DHCPv6 Leasequery

Network Working Group                                      J. Brzozowski
Request for Comments: 5007                                 Comcast Cable
Category: Standards Track                                     K. Kinnear
                                                                 B. Volz
                                                                 S. Zeng
                                                     Cisco Systems, Inc.
                                                          September 2007


                           DHCPv6 Leasequery

Status of This Memo

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

Abstract

   This document specifies a leasequery exchange for the Dynamic Host
   Configuration Protocol for IPv6 (DHCPv6) that can be used to obtain
   lease information about DHCPv6 clients from a DHCPv6 server.  This
   document specifies the scope of data that can be retrieved as well as
   both DHCPv6 leasequery requestor and server behavior.  This document
   extends DHCPv6.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  On-Demand Query  . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Anticipatory Query . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Query Types  . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Message and Option Definitions . . . . . . . . . . . . . .  6
       4.1.1.  Messages . . . . . . . . . . . . . . . . . . . . . . .  6
       4.1.2.  Options  . . . . . . . . . . . . . . . . . . . . . . .  6
       4.1.3.  Status Codes . . . . . . . . . . . . . . . . . . . . . 12
       4.1.4.  Transmission and Retransmission Parameters . . . . . . 12
     4.2.  Message Validation . . . . . . . . . . . . . . . . . . . . 12
       4.2.1.  LEASEQUERY . . . . . . . . . . . . . . . . . . . . . . 12
       4.2.2.  LEASEQUERY-REPLY . . . . . . . . . . . . . . . . . . . 13
     4.3.  DHCPv6 Leasequery Requestor Behavior . . . . . . . . . . . 13
       4.3.1.  Creation of LEASEQUERY . . . . . . . . . . . . . . . . 13
       4.3.2.  Transmission of LEASEQUERY . . . . . . . . . . . . . . 13
       4.3.3.  Receipt of LEASEQUERY-REPLY  . . . . . . . . . . . . . 14
       4.3.4.  Handling DHCPv6 Client Data from Multiple Sources  . . 15
     4.4.  DHCPv6 Leasequery Server Behavior  . . . . . . . . . . . . 16
       4.4.1.  Receipt of LEASEQUERY Messages . . . . . . . . . . . . 16
       4.4.2.  Constructing the Client's OPTION_CLIENT_DATA . . . . . 17
       4.4.3.  Transmission of LEASEQUERY-REPLY Messages  . . . . . . 17
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20

1.  Introduction

   The DHCPv6 [2] protocol specifies a mechanism for the assignment of
   both IPv6 address and configuration information to IPv6 nodes.  IPv6
   Prefix Options for DHCPv6 [4] specifies a mechanism for the automated
   delegation of IPv6 prefixes and related options.  Similar to DHCPv4
   [5], DHCPv6 servers maintain authoritative information related to
   their operations including, but not limited to, lease information for
   IPv6 addresses and delegated prefixes.

   The requirement exists in various types of IPv6 deployments,
   particularly those of a broadband variety, to leverage DHCPv6 [2] for
   retrieving data related to the operation of DHCPv6 servers
   programmatically.  In particular, it is desirable to be able to
   extract lease information about IPv6 addresses and delegated prefixes
   assigned using DHCPv6 [2] [4].  Specific examples where this
   information has illustrated value are in broadband networks to
   facilitate access control by edge devices.  This capability to
   programmatically extract lease data from the DHCPv6 server is called
   leasequery.

   The leasequery capability described in this document parallels the
   DHCPv4 leasequery capability documented in [3].  As such, it shares
   the basic motivations, background, design goals and constraints as
   described in [3].  Differences are due to the differences between
   IPv4 and IPv6 and by extension, DHCPv4 and DHCPv6.  For example,
   Neighbor Discovery [7] is used in IPv6 instead of the Address
   Resolution Protocol (ARP) [8] (Section 4.1 of [3]) and DOCSIS 3.0
   [11] defines IPv6 support for cable modem environments.

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 [1].

