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RFC 7653

Proposed STD
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DHCPv6 Active Leasequery

Updates:    5460


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Internet Engineering Task Force (IETF)                    D. Raghuvanshi
Request for Comments: 7653                                    K. Kinnear
Updates: 5460                                                 D. Kukrety
Category: Standards Track                            Cisco Systems, Inc.
ISSN: 2070-1721                                             October 2015


                        DHCPv6 Active Leasequery

Abstract

   The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) has been
   extended with a Leasequery capability that allows a requestor to
   request information about DHCPv6 bindings.  That mechanism is limited
   to queries for DHCPv6 binding data updates prior to the time the
   DHCPv6 server receives the Leasequery request.  Continuous update of
   an external requestor with Leasequery data is sometimes desired.
   This document expands on the DHCPv6 Leasequery protocol and allows
   for active transfer of real-time DHCPv6 binding information data via
   TCP.  This document also updates DHCPv6 Bulk Leasequery (RFC 5460) by
   adding new options.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7653.

Page 2 
Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................4
   3. Protocol Overview ...............................................6
   4. Interaction between Active Leasequery and Bulk Leasequery .......8
   5. Extension to DHCPv6 Bulk Leasequery .............................8
   6. Message and Option Definitions ..................................9
      6.1. Message Framing for TCP ....................................9
      6.2. Messages ...................................................9
           6.2.1. ACTIVELEASEQUERY ....................................9
           6.2.2. STARTTLS ...........................................10
           6.2.3. Response Messages ..................................10
      6.3. Options ...................................................10
           6.3.1. OPTION_LQ_BASE_TIME ................................10
           6.3.2. OPTION_LQ_START_TIME ...............................11
           6.3.3. OPTION_LQ_END_TIME .................................12
      6.4. Connection and Transmission Parameters ....................12
   7. Information Communicated by Active Leasequery ..................13
   8. Requestor Behavior .............................................14
      8.1. General Processing ........................................14
      8.2. Initiating a Connection ...................................14
      8.3. Forming an Active Leasequery ..............................15
      8.4. Processing Active Replies .................................16
           8.4.1. Processing Replies from a Request Containing an
                  OPTION_LQ_START_TIME ...............................18
      8.5. Processing Time Values in Leasequery Messages .............20
      8.6. Examples ..................................................21
           8.6.1. Query Failure ......................................21
           8.6.2. Data Missing on Server .............................21
           8.6.3. Successful Query ...................................21
      8.7. Closing Connections .......................................22
   9. Server Behavior ................................................22
      9.1. Accepting Connections .....................................22
      9.2. Rejecting Connections .....................................24
      9.3. Replying to an Active Leasequery ..........................24
      9.4. Multiple or Parallel Queries ..............................26
      9.5. Closing Connections .......................................26
   10. Security Considerations .......................................27
   11. IANA Considerations ...........................................28
   12. References ....................................................28
      12.1. Normative References .....................................28
      12.2. Informative References ...................................29
   Acknowledgments ...................................................30
   Authors' Addresses ................................................30

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1.  Introduction

   The DHCPv6 protocol [RFC3315] specifies a mechanism for the
   assignment of IPv6 address and configuration information to IPv6
   nodes.  IPv6 Prefix Delegation for DHCPv6 [RFC3633] specifies a
   mechanism for DHCPv6 delegation of IPv6 prefixes and related data.
   DHCPv6 servers maintain authoritative information including binding
   information for delegated IPv6 prefixes.

   Requirements exist for external entities to keep up to date on the
   correspondence between DHCPv6 clients and their bindings.  These
   entities need to keep up with the current binding activity of the
   DHCPv6 server.  Keeping up with this binding activity is termed
   "active" leasequery.

   The DHCPv6 Bulk Leasequery [RFC5460] capability can be used to
   recover useful information from a DHCPv6 server when some external
   entity starts up.  This entity could be one that is directly involved
   in the DHCPv6 client-server transactions (e.g., a relay agent), or it
   could be an external process that needs information present in the
   DHCPv6 server's lease state database.

   The Active Leasequery capability documented here is designed to allow
   an entity not directly involved in DHCPv6 client-server transactions
   to nevertheless keep current with the state of the DHCPv6 lease state
   information in real time.

   This document updates DHCPv6 Bulk Leasequery [RFC5460] by adding new
   options, as described in Section 6.2.1.  For DHCPv6 servers
   supporting Bulk Leasequery and not Active Leasequery, Section 9.2
   specifies the mechanism to reject incoming Active Leasequery
   requests.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   DHCPv6 terminology is defined in [RFC3315].  Terminology specific to
   DHCPv6 Active Leasequery can be found below:

   o  absolute time

      A 32-bit unsigned quantity containing the number of seconds since
      midnight (UTC), January 1, 2000, modulo 2^32.

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   o  Active Leasequery

      Keeping up to date in real time (or near real time) with DHCPv6
      binding activity.

   o  Bulk Leasequery

      Requesting and receiving information about all or some of the
      existing DHCPv6 binding information in an efficient manner, as
      defined by [RFC5460].

   o  blocked TCP connection

      A TCP connection is considered blocked if the underlying TCP
      transport will not accept new messages to be sent without blocking
      the thread that is attempting to send the message.

   o  binding change/update

      Any change in the DHCPv6 binding state.  This also includes
      expiration or deletion of the binding.

   o  catch-up information

      If a DHCPv6 Active Leasequery requestor sends an
      OPTION_LQ_START_TIME option in an ACTIVELEASEQUERY message, the
      DHCPv6 server will attempt to send the requestor the information
      that changed since the time specified in the OPTION_LQ_START_TIME
      option.  The binding information sent to satisfy this request is
      the catch-up information.

   o  catch-up phase

      The period while catch-up information is being sent is the catch-
      up phase.

   o  clock skew

      The difference between the absolute time on a DHCPv6 server and
      the absolute time on the system where a requestor of an Active or
      Bulk Leasequery is executing is termed the "clock skew" for that
      Active or Bulk Leasequery connection.  It is not absolutely
      constant but is likely to vary only slowly.  While it is easy to
      think that this can be calculated precisely after one message is
      received by a requestor from a DHCPv6 server, a more accurate
      value is derived from continuously examining the instantaneous
      value developed from each message received from a DHCPv6 server

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      and using it to make small adjustments to the existing value held
      in the requestor.

   o  DHCPv6 binding state

      Data stored on the DHCPv6 server related to binding.

   o  requestor

      The node that sends LEASEQUERY messages to one or more servers to
      retrieve information on the bindings for a client.

   o  transaction-id

      An opaque value used to match responses with queries initiated by
      an Active Leasequery requestor.

3.  Protocol Overview

   The Active Leasequery mechanism is modeled on the existing DHCPv6
   Bulk Leasequery [RFC5460]; most differences arise from the long-term
   nature of the TCP [RFC7414] connection required for Active
   Leasequery.  A DHCPv6 server that supports Active Leasequery MUST
   support Bulk Leasequery [RFC5460] as well.

