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rfc:fyi:fyi14

Network Working Group C. Weider Request for Comments: 1309 ANS FYI: 14 J. Reynolds

                                                                   ISI
                                                              S. Heker
                                                                  JvNC
                                                            March 1992
              Technical Overview of 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 overview of the X.500 standard for people not
 familiar with the technology. It compares and contrasts Directory
 Services based on X.500 with several of the other Directory services
 currently in use in the Internet. This paper also describes the
 status of the standard and provides references for further
 information on X.500 implementations and technical information.
 A primary purpose of this paper is to illustrate the vast
 functionality of the X.500 protocol and to show how it can be used to
 provide a global directory for human use, and can support other
 applications which would benefit from directory services, such as
 main programs.
 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

 As the pace of industry, science, and technological development
 quickened over the past century, it became increasingly probable that
 someone in a geographically distant location would be trying to solve
 the same problems you were trying to solve, or that someone in a
 geographically distant location would have some vital information
 which impinged on your research or business.  The stupendous growth
 in the telecommunications industry, from telegraphs to telephones to
 computer networks, has alleviated the problem of being able to

DISI Working Group [Page 1] RFC 1309 Technical Overview of X.500 March 1992

 communicate with another person, PROVIDED THAT YOU KNOW HOW TO REACH
 THEM.
 Thus, along with the expansion of the telecommunications
 infrastructure came the development of Directory Services. In this
 paper, we will discuss various models of directory services, the
 limitations of current models, and some solutions provided by the
 X.500 standard to these limitations.

2 MODELS OF DIRECTORY SERVICES

2.1 The telephone company's directory services.

 A model many people think of when they hear the words "Directory
 Services" is the directory service provided by the local telephone
 company. A local telephone company keeps an on-line list of the names
 of people with phone service, along with their phone numbers and
 their address. This information is available by calling up Directory
 Assistance, giving the name and address of the party whose number you
 are seeking, and waiting for the operator to search his database. It
 is additionally available by looking in a phone book published yearly
 on paper.
 The phone companies are able to offer this invaluable service because
 they administer the pool of phone numbers. However, this service has
 some limitations. For instance, you can find someone's number only if
 you know their name and the city or location in which they live. If
 two or more people have listings for the same name in the same
 locality, there is no additional information which with to select the
 correct number. In addition, the printed phone book can have
 information which is as much as a year out of date, and the phone
 company's internal directory can be as much as two weeks out of date.
 A third problem is that one actually has to call Directory assistance
 in a given area code to get information for that area; one cannot
 call a single number consistently.
 For businesses which advertise in the Yellow Pages, there is some
 additional information stored for each business; unfortunately, that
 information is unavailable through Directory Assistance and must be
 gleaned from the phone book.

2.2 Some currently available directory services on the Internet.

 As the Internet is comprised of a vast conglomeration of different
 people, computers, and computer networks, with none of the hierarchy
 imposed by the phone system on the area codes and exchange prefixes,
 any directory service must be able to deal with the fact that the
 Internet is not structured; for example, the hosts foo.com and

DISI Working Group [Page 2] RFC 1309 Technical Overview of X.500 March 1992

 v2.foo.com may be on opposite sides of the world, the .edu domain
 maps onto an enormous number of organizations, etc.  Let's look at a
 few of the services currently available on the Internet for directory
 type services.

2.2.1 The finger protocol.

 The finger protocol, which has been implemented for UNIX systems and
 a small number of other machines, allows one to "finger" a specific
 person or username to a host running the protocol. This is invoked by
 typing, for example, "finger clw@mazatzal.merit.edu". A certain set
 of information is returned, as this example from a UNIX system finger
 operation shows, although the output format is not specified by the
 protocol:
    Login name: clw                   In real life: Chris Weider
    Directory: /usr/clw               Shell: /bin/csh
    On since Jul 25 09:43:42          4 hours 52 minutes Idle Time
    Plan:
    Home: 971-5581
 where the first three lines of information are taken from the UNIX
 operating systems information and the line(s) of information
 following the "Plan:" line are taken from a file named .plan which
 each user modifies.  Limitations of the fingerd program include: a)
 One must already know which host to finger to find a specific person,
 b) since primarily UNIX machines run fingerd, people who reside on
 other types of operating systems are not locateable by this method,
 c) fingerd is often disabled on UNIX systems for security purposes,
 d) if one wishes to be found on more than one system, one must make
 sure that all the .plan files are consistent, and e) there is no way
 to search the .plan files on a given host to (for example) find
 everyone on mazatzal.merit.edu who works on X.500.  Thus, fingerd has
 a limited usefulness as a piece of the Internet Directory.

