Directory Service (LDAP) is a software system that stores, organizes and provides access to information in a directory, an infrastructure of shared information to be found, to contain, manage, administer and organize the similarities and network resources, the disks, folders, files, printers, users, groups, devices, phone numbers and other objects can. Server Directory Access and customers in the model of interaction client / server communication. Access to the directory is as follows: A customer calls directory interface (API Application Programming) write to a directory or read access information. The customer accesses the call information in the directory name of the client application over TCP / IP (the standard LDAP port TCP / IP – 636 for secure communication, not 389 for)-encrypted communications. The results of the operation is then returned to the customer. Servers provide a specific service for LDAP clients. Sometimes the directory server can collect customers from other servers to provide the required information to all inquiries.
LDAP server performs the following basic operations:
Entrylist input
comparisons;
; add entries, delete
entries, change entries /> Move records, records />
renown; <, br Extended operation;
authentication.

Directory services can be used:
Locating and providing information about individuals (Address pounds, yellow pages, white pages) and distributed resources such as printers,
The user authentication and authorization for Web servers or other LDAP-enabled applications;
policies that are shared by multiple applications or application instances.

Directory Server components are:
A front-end (LDAP client manages the operations on the incoming server TCP / IP);
A database backend (handles stores and retrieves directory objects from relational databases).

open source LDAP server Has usage:
Red Hat Directory Server and Fedora Directory Server. Red Hat Directory Server was originally developed by Netscape Security Solutions as a commercial product for Red Hat Enterprise Linux bought. Today Red Hat is made with the name of Red Hat Directory Server. With its policy of release for Red Hat Fedora Core also produced. It’s called Fedora Directory Server is ideal for a distributive based on RedHat. Codes of these servers more striking because the common root. In contrast to OpenLDAP, Fedora / Red Hat Directory Server have good documentation.
OpenLDAP. OpenLDAP is the evolution of slapd original. It is widespread and on different platforms such as Linux, FreeBSD, Windows and MacOS X use the website contains documentation is completely outdated, but there are not many useful by-step instructions. OpenLDAP is show time. Its functions are almost identical to Red Hat Directory Server.

commercial LDAP server are:
Novell eDirectory. All products are free for institutions of higher education. It operates through the following operating systems: Novell Netware, Windows (NT), Linux (RedHat or SUSE Enterprise), Solaris, AIX, HP-UX. They have everything in one book – all the necessary programs are provided at the time of disposal. Installation and adjustment are easy. Benefits – Documentation exclusive and affordable technical support for registered users and cross-platform functionality. Disadvantage – closed-source files.
Microsoft Active Directory. It is part of the Windows Server family. It is a perfect solution for MS networks. Benefits – a perfect integration into the system, highly skilled documentation.
Sun Java System Directory Server. SUN iPlanet merged with society and has created its new product – Sun ONE, which was subsequently renamed Sun Java System Directory Server. This is not a standalone product, but only a part of the Java Enterprise System. Requirements: Solaris 10, Solaris 9, Solaris 8 (SPARC only), Red Hat Enterprise Linux 2 1 and 3 1, HP-UX 11i, Microsoft Windows 2000, XP, 2003. Can not be bought outside of the Java Enterprise System. But if you decide to use a complex solution from Sun, you will have no problems. How engineers can help you install and configure it according to your needs.
IBM Tivoli Directory Server. LDAP solution from IBM. It is supported by the following operating systems: AIX, Solaris, Microsoft Windows 2000, HP-UX and Linux Intel and IBM eServer iSeries, pSeries and zSeries. Advantage – qualified, open and free for all documents.

. Some of them are presented below:
Microsoft Windows:
Softerra LDAP Administrator / LDAP Browser,
LDAPSoft LDAP Browser / LDAP Admin Tool; ldapadmin