The Directory Information Tree (DIT)

All data in a given Active Directory environment is stored in a database called the Directory Information Tree (DIT) or data store. Every Domain Controller maintains a partial copy of the data store containing all the relevant information for the domain the controller belongs to.

By default, the database is stored by domain controllers in C:\Windows\NTDS\ntds.dit and it has three main tables.

The Hidden Table

The hidden table contains only a single row with information used by Active Directory to configuration-related information in the data table. Most importantly, this table holds a pointer to the domain controller's NTDS Settings object in the data table.

The Data Table

Most of the data in the AD environment is stored in the data table. Every attribute defined in the Schema is represented by a column and every object has a row dedicated to it. The values of the object's attributes are stored in the cells under the corresponding columns and if the object does not have a particular attribute, then that cell is left empty.

Note

The large number of columns and the ability to add / remove new ones is one of the reasons why Microsoft does not use a classic relational database, since these are typically limited to a relatively small number of columns.

In addition to a column for each attribute, the data table contains a few special columns.

The first column is the distinguished name tag (DNT) which identifies each row (i.e. object) in the table. The DNT is not replicated which means that each object is likely to have a different DNT on different domain controllers. Furthermore, a domain controller is not allowed to reuse DNTs even after the object they refer to has been deleted. Since there can be at most DNTs, a domain controller may eventually be unable to create new objects.

The parent DNT (PDNT) column stores the DNT of the object's direct parent. When the object is moved, its PDNT is automatically update to reflect its new parent.

The NCDNT column contains the DNT of the naming contexts the object belongs to, which illustrates that directory partitions are simply logical divisions and are not reflected "physically" (i.e. by creating separate folders for them or something similar).

The Ancestors columns stores the DNTs of the all of the object's ancestors (from the root down to the object itself) which essentially represents the hierarchy.

Example: NTDS Database

DNT	PDNT	NCDNT	RDNType	RDN	Ancestors
1337	2	N/A	`dc=`	`local`	{2,1337}
1338	1337	2	`dc=`	`cybercorp`	{2,1337,1338}
7899	1338	N/A	`cn=`	`Configuration`	{2,1337,1338, 7899}
8946	7899	N/A	`cn=`	`Schema`	{2,1337,1338, 7899, 8946}
2898	8946	8946	`cn=`	`SAM-Account-Name`	{2,1337,1338, 7899, 8946, 2898}
1243	7899	7899	`cn=`	`Sites`	{2,1337,1338, 7899, 1243}
5449	1338	1338	`cn=`	`Users`	{2,1337,1338, 5449}
6345	1338	1338	`cn=`	`Computers`	{2,1337,1338, 6345}
3333	6345	1338	`cn=`	`PC01`	{2,1337,1338, 6345, 3333}