2.2.2 whois

 The whois utility, which is available on a wide of variety of
 systems, works by querying a centralized database maintained at the
 DDN NIC, which was for many years located at SRI International in
 Menlo Park, California, and is now located at GSI. This database
 contains a large amount of information which primarily deals with
 people and equipment which is used to build the Internet.  SRI (and
 now GSI) has been able to collect the information in the WHOIS
 database as part of its role as the Network Information Center for
 the TCP/IP portion of the Internet.
 The whois utility is ubiquitous, and has a very simple interface. A

DISI Working Group [Page 3] RFC 1309 Technical Overview of X.500 March 1992

 typical whois query look like:
    whois Reynolds
 and returns information like:
    Reynolds, John F. (JFR22) 532JFR@DOM1.NWAC.SEA06.NAVY.MIL
                                         (702) 426-2604 (DSN) 830-2604
    Reynolds, John J. (JJR40) amsel-lg-pl-a@MONMOUTH-EMH3.ARMY.MIL
                                         (908) 532-3817 (DSN) 992-3817
    Reynolds, John W. (JWR46) EAAV-AP@SEOUL-EMH1.ARMY.MIL
                                         (DSN) 723-3358
    Reynolds, Joseph T. (JTR10)  JREYNOLDS@PAXRV-NES.NAVY.MIL
                                     011-63-47-885-3194 (DSN) 885-3194
    Reynolds, Joyce K. (JKR1) JKREY@ISI.EDU             (213) 822-1511
    Reynolds, Keith (KR35)    keithr@SCO.CO             (408) 425-7222
    Reynolds, Kenneth (KR94)                            (502) 454-2950
    Reynolds, Kevin A. (KR39)    REYNOLDS@DUGWAY-EMH1.ARMY.MIL
                                         (801) 831-5441 (DSN) 789-5441
    Reynolds, Lee B. (LBR9)   reynolds@TECHNET.NM.ORG   (505) 345-6555
    a further lookup on Joyce Reynolds with this command line:
    whois JKR1
 returns:
    Reynolds, Joyce K. (JKR1)               JKREY@ISI.EDU
       University of Southern California
       Information Sciences Institute
       4676 Admiralty Way
       Marina del Rey, CA 90292
       (310) 822-1511
       Record last updated on 07-Jan-91.
 The whois database also contains information about Domain Name System
 (DNS) and has some information about hosts, major regional networks,
 and large parts of the MILNET system.
 The WHOIS database is large enough and comprehensive enough to
 exhibit many of the flaws of a large centralized database: a) As the
 database is maintained on one machine, a processor bottleneck forces
 slow response during times of peak querying activity, even if many of
 these queries are unrelated, b) as the database is maintained on one
 machine, a storage bottleneck forces the database administrators to
 severely limit the amount of information which can be kept on each
 entry in the database, c) all changes to the database have to be

DISI Working Group [Page 4] RFC 1309 Technical Overview of X.500 March 1992

 mailed to a "hostmaster" and then physically reentered into the
 database, increasing both the turnaround time and the likelihood for
 a mistake in transcription.

2.2.3 The Domain Name System

 The Domain Name System is used in the Internet to keep track of host
 to IP address mapping. The basic mechanism is that each domain, such
 as merit.edu or k-12.edu, is registered with the NIC, and at time of
 registration, a primary and (perhaps) some secondary nameservers are
 identified for that domain. Each of these nameservers must provide
 host name to IP address mapping for each host in the domain. Thus,
 the nameservice is supplied in a distributed fashion. It is also
 possible to split a domain into subdomains, with a different
 nameserver for each subdomain.
 Although in many cases one uses the DNS without being aware of it,
 because humans prefer to remember names and not IP addresses, it is
 possible to interactively query the DNS with the nslookup utility. A
 sample session using the nslookup utility:
    home.merit.edu(1): nslookup
    Default Server:  merit.edu
    Address:  35.42.1.42
    > scanf.merit.edu
    Server:  merit.edu
    Address:  35.42.1.42
    Name:   scanf.merit.edu
    Address: 35.42.1.92
    > 35.42.1.92
    Server:  merit.edu
    Address: 35.42.1.42
    Name:  [35.42.1.92]
    Address: 35.42.1.92
 Thus, we can explicitly determine the address associated with a given
 host.  Reverse name mapping is also possible with the DNS, as in this
 example:

