I've already mentioned a global catalog.
So what is a global catalog?
A global catalog is a partial, regionally searchable copy of all the objects in the forest.
It spreads up searches for objects that might be stored on domain controllers in a different domain
in the forest within a single domain.
The address database on each domain controller contains all the information about every object in the
domain.
However, only a subset of this information replicates on the global catalog servers in other domains
in the forest within a domain, a query for an object is directed to one of the domain controllers in
that domain.
But that query does not include results about objects in other domains in the forest For a query to
include results from other domains in the forest, you must query a domain controller that is a global
catalog server.
By default, the domain the domain controller in the forest root domain is the only hosted global catalog
server to enhance search and across domains in a forest, you should configure additional domain controllers
to each store a copy of the Global Catalog.
A global catalog does not contain all the attributes of each object.
Instead, the global catalog maintains the subset of attributes that are most likely to be useful in
gross domain searches.
These attributes include given name, display, name and male.
You can modify the set of attributes replicated to the global catalog by modifying the partial attribute
set or path in the schema.
Search in against a global catalog can be useful in many situations.
For example, when a server that is run an exchange server receives an incoming email, it needs to
search for the recipient's account so that it can decide how to route this mail this message by automatically
where in a global catalog the server can locate the recipient in a multiple domain environment.
In addition, when the user is signed into their Active Directory accounts, the domain controller that
performs the authentication must contact a global catalog to check for universal group memberships before
authenticating the user in a single domain.
You should configure all the domain controllers to hold a copy of the global catalog.
However, in a multiple domain environment, the infrastructure master should not be a global catalog
server unless all the domain controllers in the domain are also global catalog server.
So please remember again in a multiple domain environment, the infrastructure master should not be
a global catalog server unless all the domain controllers in the domain are also global catalog servers.
When you have multiple sites, you should also make at least one domain controller at each site a global
catalog server so that you are not dependent on other sites.
When you require global catalog queries, decide in which domain controllers to configure to hold a
copy of the global catalog depends on replication, traffic and network bandwidth.
Many organizations opt to make every domain controller a global catalog server.
But again, this domain controller should not be the infrastructure master.