A global catalog server is available to directory clients when Domain Name System (DNS) servers can locate it
as a global catalog server.
In which order do the following events need to occur before the catalog server is ready?
A) The Net Logon service on the domain controller has updated DNS with global-catalog-specific service(SRV)
resource records.
B) The isGlobalCatalogReady rootDSE attribute is set to TRUE.
C) The global catalog receives replication of read-only replicas to the required occupancy level.

A.
C then A, then B

B.
B then C, then A

C.
A then C, then B

D.
C then B, then A

Explanation:
initial answer : “C then B, then A Honestly not very sure on this one; couldn’t find anything on it” => false (but
he/she warned us! =))
no SRV record should be created before the replication is ok, and then isGlobalCatalogReady rootDSE attribute
is set to TRUE only when a SRV record is created
so repl=> SRV => attribute
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http://technet.microsoft.com/fr-fr/library/cc739901%28v=ws.10%29.aspx
Verify global catalog readiness
When a global catalog server has satisfied replication requirements, the isGlobalCatalogReady
rootDSE attribute is set to TRUE and the global catalog is ready to serve clients.
===============
http://technet.microsoft.com/de-de/library/how-global-catalog-servers-work%28v=ws.10%29.aspx
How the Global Catalog Works
[…]
Global Catalog Server Creation and Advertisement
By default, before a domain controller advertises itself as a global catalog server in DNS, the global
catalog contents must be replicated to the server. This process involves replication of a partial, read-only
replica of every domain in the forest except for the domain for which the new global catalog server is
authoritative. The duration of this process dependson how many domains the forest contains, the size of the
domains, and the relative locations of source and destination domain controllers. If multiple domains are in the
forest and if source domain controllers are locatedonly in distant sites, the process takes longer than if all
domains are in the same site or in only a few sites. When replication must occur between sites to create the
global catalog, replication occurs according to thesite link schedule.
Requirements for Global Catalog Readiness
By default, a global catalog server is not considered ready (the server advertises itself inDNS as a
global catalog server)until all read-only directory partitions have been fully replicatedto the new global
catalog server. The Global Catalog Partition Occupancy registry entry under HKEY_Local_Machine\System
\CurrentControlSet\Services\NTDS\Parameters determines the requirements for how many read-only directory
partitions must be present on a domain controller for it to be considered a global catalog server, from no
partitions (0) to all partitions (6).
For domain controllers that run Windows Server 2003or later, the default occupancy value requires that all
read-only directory partitions be replicated to theglobal catalog server before the Net Logon service
registers SRV resource records in DNS. For most conditions, this default provides the best option for
ensuring that a global catalog server provides a consistent view of the directory. In less common
circumstances, however, it might be useful to make the global catalog server available with an incomplete set
of partial domain directory partitionsfor example,when delay of replication of a domain that is not required by
users is jeopardizing their ability to log on.