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Versions: 00 01 draft-ietf-dhc-dhcpv4-bulk-leasequery

DHC Working Group                                            Kim Kinnear
Internet Draft                                               Bernie Volz
Intended Status: Standards Track                            Neil Russell
Expires: May 3, 2009                                          Mark Stapp
                                                     Cisco Systems, Inc.
                                                                  D. Rao
                                                                B. Joshi
                                                             P. Kurapati
                                               Infosys Technologies Ltd.
                                                        November 3, 2008


                        Bulk DHCPv4 Lease Query
           <draft-kinnear-dhc-dhcpv4-bulk-leasequery-01.txt>

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on January 7, 2009

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) has been
   extended with a Leasequery capability that allows a requestor to



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   request information about DHCPv4 bindings.  That mechanism is limited
   to queries for individual bindings.  In some situations individual
   binding queries may not be efficient, or even possible.  This
   document expands on the DHCPv4 Leasequery protocol to allow for bulk
   transfer of DHCPv4 address binding data via TCP.

Table of Contents


    1.  Introduction................................................. 3
    2.  Terminology.................................................. 4
    3.  Motivation................................................... 6
    4.  Design Goals................................................. 8
    4.1.  Information Acquisition before Data Starts................. 8
    4.2.  Lessen Negative Caching.................................... 8
    4.3.  Antispoofing in 'Fast Path'................................ 8
    4.4.  Minimize data transmission................................. 8
    5.  Protocol Overview............................................ 9
    6.  Interaction Between UDP Leasequery and Bulk Leasequery....... 10
    7.  Message and Option Definitions............................... 11
    7.1.  Message Framing for TCP.................................... 11
    7.2.  New or Changed Options..................................... 12
    7.3.  Connection and Transmission Parameters..................... 20
    8.  Requestor Behavior........................................... 20
    8.1.  Connecting and General Processing.......................... 20
    8.2.  Forming a Bulk Leasequery.................................. 21
    8.3.  Processing Bulk Replies.................................... 23
    8.4.  Processing Time Values in Leasequery messages.............. 25
    8.5.  Querying Multiple Servers.................................. 27
    8.6.  Making Sense Out of Multiple Responses Concerning a Single. 27
    8.7.  Multiple Queries to a Single Server over One Connection.... 28
    8.8.  Closing Connections........................................ 29
    9.  Server Behavior.............................................. 30
    9.1.  Accepting Connections...................................... 30
    9.2.  Replying to a Bulk Leasequery.............................. 30
    9.3.  Building a Single Reply for Bulk Leasequery................ 34
    9.4.  Multiple or Parallel Queries............................... 35
    9.5.  Closing Connections........................................ 36
    10.  Security Considerations..................................... 36
    11.  IANA Considerations......................................... 37











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    12.  Acknowledgements............................................ 38
    13.  References.................................................. 38
    13.1.  Normative References...................................... 38
    13.2.  Informative References.................................... 39
    14.  Authors' Addresses.......................................... 39
    15.  Full Copyright Statement.................................... 41
    16.  Intellectual Property....................................... 41
    17.  Acknowledgment.............................................. 41
    18.  Appendix -- Why a New Leasequery is Required................ 42



1.  Introduction

   The DHCPv4 protocol [RFC2131] [RFC2132] specifies a mechanism for the
   assignment of IPv4 address and configuration information to IPv4
   nodes.  DHCPv4 servers maintain authoritative binding information.


      +--------+
      | DHCPv4 |     +--------------+
      | Server |-...-|    DSLAM     |
      |        |     |  Relay Agent |
      +--------+     +--------------+
                          |        |
                      +------+   +------+
                      |Modem1|   |Modem2|
                      +------+   +------+
                         |        |    |
                      +-----+  +-----+ +-----+
                      |Host1|  |Host2| |Host3|
                      +-----+  +-----+ +-----+

                  Figure 1:  Example DHCPv4 configuration


   DHCPv4 relay agents receive DHCPv4 messages and frequently append a
   relay agent information option [RFC3046] before relaying them to the
   configured DHCPv4 servers (see Figure 1).  In this process, some
   relay agents also glean the lease information sent by the server and
   maintain this locally.  This information is used for a variety of
   purposes, including prevention of spoofing attempts from the DHCPv4
   clients and to install routes.  When a relay agent reboots, this
   information is frequently lost.

   The DHCPv4 Leasequery capability [RFC4388] extends the basic DHCPv4
   capability to allow an external entity, such as a relay agent, to



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   query a DHCPv4 server to recover lease state information about a
   particular IP address or client in near real-time.

