What is Global Catalog ? The global catalog is a distributed data repository that contains a searchable, fractional representation of every object in every domain in a multi domain Active Directory Domain Services (AD DS) forest. The global catalog is stored on domain controllers that take been designated as global catalog servers and is distributed through multimaster replication. Searches that are directed to the global catalog are faster because they do not involve referrals to dissimilar domain controllers.

Hither are 3 ways how you can quickly detect out all your Global catalog servers in Active Directory domain in Windows Server 2012 R2:

By using dsquery:

C:\>dsquery server -isgc -domain  "advertizement.contoso.com" # Result "CN=HQDC1,CN=Servers,CN=Default-Commencement-Site-Name,CN=Sites,CN=Configuration,DC=ad,DC=contoso,DC=com" "CN=HQDC2,CN=Servers,CN=Default-Starting time-Site-Name,CN=Sites,CN=Configuration,DC=advert,DC=contoso,DC=com" "CN=AWSDC1,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=ad,DC=contoso,DC=com"

By using nslookup:

C:\>nslookup gc._msdcs.ad.contoso.com # RESULT 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa primary proper name server = 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0. 0.0.0.0.0.0.0.ip6.arpa responsible mail service addr = (root) serial = 0 refresh = 28800 (8 hours) retry = 7200 (2 hours) elapse = 604800 (7 days) default TTL = 86400 (1 day) Server: UnKnown Address: ::1  Name: gc._msdcs.ad.contoso.com Addresses:172.18.2.224 x.0.144.163 172.18.ii.229

Besides the last option to discover out quickly is via GUI in your Windows Server 2012 R2 DC in few steps:

  1. Open Active Directory Sites and Services.
  2. In the console tree, expand the Sites container, aggrandize the site of the domain controller you lot want to check, expand the Servers container, and then expand the Server object.
  3. Correct-click the NTDS Settings object, then click Properties.
  4. On the General tab, if the Global Catalog box is selected, the domain controller is designated as a global catalog server.

In instance you are interested how to Add or Remove Global Catalog – here is KB Article – Add and Remove Global Catalog.