| Platform SDK: Active Directory, ADSI, and Directory Services |
Object Identifiers (OIDs) are unique numeric values, issued by various "Issuing Authorities" to uniquely identify data elements, syntaxes, and various other parts of distributed applications. OIDs are found in OSI applications, X.500 Directories, SNMP, and other applications where uniqueness is important. OIDs are based on a tree structure, in which a superior issuing authority (such as the ISO) allocates a "branch" of the tree to a subauthority, who in turn can allocate sub-branches.
The LDAP protocol (RFC 2251) requires a directory service to identify object classes, attributes, and syntaxes with OIDs. This is part of the LDAP X.500 legacy.
OIDs in Active Directory include some issued by the ISO for X.500 classes and attributes, and some issued by Microsoft and other issuing authorities. OID notation is a dotted string of numbers, for example 1.2.840.113556.1.5.4, which breaks down as in the following table.
| Value | Description |
|---|---|
| 1 | ISO - the "root authority", issued "1.2" to ANSI |
| 2 | ANSI – issued "1.2.840" to USA |
| 840 | USA – issued "1.2.840.113556" to Microsoft |
| 113556 | Microsoft |
| 1 | Microsoft - Active Directory Service |
| 5 | Microsoft - Active Directory Service: Classes |
| 4 | Microsoft - Active Directory Service: Classes: Builtin-Domain |
Several methods for obtaining valid OIDs for use in extending the schema are described in Obtaining a Root Object Identifier (OID).