   The existing query types in Leasequery are typically data driven; the
   relay agent initiates the Leasequery when it receives data traffic
   from or to the client.  This approach may not scale well when there
   are thousands of clients connected to the relay agent or when the
   relay agent has a need to rebuild its internal data store prior to
   processing traffic in one direction or another.

   Different query types are needed where a relay agent can query the
   server without waiting for the traffic from or for the clients, as
   well as a different transmission technique more conducive to the
   transmission of large quantities of data.

   This document extends the DHCPv4 Leasequery protocol to add support
   for queries that address these additional requirements.  There may be
   many thousands of DHCPv4 bindings returned as the result of a single
   request, so TCP [RFC4614] is specified for efficiency of data
   transfer.  We define several additional query types, each of which
   could return multiple responses, in order to meet a variety of
   requirements.


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].

   This document uses the following terms:

      o "absolute time"

        A 32-bit quantity containing the number of seconds since Jan 1,
        1970.

      o "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
        DHCPv4 relay agent functionality.

      o "active binding"

        An IP address with an active binding refers to an IP address
        which is currently associated with a DHCPv4 client where that



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        DHCPv4 client has the right to use the IP address.

      o "Bulk Leasequery"

        Requesting and receiving the existing DHCPv4 address binding
        information in an efficient manner.

      o "clock skew"

        The difference between the absolute time on a DHCPv4 server and
        the absolute time on the system where a requestor of a Bulk
        Leasequery is executing is termed the "clock skew" for that Bulk
        Leasequery connection.  It is not absolutely constant but is
        likely to vary only slowly.  It is possible that, when both
        systems run NTP, that the clock skew is zero, and this is not
        only acceptable, but desired.

        While it is easy to think that this can be calculated precisely
        after one message is received by a requestor from a DHCPv4
        server, a more accurate value is derived from continuously
        examining the instantaneous value developed from each message
        received from a DHCPv4 server and using it to make small
        adjustments to the existing value held in the requestor.

      o "DHCPv4 client"

        A DHCPv4 client is an Internet host using DHCPv4 to obtain
        configuration parameters such as a network address.

      o "DHCPv4 relay agent"

        A DHCPv4 relay agent is a third-party agent that transfers BOOTP
        and DHCPv4 messages between clients and servers residing on
        different subnets, per [RFC951] and [RFC1542].

      o "DHCPv4 server"

        A DHCPv4 server is an Internet host that returns configuration
        parameters to DHCPv4 clients.

      o "downstream"

        Refers to a direction away from the central part of a network
        and toward the edge.  In a DHCPv4 context, typically refers to a
        network direction which is away from the DHCPv4 server.

      o "IP address"




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        In this document, the term "IP address" refers to an IPv4 IP
        address.

      o "IP address binding"

        The information that a DHCPv4 server keeps regarding the
        relationship between a DHCPv4 client and an IPv4 IP address.
        This includes the identity of the DHCPv4 client and the
        expiration time, if any, of any lease that client has on a
        particular IPv4 address.  In some contexts, this may include
        information on IP addresses that are currently associated with
        DHCPv4 clients, and in others it may also include IP addresses
        with no current association to a DHCPv4 client.

      o "MAC address"

        In the context of a DHCPv4 message, a MAC address consists of
        the fields: hardware type "htype", hardware length "hlen", and
        client hardware address "chaddr".

      o "upstream"

        Refers to a direction toward the central part of a network and
        away from the edge.  In a DHCPv4 context, typically refers to a
        network direction which is toward the DHCPv4 server.

      o "stable storage"

        Stable storage is used to hold information concerning IP address
        bindings (among other things) so that this information is not
        lost in the event of a failure which requires restart of the
        network element.  DHCPv4 servers are typically expected to have
        high speed access to stable storage, while relay agents and
        access concentrators usually do not have access to stable
        storage, although they may have periodic access to such storage.

      o "xid"

        Transaction-id.  The term "xid" refers to the DHCPv4 field
        containing the transaction-id of the message.


3.  Motivation

   Consider a typical DSLAM working also as a DHCPv4 relay agent (see
   Figure 1). Typically, both a "fast path" and a "slow path" exist in
   many network elements, including DSLAMs.  Fast path processing is
   done in a network processor or in an ASIC (Application Specific



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   Integrated Circuit).  Slow path processing is done in a normal
   processor.  As much as possible, regular data handling code should be
   in the fast path.  Slow path processing should be reduced as it may
   become a bottleneck.

   For a DSLAM having multiple DSL ports, multiple IP addresses may be
   assigned using DHCPv4 to a single port and the number of DHCPv4
   clients on a port may be unknown.  The DSLAM may also not know the
   network portions of the IP addresses that are assigned to its DHCPv4
   clients.

