<s>
The	O
Lightweight	B-Protocol
Directory	I-Protocol
Access	I-Protocol
Protocol	I-Protocol
(	O
LDAP	B-Protocol
)	O
is	O
an	O
open	O
,	O
vendor-neutral	O
,	O
industry	O
standard	O
application	B-Application
protocol	I-Application
for	O
accessing	O
and	O
maintaining	O
distributed	O
directory	O
information	O
services	O
over	O
an	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
network	O
.	O
</s>
<s>
Directory	O
services	O
play	O
an	O
important	O
role	O
in	O
developing	O
intranet	B-General_Concept
and	O
Internet	O
applications	O
by	O
allowing	O
the	O
sharing	O
of	O
information	O
about	O
users	O
,	O
systems	O
,	O
networks	O
,	O
services	O
,	O
and	O
applications	O
throughout	O
the	O
network	O
.	O
</s>
<s>
LDAP	B-Protocol
is	O
specified	O
in	O
a	O
series	O
of	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
Standard	O
Track	O
publications	O
called	O
Request	O
for	O
Comments	O
(	O
RFCs	O
)	O
,	O
using	O
the	O
description	O
language	O
ASN.1	B-Protocol
.	O
</s>
<s>
A	O
common	O
use	O
of	O
LDAP	B-Protocol
is	O
to	O
provide	O
a	O
central	O
place	O
to	O
store	O
usernames	O
and	O
passwords	O
.	O
</s>
<s>
This	O
allows	O
many	O
different	O
applications	O
and	O
services	O
to	O
connect	O
to	O
the	O
LDAP	B-Protocol
server	O
to	O
validate	O
users	O
.	O
</s>
<s>
LDAP	B-Protocol
is	O
based	O
on	O
a	O
simpler	O
subset	O
of	O
the	O
standards	O
contained	O
within	O
the	O
X.500	B-Protocol
standard	O
.	O
</s>
<s>
Because	O
of	O
this	O
relationship	O
,	O
LDAP	B-Protocol
is	O
sometimes	O
called	O
X.500-lite	O
.	O
</s>
<s>
These	O
companies	O
introduced	O
the	O
concept	O
of	O
directory	O
services	O
to	O
information	B-General_Concept
technology	I-General_Concept
and	O
computer	B-Architecture
networking	I-Architecture
,	O
their	O
input	O
culminating	O
in	O
the	O
comprehensive	O
X.500	B-Protocol
specification	O
,	O
a	O
suite	O
of	O
protocols	O
produced	O
by	O
the	O
International	O
Telecommunication	O
Union	O
(	O
ITU	O
)	O
in	O
the	O
1980s	O
.	O
</s>
<s>
X.500	B-Protocol
directory	I-Protocol
services	O
were	O
traditionally	O
accessed	O
via	O
the	O
X.500	B-Protocol
Directory	I-Protocol
Access	O
Protocol	O
(	O
DAP	O
)	O
,	O
which	O
required	O
the	O
Open	O
Systems	O
Interconnection	O
(	O
OSI	O
)	O
protocol	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
LDAP	B-Protocol
was	O
originally	O
intended	O
to	O
be	O
a	O
lightweight	O
alternative	O
protocol	O
for	O
accessing	O
X.500	B-Protocol
directory	I-Protocol
services	O
through	O
the	O
simpler	O
(	O
and	O
now	O
widespread	O
)	O
TCP/IP	B-Protocol
protocol	I-Protocol
stack	I-Protocol
.	O
</s>
<s>
This	O
model	O
of	O
directory	O
access	O
was	O
borrowed	O
from	O
the	O
DIXIE	B-Protocol
and	O
Directory	B-Protocol
