Datasheet

Active Directory for Exchange Server 2007 9
By default, the entire forest has only one global catalog, and that is the first
domain controller installed in the first domain of the first tree. All others
must be configured manually. It is recommended to always add a second
global catalog for backup and load balancing. Furthermore, each domain
should have at least one global catalog to provide for more efficient Active
Directory searches and network logons.
Active Directory Sites
An Active Directory site is a group of computers that exists on one or more IP subnets. Com-
puters within a site should be connected by a fast, reliable network connection. Using Active
Directory sites helps maximize network efficiency and provide fault tolerance. DNS also uses
Windows sites to help clients find the closest domain controller to validate logon credentials.
Exchange Server 2007 makes extensive use of Active Directory information
on global catalog servers. For efficient communication, Exchange Server
2007 requires a local global catalog server.
Sites are created and configured using the Active Directory Sites and Services tool. No
direct relationship exists between Windows domains and sites, so a single domain can span
multiple sites, and a single site can span multiple domains.
One of the biggest mistakes administrators make is not defining all of the IP subnets
and assigning them to the appropriate sites. Failing to do this can block the installation of
Exchange Server 2007, causing mail-flow issues and client-connectivity problems.
Before deploying Exchange Server 2007, review the Active Directory site
configuration to ensure all IP subnets are defined and assigned properly.
Schema
A schema represents the structure of a database system—the tables and fields in that database
and how the tables and fields are related to one another. The Active Directory information is
also represented by a schema. All objects that can be stored in Active Directory are defined in
the schema.
Installing Active Directory on the first domain controller in a network creates a schema
that contains definitions of commonly used objects and attributes. The schema also defines
objects and attributes that Active Directory uses internally. When Exchange Server 2007 is
installed, Exchange setup extends the schema to support information that Exchange needs.
Updates to the schema require replication of the schema across the forest and to all domain
controllers in the forest. Additional information about how Exchange updates the schema
will be presented in Chapter 2, “Installing Exchange Server 2007.”