   The DSLAM gleans IP address or other information from DHCP
   negotiations for antispoofing and for other purposes.  The
   antispoofing itself is done in the fast path. The DSLAM keeps track
   of only one list of IP addresses: the list of IP addresses that are
   assigned by a DHCPv4 server.  Traffic for all other IP addresses is
   dropped.  If a client starts its data transfer after its DHCPv4
   negotiations are gleaned by the DSLAM, no legitimate packets will be
   dropped because of antispoofing.  In other words, antispoofing is
   effective (no legitimate packets are dropped and all spoofed packets
   are dropped) and efficient (antispoofing is done in the fast path).
   The intention is to achieve similar effective and efficient
   antispoofing in the Leasequery scenario after a DSLAM loses its
   gleaned information (for example, because of reboot).

   After a deep analysis, we found that the three existing query types
   supported by [RFC4388] do not provide effective and efficient
   antispoofing for the above scenario and a new mechanism is required.

   The existing query types

      o necessitate a data driven approach: the lease queries can only
        be done when the Access Concentrator receives data.  That
        results in increased outage time for DHCPv4 clients.

      o result in excessive negative caching consuming lot of resources
        under a spoofing attack.

      o result in antispoofing being done in the slow path instead of
        the fast path.

      o do not support an Access Concentrator which periodically uploads
        its internal table to some form of stable storage

   The deeper analysis, which led to the above conclusions, itself
   appears as an Appendix to this document.





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4.  Design Goals

   The goal of this document is to provide a lightweight mechanism for
   an Access Concentrator or other network element to retrieve IP
   address binding information available in the DHCPv4 server.  The
   mechanism should also allow an Access Concentrator to retrieve
   consolidated IP address binding information for the entire access
   concentrator or for a single connection/circuit.


4.1.  Information Acquisition before Data Starts

   The existing data driven approach required by [RFC4388] means that
   the Leasequeries can only be performed after an Access Concentrator
   receives data.  To implement antispoofing, packets need to be dropped
   until it gets the lease information from DHCPv4 server.  If an Access
   Concentrator finishes the Leasequeries before it starts receiving
   data, then there is no need to drop legitimate packets.  In this way,
   outage time may be reduced.


4.2.  Lessen Negative Caching

   If Leasequeries result in negative caches, then that puts additional
   overhead on the access concentrator.  The negative caches not only
   consume precious resources, they also need to be managed.  Hence they
   should be avoided as much as possible.  The Leasequeries should
   reduce the need for negative caching as far as possible.


4.3.  Antispoofing in 'Fast Path'

   If Antispoofing is not done in fast path, it will become a bottleneck
   and may lead to denial of service of the access concentrator.  The
   Leasequeries should make it possible to do antispoofing in fast path.


4.4.  Minimize data transmission


   It may be that a network element is able to periodically save its
   entire list of assigned IP addresses to some form of stable storage.
   In this case, it will wish to recover all of the updates to this
   information without duplicating the information it has recovered from
   its own stable storage.

   Bulk Leasequery allows specification of a query-start-time as well as
   a query-end-time.  Use of query-times allows a network element that



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   periodically commits information to stable storage to recover just
   what it lost since the last commit.


5.  Protocol Overview

   The Bulk Leasequery mechanism is modeled on the existing individual
   Leasequery protocol in [RFC4388] as well as related work on DHCPv6
   Bulk Leasequery [DHCPv6Bulk]. A Bulk Leasequery requestor opens a TCP
   connection to a DHCPv4 Server, using the DHCPv4 port 67.  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 DHCPv4 server.  No relaying of Bulk
   Leasequery messages is specified.

   After establishing a connection, the requestor sends a
   DHCPBULKLEASEQUERY message over the connection.

   The server uses the message type and additional data in the DHCPv4
   DHCPBULKLEASEQUERY message to identify any relevant bindings.

   In order to support some query types, servers may have to maintain
   additional data structures or otherwise be able to locate bindings
   that have been requested by the Leasequery requestor.

   The Bulk Leasequery mechanism is designed to provide an external
   entity with information concerning existing DHCPv4 IPv4 address
   bindings managed by the DHCPv4 server.  When complete, the DHCPv4
   server will send a DHCPLEASEQUERYDONE message.  If a connection is
   lost while processing a Bulk Leasequery, the Bulk Leasequery must be
   retried as there is no provision for determining the extent of data
   already received by the requestor for a Bulk Leasequery.

   Bulk Leasequery supports queries by MAC address, and Client
   Identifier in a way similar to [RFC4388].  The Bulk Leasequery
   protocol also adds several new queries.

      o Query by Relay Identifier

        This query asks a server for the bindings associated with a
        specific relay agent; the relay agent is identified by a DUID
        carried in a Relay-ID sub-option [RelayId]. Relay agents can
        include this sub-option while relaying messages to DHCPv4
        servers.  Servers can retain the Relay-ID and associate it with
        bindings made on behalf of the relay agent's clients. The
        bindings returned are only those for DHCPv4 clients with a
        currently active binding.




