# $OpenLDAP$
-# Copyright 1999-2003, The OpenLDAP Foundation, All Rights Reserved.
+# Copyright 1999-2011 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
H1: Introduction to OpenLDAP Directory Services
-This document describes how to build, configure, and operate OpenLDAP
-software to provide directory services. This includes details on
-how to configure and run the stand-alone {{TERM:LDAP}} daemon,
-{{slapd}}(8) and the stand-alone LDAP update replication daemon,
-{{slurpd}}(8). It is intended for newcomers and experienced
-administrators alike. This section provides a basic introduction
-to directory services and, in particular, the directory services
-provided by {{slapd}}(8).
+This document describes how to build, configure, and operate
+{{PRD:OpenLDAP}} Software to provide directory services. This
+includes details on how to configure and run the Standalone
+{{TERM:LDAP}} Daemon, {{slapd}}(8). It is intended for new and
+experienced administrators alike. This section provides a basic
+introduction to directory services and, in particular, the directory
+services provided by {{slapd}}(8). This introduction is only
+intended to provide enough information so one might get started
+learning about {{TERM:LDAP}}, {{TERM:X.500}}, and directory services.
H2: What is a directory service?
-A directory is a specialized database optimized for reading, browsing
-and searching. Directories tend to contain descriptive, attribute-based
-information and support sophisticated filtering capabilities.
-Directories generally do not support complicated transaction or
-roll-back schemes found in database management systems designed
-for handling high-volume complex updates. Directory updates are
-typically simple all-or-nothing changes, if they are allowed at
-all. Directories are tuned to give quick response to high-volume
-lookup or search operations. They may have the ability to replicate
-information widely in order to increase availability and reliability,
-while reducing response time. When directory information is
-replicated, temporary inconsistencies between the replicas may be
-okay, as long as they get in sync eventually.
+A directory is a specialized database specifically designed for
+searching and browsing, in additional to supporting basic lookup
+and update functions.
+
+Note: A directory is defined by some as merely a database optimized
+for read access. This definition, at best, is overly simplistic.
+
+Directories tend to contain descriptive, attribute-based information
+and support sophisticated filtering capabilities. Directories
+generally do not support complicated transaction or roll-back schemes
+found in database management systems designed for handling high-volume
+complex updates. Directory updates are typically simple all-or-nothing
+changes, if they are allowed at all. Directories are generally
+tuned to give quick response to high-volume lookup or search
+operations. They may have the ability to replicate information
+widely in order to increase availability and reliability, while
+reducing response time. When directory information is replicated,
+temporary inconsistencies between the replicas may be okay, as long
+as inconsistencies are resolved in a timely manner.
There are many different ways to provide a directory service.
Different methods allow different kinds of information to be stored
contain is spread across many machines, all of which cooperate to
provide the directory service. Typically a global service defines
a uniform {{namespace}} which gives the same view of the data no
-matter where you are in relation to the data itself. The Internet
-{{TERM[expand]DNS}} (DNS) is an example of a globally distributed
-directory service.
+matter where you are in relation to the data itself.
+
+A web directory, such as provided by the {{Open Directory Project}}
+<{{URL:http://dmoz.org}}>, is a good example of a directory service.
+These services catalog web pages and are specifically designed to
+support browsing and searching.
+
+While some consider the Internet {{TERM[expand]DNS}} (DNS) is an
+example of a globally distributed directory service, DNS is not
+browseable nor searchable. It is more properly described as a
+globally distributed {{lookup}} service.
H2: What is LDAP?
it is a lightweight protocol for accessing directory services,
specifically {{TERM:X.500}}-based directory services. LDAP runs
over {{TERM:TCP}}/{{TERM:IP}} or other connection oriented transfer
-services. The nitty-gritty details of LDAP are defined in
-{{REF:RFC2251}} "The Lightweight Directory Access Protocol (v3)"
-and other documents comprising the technical specification
-{{REF:RFC3377}}. This section gives an overview of LDAP from a
-user's perspective.
+services. LDAP is an {{ORG:IETF}} Standard Track protocol and is
+specified in "Lightweight Directory Access Protocol (LDAP) Technical
+Specification Road Map" {{REF:RFC4510}}.
+
+This section gives an overview of LDAP from a user's perspective.
{{What kind of information can be stored in the directory?}} The
LDAP information model is based on {{entries}}. An entry is a
values depend on the attribute type. For example, a {{EX:cn}}
attribute might contain the value {{EX:Babs Jensen}}. A {{EX:mail}}
attribute might contain the value "{{EX:babs@example.com}}". A
-{{EX:jpegPhoto}} attribute would contain a photograph in the JPEG
-(binary) format.
