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Lightweight Directory Application Protocol
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Light Directory Access Procedure
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Lightweight Directory Access Protocol
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Lightweight Data Access Protocol
EXPLANATION
LDAP, Lightweight Directory Access Protocol, is an Internet
protocol that email and other programs use to look up information from a
server.
LDAP is mostly used by medium-to-large organizations. If you
belong to one that has an LDAP server, you can use it to look up contact
info and the like. Otherwise, if you were just wondering about this
acronym, you probably don't need it. But feel free to read on to learn
the story of this bit of Internet plumbing.
Every email program has a personal address book, but how do
you look up an address for someone who's never sent you email? How can
an organization keep one centralized up-to-date phone book that
everybody has access to?
Those questions led companies such as Microsoft, IBM, Lotus, and
Netscape to support a standard called LDAP. "LDAP-aware" client
programs can ask LDAP servers to look up entries in a wide variety of
ways. LDAP servers index all the data in their entries, and "filters"
may be used to select just the person or group you want, and return just
the information you want. For example, here's an LDAP search translated
into plain English: "Search for all people located in Chicago whose
name contains "Fred" that have an email address. Please return their
full name, email, title, and description."
LDAP is not limited to contact information, or even information
about people. LDAP is used to look up encryption certificates, pointers
to printers and other services on a network, and provide "single
sign-on" where one password for a user is shared between many services.
LDAP is appropriate for any kind of directory-like information, where
fast lookups and less-frequent updates are the norm.
As a protocol, LDAP does not define how programs work on either
the client or server side. It defines the "language" used for client
programs to talk to servers (and servers to servers, too). On the client
side, a client may be an email program, a printer browser, or an
address book. The server may speak only LDAP, or have other methods of
sending and receiving data—LDAP may just be an add-on method.
If you have an email program (as opposed to web-based email), it
probably supports LDAP. Most LDAP clients can only read from a server.
Search abilities of clients (as seen in email programs) vary widely. A
few can write or update information, but LDAP does not include security
or encryption, so updates usually require additional protection such as
an encrypted SSL connection to the LDAP server.
If you have OS X and access to an LDAP server, you can enter
your LDAP account into System Preferences--Internet Accounts. At bottom
of the right pane, click Add Other Account, then choose the LDAP account
option. This lets Address Book look up info from your server.
LDAP also defines:
Permissions, set by the administrator to allow only certain people to access the LDAP database, and optionally keep certain data private.
Schema: a
way to describe the format and attributes of data in the server. For
example: a schema entered in an LDAP server might define a
"groovyPerson" entry type, which has attributes of
"instantMessageAddress", and "coffeeRoastPreference". The normal
attributes of name, email address, etc., would be inherited from one of
the standard schemas, which are rooted in X.500 (see below).
LDAP was designed at the University of Michigan to adapt a
complex enterprise directory system (called X.500) to the modern
Internet. X.500 is too complex to support on desktops and over the
Internet, so LDAP was created to provide this service "for the rest of
us."
LDAP servers exist at three levels: There are big public
servers, large organizational servers at universities and corporations,
and smaller LDAP servers for workgroups. Most public servers from around
year 2000 have disappeared, although directory.verisign.com exists for
looking up X.509 certificates. The idea of publicly listing your email
address for the world to see, of course, has been crushed by spam.
While LDAP didn't bring us the worldwide email address book, it
continues to be a popular standard for communicating record-based,
directory-like data between programs.