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Section 15.2:Pros and Cons of LDAP
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15 Lightweight Directory Access
Protocol (LDAP)
15.1 What is LDAP?
LDAP (Lightweight Directory Access Protocol) is a proposed open standard for accessing global
or local directory services over a network and/or the Internet. A directory, in this sense, is very much
like a phone book. LDAP can handle other information, but at present it is typically used to associate
names with phone numbers and email addresses. LDAP directories are designed to support a high
volume of queries, but the data stored in the directory doesn't change very often.
LDAP is much more useful than a paper phone book, because LDAP's design is intended to support
propagation over LDAP servers throughout the Internet, much like the Domain Name Service (DNS).
DNS servers help to connect computers to one another based on fully qualified domain names or the
type of service requested from a domain, such as mail exchange. Without DNS servers, hostnames
could not be translated into IP addresses, which are required for TCP/IP communication. In the future,
LDAP could provide the same type of global access to many types of directory information. Currently,
LDAP is more commonly used within a single large organization, like a college or a company, for
directory services.
LDAP is a client-server system. An LDAP client connects to an LDAP server and either queries it for
information or provides information that needs to be entered into the directory. The server either an-
swers the query, refers the query to another LDAP server, or accepts the information for incorporation
into the directory, based on the permission of the user.
LDAP is sometimes known as X.500 Lite. X.500 is an international standard for directories and full-
featured, but it is also complex, requiring a lot of computing resources and the full OSI stack. LDAP,
in contrast, can run easily on a PC and over TCP/IP. LDAP can access X.500 directories but does not
support every capability of X.500.
This chapter will refer to the configuration and use of OpenLDAP, an open source implementation
of LDAP. OpenLDAP includes slapd (a stand-alone LDAP server), slurpd (a stand-alone LDAP
replication server), libraries implementing the LDAP protocol, utilities, tools, and sample clients.
15.2 Pros and Cons of LDAP
The main benefit of using LDAP is the consolidation of certain types of information within your or-
ganization. For example, all of the different lists of users within your organization can be merged into
one LDAP directory. This directory can be queried by any LDAP-enabled applications that need this
information. It can also be used by users who need directory information.
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