   An Active Leasequery requestor opens a TCP connection to a DHCPv6
   server, using the DHCPv6 port 547.  Note that this implies that the
   Leasequery requestor has server IP address(es) available via
   configuration or some other means, and that it has unicast IP
   reachability to the DHCPv6 server.  No relaying for Active Leasequery
   is specified.

   After establishing a connection, the requestor sends an
   ACTIVELEASEQUERY message over the connection.  In response, the
   server sends updates to the requestor using LEASEQUERY-REPLY and
   LEASEQUERY-DATA messages.  This response procedure is similar to the
   procedure specified in [RFC5460], except that in the case of Active
   Leasequery, the server sends updates whenever some activity occurs to
   change the binding state -- thus the need for a long-lived
   connection.  Additionally, the Active Leasequery server SHOULD
   provide a mechanism to control which data is allowed to be included
   in the OPTION_CLIENT_DATA messages sent to the requestor.  See
   Section 9.3.

   Active Leasequery has features that allow this external entity to
   lose its connection and then reconnect and receive the latest
   information concerning any IPv6 bindings changed while it was not
   connected.

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   These features are designed to allow the Active Leasequery requestor
   to efficiently become current with respect to the lease state
   database after it has been restarted or the machine on which it is
   running has been reinitialized.  It is easy to define a protocol that
   works when the requestor is always connected to the DHCPv6 server.
   Since that isn't sufficiently robust, much of the mechanism in this
   document is designed to deal efficiently with situations that occur
   when the Active Leasequery requestor becomes disconnected from the
   DHCPv6 server from which it is receiving updates and then reconnects
   to that server.

   Central to this approach, if the Active Leasequery requestor loses
   service, it is allowed to specify the time of its most recent update
   in a subsequent Active Leasequery request, and the DHCPv6 server will
   determine whether or not data was missed while the Active Leasequery
   requestor was not connected.

   The DHCPv6 server processing the Active Leasequery request MAY limit
   the amount of data saved, and methods exist for the DHCPv6 server to
   inform the Active Leasequery requestor that data was missed (i.e.,
   not all data could be saved).  In this situation, the Active
   Leasequery requestor should issue a Bulk Leasequery [RFC5460] to
   recover information not available through an Active Leasequery.

   DHCPv6 servers are not required to keep any data corresponding to
   data missed on an Active Leasequery connection but will typically
   choose to keep data corresponding to some recent activity available
   for subsequent queries by a DHCPv6 Active Leasequery requestor whose
   connection was temporarily interrupted.  In other words, DHCPv6
   servers supporting catch-up are required to have some mechanism to
   keep/save historic information of bindings.

   An Active Leasequery requestor would typically use Bulk Leasequery to
   initialize its database with all current data when that database
   contains no binding information.  In addition, it would use Bulk
   Leasequery to recover missed information in the event that its
   connection with the DHCPv6 server was lost for a longer time than the
   DHCPv6 server would keep track of the specific changes to the IPv6
   binding information.

   The messages sent by the server in response to an Active Leasequery
   request should be identical to the messages sent by the server to a
   Bulk Leasequery request regarding the way the data is encoded into
   the Active Leasequery responses.  In addition, the actions taken by
   the Active Leasequery requestor to interpret the responses to an
   Active Leasequery request should be identical to the way that the
   requestor interprets the responses to a Bulk Leasequery request.
   Thus, the handling of OPTION_CLIENT_DATA and additional options

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   discussed in the Bulk Leasequery specification [RFC5460] are to be
   followed when implementing Active Leasequery, with the exception that
   a server responding to an Active Leasequery request SHOULD be able to
   be configured to prevent specific data items from being included in
   the OPTION_CLIENT_DATA option even if they were requested by
   inclusion in the OPTION_ORO option.

4.  Interaction between Active Leasequery and Bulk Leasequery

   Active Leasequery is an extension of the Bulk Leasequery protocol
   [RFC5460].  The format of messages returned to an Active Leasequery
   requestor is identical to that defined for the Bulk Leasequery
   protocol [RFC5460].

   Applications that employ Active Leasequery to keep a database up to
   date with respect to the DHCPv6 server's lease state database should
   use an initial Bulk Leasequery to bring their database into
   equivalence with that of the DHCPv6 server and then use Active
   Leasequery to keep that database current with respect to the DHCPv6
   server's lease state database.

   There are several differences between the Active and Bulk Leasequery
   protocols.  Active Leasequery defines a new message
   (ACTIVELEASEQUERY) to send Active Leasequery requests to the DHCPv6
   server.  An Active Leasequery connection sends all available updates
   to the requestor, based on the OPTION_LQ_QUERY option (see
   Section 6.2.1).

   An Active Leasequery connection does not ever "complete", though the
   DHCPv6 server can close the connection for a variety of reasons
   associated with some sort of exception condition.

5.  Extension to DHCPv6 Bulk Leasequery

   This document extends the capabilities of the DHCPv6 Bulk Leasequery
   protocol [RFC5460] by defining new options (OPTION_LQ_BASE_TIME,
   OPTION_LQ_START_TIME, and OPTION_LQ_END_TIME).  The DHCPv6 server
   sends the OPTION_LQ_BASE_TIME option in a Bulk Leasequery response if
   the requestor asked for the same in the Bulk Leasequery request.
   OPTION_LQ_START_TIME and OPTION_LQ_END_TIME can be used in a Bulk
   Leasequery request made to the DHCPv6 server.  More details about
   these options are specified in Section 6.3.

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6.  Message and Option Definitions

6.1.  Message Framing for TCP

   The use of TCP for the Active Leasequery protocol permits one or more
   DHCPv6 messages to be sent in response to a single Active Leasequery
   request.  The receiver needs to be able to determine how large each
   message is.  The same message framing technique used for DHCPv6 Bulk
   Leasequery [RFC5460] is used for Active Leasequery as well.

   The intent in using the same format is that code that currently knows
   how to deal with a message returned from DHCPv6 Bulk Leasequery
   [RFC5460] will be able to deal with the message held inside of the
   TCP framing.

   When using Transport Layer Security (TLS), once TLS negotiation
   completes, the connection will be encrypted and is now protected from
   eavesdropping, and normal Active Leasequery messages are sent and
   received using the TLS application data protocol services (see
   Section 10 of [RFC5246]).

6.2.  Messages

6.2.1.  ACTIVELEASEQUERY

   The new message type (ACTIVELEASEQUERY) is designed for keeping the
   requestor up to date in real time (or near real time) with DHCPv6
   bindings.  It asks the server to return DHCPv6 binding activity that
   occurs subsequent to the receipt of the Active Leasequery request.

   An ACTIVELEASEQUERY request MUST contain a transaction-id, and that
   transaction-id MUST be locally unique on the TCP connection on which
   it is sent to the DHCPv6 server.

   When sending an ACTIVELEASEQUERY request, the requestor MAY include
   the OPTION_LQ_START_TIME option in the ACTIVELEASEQUERY request.  In
   this case, the DHCPv6 server returns all the bindings changed on or
   after the OPTION_LQ_START_TIME.

