The Lightweight Directory Access Protocol is the second of three cross-platform authentication tools described in this book. In reality, though, LDAP is much more than an authentication tool; it's a protocol for accessing directories, which in this context are essentially databases designed to be read more often than they're written. As such, LDAP can store many different types of informationUnix or Windows account databases, mappings of hostnames to IP addresses, employee contact information, and so on. This chapter focuses on one narrow use for LDAP, as a network-accessible account authentication system. LDAP makes a viable alternative to NT or Active Directory domains for network authentication of both Windows and Linux servers and desktop systems. It can provide better Linux account database integration, so it's the smarter choice if you use many Linux systems. It can also provide much more than account authentication information, although such configurations are beyond the scope of this book. Using Linux as an LDAP platform gives you all of Linux's usual advantages, such as its reliability and low cost.
When setting up an LDAP authentication system, you should first understand some LDAP basics. Despite the word lightweight in the protocol's name, LDAP is a complex system, with its own terminology and peculiarities. In fact, several LDAP implementations exist, so you must pick one and install it on your Linux LDAP server. You must then set up your directories to handle authentication. Only then can you begin configuring your LDAP clients to use your network's account directory. (Note that LDAP clients can be servers for other protocols.) Of course, the details of this configuration vary between Linux and Windows clients, so you must know how to handle both.