   DHCPv6 terminology is defined in [2].  Terminology specific to DHCPv6
   leasequery can be found below:

   access concentrator
                   An access concentrator is a router or switch at the
                   broadband access provider's edge of a public
                   broadband access network.  This document assumes that
                   the access concentrator includes the DHCPv6 relay
                   agent functionality.

   client(s)       The nodes that have one or more bindings with a
                   DHCPv6 server.  This does not refer to the node
                   issuing the LEASEQUERY unless it itself has one or
                   more bindings with a DHCPv6 server.

   gleaning        Gleaning is the extraction of location information
                   from DHCPv6 messages, as the messages are forwarded
                   by the DHCP relay agent function.

   location information
                   Location information is information needed by the
                   access concentrator to forward traffic to a
                   broadband-accessible host.  This information includes
                   knowledge of the host hardware address, the port or
                   virtual circuit that leads to the host, and/or the
                   hardware address of the intervening subscriber modem.

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

3.  Protocol Overview

   The focus of this document is to extend the DHCPv6 protocol to allow
   processes and devices that wish to access information from a DHCPv6
   server to do so in a lightweight and convenient manner.  It is
   especially appropriate for processes and devices that already
   interpret DHCPv6 messages.

   The LEASEQUERY message is a query message only and does not affect
   the state of the IPv6 address or prefix, or the binding information
   associated with it.

   One important motivating example is that the LEASEQUERY message
   allows access concentrators to query DHCP servers to obtain location
   information of broadband access network devices.  This is described
   in Section 1 of [3] for IPv4.

3.1.  On-Demand Query

   The on-demand leasequery capability allows requesting just the
   information necessary to satisfy an immediate need.  If the requestor
   is an access concentrator, then the immediate need will typically be
   that it has received an IPv6 packet and it needs to refresh its
   information concerning the DHCPv6 client to which that IPv6 address
   is currently leased.  In this case, the request will be by address.
   This fits clearly into the single request/response cycle common to
   other DHCPv6 message exchanges.

   However, this approach has limitations when used with prefix
   delegation [4] as no traffic may arrive because the access
   concentrator is unable to inject the appropriate routing information
   into the routing infrastructure, such as after a reboot.  This
   approach does work if the access concentrator is configured to inject
   routing information for a prefix that aggregates potentially
   delegated prefixes.  Or, it also works if the access concentrator and
   requesting router use a routing protocol; as then the requesting
   router can trigger the access concentrator to request information
   from a DHCPv6 server and inject appropriate routing information into
   the routing infrastructure.

3.2.  Anticipatory Query

   A second approach for requesting information from a DHCPv6 server
   would be to use a leasequery-like capability to rebuild an internal
   data store containing information available from a DHCPv6 server.
   The rebuilding of the data store in this approach can take place as
   soon as possible after the need to rebuild it is discovered (such as
   on booting), and doesn't wait on the receipt of specific packets to
   trigger a piecemeal database update (as is the case for on-demand
   leasequery).  This approach would also remove the limitation
   discussed above for prefix delegation.

   This anticipatory query is not specified in this document and is an
   area of future work.

3.3.  Query Types

   Leasequery provides for the following queries:

   Query by IPv6 address -  This query allows a requestor to request
      from a server the bindings for a client that either is bound to
      the address or has been delegated the prefix that contains the
      address.

   Query by Client Identifier (DUID) -  This query allows a requestor to
      request from a server the bindings for a specific client on a
      specific link or a list of the links on which the client has one
      or more bindings.

4.  Protocol Details

4.1.  Message and Option Definitions

4.1.1.  Messages

   The LEASEQUERY and LEASEQUERY-REPLY messages use the Client/Server
   message formats described in [2], Section 6.  Two new message codes
   are defined:

   LEASEQUERY (14) -  A requestor sends a LEASEQUERY message to any
      available server to obtain information on a client's leases.  The
      options in an OPTION_LQ_QUERY determine the query.

   LEASEQUERY-REPLY (15) -  A server sends a LEASEQUERY-REPLY message
      containing client data in response to a LEASEQUERY message.