+{{EX:jpegPhoto}} attribute would contain a photograph in the
+{{TERM:JPEG}} (binary) format.
{{How is the information arranged?}} In LDAP, directory entries
are arranged in a hierarchical tree-like structure. Traditionally,
you can think of. Figure 1.1 shows an example LDAP directory tree
using traditional naming.
-!import "intro_tree.gif"; align="center"; \
+!import "intro_tree.png"; align="center"; \
title="LDAP directory tree (traditional naming)"
FT[align="Center"] Figure 1.1: LDAP directory tree (traditional naming)
Figure 1.2 shows an example LDAP directory tree using domain-based
naming.
-!import "intro_dctree.gif"; align="center"; \
+!import "intro_dctree.png"; align="center"; \
title="LDAP directory tree (Internet naming)"
FT[align="Center"] Figure 1.2: LDAP directory tree (Internet naming)
concatenating the names of its ancestor entries. For example, the
entry for Barbara Jensen in the Internet naming example above has
an RDN of {{EX:uid=babs}} and a DN of
-{{EX:uid=babs,ou=People,dc=example,dc=com}}. The full DN format
-is described in {{REF:RFC2253}}, "Lightweight Directory Access
-Protocol (v3): UTF-8 String Representation of Distinguished Names."
+{{EX:uid=babs,ou=People,dc=example,dc=com}}. The full DN format is
+described in {{REF:RFC4514}}, "LDAP: String Representation of
+Distinguished Names."
{{How is the information accessed?}} LDAP defines operations for
interrogating and updating the directory. Operations are provided
{{How is the information protected from unauthorized access?}} Some
directory services provide no protection, allowing anyone to see
-the information. LDAP provides a mechanism for a client to
-authenticate, or prove its identity to a directory server, paving
-the way for rich access control to protect the information the
-server contains. LDAP also supports privacy and integrity security
+the information. LDAP provides a mechanism for a client to authenticate,
+or prove its identity to a directory server, paving the way for
+rich access control to protect the information the server contains.
+LDAP also supports data security (integrity and confidentiality)
services.
+H2: When should I use LDAP?
+
+This is a very good question. In general, you should use a Directory
+server when you require data to be centrally managed, stored and accessible via
+standards based methods.
+
+Some common examples found throughout the industry are, but not limited to:
+
+* Machine Authentication
+* User Authentication
+* User/System Groups
+* Address book
+* Organization Representation
+* Asset Tracking
+* Telephony Information Store
+* User resource management
+* E-mail address lookups
+* Application Configuration store
+* PBX Configuration store
+* etc.....
+
+There are various {{SECT:Distributed Schema Files}} that are standards based, but
+you can always create your own {{SECT:Schema Specification}}.
+
+There are always new ways to use a Directory and apply LDAP principles to address
+certain problems, therefore there is no simple answer to this question.
+
+If in doubt, join the general LDAP forum for non-commercial discussions and
+information relating to LDAP at:
+{{URL:http://www.umich.edu/~dirsvcs/ldap/mailinglist.html}} and ask
+
+H2: When should I not use LDAP?
+
+When you start finding yourself bending the directory to do what you require,
+maybe a redesign is needed. Or if you only require one application to use and
+manipulate your data (for discussion of LDAP vs RDBMS, please read the
+{{SECT:LDAP vs RDBMS}} section).
+
+It will become obvious when LDAP is the right tool for the job.
+
+
H2: How does LDAP work?
-LDAP directory service is based on a {{client-server}} model. One
-or more LDAP servers contain the data making up the directory
-information tree (DIT). The client connects to servers and
-asks it a question. The server responds with an answer and/or
-with a pointer to where the client can get additional information
-(typically, another LDAP server). No matter which LDAP server a
-client connects to, it sees the same view of the directory; a name
-presented to one LDAP server references the same entry it would at
-another LDAP server. This is an important feature of a global
-directory service, like LDAP.
+LDAP utilizes a {{client-server model}}. One or more LDAP servers
+contain the data making up the directory information tree ({{TERM:DIT}}).
+The client connects to servers and asks it a question. The server
+responds with an answer and/or with a pointer to where the client
+can get additional information (typically, another LDAP server).
+No matter which LDAP server a client connects to, it sees the same
+view of the directory; a name presented to one LDAP server references
+the same entry it would at another LDAP server. This is an important
+feature of a global directory service.
H2: What about X.500?
gateways, LDAP is now more commonly directly implemented in X.500
servers.
