A site is a set of IP subnets connected by a highly reliable and fast link (usually a LAN). Site structure mirrors the location of user communities. Sites have two main roles: to facilitate authentication and the replication of data between sites. Active Directory replicates information in two ways: intrasite (within a site) and intersite (between sites).
For optimum network response time and application availability, place at least one domain controller in each site or two domain controllers in each domain.
Intersite replication is replication that occurs between sites.
A site link is a logical, transitive connection between two or more sites that mirrors the network links and allows replication to occur.
Bridgehead servers are the contact point for exchange of directory information between sites. When two sites are connected by a site link, the KCC automatically selects bridgehead servers. You can designate bridgehead servers manually, called "preferred" bridgehead servers.
A site link bridge is the linking of more than two sites for replication using the same transport. When more than two sites are linked for replication and use the same transport, by default, all of the site links are "bridged" in terms of cost, assuming the site links have common sites. If site link transitivity is enabled, which it is by default, creating a site link bridge has no effect. Therefore, it is seldom necessary to create site link bridges.
A global catalog server is a domain controller that stores a full copy of all objects in the directory for its host domain and a partial copy of all objects for all other domains in the forest. For optimum network response time and application availability, designate at least one domain controller in each site as the global catalog server. To optimize replication in a multiple site environment, you might need to consider adding global catalogs for specific sites.
Universal group membership caching, a new feature in Windows Server 2003, allows a site that does not contain a global catalog server to be configured to cache universal group memberships for users who log on to the domain controller in the site.
An application directory partition is a directory partition that is replicated only to specific domain controllers running Windows Server 2003. Application directory partitions are usually created by the applications that use them to store and repli¬cate data.
Replmon.exe: Active Directory Replication Monitor, Repadmin.exe: Replication Diagnostics Tool, and Dsastat.exe are provided for monitoring and troubleshooting replication. To use these tools, you must first install the Windows Support Tools on your computer.
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