Internet-Draft Ryan Moats draft-ietf-lsd-server-finding-01.txt AT&T Expires in six months January 1998 LDAP Servers Finding Other LDAP Servers Filename: draft-ietf-lsd-server-finding-01.txt Status of This Memo This document is an Internet-Draft. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document discusses methods available for an LDAP server to discover other LDAP servers. It is based on previous and ongoing IETF work. 1. Introduction The Lightweight Directory Access Protocol (LDAP) [1] can be used to build "islands" of servers that are not a priori tied into a single Directory Information Tree (DIT.) Here, it is necessary to determine how an LDAP server can discover the existence of other LDAP servers. This documents discusses the methods available based on current and previous IETF work. Expires 7/31/98 [Page 1]
INTERNET DRAFT LDAP Servers Finding Other LDAP Servers January 1998 2. Server Discovery of Other Servers A LDAP server may always hae a list of other servers configured into it by an administrator. Additionally, a LDAP server discovers other LDAP servers by either using a proposed naming scheme and the DNS, by using an additional server to server indexing protocol, or by using the Service Location Protocol [2]. Once a server discovers other servers it can collect information for returning LDAP v3 referrals (as LDAP URLs) to clients. 2.1. Discovery via DNS An LDAP server may either be registered using SRV records [3] or, if the server uses the "dc-naming" scheme ([4, 5]), it can attempt to find the server managing its parent node by using DNS to look for the LDAP server for the parent domain. Additionally, an LDAP server may be named using a common alias as described in [6]. In either case, it is necessary to include information about the root of the LDAP server's subtree by using DNS TXT records as discussed in [7]. As an example, consider a server with the RDN "dc=foo,dc=bar,dc=com" (i.e. in domain foo.bar.com) and the following DNS RRs: ldap.tcp.bar.com SRV 0 0 389 ldap1.bar.com ldap1.bar.com A 100.100.100.100 ldap1.bar.com TXT "service:wp:ldap://ldap1.bar.com:389/o=foo,c=us" To find its parent server, it would first look for a SRV record for ldap.tcp.bar.com and then follow [6] by looking for ldap.bar.com. In this case, the lookup for ldap.tcp.bar.com would provide a SRV record pointing at ldap1.bar.com. Once an A record for the parent server were found the server would then look for a TXT record for the same FQDN (here ldap1.bar.com) to determine the root of its parent server's sub-tree. Because of limitations in the size of a DNS response, each TXT record should only have one URL in it. If multiple URLs are to be specified, multiple TXT records should be used and the client is responsible for choosing between them (there is no way to specify preference between TXT records in DNS) 2.2. Discovery via the Common Indexing Protocol [8, 9] Independent of what DIT is being managed, LDAP servers could export index information about their portion of the tree via the Common Indexing Protocol. This requires some a priori discovery and set up of the index mesh and the inclusion of the root DN of the server's Expires 7/31/98 [Page 2]
INTERNET DRAFT LDAP Servers Finding Other LDAP Servers January 1998 portion of the tree in the exported index information. 2.3. Discovery via the Service Location Protocol It is also possible for a LDAP server to discover other LDAP servers via the Service Location Protocol (SRVLOC) through use of the proposed "wp" and "yp" abstract service types [10]. To advertise a LDAP server, the administator would register the LDAP server under SRVLOC, including registering the server's DN as part of the attributes of the service. A LDAP server would then issue a request and recieve URL information about advertised LDAP servers and what portions of the DIT they serve. 3. Security Considerations Since this draft only summarizes available methods, it adds no additional security considerations to those inherent in the referenced documents. Implementors are strongly recommended to read and follow the security considerations provided in the referenced documents. 4. Acknowledgments Many thanks to the members of the LSD working group, for their contributions to previous drafts. The work described in this document is partially supported by the National Science Foundation, Cooperative Agreement NCR-9218179. 5. References Request For Comments (RFC) and Internet Drafts documents are available from <URL:ftp://ftp.internic.net> and numerous mirror sites. [1] W. Yeong, T. Howes, S. Kille, "Lightweight Directory Access Protocol," RFC 1777, March 1995. [2] J. Veizades, E. Guttman, C. Perkins, S. Kaplan, "Service Location Protocol," RFC 2165, June 1997. [3] A. Gulbrandsen, P. Vixie, "A DNS RR for specifying the loca- tion of services (DNS SRV)," RFC 2052, October 1996. [4] A. Grimstad et al., "Naming Plan for an Internet Directory Service," Internet Draft (work in progress), March 19, 1997. Expires 7/31/98 [Page 3]
INTERNET DRAFT LDAP Servers Finding Other LDAP Servers January 1998 [5] S. Kille et al., "Using Domains in LDAP Distinguished Names," Internet Draft (work in progress), August 1997. [6] M. Hamilton, R. Wright, "Use of DNS Aliases for Network Ser- vices," RFC 2219 (Also BCP 17), October, 1997. [7] R. Moats, M. Hamilton, "Advertising Services," Internet Draft (work in progress), June 1997. [8] M. Mealling, J. Allen, "MIME Object Definitions for the Com- mon Indexing Protocol(CIP)," Internet Draft (work in progress), June 11, 1997. [9] M. Mealling, J. Allen, "The Architecture of the Common Indexing Protocol (CIP)," Internet Draft (work in progress), June 11, 1997. [10] R. Moats, "The 'wp' and 'yp' Abstract Service Types", Inter- net Draft (work in progress), January, 1998. 6. Author's address Ryan Moats AT&T 15621 Drexel Circle Omaha, NE 68135-2358 USA Phone: +1 402 894-9456 EMail: jayhawk@att.com Expires 7/31/98 [Page 4]