   If the requestor is interested in receiving all binding updates from
   the DHCPv6 server, it MUST NOT include the OPTION_LQ_QUERY option in
   the ACTIVELEASEQUERY message.  But if the requestor is only
   interested in specific binding updates, it MAY include an
   OPTION_LQ_QUERY option along with a query-types defined in [RFC5007]
   and [RFC5460].

   Other DHCPv6 options used in the LEASEQUERY message (as specified in
   [RFC5460]) can also be used in the ACTIVELEASEQUERY message.

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6.2.2.  STARTTLS

   The new message type (STARTTLS) is designed for establishment of a
   TLS connection between a requestor and a DHCPv6 server.  The STARTTLS
   message SHOULD be sent without any options.  Any options received in
   a STARTTLS message SHOULD be ignored.

   More details about this message are specified in Section 8.2.

6.2.3.  Response Messages

   The LEASEQUERY-REPLY message is defined in [RFC5007].  The
   LEASEQUERY-DATA and LEASEQUERY-DONE messages are defined in
   [RFC5460].

   In an Active Leasequery exchange, a single LEASEQUERY-REPLY message
   is used to indicate the success or failure of a query and to carry
   data that do not change in the context of a single query and answer,
   such as the Server-ID and Client-ID options.  If a query is
   successful, the DHCPv6 server MUST respond to it with exactly one
   LEASEQUERY-REPLY message.  If the server is returning binding data,
   the LEASEQUERY-REPLY also contains the first client's binding data in
   an OPTION_CLIENT_DATA option.  Additional binding data is returned
   using a LEASEQUERY-DATA message as explained in DHCPv6 Bulk
   Leasequery [RFC5460].  In case of a query failure, a single
   LEASEQUERY-REPLY message is returned without any binding data.

6.3.  Options

   New options (OPTION_LQ_BASE_TIME, OPTION_LQ_START_TIME, and
   OPTION_LQ_END_TIME) are defined as an extension to DHCPv6 Bulk
   Leasequery [RFC5460].  The reply messages for Active Leasequery use
   these options along with the options defined in [RFC3315], [RFC5007],
   and [RFC5460].

6.3.1.  OPTION_LQ_BASE_TIME

   The OPTION_LQ_BASE_TIME option is the current time the message was
   created to be sent by the DHCPv6 server to the requestor of the
   Active or Bulk Leasequery if the requestor asked for the same in an
   Active or Bulk Leasequery request.  This MUST be an absolute time
   (i.e., seconds since midnight January 1, 2000 UTC).  All of the other
   time-based options in the reply message are relative to this time,
   including OPTION_CLT_TIME [RFC5007].  This time is in the context of
   the DHCPv6 server that placed this option in a message.

   This is an unsigned integer in network byte order.

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   The code for this option is 100.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      OPTION_LQ_BASE_TIME      |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           base-time                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        option-code       OPTION_LQ_BASE_TIME (100)
        option-len        4
        base-time         DHCPv6 Server Base Time

6.3.2.  OPTION_LQ_START_TIME

   The OPTION_LQ_START_TIME option specifies a query start time to the
   DHCPv6 server.  If specified, only bindings that have changed on or
   after the OPTION_LQ_START_TIME should be included in the response to
   the query.  This option MAY be used in Active or Bulk Leasequery
   requests made to a DHCPv6 server.

   The requestor MUST determine the OPTION_LQ_START_TIME using lease
   information it has received from the DHCPv6 server.  This MUST be an
   absolute time in the DHCPv6 server's context (see Section 8.5).

   Typically (though this is not a requirement), the
   OPTION_LQ_START_TIME option will contain the value most recently
   received in an OPTION_LQ_BASE_TIME option by the requestor, as this
   will indicate the last successful communication with the DHCPv6
   server.

   This is an unsigned integer in network byte order.

   The code for this option is 101.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      OPTION_LQ_START_TIME     |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       query-start-time                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        option-code       OPTION_LQ_START_TIME (101)
        option-len        4
        query-start-time  DHCPv6 Server Query Start Time

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6.3.3.  OPTION_LQ_END_TIME

   The OPTION_LQ_END_TIME option specifies a query end time to the
   DHCPv6 server.  If specified, only bindings that have changed on or
   before the OPTION_LQ_END_TIME should be included in the response to
   the query.  This option MAY be used in a Bulk Leasequery request, but
   it MUST NOT be used in an Active Leasequery request.

   The requestor MUST determine the OPTION_LQ_END_TIME based on lease
   information it has received from the DHCPv6 server.  This MUST be an
   absolute time in the context of the DHCPv6 server.

   In the absence of information to the contrary, the requestor SHOULD
   assume that the time context of the DHCPv6 server is identical to the
   time context of the requestor (see Section 8.5).

   This is an unsigned integer in network byte order.

   The code for this option is 102.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      OPTION_LQ_END_TIME       |          option-len           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        query-end-time                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        option-code       OPTION_LQ_END_TIME (102)
        option-len        4
        query-end-time    DHCPv6 Server Query End Time

6.4.  Connection and Transmission Parameters

   Active Leasequery uses the same port configuration as DHCPv6 Bulk
   Leasequery [RFC5460].  It also uses the other transmission parameters
   (BULK_LQ_DATA_TIMEOUT and BULK_LQ_MAX_CONNS) as defined in [RFC5460].

   This section presents a table of values used to control Active
   Leasequery behavior, including recommended defaults.  Implementations
   MAY make these values configurable.  However, configuring too-small
   timeout values may lead to harmful behavior both to this application
   and to other traffic in the network.  As a result, timeout values
   smaller than the default values SHOULD NOT be used.

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   +------------------------+----------+-------------------------------+
   | Parameter              | Default  | Description                   |
   +------------------------+----------+-------------------------------+
   | ACTIVE_LQ_RCV_TIMEOUT  | 120 secs | Active Leasequery receive     |
   |                        |          | timeout                       |
   | ACTIVE_LQ_SEND_TIMEOUT | 120 secs | Active Leasequery send        |
   |                        |          | timeout                       |
   | ACTIVE_LQ_IDLE_TIMEOUT | 60 secs  | Active Leasequery idle        |
   |                        |          | timeout                       |
   +------------------------+----------+-------------------------------+

7.  Information Communicated by Active Leasequery

   While the information communicated by a DHCPv6 Bulk Leasequery
   [RFC5460] is taken directly from the DHCPv6 server's lease state
   database, the information communicated by an Active Leasequery is
   real-time information.  As such, it is the information that is
   currently associated with a particular binding in the DHCPv6 server's
   lease state database.

   This is of significance, because if the Active Leasequery requestor
   runs slowly or the requestor disconnects from the DHCPv6 server and
   then reconnects with an OPTION_LQ_START_TIME option (signaling a
   catch-up operation), the information communicated to the Active
   Leasequery requestor is only the most current information from the
   DHCPv6 server's lease state database.