Assistance	I-Protocol
Service	I-Protocol
protocols	O
.	O
</s>
<s>
The	O
protocol	O
was	O
originally	O
created	O
by	O
Tim	O
Howes	O
of	O
the	O
University	O
of	O
Michigan	O
,	O
Steve	O
Kille	O
of	O
Isode	O
Limited	O
,	O
Colin	O
Robbins	O
of	O
Nexor	O
and	O
Wengyik	O
Yeong	O
of	O
Performance	O
Systems	O
International	O
,	O
circa	O
1993	O
,	O
as	O
a	O
successor	O
to	O
DIXIE	B-Protocol
and	O
DAS	B-Protocol
.	O
</s>
<s>
Mark	O
Wahl	O
of	O
Critical	O
Angle	O
Inc.	O
,	O
Tim	O
Howes	O
,	O
and	O
Steve	O
Kille	O
started	O
work	O
in	O
1996	O
on	O
a	O
new	O
version	O
of	O
LDAP	B-Protocol
,	O
LDAPv3	O
,	O
under	O
the	O
aegis	O
of	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
.	O
</s>
<s>
LDAPv3	O
,	O
first	O
published	O
in	O
1997	O
,	O
superseded	O
LDAPv2	O
and	O
added	O
support	O
for	O
extensibility	O
,	O
integrated	O
the	O
Simple	O
Authentication	O
and	O
Security	O
Layer	O
,	O
and	O
better	O
aligned	O
the	O
protocol	O
to	O
the	O
1993	O
edition	O
of	O
X.500	B-Protocol
.	O
</s>
<s>
In	O
the	O
early	O
engineering	O
stages	O
of	O
LDAP	B-Protocol
,	O
it	O
was	O
known	O
as	O
Lightweight	O
Directory	O
Browsing	O
Protocol	O
,	O
or	O
LDBP	O
.	O
</s>
<s>
LDAP	B-Protocol
has	O
influenced	O
subsequent	O
Internet	B-Protocol
protocols	I-Protocol
,	O
including	O
later	O
versions	O
of	O
X.500	B-Protocol
,	O
XML	B-Protocol
Enabled	I-Protocol
Directory	I-Protocol
(	O
XED	O
)	O
,	O
Directory	B-General_Concept
Service	I-General_Concept
Markup	I-General_Concept
Language	I-General_Concept
(	O
DSML	O
)	O
,	O
Service	O
Provisioning	O
Markup	O
Language	O
(	O
SPML	O
)	O
,	O
and	O
the	O
Service	B-Protocol
Location	I-Protocol
Protocol	I-Protocol
(	O
SLP	O
)	O
.	O
</s>
<s>
It	O
is	O
also	O
used	O
as	O
the	O
basis	O
for	O
Microsoft	O
's	O
Active	B-Protocol
Directory	I-Protocol
.	O
</s>
<s>
A	O
client	O
starts	O
an	O
LDAP	B-Protocol
session	O
by	O
connecting	O
to	O
an	O
LDAP	B-Protocol
server	O
,	O
called	O
a	O
Directory	B-Application
System	I-Application
Agent	I-Application
(	O
DSA	O
)	O
,	O
by	O
default	O
on	O
TCP	B-Protocol
and	I-Protocol
UDP	I-Protocol
port	I-Protocol
389	O
,	O
or	O
on	O
port	B-Protocol
636	O
for	O
LDAPS	B-Protocol
(	O
LDAP	B-Protocol
over	O
TLS/SSL	B-Protocol
,	O
see	O
below	O
)	O
.	O
</s>
<s>
A	O
common	O
alternative	O
method	O
of	O
securing	O
LDAP	B-Protocol
communication	O
is	O
using	O
an	O
SSL	B-Protocol
tunnel	B-Protocol
.	O
</s>
<s>
The	O
default	O
port	B-Protocol
for	O
LDAP	B-Protocol
over	O
SSL	B-Protocol
is	O
636	O
.	O
</s>
<s>
The	O
use	O
of	O
LDAP	B-Protocol
over	O
SSL	B-Protocol
was	O
common	O
in	O
LDAP	B-Protocol
Version	O
2	O
(	O
LDAPv2	O
)	O
but	O
it	O
was	O
never	O
standardized	O
in	O
any	O
formal	O
specification	O
.	O
</s>
<s>
The	O
