X.500

X.500 is a standard for distributed directory services. The standard encompasses both the structure of the X.500 database and also the protocol used in querying the database. X.500 can be used for different types of directories. Its most notable implementation is a global White Pages service containing in excess of a million names contributed to by X.500 servers in dozens of countries.

X.500 provides a hierarchical database structure (for example, country/organization/organizational unit/person). The database consists of entries (one per object) which may describe persons, network resources, organizations, and so on, each with its own set of attributes.

Access

X.500 is based on the client-server model. The user with an X.500 client (known in the X.500 world as a Directory User Agent or DUA) can query an X.500 server (Directory System Agent or DSA). The server maintains the local X.500 database, but it can also communicate with other X.500 servers. If a query cannot be answered locally it may be passed on automatically to other X.500 servers and the response passed back to the user. To the user, it appears that the entire directory is accessible from the local server. As well as queries, X.500 also supports data management functions (addition, modification and deletion of entries).

A list of Public Directory Interfaces to the Nameflow Paradise service (including WWW, gopher, telnet, LDAP server) is made available by Dante at http://www.dante.net/np/pdi.html. A UK Web gateway, the Worldwide Directory Service, is at: http://www.cse.bris.ac.uk/comms/ccrjh/search-form-world.html.

TERENA

GUIDE TO NETWORK RESOURCE TOOLS

SPECIALIST SEARCH TOOLS

X.500

Access

Further information