A Global Catalog (GC) contains a forest composed of several domains. The GC incorporates the DITs for all the domains into a single, enterprise-wide super directory.
When directory users connect to a Teradata Vantage system or Unity server across domains that do not talk directly to each other, you can configure the LdapServerName property to specify a GC server local to the connection, even if the location is outside the domain inhabited by the user.
In an Active Directory forest, the GC normally registers itself in the DNS, using the form:
_gc._tcp.root_domain
where root_domain is the name of the super-domain that owns the GC.