RFC1959 - An LDAP URL Format

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　　Network Working Group T. Howes
Request for Comments: 1959 M. Smith
Category: Standards Track University of Michigan
June 1996

An LDAP URL Format

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

1. Abstract

LDAP is the Lightweight Directory Access Protocol, defined in [1] and
[2]. This document describes a format for an LDAP Uniform Resource
Locator which will allow Internet clients to have direct access to
the LDAP protocol. While LDAP currently is used only as a front end
to the X.500 directory, the URL format described here is general
enough to handle the case of stand-alone LDAP servers (i.e., LDAP
servers not back-ended by X.500).

2. URL Definition

An LDAP URL begins with the protocol prefix "ldap" and is defined by
the following grammar.

<ldapurl> ::= "ldap://" [ <hostport> ] "/" <dn> [ "?" <attributes>
[ "?" <scope> "?" <filter> ] ]

<hostport> ::= <hostname> [ ":" <portnumber> ]

<dn> ::= a string as defined in RFC1485

<attributes> ::= NULL | <attributelist>

<attributelist> ::= <attributetype>
| <attributetype> [ "," <attributelist> ]

<attributetype> ::= a string as defined in RFC1777

<scope> ::= "base" | "one" | "sub"

<filter> ::= a string as defined in RFC1558

The ldap prefix indicates an entry or entries residing in the LDAP
server running on the given <hostname> at the given <portnumber>.
The default port is TCP port 389. The <dn> is an LDAP Distinguished
Name using the string format described in [1], with any URL-illegal
characters (e.g., spaces) escaped using the % method described in RFC
1738.

The <attributes> construct is used to indicate which attributes
should be returned from the entry or entries. Individual
<attributetype> names are as defined for AttributeType in RFC1777.
If the <attributes> part is omitted, all attributes of the entry or
entries should be returned.

The <scope> construct is used to specify the scope of the search to
perform in the given LDAP server. The allowable scopes are "base"
for a base object search, "one" for a one-level search, or "sub" for
a subtree search. If <scope> is omitted, a scope of "base" is
assumed.

The <filter> is used to specify the search filter to apply to entries
within the specified scope during the search. It has the format
specified in [4], with any URL-illegal characters escaped using the %
method described in RFC1738. If <filter> is omitted, a filter of
"(objectClass=*)" is assumed.

Note that if the entry resides in the X.500 namespace, it should be
reachable from any LDAP server that is providing front-end access to
the X.500 directory. If the <hostport> part of the URL is missing,
the URL can be resolved by contacting any X.500-back-ended LDAP
server.

3. Examples

The following are some example LDAP URLs using the format defined
above. An LDAP URL referring to the University of Michigan entry,
available from any X.500-capable LDAP server:

ldap:///o=University%20of%20Michigan,c=US

An LDAP URL referring to the University of Michigan entry in a
particular ldap server:

ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US

This URL corresponds to a base object search of the "o=University of
Michigan, c=US" entry using a filter of (objectclass=*), requesting
all attributes.

An LDAP URL referring to only the postalAddress attribute of the
University of Michigan entry:

ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US?postalAddress

The corresponding LDAP search operation is the same as in the
previous example, except that only the postalAddress attribute is
requested.

An LDAP URL referring to the set of entries found by querying any
X.500-capable LDAP server and doing a subtree search of the
University of Michigan for any entry with a common name of "Babs
Jensen", retrieving all attributes:

ldap:///o=University%20of%20Michigan,c=US??sub?(cn=Babs%20Jensen)

An LDAP URL referring to all children of the c=GB entry:

ldap://ldap.itd.umich.edu/c=GB?objectClass?one

The objectClass attribute is requested to be returned along with the
entries.

4. Security Considerations

The LDAP URL format does not provide a way to specify credentials to
use when resolving the URL. Therefore, it is expected that such
requests will be unauthenticated. The security implications of
resolving an LDAP URL are the same as those of resolving any LDAP
query. See the RFC1777 for more details.

5. Prototype Implementation Availability

There is a prototype implementation of the specification defined in
this document available. It is an extension to the libwww client
library, provided in both source and binary forms. Also included are
binary versions of the Mosaic WWW client for various platforms. See
the following URL for more details:

ftp://terminator.rs.itd.umich.edu/ldap/url/

6. Bibliography

[1] Kille, S., "A String Representation of Distinguished Names",
RFC1779, March 1995.

[2] Yeong, W., Howes, T., and S. Kille, "Lightweight
Directory Access Protocol", RFC1777, March 1995.

[3] Howes, R., Kille, S., Yeong, W., and C. Robbins, "The String
Representation of Standard Attribute Syntaxes", RFC1778,
March 1995.

[4] Howes, T., "A String Representation of LDAP Search Filters",
RFC1558, December 1993.

[5] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC1738, December 1994.

7. Acknowledgements

This material is based upon work supported by the National Science
Foundation under Grant No. NCR-9416667.

8. Authors' Addresses

Tim Howes
University of Michigan
ITD Research Systems
535 W William St.
Ann Arbor, MI 48103-4943
USA

Phone: +1 313 747-4454
EMail: tim@umich.edu

Mark Smith
University of Michigan
ITD Research Systems
535 W William St.
Ann Arbor, MI 48103-4943
USA

Phone: +1 313 764-2277
EMail: mcs@umich.edu

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