DISI Working Group [Page 5] RFC 1309 Technical Overview of X.500 March 1992

    home.merit.edu(2): traceroute ans.net
    traceroute to ans.net (147.225.1.2), 30 hops max, 40 byte packets
      1 t3peer (35.1.1.33) 11 ms 5 ms 5 ms
      2 enss (35.1.1.1) 6 ms 6 ms 6 ms
            .................
      9 192.77.154.1 (192.77.154.1) 51 ms 43 ms 49 ms
     10 nis.ans.net (147.225.1.2) 53 ms 53 ms 46 ms
 At each hop of the traceroute, the program attempts to do a reverse
 lookup through the DNS and displays the results when successful.
 Although the DNS has served superlatively for the purpose it was
 developed, i.e. to allow maintenance of the namespace in a
 distributed fashion, and to provide very rapid lookups in the
 namespace, there are, of course, some limitations. Although there has
 been some discussion of including other types of information in the
 DNS, to find a given person at this time, assuming you know where she
 works, you have to use a combination of the DNS and finger to even
 make a stab at finding her. Also, the DNS has very limited search
 capabilities right now. The lack of search capabilities alone shows
 that we cannot provide a rich Directory Service through the DNS.

3: THE X.500 MODEL OF DIRECTORY SERVICE

 X.500 is a CCITT protocol which is designed to build a distributed,
 global directory.  It offers the following features:
  • Decentralized Maintenance:

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.

DISI Working Group [Page 6] RFC 1309 Technical Overview of X.500 March 1992

  • Standards-Based Directory:

As X.500 can be used to build a standards-based directory,

   applications which require directory information (e-mail,
   automated resource 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.

3.1 Acronym City, or How X.500 Works

 The '88 version of the X.500 standard talks about 3 models required
 to build the X.500 Directory Service: the Directory Model, the
 Information Model, and the Security Model. In this section, we will
 provide a brief overview of the Directory and Information Models
 sufficient to explain the vast functionality of X.500.

3.1.1 The Information Model

 To illustrate the Information Model, we will first show how
 information is held in the Directory, then we will show what types of
 information can be held in the Directory, and then we will see how
 the information is arranged so that we can retrieve the desired
 pieces from the Directory.

3.1.1.1 Entries

 The primary construct holding information in the Directory is the
 "entry".  Each Directory entry contains information about one object;
 for example, a person, a computer network, or an organization. Each
 entry is built from a collection of "attributes", each of which holds
 a single piece of information about the object. Some attributes which
 might be used to build an entry for a person would be "surname",
 "telephonenumber", "postaladdress", etc. Each attribute has an
 associated "attribute syntax", which describes the type of data that
 attribute contains, for example, photo data, a time code, or a string
 of letters and numbers. As an example, let's look at part of an entry
 for a person.
Entry for John Smith contains:
  attribute ---> surName=              Smith  <--- attribute value
           |---> telephoneNumber=   999-9999  <--- attribute value
           |---> title=              Janitor  <--- attribute value
                              ...
 The attribute syntax for the surName attribute would be
 CaseIgnoreString, which would tell X.500 that surName could contain
 any string, and case would not matter; the attribute syntax for the
 telephoneNumber attribute would be TelephoneNumber, which would

DISI Working Group [Page 7] RFC 1309 Technical Overview of X.500 March 1992

 specify that telephoneNumber could contain a string composed of
 digits, dashes, parenthesis, and a plus sign.  The attribute syntax
 for the title attribute would also be CaseIgnoreString.  A good
 analogy in database terms for what we've seen so far might be to
 think of a Directory entry as a database record, an attribute as a
 field in that record, and an attribute syntax as a field type
 (decimal number, string) for a field in a record.

3.1.1.2 Object Classes

 At this point in our description of the information model, we have no
 way of knowing what type of object a given entry represents. X.500
 uses the concept of an "object class" to specify that information,
 and an attribute named "objectClass" which each entry contains to
 specify to which object class(es) the entry belongs.
 Each object class in X.500 has a definition which lists the set of
 mandatory attributes, which must be present, and a set of optional
 attributes, which may be present, in an entry of that class. An given
 object class A may be a subclass of another class B, in which case
 object class A inherits all the mandatory and optional attributes of
 B in addition to its own.
 The object classes in X.500 are arranged in a hierarchical manner
 according to class inheritance; the following diagram shows a part of
 the object class hierarchy.