protocol	O
provides	O
an	O
interface	O
with	O
directories	O
that	O
follow	O
the	O
1993	O
edition	O
of	O
the	O
X.500	B-Protocol
model	O
:	O
</s>
<s>
Each	O
entry	O
has	O
a	O
unique	O
identifier	O
:	O
its	O
Distinguished	B-Protocol
Name	I-Protocol
(	O
DN	O
)	O
.	O
</s>
<s>
This	O
consists	O
of	O
its	O
Relative	B-Protocol
Distinguished	I-Protocol
Name	I-Protocol
(	O
RDN	O
)	O
,	O
constructed	O
from	O
some	O
attribute(s )	O
in	O
the	O
entry	O
,	O
followed	O
by	O
the	O
parent	O
entry	O
's	O
DN	O
.	O
</s>
<s>
Think	O
of	O
the	O
DN	O
as	O
the	O
full	B-Application
file	I-Application
path	I-Application
and	O
the	O
RDN	O
as	O
its	O
relative	O
filename	O
in	O
its	O
parent	O
folder	O
(	O
e.g.	O
</s>
<s>
An	O
entry	O
can	O
look	O
like	O
this	O
when	O
represented	O
in	O
LDAP	B-Protocol
Data	O
Interchange	O
Format	O
(	O
LDIF	O
)	O
,	O
a	O
plain	O
text	O
format	O
(	O
as	O
opposed	O
a	O
binary	O
protocol	O
such	O
as	O
LDAP	B-Protocol
itself	O
)	O
:	O
</s>
<s>
"	O
dn	O
"	O
is	O
the	O
distinguished	B-Protocol
name	I-Protocol
of	O
the	O
entry	O
;	O
it	O
is	O
neither	O
an	O
attribute	O
nor	O
a	O
part	O
of	O
the	O
entry	O
.	O
</s>
<s>
"	O
cn	O
=	O
John	O
Doe	O
"	O
is	O
the	O
entry	O
's	O
RDN	O
(	O
Relative	B-Protocol
Distinguished	I-Protocol
Name	I-Protocol
)	O
,	O
and	O
"	O
dc	O
=	O
example	O
,	O
dc	O
=	O
com	O
"	O
is	O
the	O
DN	O
of	O
the	O
parent	O
entry	O
,	O
where	O
"	O
dc	O
"	O
denotes	O
'	O
Domain	B-Protocol
Component	I-Protocol
 '	O
.	O
</s>
<s>
Attribute	O
names	O
are	O
typically	O
mnemonic	O
strings	O
,	O
like	O
"	O
cn	O
"	O
for	O
common	O
name	O
,	O
"	O
dc	O
"	O
for	O
domain	B-Protocol
component	I-Protocol
,	O
"	O
mail	O
"	O
for	O
e-mail	O
address	O
,	O
and	O
"	O
sn	O
"	O
for	O
surname	O
.	O
</s>
<s>
LDAP	B-Protocol
rarely	O
defines	O
any	O
ordering	O
:	O
The	O
server	O
may	O
return	O
the	O
values	O
of	O
an	O
attribute	O
,	O
the	O
attributes	O
in	O
an	O
entry	O
,	O
and	O
the	O
entries	O
found	O
by	O
a	O
search	O
operation	O
in	O
any	O
order	O
.	O
</s>
<s>
If	O
the	O
distinguished	B-Protocol
name	I-Protocol
in	O
the	O
add	O
request	O
already	O
exists	O
in	O
the	O
directory	O
,	O
then	O
the	O
server	O
will	O
not	O
add	O
a	O
duplicate	O
entry	O
but	O
will	O
set	O
the	O
result	O
code	O
in	O
the	O
add	O
result	O
to	O
decimal	O
68	O
,	O
"	O
entryAlreadyExists	O
"	O
.	O
</s>
<s>
LDAP-compliant	O
servers	O
will	O
never	O
dereference	O
the	O
distinguished	B-Protocol
name	I-Protocol
transmitted	O
in	O
the	O
add	O
request	O
when	O
attempting	O
to	O
locate	O
the	O
entry	O
,	O
that	O
is	O
,	O
distinguished	B-Protocol
names	I-Protocol
are	O
never	O
de-aliased	O
.	O
</s>
<s>
LDAP-compliant	O
servers	O
will	O
ensure	O
that	O
the	O
distinguished	B-Protocol
