X.500 Lightweight Directory Access Protocol
RFC 1487
Network Working Group W. Yeong
Request for Comments: 1487 Performance Systems International
T. Howes
University of Michigan
S. Kille
ISODE Consortium
July 1993
X.500 Lightweight Directory Access Protocol
Status of this Memo
This RFC specifies an IAB standards track protocol for the Internet
community, and requests discussion and suggestions for improvements.
Please refer to the current edition of the "IAB Official Protocol
Standards" for the standardization state and status of this protocol.
Distribution of this memo is unlimited.
Abstract
The protocol described in this document is designed to provide access
to the Directory while not incurring the resource requirements of the
Directory Access Protocol (DAP). This protocol is specifically
targeted at simple management applications and browser applications
that provide simple read/write interactive access to the Directory,
and is intended to be a complement to the DAP itself.
Key aspects of LDAP are:
- Protocol elements are carried directly over TCP or other transport,
bypassing much of the session/presentation overhead.
- Many protocol data elements are encoding as ordinary strings (e.g.,
Distinguished Names).
- A lightweight BER encoding is used to encode all protocol elements.
1. History
The tremendous interest in X.500 [1,2] technology in the Internet has
lead to efforts to reduce the high "cost of entry" associated with
use of the technology, such as the Directory Assistance Service [3]
and DIXIE [4]. While efforts such as these have met with success,
they have been solutions based on particular implementations and as
such have limited applicability. This document continues the efforts
to define Directory protocol alternatives but departs from previous
efforts in that it consciously avoids dependence on particular
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RFC 1487 X.500 LDAP July 1993
implementations.
2. Protocol Model
The general model adopted by this protocol is one of clients
performing protocol operations against servers. In this model, this
is accomplished by a client transmitting a protocol request
describing the operation to be performed to a server, which is then
responsible for performing the necessary operations on the Directory.
Upon completion of the necessary operations, the server returns a
response containing any results or errors to the requesting client.
In keeping with the goal of easing the costs associated with use of
the Directory, it is an objective of this protocol to minimize the
complexity of clients so as to facilitate widespread deployment of
applications capable of utilizing the Directory.
Note that, although servers are required to return responses whenever
such responses are defined in the protocol, there is no requirement
for synchronous behavior on the part of either client or server
implementations: requests and responses for multiple operations may
be exchanged by client and servers in any order, as long as clients
eventually receive a response for every request that requires one.
Consistent with the model of servers performing protocol operations
on behalf of clients, it is also to be noted that protocol servers
are expected to handle referrals without resorting to the return of
such referrals to the client. This protocol makes no provisions for
the return of referrals to clients, as the model is one of servers
ensuring the performance of all necessary operations in the
Directory, with only final results or errors being returned by
servers to clients.
Note that this protocol can be mapped to a strict subset of the
directory abstract service, so it can be cleanly provided by the DAP.
3. Mapping Onto Transport Services
This protocol is designed to run over connection-oriented, reliable
transports, with all 8 bits in an octet being significant in the data
stream. Specifications for two underlying services are defined here,
though others are also possible.
3.1. Transmission Control Protocol (TCP)
The LDAPMessage PDUs are mapped directly onto the TCP bytestream.
Server implementations running over the TCP should provide a protocol
listener on port 389.
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RFC 1487 X.500 LDAP July 1993
3.2. Connection Oriented Transport Service (COTS)
The connection is established. No special special use of T-Connect
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