I know the ans but i am not going to tell you guyz.
See related links.
The ports used by GC is as follows GLOBAL CATALOG 3268 GLOBAL CATALOG 3269 https(secure)
Global catalog server
Global catalog server.
The global catalog server.
Universal group caching. This feature allows users to log on to a domain at a remotesite without having a global catalog server present in that site.
Universal group caching. This feature allows users to log on to a domain at a remotesite without having a global catalog server present in that site.
Universal group caching. This feature allows users to log on to a domain at a remotesite without having a global catalog server present in that site.
It is required when adding the first domain controller in a forest
Global catalog...The global catalog provides quick object access to universal groups and UPNs within an AD forest.
Universal group membership caching, page 81 of your ITT 2008 server R2 handbook.
A Microsoft Active Directory (AD) Server can only answer directly queries about objects which are in its domain. When using LDAP, you may want to get information about objects in other domains or subdomains within the organization. Most AD servers, therefore, cache information from other AD servers using a facility called the Global Catalog. To query the Global Catalog on an AD server which is also a Global Catalog Server (GCS) you must connect to the GCS port, 3268 instead of to the default LDAP port.