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: [email protected]

  Joyce K. Reynolds
  Information Sciences Institute
  University of Southern California
  4676 Admirality Way
  Marina del Rey, CA 90292

  Phone: (310) 822-1511
  E-Mail: [email protected]











DISI Working Group                                              [Page 4]


You are viewing proxied material from gopher.fnord.one. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.