INTERNET-DRAFT Kurt D. Zeilenga
Intended Category: Experimental OpenLDAP Foundation
Expires: 20 May 2002 20 November 2001
Use of DNS SRV in LDAP Named Subordinate References
<draft-zeilenga-ldap-dnsref-02.txt>
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 an 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 <ietf-ldapext@netscape.com>. Please send editorial
comments directly to the author <Kurt@OpenLDAP.org>.
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Copyright 2001, The Internet Society. All Rights Reserved.
Please see the Copyright section near the end of this document for
more information.
Abstract
This document describes how LDAP service location information stored
on DNS SRV resource records may be used to in conjunction with named
subordinate referral objects. This document defines the dNSReferral
object class.
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Conventions
Schema definitions are provided using LDAPv3 description formats
[RFC2252]. Definitions provided here are formatted (line wrapped) for
readability.
The key words ``MUST'', ``MUST NOT'', ``REQUIRED'', ``SHALL'', ``SHALL
NOT'', ``SHOULD'', ``SHOULD NOT'', ``RECOMMENDED'', and ``MAY'' in
this document are to be interpreted as described in BCP 14 [RFC2119].
1. Background and Intended Use
Named subordinate referral [NAMEDREF] defines a specific method for
representing subordinate references in LDAP [RFC2251] directories.
This document describes a mechanism for using LDAP service location
information [LOCATE] available in DNS SRV resource records [RFC2782]
to rewrite select LDAP URLs [RFC2255] returned to clients as referrals
and search continuations.
2. Schema
A dNSReferral object is a directory entry whose structural object
class is the dNSreferral object class.
( 1.3.6.1.4.1.4203.1.4.8 NAME 'dNSReferral'
DESC 'DNS SRV aware named subordinate referral object'
SUP referral STRUCTURAL )
dNSReferral objects SHOULD have distinguished names comprising of RDNs
consisting of only dc (domainComponent) attributes (e.g.,
dc=example,dc=net) as detailed in [RFC2247].
dNSReferral objects SHALL behave like referral objects [NAMEDREF]
except as detailed in the following section.
3. Construction of Referrals and Search References
In the referral processing described by [NAMEDREF], if a LDAP URL with
no hostpart is to be returned to the client as part of a referral or
search continuation, it is replaced with one or more LDAP URLs based
upon service location information.
The server SHOULD obtain service location information [LOCATE] for the
DN [RFC2253] present in (or implied by) the LDAP URL [RFC2255]. If no
service location information is available, the server MUST return the
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LDAP URL as described in [NAMEDREF].
Otherwise, the server SHALL replace the LDAP URL with a set of
constructed LDAP URLs. For each service host port pair provided, the
server constructs an LDAP URL by replacing the empty hostport with
concatenation of the service host, ":", and the port.
4. Example
Suppose a directory server contains:
dn: dc=sub,dc=example,dc=net
dc: sub
objectClass: dNSReferral
objectClass: extensibleObject
ref: ldap:///dc=sub,dc=example,dc=net
and DNS holds the following SRV records:
_ldap._tcp.sub.example.net. IN SRV 0 0 389 l1.sub.example.net.
_ldap._tcp.sub.example.net. IN SRV 0 0 389 l2.sub.example.net.
and a client requests a compareRequest with a target DN of
"dc=sub,dc=example,dc=net". In response to this request, the server
would return:
compareResponse "referral" {
ldap://l1.sub.example.net:389/dc=sub,dc=example,dc=net
ldap://l2.sub.example.net:389/dc=sub,dc=example,dc=net
}
5. Security Considerations
This mechanism extends [NAMEDREF] based upon [LOCATE]. The security
considerations discussed in these documents generally apply to the
specification described in this document.
In addition, this mechanism requires the server to make DNS queries.
DNS responses are subject to spoofing. Use of DNSSEC is RECOMMENDED
where appropriate. Also, DNS queries may require significant time and
resources.
6. Acknowledgments
This document is borrows heavily from previous work by IETF LDAPext
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Working Group including [NAMEDREF] and [LOCATE].
7. Author's Address
Kurt D. Zeilenga
OpenLDAP Foundation
<Kurt@OpenLDAP.org>
8. Normative References
[RFC2119] S. Bradner, "Key Words for use in RFCs to Indicate
Requirement Levels", BCP 14 (Also RFC 2119), March 1997.
[RFC2247] S. Kille, M. Wahl, A. Grimstad, R. Huber, S. Sataluri,
"Using Domains in LDAP/X.500 Distinguished Names", RFC
2247, January 1998.
[RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December 1997.
[RFC2253] M. Wahl, S. Kille, T. Howes, "Lightweight Directory Access
Protocol (v3): UTF-8 String Representation of Distinguished
Names", RFC 2253, December 1997.
[RFC2255] T. Howes, M. Smith, "The LDAP URL Format", RFC 2255,
December, 1997.
[RFC2782] A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[LOCATE] M. Armijo, P. Leach, L Esibov, RL Morgan. "Discovering LDAP
Services with DNS", draft-ietf-ldapext-locate-xx.txt (work
in progress).
[NAMEDREF] K. Zeilenga (editor), "Named Subordinate References in LDAP
Directories" draft-zeilenga-ldap-namedref-xx.txt (work in
progress)
Full Copyright Statement
Copyright 2001, 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
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or assist in its implementation may be prepared, copied, published and
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