Global catalog

It is a service responsible for maintaining information about the objects and serving the requests made by the users by providing the location of the object.

Global Catalog runs on the port number 3268.

All types of queries are first heard on this port number and forward the query to port no.389 (LDAP’s).
Maintains the complete information about the objects within the same domain and partial information about other domains.

GC communicates to infrastructure master.

If DC & ADC are located in the same location only one GC is enough.

If the DC&ADC are located remotely to avoid network traffic we need to configure ADC as GC

Infrastructure master contacts global catalog for obtaining the updates about user & group membership and universal group membership.

The primary functions of GC

To maintain universal group membership information, to easily locate the objects with in the AD.:

Configuring a Global catalog server. 

Either on ADC or on Child DC
>Start >program>admin tools> ADSS
> expand sites >default first site>server>
On NTDS right click> properties
>check the box Global Catalog.