   The requestor of an Active Leasequery MUST NOT assume that every
   lease state change is communicated across an Active Leasequery
   connection.  Even if the Active Leasequery requestor remains
   connected, the DHCPv6 server is only required to transmit information
   about a binding that is current when the message is created and
   handed off to the TCP stack to send to the requestor.

   If the TCP connection blocks and the DHCPv6 server is waiting to send
   information down the connection, when the connection becomes
   available to be written, the DHCPv6 server MAY create the message to
   send at this time.  The current state of the binding will be sent,
   and any transition in state or other information that occurred while
   the TCP connection was blocked will be lost.

   Thus, the Active Leasequery protocol does not allow the requestor to
   build a complete history of every activity on every lease.  An
   effective history of the important state changes for a lease can be
   created if the parameters of the DHCPv6 server are tuned to take into
   account the requirements of an Active Leasequery requestor.  For
   instance, the period after the expiration or release of a binding
   could be configured long enough (say several minutes, well more than

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   the receive timeout), so that an Active Leasequery requestor would be
   less likely to miss any changes in the binding.

8.  Requestor Behavior

8.1.  General Processing

   A requestor attempts to establish a TCP connection to a DHCPv6 server
   in order to initiate an Active Leasequery exchange.  If the attempt
   fails, the requestor MAY retry.  Retries should not be more frequent
   than one every ACTIVE_LQ_IDLE_TIMEOUT.  See Section 6.4.

   If an Active Leasequery is terminated prematurely by a LEASEQUERY-
   DONE with a DHCPv6 status code (carried in an OPTION_STATUS_CODE
   option) of QueryTerminated or by the failure of the connection over
   which it was being submitted, the requestor MAY retry the request
   after the creation of a new connection.  Retries should not be more
   frequent than one every ACTIVE_LQ_IDLE_TIMEOUT.  See Section 6.4.

   Messages from the DHCPv6 server come as multiple responses to a
   single ACTIVELEASEQUERY message.  Thus, each ACTIVELEASEQUERY request
   MUST have a transaction-id unique on the connection on which it is
   sent, and all of the messages that come as a response to it contain
   the same transaction-id as the request.

8.2.  Initiating a Connection

   A requestor SHOULD be able to operate in either insecure or secure
   mode.  This MAY be a feature that is administratively controlled.

   When operating in insecure mode, the requestor SHOULD proceed to send
   an ACTIVELEASEQUERY message after the establishment of a TCP
   connection.

   When operating in secure mode, the requestor MUST attempt to
   negotiate a TLS [RFC5246] connection over the TCP connection.  If
   this negotiation fails, the requestor MUST close the TCP connection.
   The recommendations in [RFC7525] SHOULD be followed when negotiating
   this connection.

   A requestor requests the establishment of a TLS connection by sending
   the STARTTLS message to the DHCPv6 server as the first message over
   the TCP connection.  This message indicates to the DHCPv6 server that
   a TLS connection over this TCP connection is desired.  There are four
   possibilities after the requestor sends the STARTTLS message to the
   DHCPv6 server:

   1.  No response from the DHCPv6 server.

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   2.  The DHCPv6 server closes the TCP connection after it receives the
       STARTTLS message.

   3.  The DHCPv6 server responds with a REPLY [RFC3315] message with a
       DHCPv6 status code of TLSConnectionRefused.

   4.  The DHCPv6 server responds with a REPLY [RFC3315] message without
       a DHCPv6 status code, indicating success.

   In any of the first three possibilities, the DHCPv6 server can be
   assumed to not support TLS.  In this case, the requestor MUST close
   the TCP connection.

   In the final possibility, where the DHCPv6 server has responded with
   a REPLY message without a DHCPv6 status code in response to the
   requestor's STARTTLS message, the requestor SHOULD initiate the
   exchange of the messages involved in a TLS handshake [RFC5246].
   During the TLS handshake, the requestor MUST validate the DHCPv6
   server's digital certificate.

   If the handshake exchange yields a functioning TLS connection, then
   the requestor SHOULD transmit an ACTIVELEASEQUERY request over that
   TLS connection and use that TLS connection for all further
   interactions in which it engages with the DHCPv6 server over this TCP
   connection.

   If the handshake exchange does not yield a functioning TLS
   connection, then the requestor MUST close the TCP connection.

8.3.  Forming an Active Leasequery

   Active Leasequery is designed to create a long-lived connection
   between the requestor and the DHCPv6 server processing the active
   query.  The DHCPv6 server SHOULD send binding information back across
   this connection with minimal delay after it learns of the binding
   information.  It learns about bindings either because it makes the
   bindings itself or because it has received information about a
   binding from another server.

   An important capability of Active Leasequery is the ability of the
   requestor to specify that some recent data be sent immediately to the
   requestor in parallel with the transmission of the ongoing binding
   information in more or less real time.  This capability is used in
   order to allow an Active Leasequery requestor to recover missed
   information in the event that it temporarily loses connectivity with
   the DHCPv6 server processing a previous Active Leasequery.

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   This capability is enabled by the transmission of an
   OPTION_LQ_BASE_TIME option with each Leasequery reply sent as the
   result of a previous Active Leasequery.  The requestor SHOULD keep
   track of the highest base-time received from a particular DHCPv6
   server over an Active Leasequery connection, and in the event that
   the requestor finds it necessary (for whatever reason) to reestablish
   an Active Leasequery connection to that DHCPv6 server, the requestor
   SHOULD place this highest base-time value into an
   OPTION_LQ_START_TIME option in the new Active Leasequery request.

   Note that until all of the recent data (catch-up data) has been
   received, the requestor MUST NOT keep track of the base-time
   (OPTION_LQ_BASE_TIME) received in Leasequery reply messages to use
   later in a subsequent Active Leasequery request.

   If the requestor doesn't wish to request an update of information
   missed when it was not connected to the DHCPv6 server, then it SHOULD
   NOT include the OPTION_LQ_START_TIME option in the Active Leasequery
   request.

   If the TCP connection becomes blocked or stops being writable while
   the requestor is sending its query, the requestor SHOULD terminate
   the connection after BULK_LQ_DATA_TIMEOUT.  We make this
   recommendation to allow requestors to control the period of time they
   are willing to wait before abandoning a connection, independent of
   notifications from the TCP implementations they may be using.

8.4.  Processing Active Replies

   The requestor attempts to read a DHCPv6 LEASEQUERY-REPLY message from
   the TCP connection.  If the stream of replies becomes blocked, the
   requestor SHOULD terminate the connection after ACTIVE_LQ_RCV_TIMEOUT
   and MAY begin retry processing if configured to do so.

   The requestor examines the LEASEQUERY-REPLY message and determines
   how to proceed.  Message validation rules are specified in DHCPv6
   Leasequery [RFC5007] and DHCPv6 Bulk Leasequery [RFC5460].  If the
   reply contains a DHCPv6 status code (carried in an OPTION_STATUS_CODE
   option), the requestor should follow the recommendations in
   [RFC5007].

