INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Experimental OpenLDAP Foundation Expires: 4 Jan 2001 4 July 2000 OpenLDAP Root Service An experimental LDAP referral service Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is intended to be, after appropriate review and revision, submitted to the RFC Editor as a Experimental document. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDAP Extension Working Group mailing list . Please send editorial comments directly to the author . 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. Copyright 2000, The Internet Society. All Rights Reserved. Please see the Copyright section near the end of this document for more information. Abstract The OpenLDAP Project is operating an experimental LDAP [RFC2251] referral service known as the "OpenLDAP Root Service." The automated system generates referrals based upon service location information published in DNS [RFC1034] SRV [RFC2782] resource records. This document describes this service. Zeilenga [Page 1] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 1. Background LDAP [RFC2251] directories use a hierarchical naming scheme inherited from X.500 [X500]. Traditionally, X.500 deployments have used a geo-political naming scheme (e.g. cn=Jane Doe, ou=Engineering, o=Example, st=CA, c=US). However, registration infrastructure and location services in many portions of the naming hierarchical are inadequate or nonexistent. The construct of a global directory requires a robust registration infrastructure and location service. Use of Internet domain-based naming [RFC2247] (e.g. uid=jdoe, dc=eng, dc=example, dc=net) allows LDAP directory services to leverage the existing DNS [RFC1034] registration infrastructure and DNS SRV [RFC2782] resource records can used to locate services. 1.1. The Glue Most existing LDAP implementations do not support location of directory services using DNS SRV resource records. However, most servers support referral generation to "superior" server(s). This service provides a "root" LDAP service which servers using domain based naming may use as their superior referral service. Client may also use the service directly to locate services associated with an arbitrary Distinguished Name within the domain based hierarchy. Notice: The mechanisms used by service are experimental. The descriptions provided by this document should not be taken as being definitive. Definitive mechanisms shall be published in a Standard Track document(s). 2. Generating Referrals based upon DNS SRV RRs This service returns referrals generated from DNS SRV resource records [RFC2782]. 2.1. DN to Domain Name Mapping The service maps a DN [RFC2253] to a fully qualified domain name using the following algorithm: domain = null; Zeilenga [Page 2] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 foreach RDN left-to-right /* [1] */ { if not multi-valued RDN and RDN.type == domainComponent { if ( domain == null || domain == "." ) { // start domain = ""; } else { // append separator domain .= "."; } if ( RDN.value == "." ) { // root domain = "."; } else { // append domainComponent domain .= RDN.value; } continue; } domain = null; } Examples: Distinguished Name Domain ------------------------------ ------------ dc=example,dc=net example.net uid=jdoe,dc=example,dc=net example.net dc=. . [2] dc=example,dc=net,dc=. . [3] dc=example,dc=.,dc=net net [4] dc=example.net example.net [5] cn=Jane Doe,o=example,c=us null uid=jdoe,dc=example,c=us null dc=example,o=example,dc=net net dc=example+o=example,dc=net net dc=example,o=us+dc=net null Notes: 1) A later incarnation of this service may use a right-to-left algorithm. 2) RFC 2247 does not state how one can map the domain representing the Zeilenga [Page 3] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 root of the domain tree to a DN. We suggest the root of the domain tree be mapped to the DN "dc=." and that this be reversable. 3) RFC 2247 states that domain "example.net" should be mapped to the DN "dc=example, dc=net", not to "dc=example,dc=net,dc=.". It is not our intent to introduce or support an alternative domain to DN mapping. The algorithm ignores domainComponents to the right of dc=. 4) RFC 2247 states that domain "example.net" should be mapped to the DN "dc=example, dc=net", not to "dc=example,dc=.,dc=net". It is not our intent to introduce or support an alternative domain to DN mapping. The algorithm ignores domainComponents to the right of dc=. and dc=. if further domainComponents are found to the left. 5) RFC 2247 states that value of an DC attribute type is a domain component. It should not contain multiple domain components. A later incarnation of this service may map this domain to null or be coded to return invalid domain. If the domain is null or ".", the service aborts further processing and returns noSuchObject. Later incarnation of this service may place abort processing if the resulting domain is a top-level domain. 