4.1.2.  Options

4.1.2.1.  Query Option

   The Query option is used only in a LEASEQUERY message and identifies
   the query being performed.  The option includes the query type, link-
   address (or 0::0), and option(s) to provide data needed for the
   query.

   The format of the Query option is shown below:

        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_QUERY        |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   query-type  |                                               |
       +-+-+-+-+-+-+-+-+                                               |
       |                                                               |
       |                         link-address                          |
       |                                                               |
       |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               |                                               .
       +-+-+-+-+-+-+-+-+                                               .
       .                         query-options                         .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code      OPTION_LQ_QUERY (44)

         option-len       17 + length of query-options field.

         link-address     A global address that will be used by the
                          server to identify the link to which the
                          query applies, or 0::0 if unspecified.

         query-type       The query requested (see below).

         query-options    The options related to the query.

   The query-type and required query-options are:

   QUERY_BY_ADDRESS (1) -  The query-options MUST contain an
      OPTION_IAADDR option [2].  The link-address field, if not 0::0,
      specifies an address for the link on which the client is located
      if the address in the OPTION_IAADDR option is of insufficient
      scope.  Only the information for the client that has a lease for
      the specified address or was delegated a prefix that contains the
      specified address is returned (if available).

   QUERY_BY_CLIENTID (2) -   The query-options MUST contain an
      OPTION_CLIENTID option [2].  The link-address field, if not 0::0,
      specifies an address for the link on which the client is located.
      If the link-address field is 0::0, the server SHOULD search all of
      its links for the client.

   The query-options MAY also include an OPTION_ORO option [2] to
   indicate the options for each client that the requestor would like
   the server to return.  Note that this OPTION_ORO is distinct and
   separate from an OPTION_ORO that may be in the requestor's LEASEQUERY
   message.

   If a server receives an OPTION_LQ_QUERY with a query-type it does not
   support, the server SHOULD return an UnknownQueryType status-code.
   If a server receives a supported query-type but the query-options is
   missing a required option, the server SHOULD return a MalformedQuery
   status-code.

4.1.2.2.  Client Data Option

   The Client Data option is used to encapsulate the data for a single
   client on a single link in a LEASEQUERY-REPLY message.

   The format of the Client Data option is shown below:

        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_CLIENT_DATA      |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       .                                                               .
       .                        client-options                         .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code      OPTION_CLIENT_DATA (45)

         option-len       Length, in octets, of the encapsulated client-
                          options field.

         client-options   The options associated with this client.

   The encapsulated client-options include the OPTION_CLIENTID,
   OPTION_IAADDR, OPTION_IAPREFIX, and OPTION_CLT_TIME options and other
   options specific to the client and requested by the requestor in the
   OPTION_ORO in the OPTION_LQ_QUERY's query-options.  The server MUST
   return all of the client's statefully assigned addresses and
   delegated prefixes, with a non-zero valid lifetime, on the link.

4.1.2.3.  Client Last Transaction Time Option

   The Client Last Transaction Time option is encapsulated in an
   OPTION_CLIENT_DATA and identifies how long ago the server last
   communicated with the client, in seconds.

   The format of the Client Last Transaction Time option is shown below:

        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_CLT_TIME        |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 client-last-transaction-time                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code      OPTION_CLT_TIME (46)

         option-len       4

         client-last-transaction-time
                          The number of seconds since the server last
                          communicated with the client (on that link).

   The client-last-transaction-time is a positive value and reflects the
   number of seconds since the server last communicated with the client
   (on that link).

4.1.2.4.  Relay Data

   The Relay Data option is used only in a LEASEQUERY-REPLY message and
   provides the relay agent information used when the client last
   communicated with the server.

   The format of the Relay Data option is shown below:

        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_RELAY_DATA      |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                  peer-address (IPv6 address)                  |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       DHCP-relay-message                      |
       .                                                               .
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code      OPTION_LQ_RELAY_DATA (47)

         option-len       16 + length of DHCP-relay-message.

         peer-address     The address of the relay agent from which
                          the relayed message was received by the
                          server.

