Network Working Group                                Mark Smith, Editor
Request for Comments: DRAFT               Netscape Communications Corp.                         Pearl Crescent, LLC
Obsoletes: RFC 2255                                           Tim Howes
Expires: 25 April 13 August 2004                                   Opsware, Inc.

                                                        25 October 2003

                                                       13 February 2004

                     LDAP: Uniform Resource Locator

1.  Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   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."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   Discussion of this document should take place on the LDAP (v3)
   Revision (ldapbis) Working Group mailing list <ietf->.

Copyright (C) The Internet Society (2003). (2004).  All Rights Reserved.

2.  Abstract

   This document describes a format for an LDAP Uniform Resource Locator
   (URL).  An LDAP URL describes an LDAP search operation that is used
   to retrieve information from an LDAP directory, or, in the context of
   an LDAPv3 referral or reference, an LDAP URL describes a service
   where an LDAP operation may be progressed.

3.  Table of Contents

1.     Status of this Memo............................................1
2.     Abstract.......................................................1
3.     Table of Contents..............................................2
4.     Introduction...................................................2
5.     URL Definition.................................................2 Definition.................................................3
5.1.      Escaping Using the % Method.................................4
6.     Defaults for Fields of the LDAP URL............................5
7.     Examples.......................................................6     Examples.......................................................5
8.     Security Considerations........................................8 Considerations........................................7
9.     Normative References...........................................8
10.    Informative References.........................................9
11.    Intellectual Property Rights...................................9
12.    Acknowledgements...............................................10
13.    Authors' Address...............................................10 Addresses.............................................10
14.    Full Copyright Statement.......................................11
15.    Appendix A: Changes Since RFC 2255.............................11
15.1.     Technical Changes...........................................11
15.2.     Editorial Changes...........................................12
16.    Appendix B: Changes Since Previous Document Revision...........13
16.1.     Technical Changes...........................................14
16.2.     Editorial Changes...........................................14

4.  Introduction

   LDAP is the Lightweight Directory Access Protocol, defined in
   [Protocol].  This document specifies the LDAP URL format for version
   3 of LDAP and clarifies how LDAP URLs are resolved. This document
   also defines an extension mechanism for LDAP URLs, so that future
   documents can extend their functionality, for example, to provide
   access to new LDAPv3 extensions as they are defined.  Note:  not all
   of the parameters of the LDAP search operation described in
   [Protocol] can be expressed using the format defined in this

   This document is an integral part of the LDAP Technical Specification

   This document replaces RFC 2255. See Appendix A for a list of changes
   relative to RFC 2255.

   The key words "MUST", "MAY", and "SHOULD" used in this document are
   to be interpreted as described in [RFC2119].

5.  URL Definition

   An LDAP URL begins with the protocol prefix "ldap" and is defined by
   the following grammar, following the ABNF notation defined in

       ldapurl     = scheme COLON SLASH SLASH [hostport] [SLASH dn
                     [QUESTION [attributes] [QUESTION [scope]
                     [QUESTION [filter] [QUESTION extensions]]]]]
       scheme      = "ldap"
       hostport    = <hostport from Section 3.2.2 of [RFC2396]>
                       ; as updated by [RFC2732] to allow IPv6 literal addresses
       dn          = <distinguishedName from Section 3 of [LDAPDN]>
                       ; see the "Escaping Using the % Method" section below.
       attributes  = attrdesc *(COMMA attrdesc)
       attrdesc    = <AttributeDescription from Section 4.1.4 of [Protocol]>
                     / ASTERISK
                       ; see the "Escaping Using the % Method" section below.
       scope       = "base" / "one" / "sub"
       filter      = <filter from Section 4 of [Filters]>
                       ; see the "Escaping Using the % Method" section below.
       extensions  = extension *(COMMA extension)
       extension   = [EXCLAMATION] extype [EQUALS exvalue]
       extype      = oid / oiddescr
       exvalue     = <LDAPString from section 4.1.2 of [Protocol]>
                       ; see the "Escaping Using the % Method" section below.
       oid         = <LDAPOID from section 4.1.2 of [Protocol]>
       oiddescr    = <name from section 3.3 of [RFC3383]> [LDAPIANA]>

       EXCLAMATION = %x21 ; exclamation mark ("!")
       ASTERISK    = %x2A ; asterisk ("*")
       COLON       = %x3A ; colon (":")
       QUESTION    = %x3F ; question mark ("?")
       SLASH       = %x5C; forward slash ("/")

   The "ldap" prefix indicates an entry or entries residing in the LDAP
   server running on the given hostname at the given portnumber.  Note
   that the hostport may contain literal IPv6 addresses as specified in

   The dn is an LDAP Distinguished Name using the string format
   described in [LDAPDN]. It identifies the base object of the LDAP
   search or the target of a non-search operation.

