Chapter 1. Introduction to Directory Services

Red Hat Directory Server provides a centralized directory service for an intranet, network, and extranet information. Directory Server integrates with existing systems and acts as a centralized repository for the consolidation of employee, customer, supplier, and partner information. Directory Server can even be extended to manage user profiles, preferences, and authentication.
This chapter describes the basic ideas and concepts for understanding what a directory service does to help begin designing the directory service.

1.1. About Directory Services

The term directory service refers to the collection of software, hardware, and processes that store information about an enterprise, subscribers, or both, and make that information available to users. A directory service consists of at least one instance of Directory Server and at least one directory client program. Client programs can access names, phone numbers, addresses, and other data stored in the directory service.
An example of a directory service is a domain name system (DNS) server. A DNS server maps computer hostnames to IP addresses. Thus, all of the computing resources (hosts) become clients of the DNS server. Mapping hostnames allows users of computing resources to easily locate computers on a network by remembering hostnames rather than IP addresses. A limitation of a DNS server is that it stores only two types of information: names and IP addresses. A true directory service stores virtually unlimited types of information.
Directory Server stores all user and network information in a single, network-accessible repository. Many kinds of different information can be stored in the Directory Server:
  • Physical device information, such as data about the printers in an organization, such as location, color or black and white, manufacturer, date of purchase, and serial number.
  • Public employee information, such as name, email address, and department.
  • Private employee information, such as salary, government identification numbers, home addresses, phone numbers, and pay grade.
  • Contract or account information, such as the name of a client, final delivery date, bidding information, contract numbers, and project dates.
Directory Server serves the needs of a wide variety of applications. It also provides a standard protocol and application programming interfaces (APIs) to access the information it contains.

1.1.1. About Global Directory Services

Directory Server provides global directory services, which means that it provides information to a wide variety of applications. Rather than attempting to unify proprietary databases bundled with different applications, which is an administrative burden, Directory Server is a single solution to manage the same information.
For example, a company is running three different proprietary email systems, each with its own proprietary directory service. If users change their passwords in one directory, the changes are not automatically replicated in the others. Managing multiple instances of the same information results in increased hardware and personnel costs; the increased maintenance overhead is referred to as the n+1 directory problem.
A global directory service solves the n+1 directory problem by providing a single, centralized repository of directory information that any application can access. However, giving a wide variety of applications access to the directory service requires a network-based means of communicating between the applications and the directory service. Directory Server uses LDAP for applications to access to its global directory service.

1.1.2. About LDAP

LDAP provides a common language that client applications and servers use to communicate with one another. LDAP is a "lightweight" version of the Directory Access Protocol (DAP) described by the ISO X.500 standard. DAP gives any application access to the directory through an extensible and robust information framework but at a high administrative cost. DAP uses a communications layer that is not the Internet standard protocol and has complex directory-naming conventions.
LDAP preserves the best features of DAP while reducing administrative costs. LDAP uses an open directory access protocol running over TCP/IP and simplified encoding methods. It retains the data model and can support millions of entries for a modest investment in hardware and network infrastructure.