X.500 Part 1 CNS 4650 Fall 2004 Rev. 2

Introduction to X.500 X.500 is basis for most modern directory services (LDAP, NDS, Active Directory) X.500 is actually a collection of standards X.500 was initially created to be a international “white pages” ITU standard

X.500 Standards Doc Number TitleYear X.500The Directory: Overview of Concepts, Models, and Services1988 X.501Models1988 X.509Authentication Framework1988 X.511Abstract Service Definition1988 X.518Procedures for Distributed Operation1988 X.519Protocol Specification1988 X.520Selected Attribute Types1988 X.521Selected Object Classes1988 X.525Replication1993 X.530Use of System Management for Administration of the Directory1997

X.500 Terminology FunctionalityX.500 Term Directory EntryObject Object SubentriesAttribute Definition of Directory ContentsSchema Logical Representation of the DirectoryDirectory Information Tree (DIT) Data StorageDirectory Information Base (DIB) Subdivision of the DirectoryNaming context (partition) Data updatesReplication Server AgentDirectory Service Agent (DSA) User AgentDirectory User Agent (DUA) Query ResolutionChaining and Referral

Agents Two types of Agents User Service/System/Server Common to most modern directories

User Agent (DUA) Creates queries Directory is viewed a single unit Abstract the directory from the user NOT the UI or design

System Agent (DSA) System/Server/Service Not a single component Collection of services for fulfilling DUA’s requests Access to the “system” OSI Application layer process

X.500 Protocols Operate in the Application Layer of OSI Define Client and Server protocols Only one defined for clients

Directory Access Protocol (DAP) Defines the “language” between the client (DUA) and the server (DSA) Defines read, search, modify operations Defines the association between DSA and DUA The only protocol used by DUAs

Directory System Protocol (DSP) Defines how DSAs talk to other DSAs Referrals and Chaining Caching of queries

Directory Operational Binding Management Protocol (DOP) Defines how DSAs establish connections between one another (for DISP) Define who knows what and who is master of what

Directory Information Shadowing Protocol (DISP) Transfer data/updates between shadowing DSAs Protocols from X.400 used for actual transfer protocol

DUA, DSA and X.500 Protocols

Other Standards Association Control Service Element (ACSE) Remote Operation Service Element (ROSE) Abstract Syntax Notation One (ASN.1)

APIs XDS LDAP C API

Sources Radicati S. (1994) X.500 Directory Serivces: Technology and Deployment New York: Van Nostrand Reinhold