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Introduction to LDAP (Lightweight Directory Access Protocol)

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1.5.2 Directory Enabled Networking

As computer networks evolve to support more variety and depth of services, the complexity of network management increases accordingly. Most network devices, including routers and switches, have traditionally been configured using command-line shells. Although this configuration enables relatively consistent management of a single device, it does nothing to simplify the coordination of configurations across large numbers of devices. Such coordination is critical when you're enabling guaranteed quality of service and other offerings that span multiple devices.

Directory Enabled Networking (DEN) provides a way for devices to configure themselves based on information in a directory. Originally an initiative from Microsoft and Cisco, DEN is now part of the CIM defined by the DMTF.

CIM is a set of object-oriented, implementation-neutral schemas that represents logical and physical attributes of hardware and software. The DMTF, rather than being protocol architects like the IETF, focused primarily on creating common object definitions that allow two CIM-aware applications to store and use information consistently.

Contrary to popular belief, CIM and DEN are not LDAP-specific information models, but are instead "meta" models that can be specialized for a number of environments, of which LDAP is one. XML is an example of another way that CIM objects can be represented.

Momentum behind DEN as the killer application that would drive directories has died down to an extent over the l ast few years, and most of the work around directories has moved to identity management solutions. In this book, we will not focus on DEN as a specific application due to the current lack of software and hardware that can truly exploit this technology.

1.5.3 XML and directories

The eXtensible Markup Language (XML) is an industry standard language used to define structured documents. It offers a set of common tags for defining data about data, or metadata. This metadata can be used to describe particular document types. Instances of documents implementing these types can then be shared and used by XML-aware applications.

DSML is an XML document type that can be used to create structured documents representing information in a directory service. This information represented in DSML can include both directory entries and schema information. DSMLv2 extends the specification to cover the representation of directory operations. Documents conforming to these standards can be exchanged using non-directory protocols like HTTP, as shown in figure 1.16. Many new services that support DSML are becoming available from both large vendors (Sun and Microsoft) and startups.

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Figure 1.16
Here a DSML-enabled application talks to a DSML service that acts as an intermediary between an LDAP server and the DSML-enabled application.

DSML is most useful in applications that are already XML enabled. These include most modern application servers. DSML is especially useful in cases where direct access to the directory would normally not be permitted. For example, consider a situation in which a firewall is blocking all traffic except HTTP. To get around this limitation, a DSML encoding of a directory entry can be transmitted over the HTTP protocol for interpretation and presentation. Such a situation is shown in figure 1.17. Emerging standards like Simple Object Access Protocol (SOAP) make it clear that LDAP will not be the only standard for sharing directory information in the future.

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Figure 1.17
DSML is useful for sharing directory information across firewalls that might limit direct access to directories.


Despite the importance of having well-defined standards, it is rarely the reason for a directory services—related project to fail. Rather, the biggest headache with most new directory deployments is proper management of information in the directory. In the days when enterprise directories were used primarily for storing white pages information, it was often adequate to simply import information into the directory periodically from other, more authoritative data sources. Due to the lack of sophisticated management tools, there wasn't much choice.

Today, directory management tools for users and groups are much more sophisticated. In addition to giving a central administrator the ability to change information about objects in a directory, these tools typically allow for delegation of administrative duties and even user self-management, where appropriate.

This ability to distribute administration works well in intranet and Internet environments, but it is especially critical in extranet environments where multiple organizations are working together, potentially using the same applications and data. In such environments, the segmentation of administration and access is very important (see figure 1.18).

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Figure 1.18
Directories can be segmented such that administration can be delegated to business partners. Such separation may be logical rather than physical.

For example, a car manufacturer with just-in-time manufacturing facilities needs to give its business partners access to certain systems in its extranet. Access to applications on the extranet is controlled based on identities in each of its distributors and component suppliers. Tracking by identity offers audit trails, which will deter a random individual from anonymously ordering unauthorized parts.

The problem is, in addition to the employees at the company, such an extranet environment including suppliers and distributors may include hundreds of thousands, if not millions, of users. Trying to manage all these users centrally would be an incredible effort.

By segmenting users by company and other means, you can push administration of identities to primary contacts within each of the business partners, thereby reducing administrative overhead. Aside from reducing administration costs, this approach also ensures better accuracy by pushing identity management closer to the identities being managed.

Information that is not related to identities and groups can still be difficult to manage with off-the-shelf products. This is the case primarily because little attention has been paid to other advanced uses of directories, such as DEN, which require management of more exotic information.

In chapter 7, we will look at managing all types of directory entries, complete with example applications to reduce manual data entry and allow some degree of user self-management.


Many organizations spend months designing the schema, entry naming, and other related aspects of an enterprise directory service without considering the need for integration with existing information repositories. What usually results is a well-designed, standards-based directory service that contains stale information and is nearly useless.

Meanwhile, legacy data stores that contain mission-critical information continue to thrive because they contain fresh information, although in a way that is often inconvenient to access from new applications and nearly impossible to access from off-the-shelf applications without substantial custom development. Figure 1.19 shows how this typical scenario plays out.

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Figure 1.19
Data in legacy systems is nearly always more useful than data in poorly integrated new systems.

By designing and implementing an appropriate level of directory integration betweenlegacy data stores and the new directory service, you can dramatically increase thevalue of the new directory (see figure 1.20).

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Figure 1.20
Some level of directory integration is important in increasing the value of applications using new directory services.

Directory integration is far more complicated than simply synchronizing everything from a legacy data store into a newly created directory. It demands that you evaluate the needs of applications that depend on both new and legacy data stores. In many cases, both new and legacy applications that utilize the respective data stores. Very often, these applications need access to some set of the same information.

Without any directory integration, it is often difficult to get more than a small group of pioneers to quickly adopt the new applications. A new application may have substantially better functionality, but without the proper data it will be difficult to move the masses that use the legacy applications to the new environment. This issue is demonstrated in figure 1.21.

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Figure 1.21
It is difficult to move the masses to new applications based around a standards-based directory when important information still resides only in a legacy directory.

By using integration techniques, such as synchronization, you can create a high degree of interoperability between the two environments. This approach, shown in figure 1.22, provides the necessary data flow between the two directories, offering a relatively easy migration path to the new environment. It also ensures that the information in both environments is consistent.

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Figure 1.22
Synchronization is often necessary to offer a migration path from legacy to new applications or interoperability where legacy applications will not be migrated.

Consolidating these two environments can vastly simplify management. For example, you may find a way for a Unix-based system to use the same directory as your white pages application to store password information.

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This article was originally published on April 25, 2003

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