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396 lines
12 KiB
Plaintext
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Network Working Group C. Weider
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Request for Comments: 2696 A. Herron
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Category: Informational A. Anantha
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Microsoft
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T. Howes
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Netscape
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September 1999
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LDAP Control Extension for Simple Paged Results Manipulation
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Status of this Memo
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This memo provides information for the Internet community. It does
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not specify an Internet standard of any kind. Distribution of this
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memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (1999). All Rights Reserved.
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1. Abstract
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This document describes an LDAPv3 control extension for simple paging
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of search results. This control extension allows a client to control
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the rate at which an LDAP server returns the results of an LDAP
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search operation. This control may be useful when the LDAP client has
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limited resources and may not be able to process the entire result
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set from a given LDAP query, or when the LDAP client is connected
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over a low-bandwidth connection. Other operations on the result set
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are not defined in this extension. This extension is not designed to
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provide more sophisticated result set management.
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The key words "MUST", "SHOULD", and "MAY" used in this document are
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to be interpreted as described in [bradner97].
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2. The Control
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This control is included in the searchRequest and searchResultDone
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messages as part of the controls field of the LDAPMessage, as defined
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in Section 4.1.12 of [LDAPv3]. The structure of this control is as
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follows:
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Weider, et al. Informational [Page 1]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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pagedResultsControl ::= SEQUENCE {
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controlType 1.2.840.113556.1.4.319,
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criticality BOOLEAN DEFAULT FALSE,
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controlValue searchControlValue
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}
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The searchControlValue is an OCTET STRING wrapping the BER-encoded
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version of the following SEQUENCE:
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realSearchControlValue ::= SEQUENCE {
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size INTEGER (0..maxInt),
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-- requested page size from client
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-- result set size estimate from server
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cookie OCTET STRING
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}
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3. Client-Server Interaction
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An LDAP client application that needs to control the rate at which
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results are returned MAY specify on the searchRequest a
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pagedResultsControl with size set to the desired page size and cookie
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set to the zero-length string. The page size specified MAY be greater
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than zero and less than the sizeLimit value specified in the
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searchRequest.
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If the page size is greater than or equal to the sizeLimit value, the
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server should ignore the control as the request can be satisfied in a
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single page. If the server does not support this control, the server
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MUST return an error of unsupportedCriticalExtension if the client
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requested it as critical, otherwise the server SHOULD ignore the
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control. The remainder of this section assumes the server does not
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ignore the client's pagedResultsControl.
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Each time the server returns a set of results to the client when
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processing a search request containing the pagedResultsControl, the
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server includes the pagedResultsControl control in the
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searchResultDone message. In the control returned to the client, the
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size MAY be set to the server's estimate of the total number of
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entries in the entire result set. Servers that cannot provide such an
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estimate MAY set this size to zero (0). The cookie MUST be set to an
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empty value if there are no more entries to return (i.e., the page of
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search results returned was the last), or, if there are more entries
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to return, to an octet string of the server's choosing,used to resume
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the search.
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The client MUST consider the cookie to be an opaque structure and
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make no assumptions about its internal organization or value. When
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the client wants to retrieve more entries for the result set, it MUST
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Weider, et al. Informational [Page 2]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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send to the server a searchRequest with all values identical to the
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initial request with the exception of the messageID, the cookie, and
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optionally a modified pageSize. The cookie MUST be the octet string
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on the last searchResultDone response returned by the server.
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Returning cookies from previous searchResultDone responses besides
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the last one is undefined, as the server implementation may restrict
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cookies from being reused.
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The server will then return the next set of results from the whole
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result set. This interaction will continue until the client has
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retrieved all the results, in which case the cookie in the
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searchResultDone field will be empty, or until the client abandons
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the search sequence as described below. Once the paged search
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sequence has been completed, the cookie is no longer valid and MUST
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NOT be used.
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A sequence of paged search requests is abandoned by the client
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sending a search request containing a pagedResultsControl with the
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size set to zero (0) and the cookie set to the last cookie returned
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by the server. A client MAY use the LDAP Abandon operation to
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abandon one paged search request in progress, but this is discouraged
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as it MAY invalidate the client's cookie.
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If, for any reason, the server cannot resume a paged search operation
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for a client, then it SHOULD return the appropriate error in a
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searchResultDone entry. If this occurs, both client and server should
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assume the paged result set is closed and no longer resumable.
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A client may have any number of outstanding search requests pending,
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any of which may have used the pagedResultsControl. A server
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implementation which requires a limit on the number of outstanding
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paged search requests from a given client MAY either return
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unwillingToPerform when the client attempts to create a new paged
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search request, or age out an older result set. If the server
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implementation ages out an older paged search request, it SHOULD
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return "unwilling to perform" if the client attempts to resume the
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paged search that was aged out.