DISI Working Group [Page 8] RFC 1309 Technical Overview of X.500 March 1992

                        _____________
                       |             | "top" has one mandatory
                       | top         | attribute "objectClass",
                       |_____________| and nooptional attributes.
                        |     |    |
                        |     |    | every other object class is a
        ________________|     |    | subclass of "top"...
        |                     |   ...
  ______|________        _____|_______
 |               |     |               |"organization" inherits one
 | country       |     | organization  |mandatory attribute from
 |_______________|     |_______________|"top", "objectClass"; adds one
                                        more mandatory attribute "O"

"country" inherits one (for organization), and has mandatory attribute from "top", many optional attributes. Any "objectClass", adds one more subclass of "organization" mandatory attribute "c" (for would inherit all of the country), and has two optional mandatory and optional attributes, "description" and attributes from "organization" "searchGuide". Any subclass of including the attribute which "country" would inherit all of the "organization" inherited mandatory and optional attributes from "top". of the "country" class, including the attribute which "country" inherited from "top".

                             Figure 1.
 One major benefit of the object class concept is that it is in many
 cases very easy to create a new object class which is only a slight
 modification or extension of a previous class. For example, if I have
 already defined an object class for "person" which contains a
 person's name, phone number, address, and fax number, I can easily
 define an "Internet person" object class by defining "Internet
 person" as a subclass of "person", with the additional optional
 attribute of "e-mail address". Thus in my definition of the "Internet
 Person" object class, all my "person" type attributes are inherited
 from "person". There are other benefits which are beyond the scope of
 this paper.

3.1.1.3 X.500's namespace.

 X.500 hierarchically organizes the namespace in the Directory
 Information Base (DIB); recall that this hierarchical organization is
 called the Directory Information Tree (DIT).  Each entry in the DIB
 occupies a certain location in the DIT. An entry which has no
 children is called a leaf entry, an entry which has children is
 called a non-leaf node. Each entry in the DIT contains one or more

DISI Working Group [Page 9] RFC 1309 Technical Overview of X.500 March 1992

 attributes which together comprise the Relative Distinguished Name
 (RDN) of that entry, there is a "root" entry (which has no
 attributes, a special case) which forms the base node of the DIT. The
 Distinguished Name of a specific entry is the sequence of RDNs of the
 entries on the path from the root entry to the entry in question. A
 diagram here will help to clarify this:

Level of DIT Root RDN Distinguished Name

root * nothing { }

                       / | \

country (other / | \ things at this / | \ c=us {c=us} level) c=gb c=us c=ca

                      /  |  \
                     /   |   \
                    /    |    \

organization o=SRI o=Merit o=DEC o=Merit {c=us, o=Merit} (other things / | \ at this level) / | \

                    /    |     \

Third level cn=Chris Weider cn=Chris Weider {c=us, o=Merit,

                                                      cn=Chris Weider}
     Figure 2: Building a DN from RDNs (adapted from a
        diagram in the X.500 (88) Blue Book)
 Each entry in this tree contains more attributes than have been shown
 here, but in each case only one attribute for each entry has been
 used for that entry's RDN. As noted above, any entry in the tree
 could use more than one attribute to build its RDN. X.500 also allows
 the use of alias names, so that the entry {c=us, o=Merit, cn=Chris
 Weider} could be also found through an alias entry such as {c=us,
 o=SRI, ou=FOX Project, cn=Drone 1} which would point to the first
 entry.

3.1.2 The Directory Model

 Now that we've seen what kinds of information can be kept in the
 Directory, we should look at how the Directory stores this
 information and how a Directory users accesses the information. There
 are two components of this model: a Directory User Agent (DUA), which
 accesses the Directory on behalf of a user, and the Directory System
 Agent, which can be viewed as holding a particular subset of the DIB,
 and can also provide an access point to the Directory for a DUA.
 Now, the entire DIB is distributed through the world-wide collection
 of DSAs which form the Directory, and the DSAs employ two techniques

DISI Working Group [Page 10] RFC 1309 Technical Overview of X.500 March 1992

 to allow this distribution to be transparent to the user, called
 "chaining" and "referral".  The details of these two techniques would
 take up another page, so it suffices to say that to each user, it
 appears that the entire global directory is on her desktop. (Of
 course, if the information requested is on the other side of the
 world, it may seem that the desktop directory is a bit slow for that
 request...)

