Overview#

LinkID is a Number specified in AttributeSchema for Microsoft Active Directory which indicated a Linked AttributeLinkID Attribute Values indicate:

• Even Attribute Value are forward links
• Odd Attribute Value are BackLinks equals to the LinkID of the corresponding forward link LinkID plus one.
• Attribute Value of 0 or not present implies it is NOT a Linked Attribute

Forward links (or Forward Reference) attributes always have a even value LinkID and for every Forward link the next LinkID value is, of course, an odd value and is the LinkID to the corresponding BackLink attribute.

LDAP (Microsoft Active Directory) Attribute Definition#

The LinkID AttributeTypes is defined as:

• CN:
• OID of 1.2.840.113556.1.2.50
• NAME: LinkID
• DESC: attribute specifies an integer that indicates that the attribute is a Linked Attribute. An even integer is a forward link and an odd integer is a BackLink.
• EQUALITY:
• ORDERING:
• SYNTAX: 2.5.5.9
• LOWERBOUND:
• UPPERBOUND:
• OMSyntax: 2
• SchemaIDGUID: bf96799b-0de6-11d0-a285-00aa003049e2
• mapiID: 32965
• SINGLE-VALUE
• NO-USER-MODIFICATION
• USAGE: OperationalAttribute
• Extended Flags:
  • X-ORIGIN:
• X-SYSTEMFLAGS
  • FLAG_SCHEMA_BASE_OBJECT
• X-SCHEMAFLAGSEx
  • FLAG_ATTR_IS_CRITICAL
• X-SEARCH-FLAGS
• Used as MUST in:
• Used as MAY in:

Auto-Generated LinkID on LDAP Add Request#

If the DomainControllerFunctionality is Windows Server 2003 or greater, and an attributeSchema object is created with LDAP Add, and the Add request assigns the OID 1.2.840.113556.1.2.50 as the Attribute Value of the LinkID attribute, the DC sets the linkID attribute to an even integer that does not already appear as the linkID on a schema object. The attribute created by the Add is a Forward link attribute.

If the LDAP Add Request, assigns either the attributeID or the lDAPDisplayName of an existing forward link attribute as the value of the linkID attribute, the DC sets the linkID attribute to the LinkID of the given forward link attribute plus one. The attribute created by the Add is a BackLink attribute corresponding to the given forward link attribute.

The aforementioned values that trigger auto-generation behavior for the linkID are of syntax String(Object-Identifier) or String(Unicode), and therefore do not conform to the declared syntax of the LinkID attribute. The DC accepts these values without the error that would normally occur in such a case.

More Information#

There might be more information for this subject on one of the following:

• 1.2.840.113556.1.2.50
• AttributeSchema
• DN Syntax
• DirectReports
• LDAP_MATCHING_RULE_IN_CHAIN
• Linked Attribute
• ManagedBy
• Manager
• Member
• MemberOf

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• [#1] - 3.1.1.2.3 Attributes - based on information obtained 2020-02-16
• [#2] - 3.1.1.2.3.1 Auto-Generated linkID - based on information obtained 2020-02-16