Network Working Group Mark Smith, Editor Request for Comments: DRAFT Netscape Communications Corp. Obsoletes: RFC 2255 Tim Howes Loudcloud, Inc. 10 May 2001 The LDAP URL Format <draft-ietf-ldapbis-url-01.txt> 1. Status of this Memo This document is an Internet-Draft and is in full conformance with 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-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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Discussion of this document should take place on the LDAP (v3) Revison (ldapbis) Working Group mailing list <ietf- ldapbis@openldap.org>. After appropriate review and discussion, this document will be submitted as a Standards Track replacement for RFC 2255. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. 2. Abstract LDAP is the Lightweight Directory Access Protocol, defined in [RFC2251bis], [RFC2252bis], and [RFC2253bis]. This document describes a format for an LDAP Uniform Resource Locator. The format describes an LDAP search operation used to retrieve information from Smith & Howes Intended Category: Standards Track [Page 1]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 an LDAP directory, or, in the context of an LDAPv3 referral or reference, the format describes a service where an LDAP operation may be progressed. Note: not all of the parameters of the LDAP search operation described in [RFC2251bis] can be expressed using the format defined in this document. 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. 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]. 3. URL Definition An LDAP URL begins with the protocol prefix "ldap" and is defined by the following grammar, following the ABNF notation defined in [RFC2234]. ldapurl = scheme "://" [hostport] ["/" dn ["?" [attributes] ["?" [scope] ["?" [filter] ["?" extensions]]]]] scheme = "ldap" hostport = <hostport from Section 3.2.2 of [RFC2396]> dn = <distinguishedName from Section 3 of [RFC2253bis]> attributes = attrdesc *("," attrdesc) attrdesc = <AttributeDescription from Section 4.1.5 of [RFC2251bis]> / "*" scope = "base" / "one" / "sub" filter = <filter from Section 4 of [RFC2254bis]> extensions = extension *("," extension) extension = ["!"] extype ["=" exvalue] extype = oid / oiddescr exvalue = <LDAPString from section 4.1.2 of [RFC2251bis]> oid = <LDAPOID from section 4.1.2 of [RFC2251bis]> oiddescr = <name from section 3.2 of [LDAP-IANA]> The "ldap" prefix indicates an entry or entries residing in the LDAP server running on the given hostname at the given portnumber. The dn is an LDAP Distinguished Name using the string format described in [RFC2253bis]. It identifies the base object of the LDAP search or the target of a non-search operation. Smith & Howes Intended Category: Standards Track [Page 2]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 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 [RFC2251bis]. 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 [RFC2254bis]. 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 extension is supported by the client, the client MUST obey the extension if the extension is critical. The client SHOULD obey supported extensions that are non-critical. If an extension is unsupported by the client, the client MUST NOT process the URL if the extension is critical. If an unsupported extension is non-critical, the client MUST ignore the extension. If a critical extension cannot be processed successfully by the client, the client 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., 1.2.3.4) or the oiddesc form (e.g., myLDAPURLExtension). Use of the oiddesc form SHOULD be restricted to registered object identifier descriptive names. See [LDAP-IANA] 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 other extensions. Note that characters that are not safe (e.g., spaces) (as defined in section 2.1 of [RFC2396]), and the single Reserved character '?' Smith & Howes Intended Category: Standards Track [Page 3]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 occurring inside a dn, filter, or other element of an LDAP URL MUST be escaped using the % method described in section 2.4 of [RFC2396]. If a comma character ',' occurs inside an extension value, the character MUST also be escaped using the % method. 4. 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 of [RFC2251bis] specifies a different rule for determining the correct DN to use when it is absent in an LDAP URL that is returned as a referral. hostport 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. dn If no dn is given, the default is the zero-length DN, "". attributes 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 "*"). scope If scope is omitted, a scope of "base" is assumed. filter If filter is omitted, a filter of "(objectClass=*)" is assumed. extensions If extensions is omitted, no extensions are assumed. 5. 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 choosing: Smith & Howes Intended Category: Standards Track [Page 4]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 ldap:///o=University%20of%20Michigan,c=US The next example is an LDAP URL referring to the University of Michigan entry in a particular ldap server: ldap://ldap1.example.net/o=University%20of%20Michigan,c=US 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: ldap://ldap1.example.net/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. 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: ldap://ldap1.example.net:6666/o=University%20of%20Michigan, c=US??sub?(cn=Babs%20Jensen) The next example is an LDAP URL referring to all children of the c=GB entry: ldap://ldap1.example.com/c=GB?objectClass?one 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 '?'. ldap://ldap2.example.com/o=Question%3f,c=US?mail The next example illustrates the interaction between LDAP and URL quoting mechanisms. ldap://ldap3.example.com/o=Babsco,c=US???(int=%5c00%5c00%5c00%5c04) Smith & Howes Intended Category: Standards Track [Page 5]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 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 (int=\00\00\00\04). Because the \ character must be escaped in a URL, the \'s are escaped as %5c in the URL encoding. The following three URLs that are equivalent, assuming that the defaulting rules specified in section 4 of this document are used: ldap://ldap.example.net ldap://ldap.example.net/ ldap://ldap.example.net/? These three URLs all point to the root DSE on the ldap.example.net server. The final two examples show use of a hypothetical, experimental bind name extension (the value associated with the extension is an LDAP DN). ldap:///??sub??e-bindname=cn=Manager%2cdc=example%2cdc=com ldap:///??sub??!e-bindname=cn=Manager%2cdc=example%2cdc=com 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. 