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Network Working Group                                          C. WeiderRequest for Comments: 1308                                           ANSFYI: 13                                                      J. Reynolds                                                                     ISI                                                              March 1992Executive Introduction to Directory ServicesUsing the X.500 ProtocolStatus of this Memo   This memo provides information for the Internet community. It does   not specify an Internet standard. Distribution of this memo is   unlimited.Abstract   This document is an Executive Introduction to Directory Services   using the X.500 protocol. It briefly discusses the deficiencies in   currently deployed Internet Directory Services, and then illustrates   the solutions provided by X.500.   This FYI RFC is a product of the Directory Information Services   (pilot) Infrastructure Working Group (DISI).  A combined effort of   the User Services and the OSI Integration Areas of the Internet   Engineering Task Force (IETF).1. INTRODUCTION   The Internet is growing at a phenomenal rate, with no deceleration in   sight.  Every month thousands of new users are added. New networks   are added literally almost every day. In fact, it is entirely   conceivable that in the future every human with access to a computer   will be able to interact with every other over the Internet and her   sister networks. However, the ability to interact with everyone is   only useful if one can locate the people with whom they need to work.   Thus, as the Internet grows, one of the limitations imposed on the   effective use of the network will be determined by the quality and   coverage of Directory Services available.   Directory Services in this paper refers not only to the types of   services provided by the telephone companies' White Pages, but to   resource location, Yellow Pages services, mail address lookup, etc.   We will take a brief look at the services available today, and at the   problems they have, and then we will show how the X.500 standard   solves those problems.DISI Working Group                                              [Page 1]

RFC 1308                Executive Intro to X.500              March 19922. CURRENT SERVICES AND THEIR LIMITATIONS   In the interests of brevity, we will only look at the WHOIS service,   and at the DNS. Each will illustrate a particular philosophy, if you   will, of Directory Services.   The WHOIS service is maintained by the Defense Data Network Network   Information Center, or DDN NIC.  It is currently maintained at GSI   for the IP portion of the Internet. It contains information about IP   networks, IP network managers, a scattering of well-known personages   in the Internet, and a large amount of information related   specifically to the MILNET systems. As the NIC is responsible for   assigning new networks out of the pool of IP addresses, it is very   easily able to collect this information when a new network is   registered. However, the WHOIS database is big enough and   comprehensive enough to exhibit many of the flaws of a large   centralized database. First, centralized location of the WHOIS   database causes slow response during times of peak querying activity,   storage limitations, and also causes the entire service to be   unavailable if the link to GSI is broken. Second, centralized   administration of the database, where any changes to the database   have to be mailed off to GSI for human transcription into the   database, increases the turnaround time before the changes are   propagated, and also introduces another source of potential error in   the accuracy of the information. These particular problems affect to   different degrees any system which attempts to provide Directory   Services through a centralized database.   The Domain Name Service, or DNS, contains information about the   mapping of host and domain names, such as, "home.ans.net", to IP   addresses. This is done so that humans can use easily remembered   names for machines rather than strings of numbers. It is maintained   in a distributed fashion, with each DNS server providing nameservice   for a limited number of domains.  Also, secondary nameservers can be   identified for each domain, so that one unreachable network will not   necessarily cut off nameservice. However, even though the DNS is   superlative at providing these services, there are some problems when   we attempt to provide other Directory Services in the DNS. First, the   DNS has very limited search capabilities. Second, the DNS supports   only a small number of data types. Adding new data types, such as   photographs, would involve very extensive implementation changes.3. THE X.500 SOLUTION   X.500 is a CCITT protocol which is designed to build a distributed,   global directory. It offers the following features:   * Decentralized Maintenance:DISI Working Group                                              [Page 2]

RFC 1308                Executive Intro to X.500              March 1992     Each site running X.500 is responsible ONLY for its local part of     the Directory, so updates and maintenance can be done instantly.   * Powerful Searching Capabilities:     X.500 provides powerful searching facilities that allow users to     construct arbitrarily complex queries.   * Single Global Namespace:     Much like the DNS, X.500 provides a single homogeneous namespace     to users. The X.500 namespace is more flexible and expandable     than the DNS.   * Structured Information Framework:     X.500 defines the information framework used in the Directory,     allowing local extensions.   * Standards-Based Directory Services:     As X.500 can be used to build a standards-based directory,     applications which require directory information (e-mail,     automated resources locators, special-purpose directory tools)     can access a planet's worth of information in a uniform manner,     no matter where they are based or currently running.   With these features alone, X.500 is being used today to provide the   backbone of a global White Pages service. There is almost 3 years of   operational experience with X.500, and it is being used widely in   Europe and Australia in addition to North America. In addition, the   various X.500 implementations add some other features, such as   photographs in G3-FAX format, and color photos in JPEG format.   However, as X.500 is standards based, there are very few   incompatibilities between the various versions of X.500, and as the   namespace is consistent, the information in the Directory can be   accessed by any implementation. Also, work is being done in providing   Yellow Pages services and other information resource location tasks   in the Directory.   However, there are some limitations to the X.500 technology as it is   currently implemented. One price that is paid for the flexibility in   searching is a decline in the speed of the searching. This is because   a) searches over a part of the distributed namespace may have to   traverse the network, and some implementations cache all the   responses before giving them to the user, and b) some early   implementations performed search slowly anyway. A second problem with   the implementations is that for security reasons only a limited   amount of information is returned to the user; for example, if a   search turns up 1000 hits, only 20 or so are returned to the user.   Although this number is tunable, it does mean that someone with a big   search will have to do a lot of work. The performance of theDISI Working Group                                              [Page 3]

RFC 1308                Executive Intro to X.500              March 1992   Directory, while increasing rapidly in the last two years, is still   not able to provide real-time directory services for such things as   routing protocols.  However, work is being done to speed up service.   The X.500 Directory is taking us closer to the day when we will   indeed have the entire world on our desktops, and X.500 will help   insure that we can find whom and what we need.4: FOR FURTHER INFORMATION   For a more detailed technical introduction to X.500 and an extensive   bibliography, see "Technical Overview of Directory Services Using the   X.500 Protocol", by Weider, Reynolds, and Heker. This is available   from the NIC as FYI 14,RFC 1309.  For a catalogue of X.500   implementations, see "A Catalog of Available X.500 Implementations",   ed. Lang and Wright.  This is available from the NIC as FYI 11,RFC1292.5: SECURITY CONSIDERATIONS   Security issues are not discussed in this paper.6: AUTHORS' ADDRESSES   Chris Weider   Advanced Network and Services, Inc.   2901 Hubbard, G-1   Ann Arbor, MI 48105-2437   Phone (313) 663-2482   E-mail: weider@ans.net   Joyce K. Reynolds   Information Sciences Institute   University of Southern California   4676 Admirality Way   Marina del Rey, CA 90292   Phone: (310) 822-1511   E-Mail: jkrey@isi.eduDISI Working Group                                              [Page 4]