DC與GC的區別
DC是Domain Controller
GC是Global Catalog
GC是做什麼的, 有什麼特點詳見下面的話:
In a multi-domain forest the Active Directory database becomes partitioned. That is, each domain maintains a list of only those objects that belong in that domain. So, for example, a user created in Domain A would be listed only in Domain A's domain controllers. Global catalog (GC) servers are used to provide a global listing of all objects in the Forest. The Global catalog is held on domain controllers configured as global catalog servers. Global Catalog servers replicate to themselves all objects from all domains and hence, provide a global listing of objects in the forest. However, in order to minimize replication traffic and to keep the GC's database small, only selected attributes of each object are replicated. This is called the partial attribute set (PAS). The PAS can be modified by modifying the schema and marking attributes for replication to the GC.
簡單來說, 多個域的情況下, 每個域都會有自己的DC, DC中維護自己域當中的對象. 當需要跨域查詢對象的時候, 一個個的查詢DC是不恰當的, Active Directory採用的方式是建立一個Global Catalog(GC), 查詢一個對象的時候最保險的方法就是查詢GC. 它維護着一個列表, 存儲着各個域的所有對象. 但是爲了讓GC的數據庫小一些, 其中就只存儲某些必要的屬性. 所以在查詢GC的時候, 返回的對象並不包含所有的屬性.
可以在command prompt中使用如下的命令來測試一下從DC和GC索取對象時的結果差異.
•連接DC: ldifde -f output.txt -r ("cn=<username>")
•連接GC: ldifde -f output.txt -r ("cn=<username>") -t 3268
明顯GC返回的結果中屬性要少很多, 比如Title和Department. 因爲默認情況下這兩個屬性的In Global Catalog爲false.
http://en.wikipedia.org/wiki/Active_Directory
http://msdn.microsoft.com/en-us/library/ms675490%28VS.85%29.aspx
http://msdn.microsoft.com/en-us/library/ms680037%28VS.85%29.aspx
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