Searching the Global Catalog vs. Searching the Domain
The decision whether to search the Global Catalog or the domain is based on the scope of the search:
• When the scope of a search is the domain or an organizational unit, the query can be resolved within the domain partition by using an LDAP search.
• When the scope of a search is the forest, the query can be resolved within any partition by using a Global Catalog search.
Port 3268. This port is used for queries specifically targeted for the global catalog. LDAP requests sent to port 3268 can be used to search for objects in the entire forest. However, only the attributes marked for replication to the global catalog can be returned. For example, a user’s department could not be returned using port 3268 since this attribute is not replicated to the global catalog.
Port 389. This port is used for requesting information from the local domain controller. LDAP requests sent to port 389 can be used to search for objects only within the global catalog’s home domain. However, the requesting application can obtain all of the attributes for those objects. For example, a request to port 389 could be used to obtain a user’s department.
The Schema Manager is used to specify additional attributes (i.e ThumbnailPhoto, Department…) that should be replicated to each global catalog server. The attributes included in the global catalog are consistent across all domains in the forest.