-The stand-alone LDAP daemon, or {{slapd}}(8), can be viewed as a
+The Standalone LDAP Daemon, or {{slapd}}(8), can be viewed as a
{{lightweight}} X.500 directory server. That is, it does not
-implement the X.500's DAP. As a {{lightweight directory}} server,
-{{slapd}}(8) implements only a subset of the X.500 models.
+implement the X.500's DAP nor does it support the complete X.500
+models.
If you are already running a X.500 DAP service and you want to
continue to do so, you can probably stop reading this guide. This
It is possible to replicate data from an LDAP directory server to
a X.500 DAP {{TERM:DSA}}. This requires an LDAP/DAP gateway.
-OpenLDAP does not provide such a gateway, but our replication daemon
-can be used to replicate to such a gateway. See the {{SECT:Replication
-with slurpd}} chapter of this document for information regarding
-replication.
+OpenLDAP Software does not include such a gateway.
H2: What is the difference between LDAPv2 and LDAPv3?
LDAPv3 was developed in the late 1990's to replace LDAPv2.
LDAPv3 adds the following features to LDAP:
- - Strong Authentication via {{TERM:SASL}}
- - Integrity and Confidentiality Protection via {{TERM:TLS}} (SSL)
- - Internationalization through the use of Unicode
- - Referrals and Continuations
- - Schema Discovery
- - Extensibility (controls, extended operations, and more)
-
-LDAPv2 is historic ({{REF:RFC3494}}). As most implementations
-(including {{slapd}}(8)) of LDAPv2 do not conform to the LDAPv2
-technical specification, interoperatibility amongst implementations
-claiming LDAPv2 support will be limited. As LDAPv2 differs
-significantly from LDAPv3, deploying both LDAPv2 and LDAPv3
-simultaneously can be quite problematic. LDAPv2 should be avoided.
+ * Strong authentication and data security services via {{TERM:SASL}}
+ * Certificate authentication and data security services via {{TERM:TLS}} (SSL)
+ * Internationalization through the use of Unicode
+ * Referrals and Continuations
+ * Schema Discovery
+ * Extensibility (controls, extended operations, and more)
+
+LDAPv2 is historic ({{REF:RFC3494}}). As most {{so-called}} LDAPv2
+implementations (including {{slapd}}(8)) do not conform to the
+LDAPv2 technical specification, interoperability amongst
+implementations claiming LDAPv2 support is limited. As LDAPv2
+differs significantly from LDAPv3, deploying both LDAPv2 and LDAPv3
+simultaneously is quite problematic. LDAPv2 should be avoided.
LDAPv2 is disabled by default.
+H2: LDAP vs RDBMS
+
+This question is raised many times, in different forms. The most common,
+however, is: {{Why doesn't OpenLDAP drop Berkeley DB and use a relational
+database management system (RDBMS) instead?}} In general, expecting that the
+sophisticated algorithms implemented by commercial-grade RDBMS would make
+{{OpenLDAP}} be faster or somehow better and, at the same time, permitting
+sharing of data with other applications.
+
+The short answer is that use of an embedded database and custom indexing system
+allows OpenLDAP to provide greater performance and scalability without loss of
+reliability. OpenLDAP uses Berkeley DB concurrent / transactional
+database software. This is the same software used by leading commercial
+directory software.
+
+Now for the long answer. We are all confronted all the time with the choice
+RDBMSes vs. directories. It is a hard choice and no simple answer exists.
+
+It is tempting to think that having a RDBMS backend to the directory solves all
+problems. However, it is a pig. This is because the data models are very
+different. Representing directory data with a relational database is going to
+require splitting data into multiple tables.
+
+Think for a moment about the person objectclass. Its definition requires
+attribute types objectclass, sn and cn and allows attribute types userPassword,
+telephoneNumber, seeAlso and description. All of these attributes are multivalued,
+so a normalization requires putting each attribute type in a separate table.
+
+Now you have to decide on appropriate keys for those tables. The primary key
+might be a combination of the DN, but this becomes rather inefficient on most
+database implementations.
+
+The big problem now is that accessing data from one entry requires seeking on
+different disk areas. On some applications this may be OK but in many
+applications performance suffers.
+
+The only attribute types that can be put in the main table entry are those that
+are mandatory and single-value. You may add also the optional single-valued
+attributes and set them to NULL or something if not present.
+
+But wait, the entry can have multiple objectclasses and they are organized in
+an inheritance hierarchy. An entry of objectclass organizationalPerson now has
+the attributes from person plus a few others and some formerly optional attribute
+types are now mandatory.
+
+What to do? Should we have different tables for the different objectclasses?
+This way the person would have an entry on the person table, another on
+organizationalPerson, etc. Or should we get rid of person and put everything on
+the second table?