   The attributes construct is used to indicate which attributes should
   be returned from the entry or entries.  Individual attrdesc names are
   as defined for AttributeDescription in [Protocol].

   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.

   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 [Filters].

   The extensions construct provides the LDAP URL with an extensibility
   mechanism, allowing the capabilities of the URL to be extended in the
   future. Extensions are a simple comma-separated list of type=value
   pairs, where the =value portion MAY be omitted for options not
   requiring it. Each type=value pair is a separate extension. These
   LDAP URL extensions are not necessarily related to any of the LDAPv3
   extension mechanisms. Extensions may be supported or unsupported by
   the client resolving the URL. An extension prefixed with a '!'
   character (ASCII 33) is critical. An extension not prefixed with a
   '!' character is non-critical.

   If an LDAP URL extension is supported recognized by an implementation, the client, the client
   implementation MUST obey the
   extension if the extension is critical. The client SHOULD obey
   supported extensions that are non-critical. make use of it.  If an extension is unsupported by the client, not
   recognized and is marked critical, the client implementation MUST NOT
   process the URL if the extension is critical. URL.  If an unsupported extension is non-critical, the client MUST ignore the extension.

   If a critical extension cannot be processed successfully by the
   client, not recognized and it not marked
   critical, the client implementation MUST NOT process the URL. If a non-critical
   extension cannot be processed successfully by the client, the client
   SHOULD ignore the extension.

   The extension type (extype) MAY be specified using the oid form
   (e.g., or the oiddesc form (e.g., myLDAPURLExtension).  Use
   of the oiddesc form SHOULD be restricted to registered object
   identifier descriptive names.  See [RFC3383] [LDAPIANA] for registration
   details and usage guidelines for descriptive names.

   No LDAP URL extensions are defined in this document.  Other documents
   or a future version of this document MAY define one or more

5.1.  Escaping Using the % Method

   A generated LDAP URL MUST consist only of the restricted set of
   characters included in the uric production that is defined in section
   2 of [RFC2396].  Implementations SHOULD accept other valid UTF-8
   strings [UTF-8] [RFC3629] as input.  An octet MUST be escaped using the %
   method described in section 2.4 of [RFC2396] in any of these

      The octet is not in the reserved set defined in section 2.2 of
      [RFC2396] or in the unreserved set defined in section 2.3 of

      It is the single Reserved character '?' and occurs inside a dn,
      filter, or other element of an LDAP URL.

      It is a comma character ',' that occurs inside an extension value.

6.  Defaults for Fields of the LDAP URL

   Some fields of the LDAP URL are optional, as described above.  In the
   absence of any other specification, the following general defaults
   SHOULD be used when a field is absent.  Note:  other documents MAY
   specify different defaulting rules; for example, section 4.1.11 4.1.10 of
   [Protocol] specifies a different rule for determining the correct DN
   to use when it is absent in an LDAP URL that is returned as a

      The default LDAP port is TCP port 389. If no hostport is given,
      the client must have some apriori knowledge of an appropriate LDAP
      server to contact.

      If no dn is given, the default is the zero-length DN, "".

      If the attributes part is omitted, all user attributes of the
      entry or entries should be requested (e.g., by setting the
      attributes field AttributeDescriptionList in the LDAP search
      request to a NULL list, or (in LDAPv3) by requesting the special
      attribute name "*").

      If scope is omitted, a scope of "base" is assumed.

      If filter is omitted, a filter of "(objectClass=*)" is assumed.

      If extensions is omitted, no extensions are assumed.

7.  Examples

   The following are some example LDAP URLs using the format defined
   above.  The first example is an LDAP URL referring to the University
   of Michigan entry, available from an LDAP server of the client's


   The next example is an LDAP URL referring to the University of
   Michigan entry in a particular ldap server:


   Both of these URLs correspond to a base object search of the
   "o=University of Michigan,c=US" entry using a filter of
   "(objectclass=*)", requesting all attributes.

