Understanding Global Catalog Servers

By Author: fiona
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This lesson introduces you to the tasks involved in configuring global catalog servers. It also discusses when to MCSA 2003 exams designate a domain controller as a global catalog server and introduces you to the universal group membership caching feature.
After this lesson, you will be able to
Determine when to designate a domain controller as a global catalog server
Create a global catalog server
Remove a global catalog server
Enable the universal group membership caching logon feature

Recall from Chapter 1, "Introduction to Active Directory," that the global catalog is the central repository of information about objects in a tree or forest. By default, a global catalog is created automatically on the initial domain controller in the first domain in the forest, known as the global catalog server. A global catalog server 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. This storage strategy provides efficient searches without unnecessary referrals to other ...
... domain controllers.
The global catalog performs three key functions:
It enables a user to log on to a network by providing universal group membership
information to a domain controller when a logon process is initiated.
It enables finding directory information regardless of which domain in the forest actually contains the data.
It resolves user principal names (UPNs) when the authenticating domain controller does not have knowledge of the account.
If a global catalog is not available when a user in a universal security group logs on 70-291 practice test to a domain, the computer uses cached credentials to allow access if the user has logged on to the domain previously. If the user has not logged on to the domain previously, the user can log on only to the local computer, unless the universal group membership caching feature has been enabled.
Although the initial domain controller in a forest is designated as a global catalog server, you can configure any domain controller or designate additional domain controllers to serve this function.

You might want to continue using a global catalog in branch office locations if an application in a site is sending global catalog queries to port 3268. Universal group membership caching feature does not intercept calls made to port 3268.

If your organization uses Microsoft Exchange 2000 Server, you should try to place a global catalog server in each site that contains an Exchange server. This is because Exchange 2000 uses Active Directory as its directory service, and all mailbox names are resolved by queries through Active Directory to the global catalog server. In a large Exchange environment, a global catalog server might need to handle a large number of queries, so placing a global catalog server in each site that contains an Exchange server can ensure a+ certification that all queries are handled promptly.