Introduction to Name and Directory Services

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Introduction to Name and Directory Services

• Gang Shen (Bruce)

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Introduction

• What is
• What for
• Standard
• How does it work
• Example
• References

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What is Name or Directory Services

• Look-up operations. Given the name or some
  attributes of an object entity, more attribute
  information is obtained. Name service and
  Directory service are interchangeable. They all
  describe how a named object can be addressed and
  located by using its address.1

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What is Name or Directory Services

• A directory service is a software application
  or a set of applications that stores and
  organizes information about a computer network's
  users and network resources, and that allows
  network administrators to manage users' access to
  the resources. Additionally, directory services
  act as an abstraction layer between users and
  shared resources.3

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Purpose of Directory Service

• Enable user to reference network resources with
  short names instead of real addresses
• Locate object by attributes
• Provide a layer of abstraction so that the
  network resources can be managed independently
  without service interruption
• Added value, such as security,etc.

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Implementation

• Active Directory for Windows 2000, Server 2003
• Apple Open Directory in Mac OS X Server
• Novell eDirectory - formerly called Novell
  Directory Services (NDS) for Novell NetWare
  version 4.x-5.x
• OpenLDAP
• Sun Directory Services

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Standard

• X.500 defined by CCITT(Comité Consultatif
  International Téléphonique et Télégraphique) Now
  ITU-T (Telecommunication Standardization Sector
  of the International Telecommunications Union).
• Includes4
• DAP (Directory Access Protocol)
• DSP (Directory System Protocol)
• DISP (Directory Information Shadowing Protocol)
• DOP (Directory Operational Bindings Management
  Protocol)

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Standard

• LDAP, Lightweight Directory Access Protocol, is a
  networking protocol for querying and modifying
  directory services running over TCP/IP.5

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How does it work

• Object resolution process has two steps.
• Name resolution Map name to logical address.
  More interesting. Example, Locate a server.
  Retrieve a user object..
• Address resolution map logical address to
  physical address/network route. Its a network
  function.

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Ways to name an object

• ltattributegt,ltname,attributes,addressgt,ltname,
  type, attributes, addressgt
• Flat,hierarchy structure, structure-free name,
  value pairs
• Physical, organizational, functional

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Storage

• DIB (directory information base) from X.500. Its
  a tree structure.

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Access Mode

• DSADirectory Service Agent
• DUA- Directory User Agent
• Client Server Based model

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LDAP

• Latest technology on directory service. Client
  server architecture, based on TCP (vs. OSI),
  less operations, only support string type (vs.
  more data types), faster and easier to use. 6

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LDAP Server

• Its a fast read, slow update database. It
  organized in a very shallow tree fashion for read
  performance. All or nothing updates. It can
  return multiple result objects. It only return
  success search result or failure. It retrieve
  result from other servers on clients behalf.

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Terms

• Domain component dc
• Organizational unit ou
• Distinguished name (fully qualified name) dn
• Common name cn

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Example
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Query LDAP

• Combination of DN, filter, and scope2
• a base DN indicates where in the hierarchy to
  begin the search
• a filter specifies attribute types, assertion
  values, and matching criteria
• scope indicates what to searchbase DN,one level
  below the base DN, subtree rooted at the base DN

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Query

• base DN dc edu
• scope entire subtree
• filter objectClass person

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Opportunities

• Performance, cache, replication
• Reliability, replication
• Security

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Extent ions and Questions

• Cache
• Security

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References

• 1.Randy Chow,Theodore Johnson, Distributed
  Operating Systems Algorithms, 1998
• 2. Jeff Hodges,"Introduction to Directories and
  LDAP", June 1997
• 3. http//en.wikipedia.org/wiki/Directory_service
  
• 4. http//en.wikipedia.org/wiki/X.500
• 5. http//en.wikipedia.org/wiki/Lightweight_Direct
  ory_Access_Protocol
• 6. Timothy A. Howes, "The Lightweight Directory
  Access Protocol X.500 Lite", July 27, 1995, CITI
  Technical Report 95-8