         DHCP-relay-message
                          The last complete relayed message, excluding
                          the client's message OPTION_RELAY_MSG,
                          received by the server.

   This option is used by the server to return full relay agent
   information for a client.  It MUST NOT be returned if the server does
   not have such information, either because the client communicated
   directly (without relay agent) with the server or if the server did
   not retain such information.

   If returned, the DHCP-relay-message MUST contain a valid (perhaps
   multi-hop) RELAY-FORW message as the most recently received by the
   server for the client.  However, the (innermost) OPTION_RELAY_MSG
   option containing the client's message MUST have been removed.

   This option SHOULD only be returned if requested by the OPTION_ORO of
   the OPTION_LQ_QUERY.

4.1.2.5.  Client Link Option

   The Client Link option is used only in a LEASEQUERY-REPLY message and
   identifies the links on which the client has one or more bindings.
   It is used in reply to a query when no link-address was specified and
   the client is found to be on more than one link.

   The format of the Client Link option is shown below:

        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_CLIENT_LINK     |         option-len            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                  link-address (IPv6 address)                  |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                  link-address (IPv6 address)                  |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code      OPTION_LQ_CLIENT_LINK (48)

         option-len       Length of the list of links in octets;
                          must be a multiple of 16.

         link-address     A global address used by the server to
                          identify the link on which the client is
                          located.

   A server may respond to a query by client-id, where the 0::0 link-
   address was specified, with this option if the client is found to be
   on multiple links.  The requestor may then repeat the query once for
   each link-address returned in the list, specifying the returned link-
   address.  If the client is on a single link, the server SHOULD return
   the client's data in an OPTION_CLIENT_DATA option.

4.1.3.  Status Codes

   The following new status codes are defined:

   UnknownQueryType (7) -  The query-type is unknown to or not supported
      by the server.

   MalformedQuery (8) -  The query is not valid; for example, a required
      query-option is missing from the OPTION_LQ_QUERY.

   NotConfigured (9) -  The server does not have the target address or
      link in its configuration.

   NotAllowed (10) -  The server does not allow the requestor to issue
      this LEASEQUERY.

4.1.4.  Transmission and Retransmission Parameters

   This section presents a table of values used to describe the message
   transmission behavior for leasequery.

   Parameter     Default  Description
   ----------------------------------
   LQ_TIMEOUT     1 sec   Initial LEASEQUERY timeout
   LQ_MAX_RT     10 secs  Max LEASEQUERY timeout value
   LQ_MAX_RC      5       Max LEASEQUERY retry attempts

4.2.  Message Validation

4.2.1.  LEASEQUERY

   Requestors and clients MUST discard any received LEASEQUERY messages.

   Servers MUST discard any received LEASEQUERY messages that meet any
   of the following conditions:

   o  the message does not include an OPTION_CLIENTID option.

   o  the message includes an OPTION_SERVERID option but the contents of
      the OPTION_SERVERID option does not match the server's identifier.

   o  the message does not include an OPTION_LQ_QUERY option.

4.2.2.  LEASEQUERY-REPLY

   Requestors MUST discard any received LEASEQUERY-REPLY messages that
   meet any of the following conditions:

   o  the message does not include an OPTION_SERVERID option.

   o  the message does not include an OPTION_CLIENTID option, or the
      contents of the OPTION_CLIENTID option do not match the DUID of
      the requestor.

   o  the "transaction-id" field in the message does not match the value
      used in the original message.

   Servers and Relay Agents (on the server port, 547 [2]) MUST discard
   any received LEASEQUERY-REPLY messages.

4.3.  DHCPv6 Leasequery Requestor Behavior

   This section describes how a requestor initiates lease data retrieval
   from DHCPv6 servers.

4.3.1.  Creation of LEASEQUERY

   The requestor sets the "msg-type" field to LEASEQUERY.  The requestor
   generates a transaction ID and inserts this value in the
   "transaction-id" field.

