intro.sdf

OpenLdap是LDAP的开源项目

Initially, LDAP clients accessed gateways to the X.500 directory service.
This gateway ran LDAP between the client and gateway and X.500's
{{TERM[expand]DAP}} ({{TERM:DAP}}) between the gateway and the
X.500 server.  DAP is a heavyweight protocol that operates over a
full OSI protocol stack and requires a significant amount of
computing resources.  LDAP is designed to operate over
{{TERM:TCP}}/{{TERM:IP}} and provides most of the functionality of
DAP at a much lower cost.

While LDAP is still used to access X.500 directory service via
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
{{lightweight}} X.500 directory server.  That is, it does not
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
guide is all about running LDAP via {{slapd}}(8), without running
X.500 DAP.  If you are not running X.500 DAP, want to stop running
X.500 DAP, or have no immediate plans to run X.500 DAP, read on.

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.


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 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, interoperatibility 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: What is slapd and what can it do?

{{slapd}}(8) is an LDAP directory server that runs on many different
platforms. You can use it to provide a directory service of your
very own.  Your directory can contain pretty much anything you want
to put in it. You can connect it to the global LDAP directory
service, or run a service all by yourself. Some of slapd's more
interesting features and capabilities include:

{{B:LDAPv3}}: {{slapd}} implements version 3 of {{TERM[expand]LDAP}}.
{{slapd}} supports LDAP over both IPv4 and IPv6 and Unix IPC.

{{B:{{TERM[expand]SASL}}}}: {{slapd}} supports strong authentication
and data security (integrity and confidentiality) 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.

{{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 utilizes {{PRD:OpenSSL}} software.

{{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.

{{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:HDB}}, a hierarchical high-performance transactional 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.  The BDB and HDB backends
utilize {{ORG:Sleepycat}} {{PRD:Berkeley DB}}.  The LDBM utilizes
either {{PRD:Berkeley DB}} or {{PRD:GDBM}}.

{{B:Multiple database instances}}: {{slapd}} can be configured to
serve multiple databases at the same time. This means that a single
{{slapd}} server can respond to requests for many logically different
portions of the LDAP tree, using the same or different database
backends.

{{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
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}}).

{{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
required while providing high performance.

{{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}} supports two replication methods: {{LDAP
Sync}}-based and {{slurpd}}(8)-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.


H2: What is slurpd and what can it do?

{{slurpd}}(8) is a daemon that, with {{slapd}} help, provides
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.

See the {{SECT:Replication with slurpd}} chapter for information
about how to configure and run {{slurpd}}(8).

Alternatively, {{LDAP-Sync}}-based replication may be used to provide
a replicated service.  See the {{SECT:LDAP Sync Replication}} chapter
for details.