While reading this book, you may find yourself feeling a little like a sky diver who has just jumped out of an airplane. As you approach the ground, things come more into focus. As you squint and try to make out the color of that house far below, you suddenly realize that you are plummeting closer and closer toward the very thing you are trying to observe.
Conceptual ideas need concrete implementations in order to solidify our understanding of them. A directory access protocol is of no use without an actual implementation that allows us to put the protocol to work to solve real information problems on a network. This chapter introduces OpenLDAP, a popular, open source LDAPv3-compliant server. There are a number of popular commercial products, including Sun Microsystem's SunOne directory server (formally owned by Netscape), Novell's eDirectory (formally referred to as NDS), and Microsoft's Active Directory, although this directory encompasses much more than just LDAP.
Why are we using the OpenLDAP server instead of one from another vendor? OpenLDAP is attractive for several reasons:
 The "Open" in OpenLDAP refers to the open engineering process and community used to create OpenLDAP software.
The OpenLDAP source code is available for download from http://www.openldap.org/ under the OpenLDAP Public License. Source code can provide a great deal of information to supplement existing (or absent) documentation.
OpenLDAP 2 is compliant with the core LDAPv3 specifications.
OpenLDAP is available for multiple platforms, including Linux, Solaris, Mac OS 10.2, and Windows (in its various incarnations). For more information regarding OpenLDAP on Mac OS 10.2, see http://www.padl.com//Articles/AdvancedOpenDirectoryConf.html.
The OpenLDAP project is a continuation of the original University of Michigan LDAP server. The relationship between Michigan's LDAP server and many modern, commercial LDAP servers can be compared to the relationship between modern web browsers and the original NCSA Mosaic code base.
The examples presented in this chapter configure OpenLDAP on a Unix-based server. Therefore, they use standard Unix command-line tools such as tar, gzip, and make.