   The requestor MUST include an OPTION_CLIENTID option to identify
   itself to the server.

   The requestor MUST include an OPTION_LQ_QUERY option and set the
   query-type, link-address, and query-options as appropriate to the
   query-type (Section 4.1.2.1).

   The requestor SHOULD include an OPTION_SERVERID if it is not
   unicasting the LEASEQUERY yet only wants a response from a specific
   server.

4.3.2.  Transmission of LEASEQUERY

   The requestor MAY be configured to use a list of destination
   addresses, which MAY include unicast addresses, the All_DHCP_Servers
   multicast address, or other addresses selected by the network
   administrator.  If the requestor has not been explicitly configured,
   it MAY use the All_DHCP_Servers multicast address as the default.

   The requestor SHOULD send LEASEQUERY to one or more DHCPv6 servers
   that are known to possess authoritative information concerning the
   query target.

   In the absence of information concerning which DHCPv6 servers might
   possess authoritative information on the query target, the requestor
   SHOULD send LEASEQUERY to all DHCPv6 servers that the requestor knows
   about or is configured with.  For example, the requestor MAY send
   LEASEQUERY to the All_DHCP_Servers multicast address.

   The requestor transmits LEASEQUERY messages according to Section 14
   of [2], using the following parameters:

       IRT    LQ_TIMEOUT
       MRT    LQ_MAX_RT
       MRC    LQ_MAX_RC
       MRD    0

   If the message exchange fails, the requestor takes an action based on
   the requestor's local policy.  Examples of actions the requestor
   might take include:

   o  Select another server from a list of servers known to the
      requestor.

   o  Send to multiple servers by multicasting to the All_DHCP_Servers
      address.

   o  Terminate the request.

4.3.3.  Receipt of LEASEQUERY-REPLY

   A successful LEASEQUERY-REPLY is one without an OPTION_STATUS_CODE
   option (or an OPTION_STATUS_CODE option with a success code).  There
   are three variants:

   1.  If the server had bindings for the requested client, the message
       includes an OPTION_CLIENT_DATA option and the requestor extracts
       the client data from the LEASEQUERY-REPLY and updates its binding
       information database.  If the OPTION_CLIENT_DATA contains no
       OPTION_CLT_TIME, the requestor SHOULD silently discard the
       OPTION_CLIENT_DATA option.

   2.  If the server found bindings for the client on multiple links,
       the message includes an OPTION_CLIENT_LINK option.  The requestor
       will need to reissue LEASEQUERY messages using each of the
       returned link-addresses to obtain the client's bindings.

   3.  If the server had no bindings for the client, neither the
       OPTION_CLIENT_DATA nor OPTION_CLIENT_LINK option will be present.

   An unsuccessful LEASEQUERY-REPLY is one that has an
   OPTION_STATUS_CODE with an error code.  Depending on the status code,
   the requestor may try a different server (such as for NotAllowed,
   NotConfigured, and UnknownQueryType), try a different or corrected
   query (such as for UnknownQueryType and MalformedQuery), or terminate
   the query.

4.3.4.  Handling DHCPv6 Client Data from Multiple Sources

   A requestor may receive lease data on the same client from the same
   DHCPv6 server in response to different types of LEASEQUERY.  If a
   LEASEQUERY is sent to multiple servers, the requestor may receive
   from several servers lease data on the same DHCPv6 client.  This
   section describes how the requestor handles multiple lease data
   sources on the same DHCPv6 client from the same server or different
   servers.

   The client data from the different sources may be disjoint or
   overlapping.  The disjoint and overlapping relationship can happen
   between data from the same server or different servers.

   If client data from two sources on the same client are of different
   types or values, then the data are disjoint.  An example of data of
   different types is when a requestor receives an IPv6 address lease
   from one server and a prefix lease from another server, both assigned
   to the same client.  An example of different values (but the same
   type) is when a requestor receives two IPv6 address leases from two
   different servers, both assigned to the same client, but the leases
   are on two different IPv6 addresses.  If the requestor receives
   disjoint client data from different sources, it SHOULD merge them.