2.2. Locating LDAP services The root service locates services associated with a given fully qualified domain name by querying the Domain Name System for LDAP SRV resource records. For the domain example.net, the service would do a issue a SRV query for the domain _ldap._tcp.example.net. A successful query will return one or more resource records of form: _ldap._tcp.example.net. IN SRV 0 0 389 ldap.example.net. If no LDAP SRV resource records are returned or any DNS error occurs, the service processing and returns noSuchObject. Later incarnations of this service will better handle transient errors. 2.3. Constructing an LDAP Referrals For each DNS SRV resource record returned for the domain, a LDAP URI [RFC2255] is constructed. For the above resource record, the URI would be: ldap://ldap.example.net:389/ Zeilenga [Page 4] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 These URIs are then returned in the referral. The URI are currently returned in resolver order. That is, the server itself does not make use of priority or weight information in the SRV resource records. A later incarnation of this service may. 3. Protocol Operations This section describes how the service performs basic LDAP operations. The service supports operations extended through certain controls as described in a later section. 3.1. Basic Operations Basic (add,compare,delete,modify,rename,search) operations return a referral result if the target (or base) DN can be mapped to a set of LDAP URIs as described above. Otherwise a noSuchObject response or other appropriate response is returned. 3.2. Bind Operation The service accepts "anonymous" bind specifying version 2 or version 3 of the protocol. All other bind requests will return a non-successful resultCode. In particular, clients which submit clear text credentials. will be sent an unwillingToPerform resultCode with a cautionary text regarding providing passwords to strangers. As this service is read-only, LDAPv3 SASL bind [RFC2829] is not supported. 3.3. Unbind Operations Upon receipt of an unbind request, the server abandons all outstanding requests made by client and disconnects. 3.4. Abandon Operations Upon receipt of an abandon request, the server abandons all outstanding requests made by client. 3.5. Extended Operations The service currently does recognize any extended operation. Later Zeilenga [Page 5] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 incarnations of the service may support Start TLS [RFC2830] and other operations. 4. Controls The service supports the ManageDSAit control. Unsupported control are serviced per RFC 2251. 4.1. ManageDSAit Control The server recognizes and honors the ManageDSAit control [NAMEDREF] provided with operations. If DNS location information is available for the base DN itself, the service will return unwillingToPerform for non-search operations. For search operations, a entry will be returned if within scope and entry matches provided filter: c: searchRequest { base="dc=example,dc=net" scope=base filter=(objectclass=*) ManageDSAit } s: searchEntry { dn: dc=example, dc=net objectclass: referral objectclass: extensibleObject dc: example ref: ldap://ldap.example.net:389/ associatedDomain: example.net } s: searchResult { success } If DNS location information is available for the DC portion of a subordinate entry, the service will return noSuchObject with the matchedDN set to the DC portion of the base for search and update operations. c: searchRequest { base="cn=subordinate,dc=example,dc=net" scope=base filter=(objectclass=*) ManageDSAit Zeilenga [Page 6] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 } s: searchResult { noSuchObject matchedDN="dc=example,dc=net" } 7. Using the Service Servers may be configured to refer superior requests to . This is commonly done via a configuration directive such as: default ldap://root.openldap.org:389 Though clients may use the service directly, this is not encouraged. Clients should use a local service and only use this service when chasing a referral to the service. The service supports LDAPv3 and LDAPv2+ [LDAPv2+] clients over TCP/IPv4. Future incarnations of this service may support TCP/IPv6 or other transport/internet protocols. 6. Lessons Learned 6.1. Scaling / Reliability This service currently runs on a single host. This host and associated network resources are not yet exhausted. We expect it will be. We believe we can easily scale to meet the demand through common distributed load balancing technics. The service can also easily be duplicated locally. 