What is Global Catalog ? The global catalog is a distributed data repository that contains a searchable, partial 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 have 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 different domain controllers.
By using dsquery:
C:\>dsquery server -isgc -domain "ad.contoso.com" # RESULT "CN=HQDC1,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=ad,DC=contoso,DC=com" "CN=HQDC2,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=ad,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 126.96.36.199.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa primary name server = 188.8.131.52.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0. 0.0.0.0.0.0.0.ip6.arpa responsible mail addr = (root) serial = 0 refresh = 28800 (8 hours) retry = 7200 (2 hours) expire = 604800 (7 days) default TTL = 86400 (1 day) Server: UnKnown Address: ::1 Name: gc._msdcs.ad.contoso.com Addresses:172.18.2.224 10.0.144.163 172.18.2.229
As well the last option to find out quickly is via GUI in your Windows Server 2012 R2 DC in few steps:
- Open Active Directory Sites and Services.
- In the console tree, expand the Sites container, expand the site of the domain controller you want to check, expand the Servers container, and then expand the Server object.
- Right-click the NTDS Settings object, and then click Properties.
- On the General tab, if the Global Catalog box is selected, the domain controller is designated as a global catalog server.
In case you are interested how to Add or Remove Global Catalog – here is KB Article – Add and Remove Global Catalog.