   If client data from two sources on the same client are of the same
   type and value, then the data are overlapping.  An example of
   overlapping data is when a requestor receives a lease on the same
   IPv6 address from two different servers.  Overlapping client data are
   also called conflicting data.

   The requestor SHOULD use the OPTION_CLT_TIME to resolve data
   conflicts originated from different servers, and SHOULD accept data
   with most recent OPTION_CLT_TIME.

4.4.  DHCPv6 Leasequery Server Behavior

   A DHCPv6 server sends LEASEQUERY-REPLY messages in response to valid
   LEASEQUERY messages it receives to return the statefully assigned
   addresses, delegated prefixes, and other information that match the
   query.

4.4.1.  Receipt of LEASEQUERY Messages

   Upon receipt of a valid LEASEQUERY message, the DHCPv6 server locates
   the requested client, collects data on the client, and constructs and
   returns a LEASEQUERY-REPLY.  A LEASEQUERY message cannot be used to
   assign, release, or otherwise modify bindings or other configuration
   information.

   The server constructs a LEASEQUERY-REPLY message by setting the "msg-
   type" field to LEASEQUERY-REPLY, and copying the transaction ID from
   the LEASEQUERY message into the transaction-id field.

   If the query-type in the OPTION_LQ_QUERY option is not a known or
   supported value, the server adds an OPTION_STATUS_CODE option with
   the UnknownQueryType status code and sends the LEASEQUERY-REPLY to
   the requestor.  If the query-options do not contain the required
   options for the query-type, the server adds an OPTION_STATUS_CODE
   option with the MalformedQuery status code and sends the LEASEQUERY-
   REPLY to the client.

   A server may also restrict LEASEQUERY messages, or query-types, to
   certain requestors.  In this case, the server MAY discard the
   LEASEQUERY message or MAY add an OPTION_STATUS_CODE option with the
   NotAllowed status code and send the LEASEQUERY-REPLY to the
   requestor.

   If the OPTION_LQ_QUERY specified a non-zero link-address, the server
   MUST use the link-address to find the appropriate link for the
   client.  For a QUERY_BY_ADDRESS, if the 0::0 link-address was
   specified, the server uses the address from the OPTION_IAADDR option
   to find the appropriate link for the client.  In either of these
   cases, if the server is unable to find the link, it SHOULD return an
   OPTION_STATUS_CODE option with the NotConfigured status and send the
   LEASEQUERY-REPLY to the requestor.

   For a QUERY_BY_CLIENTID, if a 0::0 link-address was specified, the
   server MUST search all of its links for the client.  If the client is
   only found on a single link, the server SHOULD return that client's
   data in an OPTION_CLIENT_DATA option.  If the client is found on more
   than a single link, the server MUST return the list of links in the
   OPTION_CLIENT_LINK option; the server MUST NOT return any client
   data.

   Otherwise, the server uses the data in the OPTION_LQ_QUERY to
   initiate the query.  The result of the query will be zero or one
   client.  This will result in zero or one OPTION_CLIENT_DATA option
   being added to the LEASEQUERY-REPLY.

4.4.2.  Constructing the Client's OPTION_CLIENT_DATA

   An OPTION_CLIENT_DATA option in a LEASEQUERY-REPLY message MUST
   minimally contain the following options:
   1.  OPTION_CLIENTID
   2.  OPTION_IAADDR and/or OPTION_IAPREFIX
   3.  OPTION_CLT_TIME

   Depending on the bindings the client has on a link, either
   OPTION_IAADDR options, OPTION_IAPREFIX options, or both may be
   present.

   The OPTION_CLIENT_DATA SHOULD include options requested in the
   OPTION_ORO of the OPTION_LQ_QUERY option in the LEASEQUERY message
   and that are acceptable to return based on the list of "sensitive
   options", discussed below.