+
+But what do we do with a filter like (cn=*) where cn is an attribute type that
+appears in many, many objectclasses. Should we search all possible tables for
+matching entries? Not very attractive.
+
+Once this point is reached, three approaches come to mind. One is to do full
+normalization so that each attribute type, no matter what, has its own separate
+table. The simplistic approach where the DN is part of the primary key is
+extremely wasteful, and calls for an approach where the entry has a unique
+numeric id that is used instead for the keys and a main table that maps DNs to
+ids. The approach, anyway, is very inefficient when several attribute types from
+one or more entries are requested. Such a database, though cumbersomely,
+can be managed from SQL applications.
+
+The second approach is to put the whole entry as a blob in a table shared by all
+entries regardless of the objectclass and have additional tables that act as
+indices for the first table. Index tables are not database indices, but are
+fully managed by the LDAP server-side implementation. However, the database
+becomes unusable from SQL. And, thus, a fully fledged database system provides
+little or no advantage. The full generality of the database is unneeded.
+Much better to use something light and fast, like Berkeley DB.
+
+A completely different way to see this is to give up any hopes of implementing
+the directory data model. In this case, LDAP is used as an access protocol to
+data that provides only superficially the directory data model. For instance,
+it may be read only or, where updates are allowed, restrictions are applied,
+such as making single-value attribute types that would allow for multiple values.
+Or the impossibility to add new objectclasses to an existing entry or remove
+one of those present. The restrictions span the range from allowed restrictions
+(that might be elsewhere the result of access control) to outright violations of
+the data model. It can be, however, a method to provide LDAP access to preexisting
+data that is used by other applications. But in the understanding that we don't
+really have a "directory".
+
+Existing commercial LDAP server implementations that use a relational database
+are either from the first kind or the third. I don't know of any implementation
+that uses a relational database to do inefficiently what BDB does efficiently.
+For those who are interested in "third way" (exposing EXISTING data from RDBMS
+as LDAP tree, having some limitations compared to classic LDAP model, but making
+it possible to interoperate between LDAP and SQL applications):
+
+OpenLDAP includes back-sql - the backend that makes it possible. It uses ODBC +
+additional metainformation about translating LDAP queries to SQL queries in your
+RDBMS schema, providing different levels of access - from read-only to full
+access depending on RDBMS you use, and your schema.
+
+For more information on concept and limitations, see {{slapd-sql}}(5) man page,
+or the {{SECT: Backends}} section. There are also several examples for several
+RDBMSes in {{F:back-sql/rdbms_depend/*}} subdirectories.
+
+
H2: What is slapd and what can it do?
{{slapd}}(8) is an LDAP directory server that runs on many different
interesting features and capabilities include:
{{B:LDAPv3}}: {{slapd}} implements version 3 of {{TERM[expand]LDAP}}.
-{{slapd}} supports LDAP over both IPv4 and IPv6.
+{{slapd}} supports LDAP over both {{TERM:IPv4}} and {{TERM:IPv6}}
+and Unix {{TERM:IPC}}.
{{B:{{TERM[expand]SASL}}}}: {{slapd}} supports strong authentication
-services through the use of SASL. {{slapd}}'s SASL implementation
-utilizes {{PRD:Cyrus}} {{PRD:SASL}} software which supports a number
-of mechanisms including DIGEST-MD5, EXTERNAL, and GSSAPI.
+and data security (integrity and confidentiality) services through
+the use of SASL. {{slapd}}'s SASL implementation utilizes {{PRD:Cyrus
+SASL}} software which supports a number of mechanisms including
+{{TERM:DIGEST-MD5}}, {{TERM:EXTERNAL}}, and {{TERM:GSSAPI}}.
-{{B:{{TERM[expand]TLS}}}}: {{slapd}} provides privacy and integrity
-protections through the use of TLS (or SSL). {{slapd}}'s TLS
-implementation utilizes {{PRD:OpenSSL}} software.
+{{B:{{TERM[expand]TLS}}}}: {{slapd}} supports certificate-based
+authentication and data security (integrity and confidentiality)
+services through the use of TLS (or SSL). {{slapd}}'s TLS
+implementation can utilize {{PRD:OpenSSL}}, {{PRD:GnuTLS}},
+or {{PRD:MozNSS}} software.
-{{B:Topology control}}: {{slapd}} allows one to restrict access to
-the server based upon network topology. This feature utilizes
-{{TCP wrappers}}.
+{{B:Topology control}}: {{slapd}} can be configured to restrict
+access at the socket layer based upon network topology information.
+This feature utilizes {{TCP wrappers}}.
