rfc2255.txt

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RFC 2255                    LDAP URL Format                December 1997


   First, the client obtains a connection to the LDAP server referenced
   in the URL, or an LDAP server of the client's choice if no LDAP
   server is explicitly referenced.  This connection MAY be opened
   specifically for the purpose of resolving the URL or the client MAY
   reuse an already open connection. The connection MAY provide
   confidentiality, integrity, or other services, e.g., using TLS. Use
   of security services is at the client's discretion if not specified
   in the URL.

   Next, the client authenticates itself to the LDAP server.  This step
   is optional, unless the URL contains a critical bindname extension
   with a non-NULL value. If a bindname extension is given, the client
   proceeds according to the section above.

   If a bindname extension is not specified, the client MAY bind to the
   directory using a appropriate dn and authentication method of its own
   choosing (including NULL authentication).

   Next, the client performs the LDAP search operation specified in the
   URL. Additional fields in the LDAP protocol search request, such as
   sizelimit, timelimit, deref, and anything else not specified or
   defaulted in the URL specification, MAY be set at the client's
   discretion.

   Once the search has completed, the client MAY close the connection to
   the LDAP server, or the client MAY keep the connection open for
   future use.

6. Examples

   The following are some example LDAP URLs using the format defined
   above.  The first example is an LDAP URL referring to the University
   of Michigan entry, available from an LDAP server of the client's
   choosing:

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

   The next example is 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

   Both of these URLs correspond to a base object search of the
   "o=University of Michigan, c=US" entry using a filter of
   "(objectclass=*)", requesting all attributes.

   The next example is an LDAP URL referring to only the postalAddress
   attribute of the University of Michigan entry:



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     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.

   The next example is an LDAP URL referring to the set of entries found
   by querying the given LDAP server on port 6666 and doing a subtree
   search of the University of Michigan for any entry with a common name
   of "Babs Jensen", retrieving all attributes:

     ldap://host.com:6666/o=University%20of%20Michigan,
            c=US??sub?(cn=Babs%20Jensen)

   The next example is 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, and the default filter of "(objectclass=*)" is used.

   The next example is an LDAP URL to retrieve the mail attribute for
   the LDAP entry named "o=Question?,c=US" is given below, illustrating
   the use of the escaping mechanism on the reserved character '?'.

     ldap://ldap.question.com/o=Question%3f,c=US?mail

   The next example illustrates the interaction between LDAP and URL
   quoting mechanisms.

     ldap://ldap.netscape.com/o=Babsco,c=US??(int=%5c00%5c00%5c00%5c04)

   The filter in this example uses the LDAP escaping mechanism of \ to
   encode three zero or null bytes in the value. In LDAP, the filter
   would be written as (int=\00\00\00\04). Because the \ character must
   be escaped in a URL, the \'s are escaped as %5c in the URL encoding.

   The final example shows the use of the bindname extension to specify
   the dn a client should use for authentication when resolving the URL.

     ldap:///??sub??bindname=cn=Manager%2co=Foo
     ldap:///??sub??!bindname=cn=Manager%2co=Foo

   The two URLs are the same, except that the second one marks the
   bindname extension as critical. Notice the use of the % encoding
   method to encode the comma in the distinguished name value in the



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RFC 2255                    LDAP URL Format                December 1997


   bindname extension.

7. Security Considerations

   General URL security considerations discussed in [5] are relevant for
   LDAP URLs.

   The use of security mechanisms when processing LDAP URLs requires
   particular care, since clients may encounter many different servers
   via URLs, and since URLs are likely to be processed automatically,
   without user intervention. A client SHOULD have a user-configurable
   policy about which servers to connect to using which security
   mechanisms, and SHOULD NOT make connections that are inconsistent
   with this policy.

   Sending authentication information, no matter the mechanism, may
   violate a user's privacy requirements.  In the absence of specific
   policy permitting authentication information to be sent to a server,
   a client should use an anonymous connection.  (Note that clients
   conforming to previous LDAP URL specifications, where all connections
   are anonymous and unprotected, are consistent with this
   specification; they simply have the default security policy.)

   Some authentication methods, in particular reusable passwords sent to
   the server, may reveal easily-abused information to the remote server
   or to eavesdroppers in transit, and should not be used in URL
   processing unless explicitly permitted by policy.  Confirmation by
   the human user of the use of authentication information is
   appropriate in many circumstances.  Use of strong authentication
   methods that do not reveal sensitive information is much preferred.

   The LDAP URL format allows the specification of an arbitrary LDAP
   search operation to be performed when evaluating the LDAP URL.
   Following an LDAP URL may cause unexpected results, for example, the
   retrieval of large amounts of data, the initiation of a long-lived
   search, etc.  The security implications of resolving an LDAP URL are
   the same as those of resolving an LDAP search query.

8. Acknowledgements

   The LDAP URL format was originally defined at the University of
   Michigan. This material is based upon work supported by the National
   Science Foundation under Grant No. NCR-9416667. The support of both
   the University of Michigan and the National Science Foundation is
   gratefully acknowledged.






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RFC 2255                    LDAP URL Format                December 1997


   Several people have made valuable comments on this document.  In
   particular RL "Bob" Morgan and Mark Wahl deserve special thanks for
   their contributions.

9. References

   [1] Wahl, M., Kille, S., and T. Howes, "Lightweight Directory Access
   Protocol (v3): UTF-8 String Representation of Distinguished Names",
   RFC 2253, December 1997.

   [2] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory Access
   Protocol (v3)", RFC 2251, December 1997.

   [3] Wahl, M., Coulbeck, A., Howes, T. and S. Kille, "Lightweight
   Directory Access Protocol (v3): Attribute Syntax Definitions", RFC
   2252, December 1997.

   [4] Howes, T., "A String Representation of LDAP Search Filters", RFC
   2254, December 1997.

   [5] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
   Locators (URL)," RFC 1738, December 1994.

   [6] Bradner, S., "Key Words for use in RFCs to Indicate Requirement
   Levels," RFC 2119, March 1997.

Authors' Addresses

   Tim Howes
   Netscape Communications Corp.
   501 E. Middlefield Rd.
   Mountain View, CA 94043
   USA

   Phone: [phone]
   EMail: [e-mail]


   Mark Smith
   Netscape Communications Corp.
   501 E. Middlefield Rd.
   Mountain View, CA 94043
   USA

   Phone: [phone]
   EMail: [e-mail]





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RFC 2255                    LDAP URL Format                December 1997


Full Copyright Statement

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