The Evolution of Directory Services

Directory services have existed in one form or another since the early days of computing to provide basic lookup and authentication functionality for enterprise network implementations. A directory service provides detailed information about a user or object in a network, much in the same way that a phonebook is used to look up a telephone number for a provided name. For example, a user object in a directory service can store the phone number, email address, department name, and as many other attributes as an administrator desires.

Directory services are commonly referred to as the white pages of a network. They provide user and object definition and administration. Early electronic directories were developed soon after the invention of the digital computer and were used for user authentication and to control access to resources. With the growth of the Internet and the increase in the use of computers for collaboration, the use of directories expanded to include basic contact information about users. Examples of early directories included MVS PROFS (IBM), Grapevine's Registration Database, and WHOIS.

Application-specific directory services soon arose to address the specific addressing and contact-lookup needs of each product. These directories were accessible only via proprietary access methods and were limited in scope. Applications utilizing these types of directories were programs such as Novell GroupWise Directory, Lotus Notes, and the Unix sendmail /etc/aliases file.

The further development of large-scale enterprise directory services was spearheaded by Novell with the release of Novell Directory Services (NDS) in the early 1990s. It was adopted by NetWare organizations and eventually was expanded to include support for mixed NetWare/NT environments. The flat, unwieldy structure of NT domains and the lack of synchronization and collaboration between the two environments led many organizations to adopt NDS as a directory service implementation. It was these specific deficiencies in NT that Microsoft addressed with the introduction of Active Directory.

The development of the Lightweight Directory Access Protocol (LDAP) corresponded with the growth of the Internet and a need for greater collaboration and standardization. This nonproprietary method of accessing and modifying directory information that fully utilized TCP/IP was determined to be robust and functional, and new directory services implementations were written to utilize this protocol. Active Directory itself was specifically designed to conform to the LDAP standard.

The Original Microsoft Directory Systems

Exchange 5.5 ran its own directory service as part of its email environment. In fact, Active Directory took many of its key design components from the original Exchange directory service. For example, the Active Directory database uses the same Jet database format as Exchange 5.5, the same types of utilities are necessary to run maintenance on the Active Directory database, and the site replication topology is similar in many ways.

Several other Microsoft applications ran their own directory services, namely Internet Information Server and Site Server. However, each directory service was separate from the others, and integration was not very tight between the different implementations.

Key Features of Active Directory

Five key components are central to Active Directory's functionality. As compatibility with Internet standards has become required for new directory services, the existing implementations have adjusted and focused on these areas:

• TCP/IP compatibility Unlike some of the original proprietary protocols such as IPX/SPX and NetBEUI, the Transport Control Protocol/Internet Prococol (TCP/IP) was designed to be cross-platform. The subsequent adoption of TCP/IP as an Internet standard for computer communications has propelled it to the forefront of the protocol world and essentially made it a requirement for enterprise operating systems. Active Directory and Windows Server 2003 utilize the TCP/IP protocol stack as their primary method of communications.

• Lightweight Directory Access Protocol support The Lightweight Directory Access Protocol (LDAP) has emerged as the standard Internet directory protocol and is used to update and query data within the directory. Active Directory directly supports LDAP.

• Domain Name System (DNS) support DNS was created out of a need to translate simplified names that can be understood by humans (such as www.cco.com) into an IP address that is understood by a computer (such as 12.155.166.151). The Active Directory structure supports and effectively requires DNS to function properly.

• Security support Internet standards-based security support is vital to the smooth functioning of an environment that is essentially connected to millions of computers around the world. Lack of strong security is an invitation to be hacked, and Windows Server 2003 and Active Directory have taken security to greater levels. Support for IP Security (IPSec), Kerberos, Certificate Authorities, and support for Secure Sockets Layer (SSL) encryption is built into Windows Server 2003 and Active Directory. In addition, the last few years have seen a recent major push at Microsoft to further secure all aspects of its software to prevent embarrassing security melt-downs such as those caused by viruses and worms.

• Ease of administration Although often overlooked in powerful directory services implementations, the ease in which the environment is administered and configured directly affects the overall costs associated with its use. Active Directory and Windows Server 2003 are specifically designed for ease of use to lessen the learning curve associated with the use of a new environment. In addition, Windows Server 2003 includes numerous administrative improvements over Windows 2000, in the form of additional command-line tools for scripting, "headless" management capabilities, software restriction policies, and an enhanced GUI based on Windows XP.