OIDs are globally unique object identifiers. By global, I mean that these identifiers are used to define objects and attributes as they are applied to any directory service, from Microsoft Active Directory to Novell Directory Services. OIDs are issued by the International Standards Organization (ISO) issuing agency. By having a central group control how object classes and attributes are implemented, the industry can avoid incompatible network directories.
OIDs uniquely define data elements, syntaxes, and various other parts of distributed applications. ISO-issued OIDs are used in many standard technologies, including Open System Interconnection (OSI) applications, X.500 directories, Simple Network Management Protocol (SNMP), and many other applications where a unique identifier is important. Each object class and attribute must have a unique OID if it is to exist in the AD schema. OIDs are organized in a hierarchical structure managed by the ISO.
note While you probably won't need to understand the entire OID naming process, it is important to know that the OID represents a tree-like structure much like the container/subcontainer structure of AD.
LDAP is an important protocol used for accessing information in network directories, such as Microsoft Active Directory. LDAP applications use the ISO-issued OIDs to identify the objects and attributes that are available in any directory to which they connect. In other words, to be LDAP-accessible, every object and attribute within a directory must have an OID. (The OID itself becomes an attribute of each object defined.)
As stated earlier, the International Standards Organization acts as the issuing agent for new OIDs. To create a new object class or attribute within the AD schema, the first step is to apply to the ISO for an OID. The OID will be expressed as a string of numbers delimited by decimals, such as 1.2.840.xxxxxx.w.y.z. Table 12.3 describes the purpose of each piece of our sample OID.
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