6.2. Protocol interoperability This service has able avoided known interoperability issues in support variants of LDAP. 6.2.1. LDAPv3 Though the server does not fully implement LDAPv3 [RFC2251], it implements all portions required to provide the service. Zeilenga [Page 7] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 6.2.2. LDAPv2 LDAPv2 [RFC1777] does not support the return of referrals and hence may not be referred to by this service. Though a LDAPv2 client could connect, it would treat any referral returned to it as an unknown error. 6.2.3. LDAPv2+ LDAPv2+ [LDAPv2+] provides a number of extensions to LDAPv2, including referrals. LDAPv2+, like LDAPv3, does not require a bind operation before issuing of other operations. As the referral representation differ between LDAPv2+ and LDAPv3, the service returns LDAPv3 referrals in this case. However, as commonly deployed LDAPv2+ clients issue bind requests (for compatibility with LDAPv2 servers), this has not generated any interoperability issues (yet). 6.2.4. CLDAP CLDAP [RFC] does not support the return of referrals and hence is not supported. 7. Security Considerations This service provides information to "anonymous" clients. This information is derived from the public directories, namely the Domain Name System. The use of authentication would require clients to disclose information to the service. This would be an unnecessary invasion of privacy. The lack of encryption allows eavesdropping upon client requests and responses. A later incarnation of this service may support encryption (such as via Start TLS [RFC2830]). Information integrity protection is not provided as the service. The service is subject to varies forms of DNS spoofing and attacks. LDAP session or operation integrity would provide false sense of security concerning the integrity of DNS information. A later incarnation of this service may support DNSSEC and provide integrity protection (via SASL, TLS, or IPSEC). The service may be subject to a variety of denial of service attacks. The service is capable of blocking accessing by a number of factors Zeilenga [Page 8] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 (IP address, availability of reverse DNS information, etc.). These capability have yet to be used and likely would be ineffective in preventing sophisticated attacks. Later incarnations of this service will likely need more better protection from such attacks. 8. Conclusions DNS is good glue. By leveraging of the Domain Name System, global LDAP directories may be built without requiring a protocol specific registration infrastructures. In addition, use of DNS service location allows global directories to be built "ad hoc". That is, anyone with a domain name can participate. There is no requirement that the superior domain participate. 9. Additional Information Additional information about the OpenLDAP Project and the OpenLDAP Root Service can be found at . The author can be contacted at . 10. Acknowledgments Internet hosting for this experiment is hosted at the Internet Software Consortium . Computing resources were provided by Net Boolean Incorporated This experiment would not have been possible without the contributions of the volunteers of the open source community. References [RFC1034] Mockapetris, P., " Domain Names - Concepts and Facilities," STD 13, RFC 1034, November 1987. [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform Resource Locators (URL)", RFC 1738, December 1994. [RFC1777] Yeong, W., Howes, T., and S. Kille, "Lightweight Directory Access Protocol", RFC 1777, March 1995. [RFC1798] Young, A., "Connection-less Lightweight Directory Access Protocol", RFC 1798, June 1995. Zeilenga [Page 9] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate Requirement Levels," RFC 2119, March 1997. [RFC2247] Kille, S., et. al., "Using Domains in LDAP/X.500 Distinguished Names", RFC 2247, January 1998. [RFC2251] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [RFC2255] Howes, T., and M. Smith, "The LDAP URL Format", RFC 2255, December 1997. [RFC2782] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [RFC2829] Wahl, M., H. Alvestrand, J. Hodges, and R. Morgan, "Authentication Methods for LDAP", RFC 2829, May 2000. [RFC2830] Hodges, J., R. Morgan, and M. Wahl, "Lightweight Directory Access Protocol (v3): Extension for Transport Layer Security", RFC 2830, May 2000. [LOCATE] IETF LDAPext WG, "Discovering LDAP Services with DNS", draft-ietf-ldapext-locate-xx.txt (work in progress). [LDAPv2+] University of Michigan LDAP Team, "Referrals within the LDAPv2 Protocol", August 1996. [NAMEDREF] IETF LDAPext, "Named References in LDAP Directories" draft-ietf-zeilenga-namedref-xx.txt (work in progress) [X500] ITU-T Rec. X.500, "The Directory: Overview of Concepts, Models and Service", 1993. COPYRIGHT NOTICE Copyright 2000, The Internet Society. 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 Zeilenga [Page 10] INTERNET-DRAFT draft-zeilenga-ldap-root-01 2 July 2000 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 AUTHORS, 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. Zeilenga [Page 11]