.
• Topology-Related Objects in Active Directory
  • Active Directory stores replication topology information in the configuration directory partition. This topic discusses configuration objects that define the components required by the KCC to establish and implement the replication topology.
    • Site  and Subnet Objects
    • Server Objects
    • NTDS Settings Objects
    • Connection Objects
    • Site Link Objects
    • NTDS Site Settings Object
    • Cross-Reference Objects
• Replication Transports
  • Discusses the replication transports that provide the wire protocols required for data transfer
  • There are three levels of connectivity for replication of Active Directory information:
    • Uniform high-speed, synchronous RPC over IP within a site.
    • Point-to-point, synchronous, low-speed RPC over IP between sites.
    • Low-speed, asynchronous SMTP between sites.
• Replication Between Sites
  • Discusses replication between sites. 
  • Replication between sites transfers domain updates when domain controllers for a domain are located in more than one site. Intersite replication of configuration and schema changes is always required when more than one site is configured in a forest.
  • Replication between sites is accomplished by bridgehead servers, which replicate changes according to site link settings.
• KCC and Topology Generation
  • The KCC generates and maintains the replication topology for replication within sites and between sites by converting KCC-defined and administrator-defined (if any) connection objects into a configuration that is understood by the directory replication engine
  • By default, the KCC reviews and makes modifications to the Active Directory replication topology every 15 minutes to ensure propagation of data, either directly or transitively, by creating and deleting connection objects as needed.
  • The KCC recognizes changes that occur in the environment and ensures that domain controllers are not orphaned in the replication topology.
• Network Ports Used by Replication Topology
  • Discusses the network ports used by Replication Topology. 
  • Replication RPC-based replication uses dynamic port mapping. When connecting to an RPC endpoint during Active Directory replication, the RPC run time on the client contacts the RPC endpoint mapper on the server at a well-known port (port 135). The server queries the RPC endpoint mapper on this port to determine what port has been assigned for Active Directory replication on the server. This query occurs whether the port assignment is dynamic (the default) or fixed. The client never needs to know which port to use for Active Directory replication.

  • In addition to the dynamic port 135, other ports that are required for replication to occur are listed.

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