   The next example is an LDAP URL referring to only the postalAddress
   attribute of the University of Michigan entry:


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

   The next example is an LDAP URL referring to the set of entries found
   by querying the given LDAP server on port 6666 and doing a subtree
   search of the University of Michigan for any entry with a common name
   of "Babs Jensen", retrieving all attributes:


   The next example is an LDAP URL referring to all children of the c=GB


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

   The next example is an LDAP URL to retrieve the mail attribute for
   the LDAP entry named "o=Question?,c=US" is given below, illustrating
   the use of the escaping mechanism on the reserved character '?'.


   The next example (which is broken into two lines for readability)
   illustrates the interaction between the LDAP string representation of
   filters quoting mechanism and URL quoting mechanisms.



   The filter in this example uses the LDAP escaping mechanism of \ to
   encode three zero or null bytes in the value. In LDAP, the filter
   would be written as (four-octet=\00\00\00\04). Because the \
   character must be escaped in a URL, the \'s are escaped as %5c in the
   URL encoding.

   The next example illustrates the interaction between the LDAP string
   representation of DNs quoting mechanism and URL quoting mechanisms.


   The DN encoded in the above URL is:

     o=An Example\2c Inc.,c=US

   That is, the left-most RDN value is:

     An Example, Inc.

   The following three URLs that are equivalent, assuming that the
   defaulting rules specified in section 4 of this document are used:


   These three URLs all point to the root DSE on the

The final two examples show use of a hypothetical, experimental bind
name extension (the value associated with the extension is an LDAP DN).


   The two URLs are the same, except that the second one marks the e-
   bindname extension as critical. Notice the use of the % encoding
   method to encode the commas within the distinguished name value in
   the e-bindname extension.

8.  Security Considerations

   General URL security considerations discussed in [RFC2396] are
   relevant for LDAP URLs.

   The use of security mechanisms when processing LDAP URLs requires
   particular care, since clients may encounter many different servers
   via URLs, and since URLs are likely to be processed automatically,
   without user intervention. A client SHOULD have a user-configurable
   policy about which servers to connect to using which security
   mechanisms, and SHOULD NOT make connections that are inconsistent
   with this policy.  If a client chooses to reuse an existing
   connection when resolving one or more LDAP URL, it MUST ensure that
   the connection is compatible with the URL and that no security
   policies are violated.

   Sending authentication information, no matter the mechanism, may
   violate a user's privacy requirements.  In the absence of specific
   policy permitting authentication information to be sent to a server,
   a client should use an anonymous connection.  (Note that clients
   conforming to previous LDAP URL specifications, where all connections
   are anonymous and unprotected, are consistent with this
   specification; they simply have the default security policy.)  Simply
   opening a connection to another server may violate some users'
   privacy requirements, so clients should provide the user with a way
   to control URL processing.

   Some authentication methods, in particular reusable passwords sent to
   the server, may reveal easily-abused information to the remote server
   or to eavesdroppers in transit, and should not be used in URL
   processing unless explicitly permitted by policy.  Confirmation by
   the human user of the use of authentication information is
   appropriate in many circumstances.  Use of strong authentication
   methods that do not reveal sensitive information is much preferred.
   If the URL represents a referral for an update operation, strong
   authentication methods SHOULD be used.  Please refer to the Security
   Considerations section of [AuthMeth] for more information.

   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.

9.  Normative References

[AuthMeth]  Harrison, R. (editor), "LDAP: Authentication Methods",
            draft-ietf-ldapbis-authmeth-xx.txt, a work in progress.  a
            work in progress.

[LDAPDN]    Zeilenga, K. (editor), "LDAP: String Representation of
            Distinguished Names", draft-ietf-ldapbis-dn-xx.txt, a work
            in progress.

[Filters]   Smith, M. and Howes, T., "LDAP: String Representation of
            Search Filters", draft-ietf-ldapbis-filter-xx.txt, a work in

[LDAPIANA]  Zeilenga, K., "IANA Considerations for LDAP", draft-ietf-
            ldapbis-bcp64-xx.txt, a work in progress.

[RFC2119]   Bradner, S., "Key Words for use in RFCs to Indicate
            Requirement Levels," RFC 2119, BCP 14, March 1997.

[Protocol]  Sermersheim, J. (editor), "LDAP: The Protocol", draft-
   ietf-ldapbis-protocol-xx.txt, draft-ietf-
            ldapbis-protocol-xx.txt, a work in progress.

