openldap/doc/drafts/draft-ietf-ldapext-locate-xx.txt

INTERNET-DRAFT                                         Michael P. Armijo
<draft-ietf-ldapext-locate-01.txt>                          Levon Esibov
January, 2000                                                 Paul Leach
Expires: July, 2000                                Microsoft Corporation

                Discovering LDAP Services with DNS

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.  It is filed as <draft-
   ietf-ldapext-locate-01.txt>, and expires on July 4, 2000.  
   Please send comments to the authors.

1. Abstract

   This draft defines a way that native Internet LDAP servers can make 
   use of the DNS's knowledge base to provide clients a method to 
   resolve LDAP services for a given domain.


2. Introduction

   The LDAPv3 protocol [1] is designed to be a lightweight access 
   protocol for directory services supporting X.500 models. This may 
   be the X.500 directory itself, but the LDAP specification 
   explicitly allows it to be a different directory.  Let us define 
   a "native LDAP server" to be one that is not a front end to the 
   X.500 directory service. Let us further define an "Internet based 
   organization" as one that has a domain name, and an "Internet LDAP 
   server" to be one containing a directory entries for such an 
   organization.

   This draft defines a way that native Internet LDAP servers can make 
   use of the DNS's knowledge base to perform the same function, while 
   still supporting integration with the X.500 directory.

   This draft builds on RFC 2247[2] to define a mechanism by which 
   collections of native Internet LDAP servers can be integrated to 
   create a directory service. That work supports this cause by 
   defining a mapping from an LDAP DN to a DNS name that can be 
   resolved to the address of a server holding the entry corresponding 
   to the DN. For example, the DN "CN=Fred,OU=Eng,DC=example,DC=net" 
   maps to the DNS name "example.net". 

   In an Internet context, many of the names about which users seek 
   information are DNS names, or include DNS names. A native LDAP based 
   directory service for the Internet should make it convenient to 
   process such names -- there is a huge social investment spanning two 
   decades to get to the point where names like 
   "john.doe@somewhere.example" and "http://www.example.net" can 
   appear in newspaper articles, TV commercials, and on billboards 
   and millions of people understand what to do with them. As a result, 
   we assume that Internet based organizations wish to preserve this 
   investment, yet also want to deploy directory services.

   Widespread use of, and dependence on, LDAP services will require that 
   they are robust and scalable. Both of these features are typically 
   supported by replicated servers. Use of SRV records to locate LDAP 
   servers supports clients' use of replicated servers.


3. Locating LDAP servers through DNS

   LDAP server location information is to be stored using DNS Service 
   Location Record (SRV)[6].  The data in a SRV record contains the DNS 
   name of the server that provides the LDAP service, corresponding Port 
   number, and parameters that enable the client to choose an 
   appropriate server from multiple servers according to the algorithm 
   described in the SRV protocol[6].  The name of this record always has 
   the following format:

   _<Service>._<Proto>.<Domain>

   where <Service> is always "ldap", <Proto> is a protocol that can 
   be either "udp" or "tcp", and <Domain> is the domain hosted by the 
   LDAP Server.  Note that "ldap" is the symbolic name for the LDAP 
   service in Assigned Numbers [7], as required by the SRV Protocol[6].

   Presence of such records enables clients to find the LDAP servers 
   using standard DNS query [3].  As an example, a client that searches 
   for an LDAP server in the example.net domain that supports TCP protocol 
   will submit a DNS query for a set of SRV records with owner name:
 
   _ldap._tcp.example.net.

   The client will receive the list of SRV records published in DNS 
   that satisfy the requested criteria.  The following is an example 
   of such record:

   _ldap._tcp.example.net.   IN	   SRV   0 0 389 phoenix.example.net.

   The set of returned records may contain multiple records in the 
   case where multiple LDAP servers serve the same domain.  


4. Security Considerations

   This document describes a method that uses DNS SRV records to 
   discover LDAP servers.  All security considerations related to DNS
   SRV records are inherited by this document.  See the security 
   considerations section in [6] for more details.


5. References

   [1] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access 
   Protocol(v3)".  RFC 2251, December 1997.

   [2] S. Kille, M. Wahl, "Using Domains in LDAP/X.500 Distinguished 
   Names". RFC 2247, January 1998.

   [3] P. Mockapetris, RFC 1034, DOMAIN NAMES - CONCEPTS AND FACILITIES,  
   November, 1987.
 
   [4] P. Mockapetris, RFC 1035, DOMAIN NAMES - IMPLEMENTATION AND 
   SPECIFICATION, November, 1987.

   [5] T. Howes, M. Smith, "The LDAP URL Format". RFC 2255  December 1997.

   [6] A. Gulbrandsen, P. Vixie, L. Esibov, "A DNS RR for specifying the 
   location of services (DNS SRV)". 
   http://www.ietf.org/internet-drafts/draft-ietf-
   dnsind-rfc2052bis-05.txt, November 1999.

   [7] J. Reynolds, J. Postel, "Assigned Numbers", STD 2, October 1994


6. Authors' Addresses

   Michael P. Armijo
   One Microsoft Way
   Redmond, WA 98052
   micharm@microsoft.com

   Paul Leach
   One Microsoft Way
   Redmond, WA 98052
   paulle@microsoft.com

   Levon Esibov
   One Microsoft Way
   Redmond, WA 98052
   levone@microsoft.com

   Expires July, 2000