As per Relevance of the word implementation, we have this rfc below:
Network Working Group C.
Request for Comments: 1308
FYI: 13 J.
March 1992
Executive Introduction to Directory
Using the X.500
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard. Distribution of this memo
unlimited
This document is an Executive Introduction to Directory
using the X.500 protocol. It briefly discusses the deficiencies
currently deployed Internet Directory Services, and then
the solutions provided by X.500.
This FYI RFC is a product of the Directory Information
(pilot) Infrastructure Working Group (DISI). A combined effort
the User Services and the OSI Integration Areas of the
Engineering Task Force (IETF).
1.
The Internet is growing at a phenomenal rate, with no deceleration
sight. Every month thousands of new users are added. New
are added literally almost every day. In fact, it is
conceivable that in the future every human with access to a
will be able to interact with every other over the Internet and
sister networks. However, the ability to interact with everyone
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
effective use of the network will be determined by the quality
coverage of Directory Services available
Directory Services in this paper refers not only to the types
services provided by the telephone companies' White Pages, but
resource location, Yellow Pages services, mail address lookup, etc
We will take a brief look at the services available today, and at
problems they have, and then we will show how the X.500
solves those problems
DISI Working Group [Page 1]
RFC 1308 Executive Intro to X.500 March 1992
2. CURRENT SERVICES AND THEIR
In the interests of brevity, we will only look at the WHOIS service
and at the DNS. Each will illustrate a particular philosophy, if
will, of Directory Services
The WHOIS service is maintained by the Defense Data Network
Information Center, or DDN NIC. It is currently maintained at
for the IP portion of the Internet. It contains information about
networks, IP network managers, a scattering of well-known
in the Internet, and a large amount of information
specifically to the MILNET systems. As the NIC is responsible
assigning new networks out of the pool of IP addresses, it is
easily able to collect this information when a new network
registered. However, the WHOIS database is big enough
comprehensive enough to exhibit many of the flaws of a
centralized database. First, centralized location of the
database causes slow response during times of peak querying activity
storage limitations, and also causes the entire service to
unavailable if the link to GSI is broken. Second,
administration of the database, where any changes to the
have to be mailed off to GSI for human transcription into
database, increases the turnaround time before the changes
propagated, and also introduces another source of potential error
the accuracy of the information. These particular problems affect
different degrees any system which attempts to provide
Services through a centralized database
The Domain Name Service, or DNS, contains information about
mapping of host and domain names, such as, "home.ans.net", to
addresses. This is done so that humans can use easily
names for machines rather than strings of numbers. It is
in a distributed fashion, with each DNS server providing
for a limited number of domains. Also, secondary nameservers can
identified for each domain, so that one unreachable network will
necessarily cut off nameservice. However, even though the DNS
superlative at providing these services, there are some problems
we attempt to provide other Directory Services in the DNS. First,
DNS has very limited search capabilities. Second, the DNS
only a small number of data types. Adding new data types, such
photographs, would involve very extensive implementation changes
3. THE X.500
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
the Directory, so updates and maintenance can be done instantly
* Powerful Searching Capabilities
X.500 provides powerful searching facilities that allow users
construct arbitrarily complex queries
* Single Global Namespace
Much like the DNS, X.500 provides a single homogeneous
to users. The X.500 namespace is more flexible and
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
backbone of a global White Pages service. There is almost 3 years
operational experience with X.500, and it is being used widely
Europe and Australia in addition to North America. In addition,
various X.500 implementations add some other features, such
photographs in G3-FAX format, and color photos in JPEG format
However, as X.500 is standards based, there are very
incompatibilities between the various versions of X.500, and as
namespace is consistent, the information in the Directory can
accessed by any implementation. Also, work is being done in
Yellow Pages services and other information resource location
in the Directory
However, there are some limitations to the X.500 technology as it
currently implemented. One price that is paid for the flexibility
searching is a decline in the speed of the searching. This is
a) searches over a part of the distributed namespace may have
traverse the network, and some implementations cache all
responses before giving them to the user, and b) some
implementations performed search slowly anyway. A second problem
the implementations is that for security reasons only a
amount of information is returned to the user; for example, if
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
search will have to do a lot of work. The performance of
DISI Working Group [Page 3]
RFC 1308 Executive Intro to X.500 March 1992
Directory, while increasing rapidly in the last two years, is
not able to provide real-time directory services for such things
routing protocols. However, work is being done to speed up service
The X.500 Directory is taking us closer to the day when we
indeed have the entire world on our desktops, and X.500 will
insure that we can find whom and what we need
4: FOR FURTHER
For a more detailed technical introduction to X.500 and an
bibliography, see "Technical Overview of Directory Services Using
X.500 Protocol", by Weider, Reynolds, and Heker. This is
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,
1292.
5: SECURITY
Security issues are not discussed in this paper
6: AUTHORS'
Chris
Advanced Network and Services, Inc
2901 Hubbard, G-1
Ann Arbor, MI 48105-2437
Phone (313) 663-2482
E-mail: weider@ans.
Joyce K.
Information Sciences
University of Southern
4676 Admirality
Marina del Rey, CA 90292
Phone: (310) 822-1511
E-Mail: jkrey@isi.
DISI Working Group [Page 4]
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