Posts Tagged ‘Global Catalog’

By Default a Global Catalog is created automatically on the initial Domain Controller in the forest. It stores a full replica of all the objects in the directory for its host domain and a partial replica of all objects contained in the directory of every other domain in the forest. The replica is partial because it stores some, but not all, of the property values for every object in the forest.

The Global Catalog performs two key directory roles:

–  It enables network logon by providing universal group membership information to a domain controller when a logon process is initiated.

–  It enables finding directory information in the entire forest regardless of which domain in the forest actually contains the data.

When a user logs in to the network, the global catalog provides universal group membership information for the account sending the logon request to the domain controller. If there is only one domain controller in the Domain, the domain controller and the global catalog are the same server. If there are multiple domain controllers in the network, the global catalog is hosted on the domain controller configured as such. If a Global Catalog is not available when a user initiates a network logon process, the user is only able to log on to the local computer.

Note: If a user is a member of the Domain Admins group, then they will be able to log on to the network even when the Global Catalog is not available.

The Global Catalog is designed to respond to queries about objects anywhere in the forest with maximum speed and minimum network traffic, because a single Global Catalog contains information about objects in all domain in the forest, a query about an object can be resolved by a global catalog in the domain in which the query is initiated. Thus finding the information in the directory does not produce unnecessary query traffic across domain boundaries.

You can optionally configure any domain controller to host a global catalog, based on your Company’s requirements for servicing logon requests and search queries.

After Additional domain controllers are installed in the domain, you can change the default location of the global catalog to another domain controller using the Active Directory Sites and Services.




A global catalog server is a domain controller that stores two forest-wide partitions, schema and configuration, a read/write copy of the partition from its own domain, and also a partial replica of all other domain partitions in the forest. These partial replicas contain a read-only subset of the information in each domain partition.


How does replication affect the global catalog server?

When a new domain is added to a forest, the information about the new domain is stored in the configuration partition, which is replicated to all domain controllers, including global catalog servers, through normal forest-wide replication. Then each global catalog server becomes a partial replica of the new domain by contacting a domain controller for that domain and obtaining the partial replica information. The configuration partition also contains a list of all global catalog servers in the forest and provides this information to the domain controllers. Global catalog servers register special DNS records in the DNS zone that correspond to the Forest Root domain. These records, which are registered only in the Forest Root DNS zone, help clients and servers locate global catalog servers throughout the forest.