At first glance, the term LDAP seems misleading. When we talk, for instance, about the primary protocol for the web, HTTP (HyperText Transfer Protocol), we are talking about the way that web applications transfer information across the network. We are not talking about the format of the data that is moved across the network, nor are we talking about how that data is stored on or retrieved from the server.
But when we talk about LDAP, we are usually talking not only about the network protocol, but about a particular kind of server that stores data of a well-defined format inside of a special database. There is a historical reason for this seemingly misleading name.
Originally, LDAP was just a network protocol used to get data out of an X.500 directory (a directory server architecture, designed in the 1980s and standardized in 1988). This was the intent of Yeong, Howes, and Killie when they initially drafted the LDAP specification as RFC 1487 in 1993.
Tip
About RFCs
RFCs (Requests for Comments) are a series of technical documents, usually specifying standards. Each RFC is identified by number, which are organized sequentially—earlier RFCs have lower numbers. There are many websites that make the RFC database, in whole or in part, available. One exemplary source is the RFC Editor (http://www.rfc-editor.org), which is used in this book.
The first LDAP servers were gateways to X.500 directories, but these servers quickly evolved into full-fledged directory servers. Tim Howes and his colleagues at the University of Michigan created the Open Source University of Michigan LDAP Implementation, which became the reference implementation for other LDAP servers.
Note
Historical information on the University of Michigan LDAP project is still available online: http://www.umich.edu/~dirsvcs/ldap/ldap.html
As the University of Michigan's LDAP server matured, a wealth of new standards was created. LDAP picked up industry momentum. Tim Howes was hired by Netscape, and LDAP went mainstream.
By the late 1990's, Netscape, Novell, Oracle, and Microsoft (among others) all touted LDAP offerings. RFC 2251, released in 1997, standardized LDAPv3, which made vast improvements to the earlier LDAP standards.
The market for LDAP servers matured, but the University of Michigan project lost momentum. Key developers had left the university to move along to other projects.
In 1998 the OpenLDAP project was started by Kurt Zeilenga. Soon after, Howard Chu (formerly of the University of Michigan, and the current architect of the project) joined. They rescued the University of Michigan's code base, beginning development anew. The result, OpenLDAP 2.0, was highly successful, and made its way into almost every major Linux distribution.
Note
A complete list of OpenLDAP contributors, from the project's inception to the present, can be found at http://www.openldap.org/project/.
Since the late '90's, OpenLDAP has continued to mature, overseen by the OpenLDAP Foundation, and supported by contributions from industry sponsors. As of this writing, version 2.3 is the stable release, and version 2.4 is in the beta stages.
As was the intent with the University of Michigan LDAP server, OpenLDAP still adheres closely to the LDAP standards. In fact, Kurt Zeilenga is responsible for many of the updates made to the LDAP standards in June 2006.
But in addition to its high degree of standards compliance, OpenLDAP is also one of the fastest directory servers in the market, far outpacing offerings from other Open Source directory server implementations.