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Network Working Group Alan Young INTERNET-DRAFT Union Bank of Switzerland <draft-ietf-osids-cldap-00.txt> Expires 20 Apr 93 Connection-less Lightweight Directory Access Protocol 1. Status of this Memo This draft document will be submitted to the RFC Editor as a standards document. Distribution of this memo is unlimited. Please send comments to the authors, or the discussion group <osi-ds@cs.ucl.ac.uk>. This document is an Internet Draft. Internet Drafts are working docu- ments of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working docu- ments as Internet Drafts). Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other docu- ments at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any other Internet Draft. 2. 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). In particular, it is aimed at avoiding the elapsed time that is associated with connection-oriented communica- tion and it facilitates use of the directory in a manner analagous to the DNS [6,7]. It is specifically targeted at simple lookup applica- tions that require to read a small number of attribute values from a single entry. It is intended to be a complement to DAP and LDAP [5]. The protocol specification draws heavily on that of LDAP. 3. Background The Directory can be used as a repository for many kinds of information. The full power of DAP is unnecessary for applications that require sim- ple read access to a few attribute values. Applications addressing is a good example of this type of use where and application entity needs to Expires 20 Apr 93 [Page 1] CLDAP October 1993 determine the Presentation Address (PA) of a peer entity given that peer's Application Entity Title (AET). If the AET is a Directory Name (DN) then the required result can be obtained from the PA attribute of the Directory entry identified by the AET. This is very similar to DNS. Use of DAP to achieve this functionality involves a significant number of network exchanges: ___________________________________________________________ | # | Client (DUA) DAP Server (DSA) | |___|______________________________________________________| | 1| N-Connect.request -> | | 2| <- N-Connect.response | | 3| T-Connect.request -> | | 4| <- T-Connect.response | | | S-Connect.request, | | | P-Connect.request, | | | A-Associate.request, | | 5| DAP-Bind.request -> | | | S-Connect.response, | | | P-Connect.response, | | | A-Associate.response, | | 6| <- DAP-Bind.response | | 7| DAP-Read.request -> | | 8| <- DAP-Read.response | | | S-Release.request, | | | P-Release.request, | | | A-Release.request, | | 9| DAP-Unbind.request -> | | | S-Release.response, | | | P-Release.response, | | | A-Release.response, | | 10| <- DAP-Unbind.response | | | T-Disconnect.request, | | 11| N-Disconnect.request -> | | | T-Disconnect.response,| | 12| <- N-Disconnect.response | |___|______________________________________________________| This is 10 packets before the application can continue, given that it can probably do so after issuing the T-Disconnect.request. (Some minor variations arise depending upon the class of Network and Transport ser- vice that is being used; for example use of TP4 over CLNS reduces the packet count by two.) LDAP is no better in the case where the LDAP server uses full DAP to communicate with the Directory: Expires 20 Apr 93 [Page 2] CLDAP October 1993 ____________________________________________________________________ | # | Client LDAP LDAP server DAP DSA | |____|______________________________________________________________| | 1 | TCP SYN -> | | 2 | <- TCP SYN ACK | | 3 | BindReq -> | | 4 | N-Connect.req -> | | 5 | <- N-Connect.res | | 6 | T-Connect.req -> | | 7 | <- T-Connect.res | | 8 | DAP-Bind.req -> | | 9 | <- DAP-Bind.res | | 10 | <- BindRes | | 11 | SearchReq -> | | 12 | DAP-Search.req -> | | 13 | <- DAP-Search.res | | 14 | <- SearchRes | | 15 | TCP FIN -> | | 16 | DAP-Unbind.req -> | | 17 | <- DAP-Unbind.res | | 18 | N-Disconnect.req -> | | 19 | <- N-Disconnect.res| |____|______________________________________________________________| Here there are 14 packets before the application can continue. Even if the LDAP server is on the same host as the DSA (so packet delay is negligible), or if the DSA supports LDAP directly, then there are still 6 packets. ____________________________________ | #| Client LDAP LDAP server| | | | |__|________________________________| | 1| TCP SYN -> | | 2| <- TCP SYN ACK| | 3| BindReq -> | | 4| <- BindRes | | 5| SearchReq -> | | 6| <- SearchRes | |__|________________________________| This protocol provides for simple access to the Directory where the delays inherent in the above exchanges are unacceptable and where the additional functionality provided by connection-mode operation is not required. Expires 20 Apr 93 [Page 3] CLDAP October 1993 4. Protocol Model CLDAP is based directly on LDAP [5] and inherits most of the key aspects of the LDAP protocol: - Many protocol data elements are encoding as ordinary strings (e.g., Distinguished Names). - A lightweight BER encoding is used to encode all protocol elements. It is different to LDAP in that: - Protocol elements are carried directly over UDP or other connection-less transport, bypassing much of the session/presentation overhead and that of connections (LDAP uses a connection-mode transport service). - The Bind and Unbind operations are not available. The definitions of protocol elements are inherited from LDAP. 