[RFC2234]   Crocker, D., Overell, P., "Augmented BNF for Syntax
            Specifications: ABNF", RFC 2234, November 1997.

[RFC2396]   Berners-Lee, T., Fielding, R., and Masinter, L., "Uniform
            Resource Identifiers (URI): Generic Syntax", RFC 2396,
            August 1998.

[RFC2732]   Hinden, R., Carpenter, B., Masinter, L., "Format for Literal
            IPv6 Addresses in URL's", RFC 2732, December 1999.

   [RFC3383] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
    Considerations for the Lightweight Directory Access Protocol
   (LDAP)", RFC 3383, September 2002.

   [AuthMeth] Harrison, R. (editor), "LDAP: Authentication Methods",
   draft-ietf-ldapbis-authmeth-xx.txt, a work in progress.  a work in

[Roadmap]   K. Zeilenga (editor), "LDAP: Technical Specification Road
            Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in progress.


[RFC3629]   Yergeau, F., "UTF-8, a transformation format of ISO 10646",
   draft-yergeau-rfc2279bis-xx.txt, a work in progress.
            RFC 3629, November 2003.

10.  Informative References


11.  Intellectual Property Rights

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive

12.  Acknowledgements

   The LDAP URL format was originally defined at the University of
   Michigan. This material is based upon work supported by the National
   Science Foundation under Grant No. NCR-9416667. The support of both
   the University of Michigan and the National Science Foundation is
   gratefully acknowledged.

   This document is an update to RFC 2255 by Tim Howes and Mark Smith.
   Changes included in this revised specification are based upon
   discussions among the authors, discussions within the LDAP (v3)
   Revision Working Group (ldapbis), and discussions within other IETF
   Working Groups.  The contributions of individuals in these working
   groups is gratefully acknowledged.  Several people in particular have
   made valuable comments on this document; RL "Bob" Morgan, Mark Wahl,
   Kurt Zeilenga, Jim Sermersheim, and Hallvard Furuseth deserve special
   thanks for their contributions.

13.  Authors' Address Addresses

   Mark Smith, Editor
   Netscape Communications Corp.
   360 W. Caribbean Drive
   Sunnyvale, CA 94089
   Pearl Crescent, LLC
   447 Marlpool Dr.
   Saline, MI 48176
   +1 650 937-3477 734 944-2856

   Tim Howes
   Opsware, Inc.
   599 N. Mathilda Ave.
   Sunnyvale, CA 94085
   +1 408 744-7509

14.  Full Copyright Statement

   Copyright (C) The Internet Society (2003). (2004).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

15.  Appendix A: Changes Since RFC 2255

15.1.  Technical Changes

   The following technical changes were made to the contents of the "URL
   Definition" section:

   Revised all of the ABNF to use common productions from [Models].

   Added note and references to [RFC2732] to allow literal IPv6
   addresses inside the hostport portion of the URL.

   Added missing ASTERISK as an alternative for the attrdesc part of the
   URL.  It is believed that existing implementations of RFC 2255
   already support this.

   Added angle brackets around free-form prose in the "dn", "hostport",
   "attrdesc", "filter", and "exvalue" rules.

   Changed the ABNF for ldapurl to group the dn component with the
   preceding slash.

   Changed the extype rule to be an LDAPOID from [Protocol] or an OID
   description from [RFC3383]. [LDAPIANA].

   Changed the text about extension types so it references [RFC3383]. [LDAPIANA].
   Reordered rules to more closely follow the order the elements appear
   in the URL.

   "Bindname Extension": removed due to lack of known implementations.

15.2.  Editorial Changes

   Changed document title to include "LDAP:" prefix.

   IESG Note: removed note about lack of satisfactory mandatory
   authentication mechanisms.

   "Status of this Memo" section: updated boilerplate to match current
   I-D guidelines.

   "Abstract" section: separated from introductory material.

   "Table of Contents" section: added.

   "Introduction" section: new section; separated from the Abstract.
   Changed the text indicate that RFC 2255 is replaced by this document
   (instead of RFC 1959).  Added text to indicate that LDAP URLs are
   used for references and referrals.  Fixed typo (replaced the nonsense
   phrase "to perform to retrieve" with "used to retrieve").  Added a
   note to let the reader know that not all of the parameters of the
   LDAP search operation described in [Protocol] can be expressed using
   this format.

