Network Working Group                                        Tim Howes
INTERNET DRAFT                                              Mark Smith
OBSOLETES: RFC 1959                      Netscape Communications Corp.
                                                            March 1997

                          The LDAP URL Format

1.  Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are  working  docu-
ments  of the Internet Engineering Task Force (IETF), its areas, and its
working groups.  Note that other  groups  may  also  distribute  working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum  of  six  months
and  may  be  updated,  replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as ``work in progress.''

To learn the current status of  any  Internet-Draft,  please  check  the
``1id-abstracts.txt''  listing  contained in the Internet- Drafts Shadow
Directories on (US East Coast),  (Europe), (US West Coast), or (Pacific Rim).

2.  Abstract

LDAP is the Lightweight Directory Access Protocol, defined  in  [2]  and
[3].   This  document  describes  a  format for an LDAP Uniform Resource
Locator.  The format describes an LDAP search operation  to  perform  to
retrieve  information from an LDAP directory. This document replaces RFC
1959. It updates the LDAP URL format for version 3 of LDAP and defines a
way  to  indicate  whether  the URL references a master or slave server.
This document also defines a second URL scheme prefix for  LDAP  running
over the secure sockets layer protocol.

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3.  URL Definition

An LDAP URL begins with  the  protocol  prefix  "ldap"  (or  the  prefix
"ldaps" for LDAP over SSL) and is defined by the following grammar.

    <ldapurl> ::= <scheme> "://" [ <hostport> ] "/"
                [ <dn> [ "?" [ <attributes> ] [ "?" [ <scope> ]
                [ "?" [ <filter> ] [ "?" <masterorslave> ] ] ] ] ]

    <scheme> ::= "ldap" | "ldaps"

    <hostport> ::= <hostname> [ ":" <portnumber> ]

    <dn> ::= a distinguished name string as defined in [1]

    <attributes> ::= NULL
                   | <attributedesc>
                   | <attributedesc> [ "," <attributes> ]

    <attributedesc> ::= an AttributeDescription string as defined in [3]

    <scope> ::= "base" | "one" | "sub"

    <filter> ::= a filter string as defined in [4]

    <masterorslave> ::= "master" | "slave"

The "ldap" and "ldaps" prefixes indicate an entry or entries residing in
the  LDAP  server  running  on  the given <hostname> at the given <port-
number>.  For regular LDAP servers, the default port is  TCP  port  389.
For  LDAP  servers  running over secure sockets layer transport [6], the
default port is 636.

The <dn> is an LDAP Distinguished Name using the string format described
in [1]. It identifies the base object of the LDAP search.

The <attributes> construct is used to indicate which  attributes  should
be returned from the entry or entries.  Individual <attributetype> names
are as defined for AttributeType in RFC 1777.  If the <attributes>  part
is omitted, all attributes of the entry or entries should be returned.

The <scope> construct is used to specify the scope of the search to per-
form  in  the  given LDAP server.  The allowable scopes are "base" for a
base object search, "one" for a one-level search, or "sub" for a subtree
search.  If <scope> is omitted, a scope of "base" is assumed.

The <filter> is used to specify the search filter to  apply  to  entries
within  the  specified  scope  during  the  search.   It  has the format

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INTERNET DRAFT                                                March 1997

specified in [4].  If <filter> is omitted, a filter of "(objectClass=*)"
is assumed.

The <masterorslave> construct is optionally used to indicate whether the
LDAP  URL  refers  to a master LDAP server (i.e., one able to update the
data referenced) or a slave LDAP server (i.e., one unable to update  the
data referenced).

Note that if the entry or entries reside in the  X.500  namespace,  they
should  be  reachable  from  any LDAP server that is providing front-end
access to the X.500 directory.  If the <hostport> part  of  the  URL  is
missing, the URL can be resolved by contacting any X.500-back-ended LDAP

Note that any any URL-illegal characters (e.g., spaces) occurring inside
a  <dn>, <filter>, or other element of an LDAP URL must be escaped using
the % method described in RFC 1738.

4.  Examples

The following are some example LDAP URLs using the format defined above.
An  LDAP  URL  referring  to the University of Michigan entry, available
from any X.500-capable LDAP server:


An LDAP URL referring to the University of Michigan entry in a  particu-
lar ldap server:


This URL corresponds to a base object search  of  the  "o=University  of
Michigan,  c=US" entry using a filter of (objectclass=*), requesting all

An LDAP URL referring to only the postalAddress attribute of the Univer-
sity of Michigan entry:


The corresponding LDAP search operation is the same as in  the  previous
example, except that only the postalAddress attribute is requested.

An LDAP URL referring to the  set  of  entries  found  by  querying  any
X.500-capable  LDAP  server and doing a subtree search of the University
of Michigan for any entry with a common name of "Babs Jensen",  retriev-
ing all attributes:

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A secure LDAP URL referring to the master server containing all children
of the c=GB entry:


The objectClass attribute is requested to be  returned  along  with  the
entries, and the default filter of "(objectclass=*)" is used.

5.  Security Considerations

The LDAP URL format does not provide a way to specify credentials to use
when  resolving  the  URL.  Therefore, it is expected that such requests
will be unauthenticated, unless some out-of-band mechanism is used.

The LDAP URL format allows the specification of an arbitrary LDAP search
operation  to  be  performed when evaluating the LDAP URL.  Following an
LDAP URL may cause unexpected results, for  example,  the  retrieval  of
large  amounts of data, the initiation of a long-lived search, etc.  The
security implications of resolving an LDAP URL are the same as those  of
resolving an LDAP search query.

6.  Bibliography

[1]  Lightweight Directory Access Protocol (v3): UTF-8 String  Represen-
     tation  of  Distinguished  Names.   M.  Wahl, S. Kille, draft-ietf-
     asid-ldapv3-dn-02.txt, March 1997.

[2]  Lightweight Directory Access Protocol (v3).  M. Wahl, T. Howes,  S.
     Kille, draft-ietf-asid-ldapv3-protocol-04.txt, March 1997.

[3]  Lightweight Directory Access Protocol (v3): Attribute Syntax Defin-
     itions.   M.  Wahl,  A.  Coulbeck,  T. Howes, S. Kille, draft-ietf-
     asid-ldapv3-attributes-04.txt, March 1997.

[4]  A String Representation of LDAP Search Filters.  T.  Howes,  draft-
     ietf-asid-ldapv3-filter.00.txt, March 1997.

[5]  Uniform Resource Locators (URL). T. Berners-Lee,  L.  Masinter,  M.
     McCahill, Request for Comment (RFC) 1738, December 1994.

[6]  The SSL Protocol Version 3.0. A. Freier,  P.  Karlton,  P.  Kocher,
     draft-ietf-tls-ssl-version3-00.txt, November 1996.

7.  Author's Address

   Tim Howes

Howes & Smith                                                   [Page 4]

INTERNET DRAFT                                                March 1997

   University of Michigan
   ITD Research Systems
   535 W William St.
   Ann Arbor, MI 48103-4943
   +1 313 747-4454

   Mark Smith
   University of Michigan
   ITD Research Systems
   535 W William St.
   Ann Arbor, MI 48103-4943
   +1 313 764-2277

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