RFC 1308 (rfc1308) - Page 2 of 4

Executive Introduction to Directory Services Using the X

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