3.2 The functionality of X.500

 To describe the functionality of X.500, we will need to separate
 three stages in the evolution of X.500: 1) the 1988 standard, 2)
 X.500 as implemented in QUIPU, and 3) the (proposed) 1992 standard.
 We will list some of the features described in the 1988 standard,
 show how they were implemented in QUIPU, and discuss where the 1992
 standard will take us.  The QUIPU implementation was chosen because
 a) it is widely used in the U.S. and European Directory Services
 Pilot projects, and b) it works well. For a survey of other X.500
 implementations and a catalogue of DUAs, see [Lang].

3.2.1 Functionality in X.500 (88)

 There are a number of advantages that the X.500 Directory accrues
 simply by virtue of the fact that it is distributed, not limited to a
 single machine. Among these are:
  • An enormously large potential namespace.

Since the Directory is not limited to a single machine, many

   hundreds of machines can be used to store Directory entries.
  • The ability to allow local administration of local data.

An organization or group can run a local DSA to master their

   information, facilitating much more accurate data throughout
   the Directory.
 The functionality built into the X.500(88) standard includes:
  • Advanced searching capabilities.

The Directory supports arbitrarily complex searches at an

   attribute level. As the object classes a specific entry
   belongs to is maintained in the objectClass attribute, this
   also allows Directory searches for specific types of objects.
   Thus, one could search the c=US subtree for anyone with a last
   name beginning with S, who also has either a fax number in the
   (313) area code or an e-mail address ending in umich.edu.
   This feature of X.500 also helps to provide the basic
   functionality for a Yellow Pages service.

DISI Working Group [Page 11] RFC 1309 Technical Overview of X.500 March 1992

  • A uniform namespace with local extensibility.

The Directory provides a uniform namespace, but local

   specialized directories can also be implemented.  Locally
   defined extensions can include new object classes, new
   attributes, and new attribute types.
  • Security issues.

The X.500 (88) standards define two types of security for

   Directory data: Simple Authentication (which uses passwords),
   and Strong Authentication (which uses cryptographic keys).
   Simple authentication has been widely implemented, strong
   authentication has been less widely implemented.  Each of
   these authentication techniques are invoked when a user or
   process attempts a Directory operation through a DUA.
 In addition to the global benefits of the X.500 standard, there are
 many local benefits. One can use their local DSA for company or
 campus wide directory services; for example, the University of
 Michigan is providing all the campus directory services through
 X.500. The DUAs are available for a wide range of platforms,
 including X-Windows systems and Macintoshes.

3.2.2 Functionality added by QUIPU.

 Functionality beyond the X.500 (88) standard implemented by QUIPU
 includes:
  • Access control lists.

An access control list is a way to provide security for each

   attribute of an entry.  For example, each attribute in a given
   entry can be permitted for detect, compare, read, and modify
   permissions based on the reader's membership in various groups.
   For example, one can specify that some information in a given
   entry is public, some can be read only by members of the
   organization, and some can only be modified by the owner of
   the entry.
  • Replication.

Replication provides a method whereby frequently accessed

   information in a DSA other than the local one can be kept by
   the local DSA on a "slave" basis, with updates of the "slave"
   data provided automatically by QUIPU from the "master" data
   residing on the foreign DSA.  This provides alternate access
   points to that data, and can make searches and retrievals
   more rapid as there is much less overhead in the form or
   network transport.

DISI Working Group [Page 12] RFC 1309 Technical Overview of X.500 March 1992

3.3 Current limitations of the X.500 standard and implementations.

 As flexible and forward looking as X.500 is, it certainly was not
 designed to solve everyone's needs for all time to come. X.500 is not
 a general purpose database, nor is it a Data Base Management System
 (DBMS). X.500 defines no standards for output formats, and it
 certainly doesn't have a report generation capability. The technical
 mechanisms are not yet in place for the Directory to contain
 information about itself, thus new attributes and new attribute types
 are rather slowly distributed (by hand).
 Searches can be slow, for two reasons: a) searches across a widely
 distributed portion of the namespace (c=US, for example) has a delay
 which is partially caused by network transmission times, and can be
 compounded by implementations that cache the partial search returns
 until everyone has reported back, and b) some implementations are
 slow at searching anyway, and this is very sensitive to such things
 as processor speed and available swap space.  Another implementation
 "problem" is a tradeoff with security for the Directory: most
 implementations have an administrative limit on the amount of
 information which can be returned for a specific search.  For
 example, if a search returns 1000 hits, 20 of those might be
 displayed, with the rest lost. Thus a person performing a large
 search might have to perform a number of small searches.  This was
 implemented because an organization might want to make it hard to
 "troll" for the organization's entire database.
 Also, there is at the moment no clear consensus on the ideal shape of
 the DIT, or on the idea structure of the object tree.  This can make
 it hard to add to the current corpus of X.500 work, and the number of
 RFCs on various aspects of the X.500 deployment is growing monthly.
 Despite this, however, X.500 is very good at what it was designed to
 do; i.e., to provide primary directory services and "resource
 location" for a wide band oftypes of information.

