Internet Draft J. Sermersheim Personal Submission R. Harrison Intended Category: Standard Track Novell, Inc Document: draft-sermersheim-ldap-chaining-02.txt Feb 2004 LDAP Control to Specify Chaining Behavior 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. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDAP Extensions Working Group mailing list <ldapext@ietf.org>. Editorial comments may be sent to the author <jimse@novell.com>. Abstract This document describes a Lightweight Directory Access Protocol (LDAP) request control that allows specification of chaining behavior for LDAP operations. By using the control with various LDAP operations, a directory client (DUA), or directory server (DSA) specifies whether or not a DSA or secondary DSA chains operations to other DSAs or returns referrals and/or search result references to the client. 1. Introduction Many directory servers have the ability through the use of various mechanisms to participate in a distributed directory model. A distributed directory is one where the DIT is distributed over multiple DSAs. One operation completion mechanism used by DSAs in a distributed directory is chaining. Chaining is defined in [X.518], and is the act of one DSA communicating a directory operation that Sermersheim, Harrison Internet-Draft - Exp. Aug 2004 Page 1  LDAP Control to Specify Chaining Behavior originated from a DUA to another DSA in a distributed directory. Contrast this with the act of passing referrals (4.1.11 of [RFC2251]) and SearchResultReferences (4.5.2 of [RFC2251]) back to the client. Chaining may happen during the name resolution part of an operation or during other parts of operations like search which apply to a number of entries in a subtree. This document does not attempt to define the distributed directory model, nor does it attempt to define the manner in which DSAs chain requests. This document defines a request control that the client can use to specify whether parts of an operation should or should not be chained. 2. Conventions The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" used in this document carry the meanings described in [RFC2119]. The term chaining may apply to uni-chaining as well as multi-chaining (see [X.518]) depending on the capabilities and configuration of the DSAs. 3. The Control Support for the control is advertised by the presence of its controlType in the supportedControl attribute of a server's root DSE. This control MAY be included in any LDAP request operation except abandon, unbind, and StartTLS as part of the controls field of the LDAPMessage, as defined in Section 4.1.12 of [RFC2251]: The controlType is set to <IANA-ASSIGNED-OID.1>. The criticality MAY be set to either TRUE or FALSE. The controlValue is an OCTET STRING, whose value is the following ChainingBehavior type, BER encoded following the rules in Section 5.1 of [RFC2251]: ChainingBehavior ::= SEQUENCE { resolveBehavior Behavior OPTIONAL, continuationBehavior Behavior OPTIONAL } Behavior :: = ENUMERATED { chainingPreferred (0), chainingRequired (1), referralsPreferred (2), referralsRequired (3) } resolveBehavior instructs the DSA what to do when a referral is encountered during the local name resolution part of an operation. If this field is not specified, other policy dictates the DSA's behavior. Sermersheim, Harrison Internet-Draft - Exp. Aug 2004 Page 2  LDAP Control to Specify Chaining Behavior continuationBehavior instructs the DSA what to do when a referral is encountered after the name resolution part of an operation has completed. This scenario occurs during search operations, and may occur during yet to be defined future operations. If this field is not specified, other policy dictates the DSA's behavior. Behavior specifies whether the DSA should chain the operation or return referrals when a target object is held by a remote service. chainingPreferred indicates that the preference is that chaining, rather than referrals, be used to provide the service. When this value is set, the server attempts to chain the request but if it can't it returns referrals. chainingRequired indicates that chaining is to be used rather than referrals to service the request. When this value is set, the server MUST NOT return referrals. It either chains the request or fails. referralsPreferred indicates that the client wishes to receive referrals rather than allow the server to chain the operation. When this value is set, the server return referrals and search references when possible, but may chain the operation otherwise. referralsRequired indicates that chaining is prohibited. When this value is set, the server MUST NOT chain the request to other DSAs. Instead it returns referrals as necessary, or fails. The following list assigns meanings to some of the result codes that may occur due to this control being present: - chainingRequired (IANA-ASSIGNED-1) Unable to process without chaining. - cannotChain (IANA-ASSIGNED-2) Unable to chain the request. 