   DHCPv6 servers SHOULD be configurable with a list of "sensitive
   options" that must not be returned to the requestor when specified in
   the OPTION_ORO of the OPTION_LQ_QUERY option in the LEASEQUERY
   message.  Any option on this list MUST NOT be returned to a
   requestor, even if requested by that requestor.

4.4.3.  Transmission of LEASEQUERY-REPLY Messages

   The server sends the LEASEQUERY-REPLY message as described in the
   "Transmission of Reply Messages" section of [2].

5.  Security Considerations

   Access concentrators are expected to be common leasequery requestors.
   Access concentrators that use DHCPv6 gleaning (i.e., [10]), refreshed
   with LEASEQUERY messages, will maintain accurate client/binding
   information.  This ensures that the access concentrator can forward
   data traffic to the intended destination in the broadband access
   network, can perform IPv6 source address verification of datagrams
   from the access network, and can encrypt traffic that can only be
   decrypted by the intended access modem (e.g., [12] and [13]).  Thus,
   the leasequery capability allows an access concentrator to provide
   considerably enhanced security.

   The "Security Considerations" section of [2] details the general
   threats to DHCPv6, and thus to LEASEQUERY messages.  The
   "Authentication of DHCP Messages" section of [2] describes securing
   communication between relay agents and servers, as well as clients
   and servers.  If the requestor is an access concentrator, the IPsec-
   based [9] security as described in [2] Section 21.1 SHOULD be used.
   Other types of requestors are essentially DHCPv6 clients.  Thus,
   DHCPv6 authentication, Section 21 of [2], is an appropriate mechanism
   for securing LEASEQUERY and LEASEQUERY-REPLY messages.  As the number
   of leasequery requestors and servers in an administrative domain is
   relatively small, any shared key distribution issues are minimized.

   After implementing the above approaches, the DHCPv6 server should
   only be communicating with trusted LEASEQUERY requestors, and so
   security needs should be met.

   However, not all traffic originates directly from these trusted
   requestors.  For example, trusted relay agents can relay LEASEQUERY
   messages from untrusted requestors or elsewhere in the network.  This
   SHOULD be prevented at least at the perimeter relay agents (or on all
   relay agents unless relayed LEASEQUERY messages are required for some
   requestors).  DHCPv6 servers MAY be configured to discard relayed
   LEASEQUERY messages or restrict relay chaining.

   DHCPv6 servers SHOULD also provide for the ability to restrict the
   information returned for a client in a LEASEQUERY-REPLY even to a
   trusted LEASEQUERY requestor, as described in Section 4.4.2.

   Since even trusted access concentrators may generate LEASEQUERY
   requests as a result of activity external to the access concentrator,
   access concentrators SHOULD minimize potential denial-of-service
   attacks on the DHCPv6 servers by minimizing the generation of
   LEASEQUERY messages.  In particular, the access concentrator SHOULD
   employ negative caching (i.e., cache the fact that a particular
   recent query failed to return client data) and address restrictions
   where possible (i.e., don't send a LEASEQUERY message for addresses
   outside the range of the attached broadband access networks).
   Together, these mechanisms limit the access concentrator to
   transmitting one LEASEQUERY message (excluding message retries) per
   legitimate broadband access network address after a reboot event.

   Packet-flooding denial-of-service attacks can result in the
   exhaustion of processing resources, thus preventing the server from
   serving legitimate and regular DHCPv6 clients as well as legitimate
   DHCPv6 LEASEQUERY requestors, denying configurations to legitimate
   DHCPv6 clients as well lease information to legitimate DHCPv6
   LEASEQUERY requestors.  While these attacks are unlikely when only
   communicating with trusted LEASEQUERY requestors, the possibility
   always exists that the trust is misplaced, security techniques are
   compromised, or even trusted requestors can have bugs in them.
   Therefore, techniques for defending against packet-flooding denial of
   service are always a good idea, and they include good perimeter
   security, as mentioned earlier, and rate limiting DHCPv6 traffic by
   relay agents, other network elements, or the server itself.