   Note that the connection resulting from accepting an Active
   Leasequery request may be long-lived and may not have data
   transferring continuously during its lifetime.  Therefore, the DHCPv6
   server SHOULD send a LEASEQUERY-DATA message without binding data
   (OPTION_CLIENT_DATA) every ACTIVE_LQ_IDLE_TIMEOUT seconds (default
   60) in order for the requestor to know that the connection remains
   alive.  This approach is followed only when connection is idle (i.e.,

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   server has no binding data to send).  During a normal exchange of
   binding data, receiving a LEASEQUERY-DATA message signifies that
   connection is active.  Note that the default for
   ACTIVE_LQ_RCV_TIMEOUT is 120 seconds, twice the value of the
   ACTIVE_LQ_IDLE_TIMEOUT's default of 60 seconds, which drives the
   DHCPv6 server to send messages.  Thus, ACTIVE_LQ_RCV_TIMEOUT controls
   how sensitive the requestor is to delays by the DHCPv6 server in
   sending updates or LEASEQUERY-DATA messages.

   A single Active Leasequery can and usually will result in a large
   number of replies.  The requestor MUST be prepared to receive more
   than one reply with transaction-ids matching a single
   ACTIVELEASEQUERY message from a single DHCPv6 server.

   An Active Leasequery has two regimes: during the catch-up phase (if
   any) and after any catch-up phase.  If the Active Leasequery was
   requested with an OPTION_LQ_START_TIME option, the Active Leasequery
   starts out in the catch-up phase.  See Section 8.4.1 for information
   on processing during the catch-up phase, as well as how to determine
   when the catch-up phase is complete.

   The updates sent by the DHCPv6 server during the catch-up phase are
   not in the order that the lease state data was updated.  Therefore,
   the OPTION_LQ_BASE_TIME option from messages during this phase MUST
   NOT be saved and used to compute the subsequent ACTIVELEASEQUERY
   message's OPTION_LQ_START_TIME option.

   After the catch-up phase, or during the entire series of messages
   received as the response to an Active Leasequery request with no
   OPTION_LQ_START_TIME (and therefore no catch-up phase), the
   OPTION_LQ_BASE_TIME option of the most recent message SHOULD be saved
   as a record of the most recent time that data was received.  This
   base-time (in the context of the DHCPv6 server) can be used in a
   subsequent Active Leasequery message's OPTION_LQ_START_TIME after a
   loss of the Active Leasequery connection.

   The LEASEQUERY-DONE message MAY unilaterally terminate a successful
   Active Leasequery request that is currently in progress in the event
   that the DHCPv6 server determines that it cannot continue processing
   an Active Leasequery request.  For example, when a server is
   requested to shut down, it SHOULD send a LEASEQUERY-DONE message with
   a DHCPv6 status code of QueryTerminated and include the
   OPTION_LQ_BASE_TIME option in the message.  This MUST be the last
   message on that connection, and once the message has been
   transmitted, the server MUST close the connection.

   After receiving LEASEQUERY-DONE with a QueryTerminated status from a
   server, the requestor MAY close the TCP connection to that server.

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8.4.1.  Processing Replies from a Request Containing an
        OPTION_LQ_START_TIME

   If the Active Leasequery was requested with an OPTION_LQ_START_TIME
   option, the DHCPv6 server will attempt to send information about all
   bindings that changed since the time specified in the
   OPTION_LQ_START_TIME.  This is the catch-up phase of the Active
   Leasequery processing.  The DHCPv6 server MAY also send information
   about real-time binding updates over the same connection.  Thus, the
   catch-up phase can run in parallel with the normal updates generated
   by the Active Leasequery request.

   A DHCPv6 server MAY keep only a limited amount of time-ordered
   information available to respond to an Active Leasequery request
   containing an OPTION_LQ_START_TIME option.  Thus, it is possible that
   the time specified in the OPTION_LQ_START_TIME option represents a
   time not covered by the time-ordered information kept by the DHCPv6
   server.  In such case, when there is not enough data saved in the
   DHCPv6 server to satisfy the request specified by the
   OPTION_LQ_START_TIME option, the DHCPv6 server will reply immediately
   with a LEASEQUERY-REPLY message with a DHCPv6 status code of
   DataMissing with a base-time option equal to the server's current
   time.  This will signal the end of the catch-up phase, and the only
   updates that will subsequently be received on this connection are the
   real-time updates from the Active Leasequery request.

   If there is enough data saved to satisfy the request, then
   LEASEQUERY-REPLY (with OPTION_STATUS_CODE of Success or reply without
   the OPTION_STATUS_CODE option) and LEASEQUERY-DATA messages will
   begin to arrive from the DHCPv6 server.  Some of these messages will
   be related to the OPTION_LQ_START_TIME request and be part of the
   catch-up phase.  Some of these messages will be real-time updates of
   binding changes taking place in the DHCPv6 server.  In general, there
   is no way to determine the source of each message.

   The updates sent by the DHCPv6 server during the catch-up phase are
   not in the order that the binding data was updated.  Therefore, until
   the catch-up phase is complete, the latest base-time value received
   from a DHCPv6 server processing an Active Leasequery request cannot
   be reset from the incoming messages (and used in a subsequent Active
   Leasequery's query-start-time option), because to do so would
   compromise the ability to recover lost information if the Active
   Leasequery were to terminate prior to the completion of the catch-up
   phase.

   The requestor will know that the catch-up phase is complete when the
   DHCPv6 server transmits a LEASEQUERY-DATA message with the DHCPv6
   status code of CatchUpComplete (or a LEASEQUERY-REPLY message with a

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   DHCPv6 status code of DataMissing, as discussed above).  Once this
   message is transmitted, all additional LEASEQUERY-DATA messages will
   relate to real-time ("new") binding changes in the DHCPv6 server.

   As discussed in Section 8.4, the requestor SHOULD keep track of the
   latest base-time option value received over a particular connection,
   to be used in a subsequent Active Leasequery request, but only if the
   catch-up phase is complete.  Prior to the completion of the catch-up
   phase, if the connection should go away or if the requestor receives
   a LEASEQUERY-DONE message, then when it reconnects, it MUST use the
   base-time value from the previous connection and not any base-time
   value received from the recently closed connection.

   In the event that there was enough data available to the DHCPv6
   server to begin to satisfy the request implied by the
   OPTION_LQ_START_TIME option but during the processing of that data,
   the server found that it was unable to continue (during transmission,
   the aging algorithm causes [some of] the saved data to become
   unavailable), the DHCPv6 server will terminate the catch-up phase of
   processing immediately by sending a LEASEQUERY-DATA message with a
   DHCPv6 status code of DataMissing and with a base-time option of the
   current time.

   The requestor MUST NOT assume that every individual state change of
   every binding during the period from the time specified in the
   OPTION_LQ_START_TIME and the present is replicated in an Active
   Leasequery reply message.  The requestor MAY assume that at least one
   Active Leasequery reply message will exist for every binding that had
   one or more changes of state during the period specified by the
   OPTION_LQ_START_TIME and the current time.  The last message for each
   binding will contain the state at the current time, and there can be
   one or more messages concerning a single binding during the catch-up
   phase of processing.