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A client may safely assume that all entries that satisfy a given
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search query are returned once and only once during the set of paged
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search requests/responses necessary to enumerate the entire result
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set, unless the result set for that query has changed since the
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searchRequest starting the request/response sequence was processed.
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In that case, the client may receive a given entry multiple times
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and/or may not receive all entries matching the given search
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criteria.
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Weider, et al. Informational [Page 3]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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4. Example
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The following example illustrates the client-server interaction
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between a client doing a search requesting a page size limit of 3.
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The entire result set returned by the server contains 5 entries.
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Lines beginning with "C:" indicate requests sent from client to
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server. Lines beginning with "S:" indicate responses sent from server
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to client. Lines beginning with "--" are comments to help explain the
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example.
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-- Client sends a search request asking for paged results
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-- with a page size of 3.
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C: SearchRequest + pagedResultsControl(3,"")
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-- Server responds with three entries plus an indication
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-- of 5 total entries in the search result and an opaque
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-- cooking to be used by the client when retrieving subsequent
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-- pages.
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S: SearchResultEntry
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S: SearchResultEntry
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S: SearchResultEntry
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S: SearchResultDone + pagedResultsControl(5, "opaque")
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-- Client sends an identical search request (except for
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-- message id), returning the opaque cooking, asking for
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-- the next page.
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C: SearchRequest + PagedResultsControl(3, "opaque")
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-- Server responds with two entries plus an indication
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-- that there are no more entries (null cookie).
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S: SearchResultEntry
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S: SearchResultEntry
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S: SearchResultDone + pagedResultsControl(5,"")
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5. Relationship to X.500
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For LDAP servers providing a front end to X.500 (93) directories, the
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paged results control defined in this document may be mapped directly
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onto the X.500 (93) PagedResultsRequest defined in X.511 [x500]. The
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size parameter may be mapped onto pageSize. The cookie parameter may
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be mapped onto queryReference. The sortKeys and reverse fields in
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the X.500 PagedResultsRequest are excluded.
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Weider, et al. Informational [Page 4]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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6. Security Considerations
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Server implementors should consider the resources used when clients
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send searches with the simple paged control, to ensure that a
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client's misuse of this control does not lock out other legitimate
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operations.
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Servers implementations may enforce an overriding sizelimit, to
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prevent the retrieval of large portions of a publically-accessible
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directory.
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Clients can, using this control, determine how many entries match a
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particular filter, before the entries are returned to the client.
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This may require special processing in servers which perform access
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control checks on entries to determine whether the existence of the
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entry can be disclosed to the client.
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7. References
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[LDAPv3] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory
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Access Protocol (v3)", RFC 2251, December 1997.
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[Bradner97] Bradner, S., "Key Words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
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Weider, et al. Informational [Page 5]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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8. Authors' Addresses
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Chris Weider
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Microsoft Corp.
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1 Microsoft Way
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Redmond, WA 98052
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USA
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Phone: +1 425 882-8080
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EMail: cweider@microsoft.com
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Andy Herron
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Microsoft Corp.
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1 Microsoft Way
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Redmond, WA 98052
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USA
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Phone: +1 425 882-8080
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EMail: andyhe@microsoft.com
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Anoop Anantha
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Microsoft Corp.
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1 Microsoft Way
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Redmond, WA 98052
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USA
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Phone: +1 425 882-8080
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EMail: anoopa@microsoft.com
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Tim Howes
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Netscape Communications Corp.
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501 E. Middlefield Road
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Mountain View, CA 94043
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USA
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Phone: +1 415 937-2600
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EMail: howes@netscape.com
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Weider, et al. Informational [Page 6]
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RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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9. Full Copyright Statement
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Copyright (C) The Internet Society (1999). All Rights Reserved.
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This document and translations of it may be copied and furnished to
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others, and derivative works that comment on or otherwise explain it
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or assist in its implementation may be prepared, copied, published
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and distributed, in whole or in part, without restriction of any
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kind, provided that the above copyright notice and this paragraph are
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included on all such copies and derivative works. However, this
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document itself may not be modified in any way, such as by removing
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the copyright notice or references to the Internet Society or other
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Internet organizations, except as needed for the purpose of
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developing Internet standards in which case the procedures for
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copyrights defined in the Internet Standards process must be
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followed, or as required to translate it into languages other than
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English.
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The limited permissions granted above are perpetual and will not be
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revoked by the Internet Society or its successors or assigns.
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This document and the information contained herein is provided on an
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"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Acknowledgement
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Funding for the RFC Editor function is currently provided by the
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Internet Society.
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Weider, et al. Informational [Page 7]
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