   One way to attack an access concentrator (as opposed to a DHCPv6
   server) as a LEASEQUERY requestor is the establishment of a malicious
   server with the intent of providing incorrect lease or route
   information to the access concentrator, thwarting source IPv6 address
   verification, and preventing correct routing.  This type of attack
   can be minimized by using IPsec as described in Section 21.1 of [2].

6.  IANA Considerations

   IANA has assigned the following new DHCPv6 Message types in the
   registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters:

      LEASEQUERY
      LEASEQUERY-REPLY

   IANA has assigned the following new DHCPv6 Option Codes in the
   registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters:

      OPTION_LQ_QUERY
      OPTION_CLIENT_DATA
      OPTION_CLT_TIME
      OPTION_LQ_RELAY_DATA
      OPTION_LQ_CLIENT_LINK

   IANA has assigned the following new DHCPv6 Status Codes in the
   registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters:

      UnknownQueryType
      MalformedQuery
      NotConfigured
      NotAllowed
   IANA has created a new registry for the OPTION_LQ_QUERY option query-
   type codes in the registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters with the following
   initial assignments:

      QUERY_BY_ADDRESS       1
      QUERY_BY_CLIENTID      2

   New OPTION_LQ_QUERY option query-type codes are assigned through
   Standards Action, as defined in [6].

7.  Acknowledgements

   Thanks to Ralph Droms, Richard Johnson, Josh Littlefield, Hemant
   Singh, Pak Siripunkaw, Markus Stenberg, and Ole Troan for their
   input, ideas, and review during the production of this document.

8.  References

8.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
         Carney, "Dynamic Host Configuration Protocol for IPv6
         (DHCPv6)", RFC 3315, July 2003.

   [3]   Woundy, R. and K. Kinnear, "Dynamic Host Configuration Protocol
         (DHCP) Leasequery", RFC 4388, February 2006.

   [4]   Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
         Configuration Protocol (DHCP) version 6", RFC 3633,
         December 2003.

8.2.  Informative References

   [5]   Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
         March 1997.

   [6]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434,
         October 1998.

   [7]   Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
         for IP Version 6 (IPv6)", RFC 2461, December 1998.

   [8]   Plummer, D., "Ethernet Address Resolution Protocol: Or
         converting network protocol addresses to 48.bit Ethernet
         address for transmission on Ethernet hardware", STD 37,
         RFC 826, November 1982.

   [9]   Kent, S. and K. Seo, "Security Architecture for the Internet
         Protocol", RFC 4301, December 2005.

   [10]  Droms, R., "DHCPv6 Relay Agent Assignment Notification (RAAN)
         Option", Work in Progress, November 2006.

   [11]  CableLabs, "Data-Over-Cable Service Interface Specifications:
         DOCSIS 3.0, MAC and Upper Layer Protocols Interface
         Specification, CM-SP-MULPIv3.0-I04-070518", May 2007, available
         at http://www.cablemodem.com/.

   [12]  SCTE Data Standards Subcommittee, "Data-Over-Cable Service
         Interface Specifications: DOCSIS 1.0 Baseline Privacy Interface
         Specification SCTE 22-2 2002", 2002, available at
         http://www.scte.org/standards/.

   [13]  CableLabs, "Data-Over-Cable Service Interface Specifications:
         Baseline Privacy Plus Interface Specification CM-SP-BPI+_I12-
         050812", August 2005, available at http://www.cablemodem.com/.

Authors' Addresses

   John Jason Brzozowski
   Comcast Cable
   1800 Bishops Gate Boulevard
   Mt. Laurel, NJ  08054
   USA

   Phone: +1 856 324 2671
   EMail: john_brzozowski@cable.comcast.com


   Kim Kinnear
   Cisco Systems, Inc.
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

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


   Bernard Volz
   Cisco Systems, Inc.
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

   Phone: +1 978 936 0000
   EMail: volz@cisco.com


   Shengyou Zeng
   Cisco Systems, Inc.
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

   Phone: +1 978 936 0000
   EMail: szeng@cisco.com

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