> Schema Extensions
> AD is packaged with many object classes, including default containers for Computer and User objects as well as classes for OU containers and classes to represent computer and user entities. AD can be extended to include new object classes such as those provided by Dell to simplify the administration of access controls; such extensions are usually referred to as “schema extensions” and are at the heart of the Dell Extended Schema feature described in this document. These schema extensions provide customized object classes to represent Dell Remote Console Switches, access control information, and a type of container used to associate specific access control information with specific instances of Dell Remote Console Switches and Users. It is important to note that each attribute type and object class used in AD must have a globally unique identifier, known as an Object Identifier (OID). These unique identifiers are ultimately managed by internationally recognized authorities. For AD, the OID space is managed secondarily by Microsoft. Dell has obtained OIDs for the custom object classes and attribute types used in the Dell Extended Schema feature. The following is a summary of the OIDs Dell obtained:
> Dell extension is : dell
> Dell base OID is: 1.2.840.113556.1.8000.1280
> RCS LinkID range is: 12070 to 12079
> The Active Directory OID database maintained by Microsoft can be viewed at http://msdn.microsoft.com/certification/ADAcctInfo.asp by entering the extension: Dell.
> The suite of Dell Remote Console Switches is also designed to function using only object classes present in the AD packaged classes; this option is known as the Standard Schema. Under this option, the Computer object class is used to represent Dell Remote Console Switches and standard Group objects are used to associate specific access control information with specific instances of Dell Remote Console Switches and Users. In this case, access control information is stored in a specific attribute type in the Group object.
> The hierarchical structures present in AD can complicate your ability to access information stored in the directory objects. To avoid potential delays associated with navigation of the hierarchies, the suite of Dell Remote Console Switches is designed to use an aspect of AD known as the Global Catalog (GC). The GC provides a “quick look-up” service by providing access to a subset of the data stored in the complete AD database and by “collapsing” all of the hierarchies and geographic distribution into a single relatively flat structure. The GC is queried using the same LDAP directory queries that work on the complete AD database. The AD product requires at least one of the Domain Controllers in an enterprise to also be configured to provide GC services and actual deployments of AD can have any or all of the Domain Controllers configured to provide GC services. The suite of Dell Remote Console Switches uses DNS to determine the network coordinates of each GC server so that the Dell Remote Console Switches can gracefully handle situations where some GC servers are not available on the network. DNS SRV records are used for this purpose so that the Dell Remote Console Switches always attempt to contact alternative GC servers at the “nearest” site first, depending on the administrative settings configured in the SRV records.