RFC 1308 (rfc1308) - Page 2 of 4
Executive Introduction to Directory Services Using the X
Alternative Format: Original Text Document
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