   "URL Definition" section: removed second copy of ldapurl grammar and
   following two paragraphs (editorial error in RFC 2255).  Fixed line
   break within '!' sequence.  Reworded last paragraph to clarify which
   characters must be URL escaped.   Added text to indicate that LDAP
   URLs are used for references and referrals.  Added text that refers
   to the ABNF from RFC 2234.  Clarified and strengthened the
   requirements with respect to processing of URLs that contain
   recognized and unrecognized extensions (the approach now matches that
   specified in [Protocol] for LDAP controls).

   "Defaults for Fields of the LDAP URL" section: added; formed by
   moving text about defaults out of the "URL Definition" section.

   "URL Processing" section: clarified that connections MAY be reused
   only if the open connection is compatible with the URL.  Added text
   to indicate that use of security services is encouraged and that they
   SHOULD be used when updates are involved.  Removed "dn" from
   discussion of authentication methods.  Added note that the client MAY
   interrogate the server to determine the most appropriate method.

   "Examples" section: Modified examples to use and hostnames.  Added missing '?' to the LDAP URL example
   whose filter contains three null bytes.  Removed space after one
   comma within a DN.  Revised the bindname example to use e-bindname.
   Changed the name of an attribute used in one example from "int" to
   "four-octet" to avoid potential confusion.  Added an example that
   demonstrates the interaction between DN escaping and URL escaping.
   Added some examples to show URL equivalence with respect to the dn
   portion of the URL.

   "Security Considerations" section: Added a note about connection
   reuse.  Added a note about using strong authentication methods for
   updates.  Added a reference to RFC 2829. [AuthMeth].  Added note that simply
   opening a connection may violate some users' privacy requirements.

   "Acknowledgements" section: added statement about this being an
   update to RFC 2255.  Added Kurt Zeilenga, Jim Sermersheim, and
   Hallvard Furuseth.

   "Normative References" section: renamed from "References" per new RFC
   guidelines. Changed from [1] style to [Protocol] style throughout the
   document.  Added references to RFCs RFC 2234, 2829, RFC 2732, and 3383. RFC 3629.
   Updated all RFC 1738 references to point to the appropriate sections
   within RFC 2396.  Updated the LDAP references to refer to LDAPBis WG
   documents.  Removed the reference to the LDAP Attribute Syntaxes
   document and added a
   reference references to the Roadmap document. [AuthMeth], [LDAPIANA], and
   [Roadmap] documents.

   "Informative References" section: added for clarity.

   Header and "Authors' Address" Addresses" sections: added "editor" next to Mark
   Smith's name.  Updated affiliation and contact information.

   Copyright: updated the year.

16.  Appendix B: Changes Since Previous Document Revision

   This appendix lists all changes relative to the previously published
   revision, draft-ietf-ldapbis-url-03.txt. draft-ietf-ldapbis-url-04.txt.  Note that when appropriate
   these changes are also included in Appendix A, but are also included
   here for the benefit of the people who have already reviewed draft-
   ietf-ldapbis-url-04.txt. This section will be removed before this
   document is published as an RFC.

16.1.  Technical Changes


   Clarified and strengthened the requirements with respect to
   processing of URLs that contain recognized and unrecognized
   extensions (the approach now matches that specified in [Protocol] for
   LDAP controls).

16.2.  Editorial Changes

   "URL Definition" section: added comments in the ABNF to point the
   reader to the "Escaping Using the % Method" section, which was
   changed into corrected a section of its own reference to highlight the importance of
   escaping the URL components correctly.

   "Examples" section: changed the name of an attribute used improved formatting and fixed a typographic error
   (removed extraneous "IP") in one
   example from "int" to "four-octet" to avoid potential confusion.

   Replaced all occurrences of "asterix" with the correctly spelled
   "asterisk." "four-octet" example.

   "Normative References" section: changed the UTF-8 reference to point
   to RFC 3629, changed the RFC 3383 reference to point to the UTF-8 Internet Draft; replace [LDAPIANA] LDAP IANA
   Internet Draft reference
   with a Draft, and indented the reference descriptions to RFC 3383.

   "Intellectual Property Rights" section: added.

   Author's enhance

   Authors' Addresses section: New email address contact information for Mark Smith.

   "Full Copyright Statement" section: updated text

   Updated the copyright year to match latest IETF
   guidelines. 2004.

This Internet Draft expires on 25 April 13 August 2004.