name	I-Protocol
and	O
all	O
attributes	O
conform	O
to	O
naming	O
standards	O
.	O
</s>
<s>
should	O
be	O
encrypted	O
using	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	B-Protocol
)	O
.	O
</s>
<s>
TLS	B-Protocol
.	O
</s>
<s>
BIND	O
also	O
sets	O
the	O
LDAP	B-Protocol
protocol	O
version	O
by	O
sending	O
a	O
version	O
number	O
in	O
the	O
form	O
of	O
an	O
integer	O
.	O
</s>
<s>
default	O
in	O
the	O
protocol	O
but	O
not	O
always	O
in	O
LDAP	B-Protocol
libraries	O
.	O
</s>
<s>
To	O
delete	O
an	O
entry	O
,	O
an	O
LDAP	B-Protocol
client	O
transmits	O
a	O
properly	O
formed	O
delete	O
request	O
to	O
the	O
server	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
filter	O
( &( 	O
objectClass	B-Protocol
=	O
person	O
)	O
( |( givenName	O
=	O
John	O
)	O
(	O
mail	O
=	O
john*	O
)	O
)	O
)	O
will	O
select	O
"	O
persons	O
"	O
(	O
elements	O
of	O
objectClass	B-Protocol
person	O
)	O
where	O
the	O
matching	O
rules	O
for	O
givenName	O
and	O
mail	O
determine	O
whether	O
the	O
values	O
for	O
those	O
attributes	O
match	O
the	O
filter	O
assertion	O
.	O
</s>
<s>
Note	O
that	O
a	O
common	O
misconception	O
is	O
that	O
LDAP	B-Protocol
data	O
is	O
case-sensitive	O
,	O
whereas	O
in	O
fact	O
matching	O
rules	O
and	O
ordering	O
rules	O
determine	O
matching	O
,	O
comparisons	O
,	O
and	O
relative	O
value	O
relationships	O
.	O
</s>
<s>
The	O
MODIFY	O
operation	O
is	O
used	O
by	O
LDAP	B-Protocol
clients	O
to	O
request	O
that	O
the	O
LDAP	B-Protocol
server	O
make	O
changes	O
to	O
existing	O
entries	O
.	O
</s>
<s>
The	O
MODIFY	O
operation	O
requires	O
that	O
the	O
distinguished	B-Protocol
name	I-Protocol
(	O
DN	O
)	O
of	O
the	O
entry	O
be	O
specified	O
,	O
and	O
a	O
sequence	O
of	O
changes	O
.	O
</s>
<s>
When	O
LDAP	B-Protocol
servers	O
are	O
in	O
a	O
replicated	O
topology	O
,	O
LDAP	B-Protocol
clients	O
should	O
consider	O
using	O
the	O
post-read	O
control	O
to	O
verify	O
updates	O
instead	O
of	O
a	O
search	O
after	O
an	O
update	O
.	O
</s>
<s>
The	O
post-read	O
control	O
is	O
designed	O
so	O
that	O
applications	O
need	O
not	O
issue	O
a	O
search	O
request	O
after	O
an	O
update	O
–	O
it	O
is	O
bad	O
form	O
to	O
retrieve	O
an	O
entry	O
for	O
the	O
sole	O
purpose	O
of	O
checking	O
that	O
an	O
update	O
worked	O
because	O
of	O
the	O
replication	O
eventual	B-General_Concept
consistency	I-General_Concept
model	O
.	O
</s>
<s>
An	O
LDAP	B-Protocol
client	O
should	O
not	O
assume	O
that	O
it	O
connects	O
to	O
the	O
same	O
directory	O
server	O
for	O
each	O
request	O
because	O
architects	O
may	O
have	O
placed	O
load-balancers	O
or	O
LDAP	B-Protocol
proxies	O
or	O
both	O
between	O
LDAP	B-Protocol
clients	O
and	O
servers	O
.	O
</s>
<s>
Modify	O
DN	O
(	O
move/rename	O
entry	O
)	O
