Replication within sites requires little or no planning because it is fully automatic. However, when you have multiple sites, the following steps can be used to plan how replication occurs between them:
1.
Identify sites that are well connected through backbones, and create low-cost site links between these sites.
2.
Identify sites that are all connected to each other with a comparable transport, and create medium-cost site links between them — for example, full mesh links (remote sites that are connected over telecommunication links), frame relay cloud links (a point-to-point system that uses a private virtual circuit), medium area network (MAN) links with T1 connections.
3.
Identify remaining WAN links.
4.
Create a site link for each pair of sites that cross a WAN link.
5.
Create a schedule that meets user needs.
Avoid high-frequency times. Site links must have windows of time in common that are available for routing.
For information about planning sites and site topology for Active Directory, see "Designing the Active Directory Structure" in the Deployment Planning Guide .
Top Of Page
Managing Site Links
Connection objects are created automatically by the KCC for replication both within a site and between sites. For connection objects to be created between two sites, however, you must manually create a link that connects the two sites. These links, implemented through site link objects in Active Directory, identify the transport protocol and scheduling required to replicate between two sites. Administrators use Active Directory Sites and Services to create the site links, and the KCC creates the connections accordingly when it generates the intersite topology.
Site link objects can be created in two transport-specific containers within the Inter-Site Transports container in Active Directory Sites and Services. By creating the link in one or the other container, you associate the link with the respective replication transport. The Inter-Site Transports container is a child of the Sites container, and it also has child containers:
•
The IP container, which contains site link objects that use RPC over IP synchronous replication transport.
•
The SMTP container, which contains site link objects that use SMTP over IP asynchronous replication transport.
When the KCC configures the connection objects for replication between sites, it takes the settings on the site link object into account to create the best connection. For example, one of the site link settings is the cost of the connection. When it has a choice, the KCC chooses a remote site whose link has the lowest cost when it forms connections.
For IP transport, a typical site link connects only two sites and corresponds to an actual WAN link. An IP site link connecting more than two sites might correspond to an ATM backbone that connects, for example, more than two clusters of buildings on a large campus or connects several offices in a large metropolitan area that are connected by leased lines and IP routers.
A site can be connected to other sites by any number of site link objects. Each site in a multi-site directory must be connected by at least one site link. Otherwise, it cannot replicate with domain controllers in any other site, so the directory is disconnected. Therefore, if there is more than one site in the forest, you must configure at least one site link.
Figure 6.6 shows two sites that are connected by one site link. A single domain has domain controllers in both sites. When topology generation occurs, connection objects between bridgehead servers in the site are created by the KCC and replication occurs according to the settings on the site link.
Cc961783.DSBH18(en-us,TechNet.10).gif
Figure 6.6 Two Sites That Are Connected by a Site Link
Figure 6.7 shows three sites connected by two site links. By default, site links are transitive. Therefore, replication
