Microsoft INF200.1x, Windows Server 2012 Fundamentals: Infrastructure - Windows Sites

   

What are sites?

Sites represent the physical network in a logical way

Sites in AD DS represent the physical structure, or topology, of your network. AD DS uses network topology information, which is stored in the directory as site, subnet, and site link objects, to build the most efficient replication topology between your domain controllers.

Initially there is only one site

When you add the Active Directory Domain Services server role to create the first domain controller in a forest, a default site (Default-First-Site-Name) is created in AD DS. As long as this site is the only site in the directory, all domain controllers and servers that you add to the forest are assigned to this site.

When should you create more sites?

Sites identify networks that have good network connectivity. By creating more sites, domain controllers and other servers that use AD DS can take advantage of this connectivity. This means sites can help with improving the efficiency of these activities.  

Sites are created due to the following reasons.

• Slow Links: A slow link separates part of the network. If two locations are connected by a slow link, you should configure each location as a separate AD DS site. A slow link typically is considered one that has a connection of less than 512 kilobits per second (Kbps). However, for AD DS design, consider a larger threshold value.
• User Locations: If a network location has a sufficient number of users for whom the inability to authenticate would be problematic, put a domain controller in the location to support authentication within the location. After you include a domain controller or other distributed service in a location that will support those users, you might want to manage Active Directory replication to the location or localize service use by configuring an Active Directory site to represent the location.
• Server Localization: You want to control service localization. By establishing AD DS sites, you can make sure that clients use domain controllers that are nearest to them for authentication, which reduces authentication latency and traffic on WAN connections. In most scenarios, each site will contain a domain controller (and often two for redundancy). However, you might configure sites to localize services other than authentication, such as DFS, BranchCache, and Exchange Server services. In this case, some sites might be configured without a domain controller present in the site.
• Replication: You want to control replication between domain controllers. There might be scenarios in which two well-connected domain controllers are allowed to communicate only at certain times of the day. Creating sites allows you to control how and when replication takes place between domain controllers.