takes	O
the	O
new	O
RDN	O
(	O
Relative	B-Protocol
Distinguished	I-Protocol
Name	I-Protocol
)	O
,	O
optionally	O
the	O
new	O
parent	O
's	O
DN	O
,	O
and	O
a	O
flag	O
that	O
indicates	O
whether	O
to	O
delete	O
the	O
value(s )	O
in	O
the	O
entry	O
that	O
match	O
the	O
old	O
RDN	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
LDAP	B-Protocol
does	O
not	O
define	O
transactions	O
of	O
multiple	O
operations	O
:	O
If	O
you	O
read	O
an	O
entry	O
and	O
then	O
modify	O
it	O
,	O
another	O
client	O
may	O
have	O
updated	O
the	O
entry	O
in	O
the	O
meantime	O
.	O
</s>
<s>
The	O
Extended	O
Operation	O
is	O
a	O
generic	O
LDAP	B-Protocol
operation	O
that	O
can	O
define	O
new	O
operations	O
that	O
were	O
not	O
part	O
of	O
the	O
original	O
protocol	O
specification	O
.	O
</s>
<s>
The	O
StartTLS	O
operation	O
establishes	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
the	O
descendant	O
of	O
SSL	B-Protocol
)	O
on	O
the	O
connection	O
.	O
</s>
<s>
During	O
TLS	B-Protocol
negotiation	O
the	O
server	O
sends	O
its	O
X.509	O
certificate	O
to	O
prove	O
its	O
identity	O
.	O
</s>
<s>
By	O
using	O
the	O
SASL/EXTERNAL	O
,	O
the	O
client	O
requests	O
the	O
server	O
derive	O
its	O
identity	O
from	O
credentials	O
provided	O
at	O
a	O
lower	O
level	O
(	O
such	O
as	O
TLS	B-Protocol
)	O
.	O
</s>
<s>
Though	O
technically	O
the	O
server	O
may	O
use	O
any	O
identity	O
information	O
established	O
at	O
any	O
lower	O
level	O
,	O
typically	O
the	O
server	O
will	O
use	O
the	O
identity	O
information	O
established	O
by	O
TLS	B-Protocol
.	O
</s>
<s>
Servers	O
also	O
often	O
support	O
the	O
non-standard	O
"	O
LDAPS	B-Protocol
"	O
(	O
"	O
Secure	O
LDAP	B-Protocol
"	O
,	O
commonly	O
known	O
as	O
"	O
LDAP	B-Protocol
over	O
SSL	B-Protocol
"	O
)	O
protocol	O
on	O
a	O
separate	O
port	B-Protocol
,	O
by	O
default	O
636	O
.	O
</s>
<s>
LDAPS	B-Protocol
differs	O
from	O
LDAP	B-Protocol
in	O
two	O
ways	O
:	O
</s>
<s>
2	O
)	O
the	O
LDAPS	B-Protocol
connection	O
must	O
be	O
closed	O
upon	O
TLS	B-Protocol
closure	O
.	O
</s>
<s>
Some	O
"	O
LDAPS	B-Protocol
"	O
client	O
libraries	O
only	O
encrypt	O
communication	O
;	O
they	O
do	O
not	O
check	O
the	O
host	O
name	O
against	O
the	O
name	O
in	O
the	O
supplied	O
certificate	O
.	O
</s>
<s>
An	O
LDAP	B-Protocol
uniform	B-Protocol
resource	I-Protocol
identifier	I-Protocol
(	O
URI	B-Protocol
)	O
scheme	O
exists	O
,	O
which	O
clients	O
support	O
in	O
varying	O
degrees	O
,	O
and	O
servers	O
return	O
in	O
referrals	O
and	O
continuation	O
references	O
(	O
see	O
RFC	O
4516	O
)	O
:	O
</s>
<s>
host	O
is	O
the	O
FQDN	B-Protocol
or	O
IP	O
address	O
of	O
the	O
LDAP	B-Protocol
server	O
to	O
search	O
.	O
</s>
<s>
port	B-Protocol
is	O
the	O
network	B-Protocol