   Bindings can change multiple times while the requestor is not
   connected (that is, during the time from the OPTION_LQ_START_TIME to
   the present).  The requestor will only receive information about the
   current state of the binding, not information about each state change
   that occurred during the period from the OPTION_LQ_START_TIME to the
   present.

   If the LEASEQUERY-REPLY or LEASEQUERY-DATA message containing a
   DHCPv6 status code of DataMissing is received and the requestor is
   interested in keeping its database up to date with respect to the
   current state of bindings in the DHCPv6 server, then the requestor
   SHOULD issue a Bulk Leasequery request to recover the information
   missing from its database.  This Bulk Leasequery request SHOULD
   include an OPTION_LQ_START_TIME option with the same value as the

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   OPTION_LQ_START_TIME option previously included in the Active
   Leasequery responses from the DHCPv6 server and an OPTION_LQ_END_TIME
   option equal to the OPTION_LQ_BASE_TIME option returned by the DHCPv6
   server in the LEASEQUERY-REPLY or LEASEQUERY-DATA message with the
   DHCPv6 status code of DataMissing.

   Typically, the requestor would have one connection open to a DHCPv6
   server for an Active Leasequery request and possibly one additional
   connection open for a Bulk Leasequery request to the same DHCPv6
   server to fill in the data that might have been missed prior to the
   initiation of the Active Leasequery.  The Bulk Leasequery connection
   would typically run to completion and be closed, leaving one Active
   Leasequery connection open to a single DHCPv6 server.

8.5.  Processing Time Values in Leasequery Messages

   Active or Bulk Leasequery requests can be made to a DHCPv6 server
   whose absolute time may not be synchronized with the local time of
   the requestor.  Thus, there are at least two time contexts in even
   the simplest Active or Bulk Leasequery response.

   If the requestor of an Active or Bulk Leasequery is saving the data
   returned in some form, it has a requirement to store a variety of
   time values; some of these will be time in the context of the
   requestor, and some will be time in the context of the DHCPv6 server.

   When receiving an Active or Bulk Leasequery reply message from the
   DHCPv6 server, the message will contain an OPTION_LQ_BASE_TIME
   option.  The time contained in this OPTION_LQ_BASE_TIME option is in
   the context of the DHCPv6 server.  As such, it is an ideal time to
   save and use as input to an Active or Bulk Leasequery message in the
   OPTION_LQ_START_TIME or OPTION_LQ_END_TIME options should the
   requestor need to ever issue an Active or Bulk Leasequery message
   using these options as part of a later query, since these options
   require a time in the context of the DHCPv6 server.

   In addition to saving the OPTION_LQ_BASE_TIME for possible future use
   in the OPTION_LQ_START_TIME or OPTION_LQ_END_TIME options, the
   OPTION_LQ_BASE_TIME option is used as part of the conversion of the
   other times in the Leasequery message to values that are meaningful
   in the context of the requestor.

   In systems whose clocks are synchronized, perhaps using the Network
   Time Protocol (NTP), the clock skew will usually be zero, which is
   not only acceptable, but desired.

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8.6.  Examples

   These examples illustrate what a series of queries and responses
   might look like.  These are only examples -- there is no requirement
   that these sequences must be followed.

8.6.1.  Query Failure

   This example illustrates the message flows in case the DHCPv6 server
   identifies that it cannot accept and/or process an Active Leasequery
   request from the requestor.  This could be because of various reasons
   (i.e., UnknownQueryType, MalformedQuery, NotConfigured, NotAllowed,
   and NotSupported).

      Client                          Server
      ------                          ------
      ACTIVELEASEQUERY xid 1  ----->
                              <-----  LEASEQUERY-REPLY xid 1 (w/error)

8.6.2.  Data Missing on Server

   This example illustrates the message flows in case the DHCPv6 server
   identifies that it does not have enough data saved to satisfy the
   request specified by the OPTION_LQ_START_TIME option.

   In this case, the DHCPv6 server will reply immediately with a
   LEASEQUERY-REPLY message with a DHCPv6 status code of DataMissing
   with a base-time option equal to the server's current time.  This
   will signal the end of the catch-up phase, and the only updates that
   will subsequently be received on this connection are the real-time
   updates from the Active Leasequery request.

      Client                          Server
      ------                          ------
      ACTIVELEASEQUERY xid 2  ----->
                              <-----  LEASEQUERY-REPLY xid 2 (w/error)
                              <-----  LEASEQUERY-DATA xid 2
                              <-----  LEASEQUERY-DATA xid 2
                              <-----  LEASEQUERY-DATA xid 2

8.6.3.  Successful Query

   This example illustrates the message flows in case of successful
   query processing by the DHCPv6 server.

   In this case, the DHCPv6 server will reply immediately with a
   LEASEQUERY-REPLY message (with OPTION_STATUS_CODE of Success or reply
   without OPTION_STATUS_CODE option), followed by binding data in

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   LEASEQUERY-DATA messages.  In case the DHCPv6 server wants to abort
   an in-process request and terminate the connection due to some
   reason, it sends LEASEQUERY-DONE with an error code present in the
   OPTION_STATUS_CODE option.

      Client                          Server
      ------                          ------
      ACTIVELEASEQUERY xid 3  ----->
                              <-----  LEASEQUERY-REPLY xid 3
                              <-----  LEASEQUERY-DATA xid 3
                              <-----  LEASEQUERY-DATA xid 3
                              <-----  LEASEQUERY-DATA xid 3
                              <-----  LEASEQUERY-DATA xid 3
                              <-----  LEASEQUERY-DONE xid 3 (w/error)

8.7.  Closing Connections

   The requestor or DHCPv6 Leasequery server MAY close its end of the
   TCP connection at any time.  The requestor MAY choose to retain the
   connection if it intends to issue additional queries.  Note that this
   requestor behavior does not guarantee that the connection will be
   available for additional queries: the server might decide to close
   the connection based on its own configuration.

9.  Server Behavior

   A DHCPv6 server that supports Active Leasequery MUST support DHCPv6
   Bulk Leasequery [RFC5460] along with the updates mentioned in this
   document.

9.1.  Accepting Connections

   DHCPv6 servers that implement DHCPv6 Active Leasequery listen for
   incoming TCP connections.  The approach used in accepting the
   requestor's connection is the same as specified in DHCPv6 Bulk
   Leasequery [RFC5460], with the exception that support for Active
   Leasequery MUST NOT be enabled by default and MUST require an
   explicit configuration step to be performed before it will operate.

   DHCPv6 servers SHOULD be able to operate in either insecure or secure
   mode.  This MAY be a mode that is administratively controlled, where
   the server will require a TLS connection to operate or will only
   operate without a TLS connection.  In either case, operation in
   insecure mode MUST NOT be the default, even if operation in secure
   mode is not supported.  Operation in insecure mode MUST always
   require an explicit configuration step, separate from the
   configuration step required to enable support for Active Leasequery.