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. Note that, although servers are required to return responses whenever such responses are defined in the protocol, there is no requirement for synchronous behaviour on the part of either client or server implementa- tions: requests and responses for multiple operations may be exchanged by client and servers in any order, as long as servers eventually send a response for every request that requires one. Because the protocol is implemented over a connection-less transport service clients must be prepared for either requests or responses to be lost. Clients should use a retry mechanism with timeouts in order to achieve the desired level of reliability. It is not necessary for a client to abandon any requests to which no response has been received and for which a reply is no longer required (because the request has been timed out), but they are not prohibited from doing so. 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 Expires 20 Apr 93 [Page 4] CLDAP October 1993 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 direc- tory abstract service, so it can be cleanly provided by the DAP. 5. Mapping Onto Transport Services This protocol is designed to run over connection-less transports, with all 8 bits in an octet being significant in the data stream. Specifica- tions for two underlying services are defined here, though others are also possible. 5.1. User Datagram Protocol (UDP) The LDAPMessage PDUs are mapped directly onto UDP datagrams. Only one request may be sent in a single datagram. Only one response may be sent in a single datagram with the exception, as an option, that multiple search responses resulting from a single search request may be sent in a single datagram. Server implementations running over the UDP should provide a protocol listener on port 389. 5.2. Connection-less Transport Service (CLTS) Each LDAPMessage PDU is mapped directly onto T-Unit-Data with the excep- tion that multiple search responses resulting from a single search request may be sent in a single T-Unit-Data. 6. Elements of Protocol The protocol is the same as LDAP with the restriction that Bind and Unbind and not available. The following operations are available: Search Modify Add Delete ModifyRDN Compare Abandon Given the lack of Bind, and the consequent lack of identification of the Directory User to the Directory Service, one would not generally expect Modify, Add, Delete or ModifyRDN to be honoured by the Directory Ser- vice. They are not however, excluded from the protocol. Expires 20 Apr 93 [Page 5] CLDAP October 1993 6.1. Errors The following error code is added to the LDAPResult.resultCode enumera- tion of [5]: resultsTooLarge (70), This error will be returned when the LDAPMessage PDU containing the results of an operation are too large to be sent in a single datagram or PDU or, in the case that the multiple results of a search are to be returned in a single datagram or PDU, that these combined results are too large. 6.2. Example A simple lookup can be performed in 4 packets. This is reduced to 2 if either the DSA implements the CLDAP protocol, the CLDAP server has a cache of the desired results, or the CLDAP server and DSA are co-located such that there is insignificant delay between them. _______________________________________________________________ | #| Client CLDAP CLDAP server DAP DSA | |__|___________________________________________________________| | 1| SearchReq -> | | 2| DAP-Search.req -> | | 3| <- DAP-Search.res| | 4| <- SearchRes | |__|___________________________________________________________| 7. Implementation Considerations The following subsections provide guidance on the implementation of clients and servers using the CLDAP protocol. 7.1. Server Implementations Given that the goal of this protocol is to minimise the elapsed time between making a directory request and receiving the response, a server which uses DAP to access the directory should use techniques that assist in this. - A server should not be too keen to unbind from the Directory during idle periods or should remain bound permanently. - Cacheing of results is highly desirable but this must be tempered by the need to provide up-to-date results given the lack of a cache invalidation protocol in DAP (either implicit via timers or expli- cit) and the lack of a dontUseCopy service control in the protocol. Expires 20 Apr 93 [Page 6] CLDAP October 1993 Of course these issues are irrelevant if the CLDAP protocol is directly supported by a DSA. 7.2. Client Implementations For simple lookup applications, use of a retry algorithm with multiple servers similar to that commonly used in DNS stub resolver implementa- tions is recommended. The location of a CLDAP server or servers may be better specified using IP addresses (simple or broadcast) rather than names that must first be looked up in another directory such as DNS. 8. Security Considerations This protocol provides no facilities for authentication. It is expected that servers will bind to the Directory either anonymously or using sim- ple authentication without a password. 9. Bibliography [1] The Directory: Overview of Concepts, Models and Service. CCITT Recommendation X.500, 1988 [2] Information Processing Systems -- Open Systems Interconnection -- The Directory: Overview of Concepts, Models and Service. ISO/IEC JTC 1/SC21; International Standard 9594-1, 1988 [3] The Directory: Models. CCITT Recommendation X.501 ISO/IEC JTC 1/SC21; International Standard 9594-2, 1988 [4] The Directory: Abstract Service Definition. CCITT Recommendation X.511, ISO/IEC JTC 1/SC21; International Standard 9594-3, 1988 [5] X.500 Lightweight Directory Access Protocol. W. Yeong, T. Howes, S. Kille; RFC 1487, July 1993. [6] Domain names - implementation and specification. P. Mockapetris; RFC 1035, November 1987. [7] Domain names - concepts and facilities. P. Mockapetris; RFC 1034, November 1987. 10. Author's Addresses Alan Young Union Bank of Switzerland VA213- EFTS-YON Postfach CH-8021 Zurich Expires 20 Apr 93 [Page 7] CLDAP October 1993 +41 1 23 67866 ALAN.YOUNG@ZH014.UBS.UBS.CH G=ALAN; S=YOUNG; OU=ZH014; O=UBS; P=UBS; A=ARCOM; C=CH Expires 20 Apr 93 [Page 8]