X.500 is a series of computer networking standards covering electronic Directory Services.

The X.500 series was developed by ITU-T, formerly known as CCITT. The Directory Services were developed in order to support the requirements of X.400 electronic mail exchange and name lookup. ISO was a partner in developing the standards, incorporating them into the Open Systems Interconnection suite of protocols. ISO/IEC 9594 is the corresponding ISO identification.

LDAP vs X.500#

This architectural argument would pack networking conference sessions, divide the room and ignite heated shouting matches in the early-to-mid-1990s. It was a case of the student overtaking the mentor as the Lightweight Directory Access Protocol was at first a simple alternative to X.500’s Directory Access Protocol (DAP). LDAP was used for accessing X.500 directories via the TCP/IP protocol. With the advent of the Internet and its reliance on TCP/IP, X.500 faded into the background even though it was later modified for use over TCP/IP.

"The market was screaming for a standard client protocol" in 1999, LDAP co-inventor Tim Howes told Network World in 2002.

X.500 didn’t have it. In addition, X.500, developed in the 1980s with input from telecom firms, required an OSI stack and an X.500 Server.

To go with the client protocol, LDAP Directory Servers soon popped up that had vestiges of X.500 still lurking in their depths. But like villagers in the comedy classic “Monty Python and the Holy Grail,” X.500 is not dead yet.

Some of its supporting protocols remain important directory security constructs, namely the X.509 authentication framework that is the cornerstone of PKI-based certificates. And LDAP has had its own evolutionary issues. LDAPv3, the last iteration of the protocol, lacks widely adopted access control and back-end integration extensions, namely replication, that have kept the protocol largely behind the firewall.

More Information#

There might be more information for this subject on one of the following:
  • [#1] - X.500 - based on information obtained 2013-04-10