Understanding Sites and Replication
Understanding how sites and replication work is a prerequisite for being able to con?figure and manage sites and replication for Active Directory. This lesson introduces you to how sites and replication work to represent the physical structure of Active Directory.
Recall from Chapter 1, “Introduction to Active Directory,” that a site is a set of Internet Protocol (IP) subnets connected by a highly reliable and fast link, usually a local area network (LAN). A subnet is a subdivision of an IP network. Typically, networks with a bandwidth of at least 512 kilobits per second (Kbps) are considered fast networks. An available bandwidth of 128 Kbps and higher is sufficient for designating a site. Available bandwidth is the amount of bandwidth that is actually available for use during peak traffic after normal network traffic is handled.
In Active Directory, site structure mirrors the location of user communities. Site struc-ture corresponds to the physical environment and is maintained separately from the logical environment, which is represented by the domain structure. Because sites are independent of the domain structure, a single domain can include a single site or mul-tiple sites, and a single site can include multiple domains.
The main purpose of a site is to physically group computers to optimize network traffic. Sites act to confine authentication and replication traffic to only the devices within a site. Because network traffic is prevented from unnecessarily crossing become mcitp slow wide area network (WAN) links, WAN traffic is limited. Sites have two main roles-.
To facilitate authentication, by determining the nearest domain controller when a user logs on from a workstation
To facilitate the replication of data between sites
Because site names are used in the records registered in the Domain Name System (DNS) by the domain locator, they must be valid DNS names. Recall that valid DNS names consist of the standard characters A-Z, a-z, 0-9, and hyphen (-).
In Active Directory, all of the objects in the forest are represented in the directory tree, a hierarchy of objects and containers. For each forest, the directory tree is partitioned to allow sections to be distributed to domain controllers in different domains within the forest. Each domain controller stores a copy of a specific part of the directory tree, called a directory partition. A directory partition is also known as a naming context. The copy of the directory partition is called a replica. A replica contains all attributes for each directory partition object and is readable and writable. In the Microsoft Windows Server 2003 operating system, the replication process ensures free test questions that changes made to a replica on one domain controller are synchronized to replicas on all other domain controllers within the domain.
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