4. Notes to Implementors <todo: add some> 4.1 Unbind and Abandon Clients MUST NOT include the ChainingBehavior control with an Abandon operation or an Unbind operation. Servers MUST ignore any chaining control on the abandon and unbind requests. Servers that chain operation are responsible to keep track of where an operation was chained to for the purposes of unbind and abandon. 4.2 StartTLS This operation cannot be chained because the TLS handshake protocol does not allow man-in-the-middle attacks. Sermersheim, Harrison Internet-Draft - Exp. Aug 2004 Page 3  LDAP Control to Specify Chaining Behavior 5. Relationship with other Extensions This control MAY be used with other controls or with extended operations. When it is used with other controls or with extended operations not listed here, server behavior is undefined unless otherwise specified. 5.1 Relationship with ManageDsaIT When this control is used along with the ManageDsaIT control, the resolveBehavior value is evaluated. If resolveBehavior is such that chaining is allowed, the DSA is allowed to chain the operation as necessary until the last RDN is found. For example: DSA1 holds the naming context <dc=net> and a subordinate reference to <dc=example,dc=net>, DSA2 holds the naming context <dc=example,dc=net> and a subordinate reference to <dc=hostc,dc=example,dc=net>. A modify operation accompanied by the ManageDsaIT control alone is sent to DSA1. The base object of the modify operation is set to <dc=hostc,dc=example,dc=net>. Since DSA1 does not hold the <dc=hostc,dc=example,dc=net> IT DSE, a referral is returned for <dc=example,dc=net>. Next, the same modify operation is accompanied by both the ManageDsaIT and the ChainingBehavior control where the ChainingBehavior.resolveBehavior is set to chainingPreferred. In this case, DSA1 chains to DSA2 when it encounters <dc=example,dc=net> and DSA2 continues the operation. Since DSA2 holds the IT DSE <dc=hostc,dc=example,dc=net>, the resolve portion completes, and the rest of the operation proceeds. 6. Security Considerations Because this control directs a DSA to chain requests to other DSAs, it may be used in a denial of service attack. Implementers should be cognizant of this possibility. This control may be used to allow access to hosts and portions of the DIT not normally available to clients. Servers supporting this control should provide sufficient policy to prevent unwanted occurrences of this. 7. IANA Considerations Registration of the following values is requested [RFC3383]. Sermersheim, Harrison Internet-Draft - Exp. Aug 2004 Page 4  LDAP Control to Specify Chaining Behavior 7.1. Object Identifiers It is requested that IANA register upon Standards Action an LDAP Object Identifier in identifying the protocol elements defined in this technical specification. The following registration template is suggested: Subject: Request for LDAP OID Registration Person & email address to contact for further information: Jim Sermersheim jimse@novell.com Specification: RFCXXXX Author/Change Controller: IESG Comments: One delegation will be made under the assigned OID: IANA-ASSIGNED-OID.1 Chaining Behavior Request Control 7.2. LDAP Protocol Mechanism It is requested that IANA register upon Standards Action the LDAP protocol mechanism described in this document. The following registration template is suggested: Subject: Request for LDAP Protocol Mechanism Registration Object Identifier: IANA-ASSIGNED-OID.1 Description: Chaining Behavior Request Control Person & email address to contact for further information: Jim Sermersheim jimse@novell.com Usage: Control Specification: RFCXXXX Author/Change Controller: IESG Comments: none 7.3. LDAP Result Codes It is requested that IANA register upon Standards Action the LDAP result codes: chainingRequired (IANA-ASSIGNED-1) cannotChain (IANA-ASSIGNED-2) The following registration template is suggested: Subject: LDAP Result Code Registration Person & email address to contact for further information: Jim Sermersheim jimse@novell.com Result Code Name: chainingRequired Result Code Name: cannotChain Specification: RFCXXXX Sermersheim, Harrison Internet-Draft - Exp. Aug 2004 Page 5  LDAP Control to Specify Chaining Behavior Author/Change Controller: IESG Comments: request consecutive result codes be assigned 8. Normative References [X.518] ITU-T Rec. X.511, "The Directory: Abstract Service Definition", 1993. [RFC2119] Bradner, Scott, "Key Words for use in RFCs to Indicate Requirement Levels", Internet Draft, March 1997. Available as RFC2119. [RFC2251] Wahl, M, S. Kille and T. Howes, "Lightweight Directory Access Protocol (v3)", Internet Standard, December, 1997. Available as RFC2251. 9. Authors' Addresses Jim Sermersheim Novell, Inc. 1800 South Novell Place Provo, Utah 84606, USA jimse@novell.com +1 801 861-3088 Roger Harrison Novell, Inc. 1800 South Novell Place Provo, Utah 84606, USA rharrison@novell.com +1 801 861-2642 Sermersheim, Harrison Internet-Draft - Exp. 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