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   When operating in insecure mode, the DHCPv6 server simply waits for
   the requestor to send the Active Leasequery request after the
   establishment of a TCP connection.  If it receives a STARTTLS
   message, it MUST respond with a REPLY [RFC3315] message with a DHCPv6
   status code of TLSConnectionRefused.

   When operating in secure mode, DHCPv6 servers MUST support TLS
   [RFC5246] to protect the integrity and privacy of the data
   transmitted over the TCP connection.  When operating in secure mode,
   DHCPv6 servers MUST be configurable with regard to which requestors
   they will communicate.  The certificate presented by a requestor when
   initiating the TLS connection is used to distinguish between
   acceptable and unacceptable requestors.

   When operating in secure mode, the DHCPv6 server MUST begin to
   negotiate a TLS connection with a requestor who asks for one and MUST
   close the TCP connections that are not secured with TLS or for which
   the requestor's certificate is deemed unacceptable.  The
   recommendations in [RFC7525] SHOULD be followed when negotiating a
   TLS connection.

   A requestor will request a TLS connection by sending a STARTTLS as
   the first message over a newly created TCP connection.  If the DHCPv6
   server supports TLS connections and has not been configured to not
   allow them on this link, the DHCPv6 server MUST respond to this
   STARTTLS message by sending a REPLY [RFC3315] message without a
   DHCPv6 status code back to the requestor.  This indicates to the
   requestor that the DHCPv6 server will support the negotiation of a
   TLS connection over this existing TCP connection.

   If for some reason the DHCPv6 server cannot support a TLS connection
   or has been configured to not support a TLS connection, then it
   SHOULD send a REPLY message with a DHCPv6 status code of
   TLSConnectionRefused back to the requestor.

   In the event that the DHCPv6 server sends a REPLY message without a
   DHCPv6 status code option included (which indicates success), the
   requestor is supposed to initiate a TLS handshake [RFC5246] (see
   Section 8.2).  During the TLS handshake, the DHCPv6 server MUST
   validate the requestor's digital certificate.  In addition, the
   digital certificate presented by the requestor is used to decide if
   this requestor is allowed to perform an Active Leasequery.  If this
   requestor's certificate is deemed unacceptable, the server MUST abort
   the creation of the TLS connection.

   All TLS connections established between a requestor and a DHCPv6
   server for the purposes of supporting Active Leasequery MUST be
   mutually authenticated.

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   If the TLS handshake is not successful in creating a TLS connection,
   the server MUST close the TCP connection.

9.2.  Rejecting Connections

   Servers that do not implement DHCPv6 Active and Bulk Leasequery
   SHOULD NOT listen for incoming TCP connections for these requests.

   If the DHCPv6 server supporting Bulk Leasequery and not Active
   Leasequery receives an Active Leasequery request, it SHOULD send a
   LEASEQUERY-REPLY with a DHCPv6 status code of NotSupported.  It
   SHOULD close the TCP connection after this error is signaled.

9.3.  Replying to an Active Leasequery

   The DHCPv6 Leasequery [RFC5007] specification describes the initial
   construction of LEASEQUERY-REPLY messages.  Use of the LEASEQUERY-
   REPLY and LEASEQUERY-DATA messages to carry multiple bindings is
   described in DHCPv6 Bulk Leasequery [RFC5460].  Message transmission
   and framing for TCP is described in Section 6.1.

   If the connection becomes blocked while the server is attempting to
   send reply messages, the server SHOULD terminate the TCP connection
   after ACTIVE_LQ_SEND_TIMEOUT.  This timeout governs for how long the
   DHCPv6 server is prepared to wait for the requestor to read and
   process enough information to unblock the TCP connection.  The
   default is two minutes, which means that if more than two minutes
   goes by without the requestor reading enough information to unblock
   the TCP connection, the DHCPv6 server SHOULD close the TCP
   connection.

   If the DHCPv6 server encounters an error during the initial
   processing of the ACTIVELEASEQUERY message, it SHOULD send a
   LEASEQUERY-REPLY message containing an error code of some kind in a
   DHCPv6 status code option.  It SHOULD close the connection after this
   error is signaled.

   If the DHCPv6 server encounters an error during later processing of
   the ACTIVELEASEQUERY message, it SHOULD send a LEASEQUERY-DONE
   containing an error code of some kind in a DHCPv6 status code option.
   It SHOULD close the connection after this error is signaled.

   If the server finds any bindings satisfying a query, it SHOULD send
   each binding's data in a reply message.  The first reply message is a
   LEASEQUERY-REPLY.  The binding data is carried in an
   OPTION_CLIENT_DATA option, as specified in [RFC5007].  The server
   SHOULD send subsequent bindings in LEASEQUERY-DATA messages, which
   can avoid redundant data (such as the requestor's Client-ID).

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   Every reply to an Active Leasequery request MUST contain the
   information specified in replies to a DHCPv6 Bulk Leasequery request
   [RFC5460], with the exception that a server implementing Active
   Leasequery SHOULD be able to be configured to prevent specific data
   items from being sent to the requestor even if these data items were
   requested in the OPTION_ORO option.

   Some servers can be configured to respond to a DHCPv6 Leasequery
   [RFC5007] and DHCPv6 Bulk Leasequery [RFC5460] for an IPv6 binding
   that is reserved in such a way that it appears that the IPv6 binding
   is leased to the DHCP client for which it is reserved.  These servers
   SHOULD also respond to an Active Leasequery request with the same
   information as they would to a Bulk Leasequery request when they
   first determine that the IPv6 binding is reserved to a DHCP client.

   If an Active Leasequery or Bulk Leasequery request contains the
   OPTION_LQ_BASE_TIME option code present in OPTION_ORO, the DHCPv6
   server MUST include the OPTION_LQ_BASE_TIME option in every reply for
   this request.  The value for the base-time option is the current
   absolute time in the DHCPv6 server's context.

   If an Active Leasequery request contains an OPTION_LQ_START_TIME
   option, it indicates that the requestor would like the DHCPv6 server
   to send it not only messages that correspond to DHCPv6 binding
   activity that occurs subsequent to the receipt of the Active
   Leasequery request, but also messages that correspond to DHCPv6
   binding activity that occurred prior to the Active Leasequery
   request.

   If the OPTION_LQ_END_TIME option appears in an Active Leasequery
   request, the DHCPv6 server SHOULD send a LEASEQUERY-REPLY message
   with a DHCPv6 status code of MalformedQuery and terminate the
   connection.

   In order to implement a meaningful response to this query, the DHCPv6
   server MAY keep track of the binding activity and associate changes
   with particular base-time values from the messages.  Then, when
   requested to do so by an Active Leasequery request containing a
   OPTION_LQ_START_TIME option, the DHCPv6 server can respond with
   replies for all binding activity occurring on that
   OPTION_LQ_START_TIME or later times.

