Forward link
Forward link (or Forward Reference) is part of the Linked Attribute Relationship

Forward links in Microsoft Active Directory may be SINGLE-VALUE or MULTI-VALUE and could be any of these Distinguished Name Microsoft Active Directory Syntax:

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

As far as Ldapwiki knows, any DN Syntax Forward link can be used with LDAP_MATCHING_RULE_IN_CHAIN

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