6. 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 Smith & Howes Intended Category: Standards Track [Page 6]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 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 [RFC2829bis] 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. 7. 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, and Jim Sermersheim deserve special thanks for their contributions. 8. References [LDAP-IANA] IETF LDAPBis WG, "IANA Considerations for LDAP", a work in progress. [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate Smith & Howes Intended Category: Standards Track [Page 7]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 Requirement Levels," RFC 2119, March 1997. [RFC2234] Crocker, D., Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC2251bis] IETF LDAPBis WG, "Lightweight Directory Access Protocol (v3)", a work in progress. [RFC2252bis] IETF LDAPBis WG, "Lightweight Directory Access Protocol (v3): Attribute Syntax Definitions", a work in progress. [RFC2253bis] IETF LDAPBis WG, "Lightweight Directory Access Protocol (v3): UTF-8 String Representation of Distinguished Names", a work in progress. [RFC2254bis] IETF LDAPBis WG, "A String Representation of LDAP Search Filters", a work in progress. [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [RFC2396] Berners-Lee, T., Fielding, R., and Masinter, L., "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [RFC2829bis] IETF LDAPBis WG, "Authentication Methods for LDAP", a work in progress. 9. Authors' Address Mark Smith, Editor Netscape Communications Corp. Mailstop USCA17-201 4170 Network Circle Santa Clara, CA 95054 USA +1 650 937-3477 mcs@netscape.com Tim Howes Loudcloud, Inc. 599 N. Mathilda Ave. Sunnyvale, CA 94086 USA +1 408 744-7509 howes@loudcloud.com Smith & Howes Intended Category: Standards Track [Page 8]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 10. Full Copyright Statement Copyright (C) The Internet Society (2001). 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 English. 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 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 11. Appendix A: Changes Since RFC 2255 11.1. Technical Changes "URL Definition" section: added missing "*" 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 RFC2251bis or an OID description from LDAP- IANA. Changed the text about extension types so it references LDAP- IANA. Reordered rules to more closely follow the order the elements appear in the URL. "Bindname Extension": removed due to lack of known implementations. Smith & Howes Intended Category: Standards Track [Page 9]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 11.2. Editorial Changes "Abstract" section: 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 [RFC2251bis] can be expressed using this format. IESG Note: removed note about lack of satisfactory mandatory authentication mechanisms. "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. "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 example.com and example.net 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. 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. 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 added Kurt Zeilenga and Jim Sermersheim. "References" section: changed from [1] style to [RFC2251bis] style throughout the document. Added references to RFCs 2234 and 2829. Updated RFC 1738 references to the appropriate sections within RFC Smith & Howes Intended Category: Standards Track [Page 10]
INTERNET-DRAFT The LDAP URL Format 10 May 2001 2396. Updated the references to refer to LDAPBis WG documents. Added a reference to the LDAP IANA document. Header and "Authors' Addresses" sections: added "editor" next to Mark Smith's name. Updated affiliation and contact information. Copyright: updated the year. "Table of Contents" section: added. 12. Appendix B: Changes Since Previous Document Revision This appendix lists all changes relative to the last published revision, draft-ietf-ldapbis-url-00.txt. Note that these changes are also included in Appendix A, but are included here for those who have already reviewed draft-ietf-ldapbis-url-00.txt. 12.1. Technical Changes "URL Definition" section: changed the ABNF for ldapurl to group the dn component with the preceding slash. Changed the extype rule to be is an LDAPOID from RFC2251bis or an OID description from LDAP-IANA. Changed the text about extension types so it references LDAP-IANA. "Bindname Extension": removed due to lack of known implementations. 12.2. Editorial Changes "Examples" section: revised the bindname example to use e-bindname and added some examples to show URL equivalence with respect to the dn portion of the URL. "Appendix C: Loose Ends": removed this section entirely. References: updated references to refer to LDAPBis WG documents. Added a reference to the LDAP IANA document. This Internet Draft expires on 10 November 2001. Smith & Howes Intended Category: Standards Track [Page 11]
1. Status of this Memo............................................1 2. Abstract.......................................................1 3. URL Definition.................................................2 4. Defaults for Fields of the LDAP URL............................4 5. Examples.......................................................4 6. Security Considerations........................................6 7. Acknowledgements...............................................7 8. References.....................................................7 9. Authors' Address...............................................8 10. Full Copyright Statement.......................................9 11. Appendix A: Changes Since RFC 2255.............................9 11.1. Technical Changes...........................................9 11.2. Editorial Changes...........................................10 12. Appendix B: Changes Since Previous Document Revision...........11 12.1. Technical Changes...........................................11 12.2. Editorial Changes...........................................11