port	I-Protocol
(	O
default	O
port	B-Protocol
389	O
)	O
of	O
the	O
LDAP	B-Protocol
server	O
.	O
</s>
<s>
DN	O
is	O
the	O
distinguished	B-Protocol
name	I-Protocol
to	O
use	O
as	O
the	O
search	O
base	O
.	O
</s>
<s>
For	O
example	O
,	O
(	O
objectClass	B-Protocol
=	O
*	O
)	O
as	O
defined	O
in	O
RFC	O
4515	O
.	O
</s>
<s>
extensions	O
are	O
extensions	O
to	O
the	O
LDAP	B-Protocol
URL	O
format	O
.	O
</s>
<s>
For	O
example	O
,	O
"	O
ldap://ldap.example.com/cn	O
=	O
John%20Doe	O
,	O
dc	O
=	O
example	O
,	O
dc	O
=	O
com	O
"	O
refers	O
to	O
all	O
user	O
attributes	O
in	O
John	O
Doe	O
's	O
entry	O
in	O
ldap.example.com,	O
while	O
"	O
ldap:///dc	O
=	O
example	O
,	O
dc	O
=	O
com	O
??	O
sub	O
?	O
</s>
<s>
There	O
is	O
a	O
similar	O
non-standard	O
ldaps	B-Protocol
URI	B-Protocol
scheme	O
for	O
LDAP	B-Protocol
over	O
SSL	B-Protocol
.	O
</s>
<s>
This	O
should	O
not	O
be	O
confused	O
with	O
LDAP	B-Protocol
with	O
TLS	B-Protocol
,	O
which	O
is	O
achieved	O
using	O
the	O
StartTLS	O
operation	O
using	O
the	O
standard	O
ldap	B-Protocol
scheme	O
.	O
</s>
<s>
The	O
contents	O
of	O
the	O
entries	O
in	O
a	O
subtree	O
are	O
governed	O
by	O
a	O
directory	B-Application
schema	I-Application
,	O
a	O
set	O
of	O
definitions	O
and	O
constraints	O
concerning	O
the	O
structure	O
of	O
the	O
directory	O
information	O
tree	O
(	O
DIT	O
)	O
.	O
</s>
<s>
Each	O
entry	O
must	O
have	O
an	O
objectClass	B-Protocol
attribute	O
,	O
containing	O
named	O
classes	O
defined	O
in	O
the	O
schema	O
.	O
</s>
<s>
A	O
parallel	O
to	O
the	O
schema	O
of	O
an	O
objectClass	B-Protocol
is	O
a	O
class	O
definition	O
and	O
an	O
instance	O
in	O
Object-oriented	B-Language
programming	I-Language
,	O
representing	O
LDAP	B-Protocol
objectClass	B-Protocol
and	O
LDAP	B-Protocol
entry	O
,	O
respectively	O
.	O
</s>
<s>
Directory	O
servers	O
may	O
publish	O
the	O
directory	B-Application
schema	I-Application
controlling	O
an	O
entry	O
at	O
a	O
base	O
DN	O
given	O
by	O
the	O
entry	O
's	O
subschemaSubentry	O
operational	O
attribute	O
.	O
</s>
<s>
A	O
schema	O
for	O
representing	O
individual	O
people	O
within	O
organizations	O
is	O
termed	O
a	O
white	B-Application
pages	I-Application
schema	I-Application
.	O
</s>
<s>
Most	O
parts	O
of	O
LDAP	B-Protocol
are	O
extensible	O
.	O
</s>
<s>
As	O
LDAP	B-Protocol
has	O
gained	O
momentum	O
,	O
vendors	O
have	O
provided	O
it	O
as	O
an	O
access	O
protocol	O
to	O
other	O
services	O
.	O
</s>
<s>
The	O
implementation	O
then	O
recasts	O
the	O
data	O
to	O
mimic	O
the	O
LDAP/X.500	O
model	O
,	O
but	O
how	O
closely	O
this	O
model	O
is	O
followed	O
varies	O
.	O
</s>
<s>
For	O
example	O
,	O
there	O
is	O
software	O
to	O
access	O
SQL	B-Language
databases	I-Language
through	O
LDAP	B-Protocol