   These replies based on the OPTION_LQ_START_TIME MAY be interleaved
   with the messages generated due to current binding activity.

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   Once the transmission of the DHCPv6 Leasequery messages associated
   with the OPTION_LQ_START_TIME option are complete, a LEASEQUERY-DATA
   message MUST be sent with a DHCPv6 status code value of
   CatchUpComplete.

   The DHCPv6 server SHOULD, but is not required to, keep track of a
   limited amount of previous binding activity.  The DHCPv6 server MAY
   choose to only do this in the event that it has received at least one
   Active Leasequery request in the past, as to do so will almost
   certainly entail some utilization of resources that would be wasted
   if there are no Active Leasequery requestors for this DHCPv6 server.
   The DHCPv6 server SHOULD make the amount of previous binding activity
   it retains configurable.  There is no requirement on the DHCPv6
   server to retain this information over a server restart (or even to
   retain such information at all).

   Unless there is an error or some requirement to cease processing a
   Active Leasequery request yielding a LEASEQUERY-DONE message, such as
   a server shutdown, there will be no LEASEQUERY-DONE message at the
   conclusion of the Active Leasequery processing because that
   processing will not conclude but will continue until either the
   requestor or the server closes the connection.

9.4.  Multiple or Parallel Queries

   Every Active Leasequery request MUST be made on a single TCP
   connection where there is no other request active at the time the
   request is made.

   Typically, a requestor of an Active Leasequery would not need to send
   a second Active Leasequery while the first is still active.  However,
   sending an Active Leasequery and a Bulk Leasequery in parallel would
   be possible and reasonable.  In case of parallel Active and Bulk
   Leasequeries, the requestor MUST use different TCP connections.

   This MAY be a feature that is administratively controlled.  Servers
   that are able to process queries in parallel SHOULD offer
   configuration that limits the number of simultaneous queries
   permitted from any one requestor, in order to control resource use if
   there are multiple requestors seeking service.

9.5.  Closing Connections

   The server MUST close its end of the TCP connection if it encounters
   an error sending data on the connection.  The server MUST close its
   end of the TCP connection if it finds that it has to abort an in-
   process request.  A server aborting an in-process request SHOULD
   attempt to signal that to its requestors by using the QueryTerminated

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   status code in the DHCPv6 status code option in a LEASEQUERY-DONE
   message.  If the server detects that the requestor end has been
   closed, the server MUST close its end of the connection.

   The server SHOULD limit the number of connections it maintains and
   SHOULD close idle connections to enforce the limit.

10.  Security Considerations

   The Security Considerations section of [RFC3315] details the general
   threats to DHCPv6.  The DHCPv6 Leasequery specification [RFC5007]
   describes recommendations for the Leasequery protocol, especially
   with regard to relayed Leasequery messages, mitigation of packet-
   flooding denial-of-service (DoS) attacks, restriction to trusted
   requestors, and use of IPsec [RFC4301].

   The use of TCP introduces some additional concerns.  Attacks that
   attempt to exhaust the DHCPv6 server's available TCP connection
   resources can compromise the ability of legitimate requestors to
   receive service.  Malicious requestors who succeed in establishing
   connections but who then send invalid queries, partial queries, or no
   queries at all can also exhaust a server's pool of available
   connections.

   When operating in secure mode, TLS [RFC5246] is used to secure the
   connection.  The recommendations in [RFC7525] SHOULD be followed when
   negotiating a TLS connection.

   Servers SHOULD offer configuration parameters to limit the sources of
   incoming connections through validation and use of the digital
   certificates presented to create a TLS connection.  They SHOULD also
   limit the number of accepted connections and limit the period of time
   during which an idle connection will be left open.

   The data acquired by using an Active Leasequery is subject to the
   same potential abuse as the data held by the DHCPv6 server from which
   it was acquired and SHOULD be secured by mechanisms as strong as
   those used for the data held by that DHCPv6 server.  The data
   acquired by using an Active Leasequery SHOULD be deleted as soon as
   possible after the use for which it was acquired has passed.

   Authentication for DHCP messages [RFC3315] MUST NOT be used to
   attempt to secure transmission of the messages described in this
   document.

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11.  IANA Considerations

   IANA has assigned new DHCPv6 option codes in the "Option Codes"
   registry maintained at <http://www.iana.org/assignments/
   dhcpv6-parameters>:

      OPTION_LQ_BASE_TIME (100)

      OPTION_LQ_START_TIME (101)

      OPTION_LQ_END_TIME (102)

   IANA has assigned new values in the DHCPv6 "Status Codes" registry
   maintained at <http://www.iana.org/assignments/dhcpv6-parameters>:

      DataMissing (12)

      CatchUpComplete (13)

      NotSupported (14)

      TLSConnectionRefused (15)

   IANA has assigned values for the following new DHCPv6 message types
   in the "Message Types" registry maintained at
   <http://www.iana.org/assignments/dhcpv6-parameters>:

      ACTIVELEASEQUERY (22)

      STARTTLS (23)

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

Top      ToC       Page 29 
   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              DOI 10.17487/RFC3633, December 2003,
              <http://www.rfc-editor.org/info/rfc3633>.

   [RFC5007]  Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
              "DHCPv6 Leasequery", RFC 5007, DOI 10.17487/RFC5007,
              September 2007, <http://www.rfc-editor.org/info/rfc5007>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5460]  Stapp, M., "DHCPv6 Bulk Leasequery", RFC 5460,
              DOI 10.17487/RFC5460, February 2009,
              <http://www.rfc-editor.org/info/rfc5460>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

12.2.  Informative References

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <http://www.rfc-editor.org/info/rfc4301>.

   [RFC7414]  Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
              Zimmermann, "A Roadmap for Transmission Control Protocol
              (TCP) Specification Documents", RFC 7414,
              DOI 10.17487/RFC7414, February 2015,
              <http://www.rfc-editor.org/info/rfc7414>.

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Acknowledgments

   Some of the concepts and content present in this document are based
   on DHCPv4 Active Leasequery, which was originally proposed by Kim
   Kinnear, Bernie Volz, Mark Stapp, and Neil Russell.

   Useful review comments were provided by Scott Bradner, Francis
   Dupont, and Stephen Farrell.  The privacy protections were
   substantially upgraded due to these comments and discussions.

Authors' Addresses

   Dushyant Raghuvanshi
   Cisco Systems, Inc.
   Cessna Business Park
   Varthur Hobli, Outer Ring Road
   Bangalore, Karnataka  560037
   India

   Phone: +91 80 4426-7372
   Email: draghuva@cisco.com


   Kim Kinnear
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, Massachusetts  01719
   United States

   Phone: +1 978 936-0000
   Email: kkinnear@cisco.com


   Deepak Kukrety
   Cisco Systems, Inc.
   Cessna Business Park
   Varthur Hobli, Outer Ring Road
   Bangalore, Karnataka  560037
   India

   Phone: +91 80 4426-7346
   Email: dkukrety@cisco.com