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.
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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
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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.
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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.
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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].
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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
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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
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LDAP Control to Specify Chaining Behavior
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