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rfc:rfc1959

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

Howes & Smith Standards Track [Page 1] RFC 1959 An LDAP URL Format June 1996

 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.

Howes & Smith Standards Track [Page 2] RFC 1959 An LDAP URL Format June 1996

 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/

Howes & Smith Standards Track [Page 3] RFC 1959 An LDAP URL Format June 1996

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

Howes & Smith Standards Track [Page 4]

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