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+Network Working Group                                          C. Weider
+Request for Comments: 1308                                           ANS
+FYI: 13                                                      J. Reynolds
+                                                                     ISI
+                                                              March 1992
+
+
+              Executive Introduction to Directory Services
+                        Using the X.500 Protocol
+
+Status 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 1992
+
+
+2. 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 the
+
+
+
+DISI 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, RFC
+   1292.
+
+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.edu
+
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+DISI Working Group                                              [Page 4]
+
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