Network Working Group                                           T. Howes
Request for Comments: 1959                                      M. Smith
Category: Standards Track                         University of Michigan
                                                               June 1996


                           An LDAP URL Format

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

1.  Abstract

   LDAP is the Lightweight Directory Access Protocol, defined in [1] and
   [2].  This document describes a format for an LDAP Uniform Resource
   Locator which will allow Internet clients to have direct access to
   the LDAP protocol.  While LDAP currently is used only as a front end
   to the X.500 directory, the URL format described here is general
   enough to handle the case of stand-alone LDAP servers (i.e., LDAP
   servers not back-ended by X.500).

2.  URL Definition

   An LDAP URL begins with the protocol prefix "ldap" and is defined by
   the following grammar.

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

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

    <dn> ::= a string as defined in RFC 1485

    <attributes> ::= NULL | <attributelist>

    <attributelist> ::= <attributetype>
                        | <attributetype> [ "," <attributelist> ]

    <attributetype> ::= a string as defined in RFC 1777

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

    <filter> ::= a string as defined in RFC 1558

   The ldap prefix indicates an entry or entries residing in the LDAP
   server running on the given <hostname> at the given <portnumber>.
   The default port is TCP port 389.  The <dn> is an LDAP Distinguished
   Name using the string format described in [1], with any URL-illegal
   characters (e.g., spaces) escaped using the % method described in RFC
   1738.

   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
   perform 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
   specified in [4], with any URL-illegal characters escaped using the %
   method described in RFC 1738.  If <filter> is omitted, a filter of
   "(objectClass=*)" is assumed.

   Note that if the entry resides in the X.500 namespace, it 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
   server.

3.  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:

  ldap:///o=University%20of%20Michigan,c=US

   An LDAP URL referring to the University of Michigan entry in a
   particular ldap server:

  ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US

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

   An LDAP URL referring to only the postalAddress attribute of the
   University of Michigan entry:

  ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US?postalAddress

   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", retrieving all attributes:

  ldap:///o=University%20of%20Michigan,c=US??sub?(cn=Babs%20Jensen)

   An LDAP URL referring to all children of the c=GB entry:

  ldap://ldap.itd.umich.edu/c=GB?objectClass?one

The objectClass attribute is requested to be returned along with the
entries.

4.  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. The security implications of
   resolving an LDAP URL are the same as those of resolving any LDAP
   query. See the RFC 1777 for more details.

5.  Prototype Implementation Availability

   There is a prototype implementation of the specification defined in
   this document available.  It is an extension to the libwww client
   library, provided in both source and binary forms.  Also included are
   binary versions of the Mosaic WWW client for various platforms.  See
   the following URL for more details:

        ftp://terminator.rs.itd.umich.edu/ldap/url/

6.  Bibliography

   [1]  Kille, S., "A String Representation of Distinguished Names",
        RFC 1779, March 1995.

   [2]  Yeong, W., Howes, T., and S. Kille, "Lightweight
        Directory Access Protocol", RFC 1777, March 1995.

   [3]  Howes, R., Kille, S., Yeong, W., and C. Robbins, "The String
        Representation of Standard Attribute Syntaxes", RFC 1778,
        March 1995.

   [4]  Howes, T., "A String Representation of LDAP Search Filters",
        RFC 1558, December 1993.

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

7.  Acknowledgements

   This material is based upon work supported by the National Science
   Foundation under Grant No. NCR-9416667.

8.  Authors' Addresses

   Tim Howes
   University of Michigan
   ITD Research Systems
   535 W William St.
   Ann Arbor, MI 48103-4943
   USA

   Phone: +1 313 747-4454
   EMail: tim@umich.edu


   Mark Smith
   University of Michigan
   ITD Research Systems
   535 W William St.
   Ann Arbor, MI 48103-4943
   USA

   Phone: +1 313 764-2277
   EMail: mcs@umich.edu