Active Directory Domain Services (AD DS)
Lesson 14

Active Directory sites

By Sai Kurada
September 17, 2023
Active Directory sites are a logical construct within an Active Directory (AD) environment that allow administrators to define and manage the physical topology of their network. Sites are used to optimize AD replication and authentication traffic between domain controllers (DCs) in different geographic locations.
Here are some key points about Active Directory sites:

  • A site represents a physical location in a network, which can be a single building, a campus, or even an entire city.

Site Components:
  • A site contains one or more IP subnets that are associated with the physical location. Each site has at least one domain controller, known as the "preferred bridgehead server," that is responsible for replication with other sites.

Optimizing Replication:
  • Sites are used to control the replication of AD data between domain controllers. Replication traffic is reduced by designating specific domain controllers as bridgehead servers responsible for handling replication traffic to and from other sites.

Costed Site Links:
  • Site links represent the network connections between sites. Each site link has a cost associated with it, which determines the preferred path for replication. Lower costs indicate faster, more reliable connections.

Inter-Site Replication Schedule:
  • Administrators can configure when replication occurs between sites. By default, replication between sites occurs every three hours.

Intrasite Replication:
  • Replication within a site happens automatically and frequently (usually within seconds) to ensure that changes are quickly propagated to all domain controllers in the same site.

Global Catalog Servers:
  • Each site can have one or more Global Catalog (GC) servers. Having GC servers in multiple sites can improve the efficiency of user authentication and searches in a multi-site environment.

Site Links and Bridgehead Servers:
  • Bridgehead servers are responsible for replicating changes between sites. Site links define the connections between sites and the schedule for replication.

  • Subnets are associated with sites to help AD-joined devices identify their location. This helps clients select the nearest domain controller for authentication and reduces WAN traffic.

Disaster Recovery Planning:
  • Properly configured sites are crucial for disaster recovery planning. They help ensure that essential services and data are available in the event of a failure in one part of the network.

Site Topology Design:
  • Site topology should reflect the physical network topology to ensure that replication and authentication traffic are routed efficiently.

Active Directory sites play a critical role in maintaining a well-functioning and efficient network, particularly in geographically distributed environments. Properly configuring and managing sites is essential for optimizing AD replication and ensuring reliable authentication services.