{{B:Access control}}: {{slapd}} provides a rich and powerful access
control facility, allowing you to control access to the information
in your database(s). You can control access to entries based on
LDAP authorization information, {{TERM:IP}} address, domain name
-and other criteria. {{slapd}} supports both {{static}} and
-{{dynamic}} access control information.
+and other criteria. {{slapd}} supports both {{static}} and {{dynamic}}
+access control information.
{{B:Internationalization}}: {{slapd}} supports Unicode and language
tags.
{{B:Choice of database backends}}: {{slapd}} comes with a variety
of different database backends you can choose from. They include
{{TERM:BDB}}, a high-performance transactional database backend;
-{{TERM:LDBM}}, a lightweight DBM based backend; {{SHELL}}, a backend
-interface to arbitrary shell scripts; and PASSWD, a simple backend
-interface to the {{passwd}}(5) file. BDB utilizes {{ORG:Sleepycat}}
-{{PRD:Berkeley DB}}. LDBM utilizes either {{PRD:Berkeley DB}} or
-{{PRD:GDBM}}.
+{{TERM:HDB}}, a hierarchical high-performance transactional
+backend; {{SHELL}}, a backend interface to arbitrary shell scripts;
+and PASSWD, a simple backend interface to the {{passwd}}(5) file.
+The BDB and HDB backends utilize {{ORG:Oracle}} {{PRD:Berkeley
+DB}}.
{{B:Multiple database instances}}: {{slapd}} can be configured to
serve multiple databases at the same time. This means that a single
portions of the LDAP tree, using the same or different database
backends.
-{{B:Generic modules API}}: If you require even more customization,
+{{B:Generic modules API}}: If you require even more customization,
{{slapd}} lets you write your own modules easily. {{slapd}} consists
of two distinct parts: a front end that handles protocol communication
with LDAP clients; and modules which handle specific tasks such as
-database operations. Because these two pieces communicate via a
+database operations. Because these two pieces communicate via a
well-defined {{TERM:C}} {{TERM:API}}, you can write your own
customized modules which extend {{slapd}} in numerous ways. Also,
a number of {{programmable database}} modules are provided. These
allow you to expose external data sources to {{slapd}} using popular
-programming languages ({{PRD:Perl}}, {{shell}}, {{PRD:SQL}}, and
-{{PRD:TCL}}).
+programming languages ({{PRD:Perl}}, {{shell}}, and {{TERM:SQL}}).
{{B:Threads}}: {{slapd}} is threaded for high performance. A single
-multi-threaded {{slapd}} process handles all incoming requests
-using a pool of threads. This reduces the amount of system overhead
+multi-threaded {{slapd}} process handles all incoming requests using
+a pool of threads. This reduces the amount of system overhead
required while providing high performance.
-{{B:Replication}}: {{slapd}} can be configured to maintain replica
-copies of its database. This {{single-master/multiple-slave}}
+{{B:Replication}}: {{slapd}} can be configured to maintain shadow
+copies of directory information. This {{single-master/multiple-slave}}
replication scheme is vital in high-volume environments where a
-single {{slapd}} just doesn't provide the necessary availability
-or reliability. {{slapd}} also includes experimental support for
-{{multi-master}} replication.
+single {{slapd}} installation just doesn't provide the necessary availability
+or reliability. For extremely demanding environments where a
+single point of failure is not acceptable, {{multi-master}} replication
+is also available. {{slapd}} includes support for {{LDAP Sync}}-based
+replication.
+
+{{B:Proxy Cache}}: {{slapd}} can be configured as a caching
+LDAP proxy service.
{{B:Configuration}}: {{slapd}} is highly configurable through a
single configuration file which allows you to change just about
everything you'd ever want to change. Configuration options have
-reasonable defaults, making your job much easier.
-
-{{slapd}} also has its limitations, of course. The main BDB
-backend does not handle range queries or negation queries
-very well.
-
-
-H2: What is slurpd and what can it do?
-
-{{slurpd}}(8) is a daemon that helps {{slapd}} provide replicated
-service. It is responsible for distributing changes made to the
-master {{slapd}} database out to the various {{slapd}} replicas.
-It frees {{slapd}} from having to worry that some replicas might
-be down or unreachable when a change comes through; {{slurpd}}
-handles retrying failed requests automatically. {{slapd}} and
-{{slurpd}} communicate through a simple text file that is used to
-log changes.
+reasonable defaults, making your job much easier. Configuration can
+also be performed dynamically using LDAP itself, which greatly
+improves manageability.
-See the {{SECT:Replication with slurpd}} chapter for information
-about how to configure and run {{slurpd}}(8).
projects / openldap / blobdiff