3.4 Things to be added in X.500 (92).

 The 1988 version of the X.500 standard proved to be quite sufficient
 to start building a Directory Service. However, many of the new
 functions implemented in QUIPU were necessary if the Directory were
 to function in a reasonable manner. X.500 (92) will include
 formalized and standardized versions of those advances, including
  • A formalized replication procedure.
  • Enhanced searching capacities.

DISI Working Group [Page 13] RFC 1309 Technical Overview of X.500 March 1992

  • Formalization of access control mechanisms, including access

control lists.

 Each of these will provide a richer Directory, but you don't have to
 wait for them! You can become part of the Directory today!

4: WHAT X.500 CAN DO FOR YOU TODAY

4.1 Current applications of X.500

 X.500 is filling Directory Services needs in a large number of
 countries.  As a directory to locate people, it is provided in the
 U.S. as the White Pages Pilot Project, run by PSI, and in Europe
 under the PARADISE Project as a series of nation-wide pilots.  It is
 also being used by the FOX Project in the United States to provide
 WHOIS services for people and networks, and to provide directories of
 objects as disparate as NIC Profiles and a pilot K-12 Educators
 directory. It is also being investigated for its ability to provide
 resource location facilities and to provide source location for WAIS
 servers. In fact, in almost every area where one could imagine
 needing a directory service (particularly for distributed directory
 services), X.500 is either providing those services or being expanded
 to provide those services.
 In particular, X.500 was envisioned by its creators as providing
 directory services for electronic mail, specifically for X.400. It is
 being used in this fashion today at the University of Michigan:
 everyone at the University has a unified mail address, e.g.
 Chris.Weider@umich.edu. An X.500 server then reroutes that mail to
 the appropriate user's real mail address in a transparent fashion.
 Similarly, Sprint is using X.500 to administrate the address space
 for its internal X.400 mail systems.
 Those of us working on X.500 feel that X.500's strengths lie in
 providing directory services for people and objects, and for
 providing primary resource location for a large number of online
 services. We think that X.500 is a major component (though not the
 only one) of a global Yellow Pages service. We would also like to
 encourage each of you to join your national pilot projects; the more
 coverage we can get, the easier you will be able to find the people
 you need to contact.

DISI Working Group [Page 14] RFC 1309 Technical Overview of X.500 March 1992

5. For Further Information

 For further information, the authors recommend the following
 documents:
    Weider, C., and J. Reynolds, "Executive Introduction to Directory
    Services Using the X.500 Protocol", FYI 13, RFC 1308, ANS, ISI,
    March 1992.
    Lang, R., and R. Wright, Editors, "A Catalog of Available X.500
    Implementations", FYI 11, RFC 1292, SRI International, Lawrence
    Berkeley Laboratory, January 1992.
    Barker, P., and S. Hardcastle-Kille, "The COSINE and Internet
    X.500 Schema", RFC 1274, University College London, November 1991.
    Hardcastle-Kille, S., "Replication Requirements to provide an
    Internet Directory using X.500", RFC 1275, University College
    London, November, 1991.
    Hardcastle-Kille, S., "Replication and Distributed Operations
    extensions to provide an Internet Directory using X.500", RFC
    1276, University College London, November 1991.
    Hardcastle-Kille, S., "Encoding Network Addresses to support
    operation over non-OSI lower layers", RFC 1277, University College
    London, November 1991.
    Hardcastle-Kille, S., " A string encoding of Presentation
    Address", RFC 1278, University College London, November 1991.
    Hardcastle-Kille, S., "X.500 and Domains", RFC 1279, University
    College London, November 1991.

6. Security Considerations

    Security issues are discussed in section 3.

DISI Working Group [Page 15] RFC 1309 Technical Overview of X.500 March 1992

7. 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
    EMail: jkrey@isi.edu
    Sergio Heker
    JvNCnet
    Princeton University
    6 von Neumann Hall
    Princeton, NJ 08544
    Phone: (609) 258-2400
    Email: heker@nisc.jvnc.net

DISI Working Group [Page 16]

/data/webs/external/dokuwiki/data/pages/rfc/fyi/fyi14.txt · Last modified: 1992/03/12 00:14 (external edit)