,	O
even	O
though	O
LDAP	B-Protocol
does	O
not	O
readily	O
lend	O
itself	O
to	O
this	O
.	O
</s>
<s>
X.500	B-Protocol
servers	O
may	O
support	O
LDAP	B-Protocol
as	O
well	O
.	O
</s>
<s>
Similarly	O
,	O
data	O
previously	O
held	O
in	O
other	O
types	O
of	O
data	O
stores	O
are	O
sometimes	O
moved	O
to	O
LDAP	B-Protocol
directories	O
.	O
</s>
<s>
For	O
example	O
,	O
Unix	O
user	O
and	O
group	O
information	O
can	O
be	O
stored	O
in	O
LDAP	B-Protocol
and	O
accessed	O
via	O
PAM	B-Application
and	O
NSS	B-Protocol
modules	O
.	O
</s>
<s>
LDAP	B-Protocol
is	O
often	O
used	O
by	O
other	O
services	O
for	O
authentication	O
and/or	O
authorization	O
(	O
what	O
actions	O
a	O
given	O
already-authenticated	O
user	O
can	O
do	O
on	O
what	O
service	O
)	O
.	O
</s>
<s>
For	O
example	O
in	O
Active	B-Protocol
Directory	I-Protocol
Kerberos	B-Protocol
is	O
used	O
in	O
the	O
authentication	O
step	O
,	O
while	O
LDAP	B-Protocol
is	O
used	O
in	O
the	O
authorization	O
step	O
.	O
</s>
<s>
An	O
example	O
of	O
such	O
data	O
model	O
is	O
the	O
GLUE	O
Schema	O
,	O
which	O
is	O
used	O
in	O
a	O
distributed	O
information	O
system	O
based	O
on	O
LDAP	B-Protocol
that	O
enable	O
users	O
,	O
applications	O
and	O
services	O
to	O
discover	O
which	O
services	O
exist	O
in	O
a	O
Grid	O
infrastructure	O
and	O
further	O
information	O
about	O
their	O
structure	O
and	O
state	O
.	O
</s>
<s>
An	O
LDAP	B-Protocol
server	O
may	O
return	O
referrals	O
to	O
other	O
servers	O
for	O
requests	O
that	O
it	O
cannot	O
fulfill	O
itself	O
.	O
</s>
<s>
This	O
requires	O
a	O
naming	O
structure	O
for	O
LDAP	B-Protocol
entries	O
so	O
one	O
can	O
find	O
a	O
server	O
holding	O
a	O
given	O
distinguished	B-Protocol
name	I-Protocol
(	O
DN	O
)	O
,	O
a	O
concept	O
defined	O
in	O
the	O
X.500	B-Protocol
Directory	I-Protocol
and	O
also	O
used	O
in	O
LDAP	B-Protocol
.	O
</s>
<s>
Another	O
way	O
of	O
locating	O
LDAP	B-Protocol
servers	O
for	O
an	O
organization	O
is	O
a	O
DNS	B-Protocol
server	B-Protocol
record	I-Protocol
(	O
SRV	O
)	O
.	O
</s>
<s>
An	O
organization	O
with	O
the	O
domain	O
example.org	O
may	O
use	O
the	O
top	O
level	O
LDAP	B-Protocol
DN	O
dc	O
=	O
example	O
,	O
dc	O
=	O
org	O
(	O
where	O
dc	O
means	O
domain	B-Protocol
component	I-Protocol
)	O
.	O
</s>
<s>
If	O
the	O
LDAP	B-Protocol
server	O
is	O
also	O
named	O
ldap.example.org,	O
the	O
organization	O
's	O
top	O
level	O
LDAP	B-Protocol
URL	O
becomes	O
ldap://ldap.example.org/dc	O
=	O
example	O
,	O
dc	O
=	O
org	O
.	O
</s>
<s>
Primarily	O
two	O
common	O
styles	O
of	O
naming	O
are	O
used	O
in	O
both	O
X.500	B-Protocol
 [ 2008 ] 	O
and	O
LDAPv3	O
.	O
</s>
<s>
The	O
domain	B-Protocol
component	I-Protocol
model	O
uses	O
the	O
model	O
described	O
above	O
.	O
</s>