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      o Query by Remote ID

        This query asks a server for the bindings associated with a
        Relay Agent Remote-ID sub-option [RFC3046] value. The bindings
        returned are only those for DHCPv4 clients with a currently
        active binding.

      o Query for All Configured IP Addresses

        This query asks a server for information concerning all IP
        addresses configured in that DHCPv4 server, by specifying no
        other type of query. In this case, the bindings returned are for
        all configured IP addresses, whether or not they contain a
        currently active binding to a DHCPv4 client, since one point of
        this type of query is to update an existing database with
        changes after a particular point in time.

   Any of the above queries can be qualified by the specification of a
   query-start-time or a query-end-time (or both). In the event these
   times are used as qualifiers they indicate that a binding should be
   included if it changed on or after the query-start-time and on or
   before the query-end-time.

   In addition, any of the above queries can be qualified by the
   specification of a vpn-id option [VpnId] to select the VPN on which
   the query should be processed.  The vpn-id option is also extended to
   allow queries across all available VPNs. By default, only the default
   VPN is used to satisfy the query.


6.  Interaction Between UDP Leasequery and Bulk Leasequery

   Bulk Leasequery can be seen as an extension of the existing UDP
   Leasequery protocol [RFC4388].  This section clarifies the
   relationship between the two protocols.

   Only the DHCPBULKLEASEQUERY request is supported over the Bulk
   Leasequery connection. No other DHCPv4 requests are supported.  The
   Bulk Leasequery connection is not an alternative DHCPv4 communication
   option for clients seeking other DHCPv4 services.

   Two of the query-types introduced in the UDP Leasequery protocol can
   be used in the Bulk Leasequery protocol -- query by MAC address and
   query by client-id.

   One change in behavior for these existing queries is required when
   Bulk Leasequery is used.  [RFC4388], in sections 6.1, 6.4.1, and
   6.4.2 specifies the use of an associated-ip option in DHCPLEASEACTIVE



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   messages in cases where multiple bindings were found.  When Bulk
   Leasequery is used, this mechanism is not necessary; a server
   returning multiple bindings simply does so directly as specified in
   this document.  The associated-ip option MUST NOT appear in Bulk
   Leasequery replies.

   The contents of the reply messages are similar between the existing
   UDP Leasequery protocol and the Bulk Leasequery protocol, though more
   information is returned in the Bulk Leasequery messages and, as
   discussed above, the associated-ip option MUST NOT be used.

7.  Message and Option Definitions


7.1.  Message Framing for TCP

   The use of TCP for the Bulk Leasequery protocol permits multiple
   messages to be sent from one end of the connection to the other
   without requiring a request/response paradigm as does UDP DHCPv4
   [RFC2131].  The receiver needs to be able to determine the size of
   each message it receives.  Two octets containing the message size in
   network byte-order are prepended to each DHCPv4 message sent on a
   Bulk Leasequery TCP connection. The two message-size octets 'frame'
   each DHCPv4 message.

   The maximum message size is 65535 octets.

   DHCPv4 message framed for TCP:























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       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         message-size          |    op (1)     |   htype (1)   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   hlen (1)    |   hops (1)    |              ....             |
      +---------------+---------------+                               +
      |                                                               |
      .                  remainder of DHCPv4 message,
      .                   from Figure 1 of [RFC2131]                  .
      .                                                               .
      .                           (variable)                          .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


           message-size    the number of octets in the message that
                           follows, as a 16-bit integer in network
                           byte-order.

           All other fields are as specified in DHCPv4 [RFC2131].


                  Figure 2:  Format of a DHCPv4 message in TCP

   The intent in using this format is that code which currently knows
   how to deal with sending or receiving a message in [RFC2131] format
   will easily be able to deal with the message contained in the TCP
   framing.

7.2.  New or Changed Options

   The existing messages DHCPLEASEUNASSIGNED and DHCPLEASEACTIVE are
   used as the value of the dhcp-message-type option to indicate an IP
   address which is currently not leased or currently leased to a DHCPv4
   client, respectively [RFC4388].

   Additional options have also been defined to enable the Bulk
   Leasequery protocol to communicate useful information to the
   requestor.


7.2.1.  dhcp-message-type

   The dhcp-message-type option (option 53) from Section 9.6 of
   [RFC2132] requires new values.  The values of these message types are



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   shown below in an extension of the table from Section 9.6 of
   [RFC2132]:

            Value   Message Type
            -----   ------------
              14    DHCPBULKLEASEQUERY
              15    DHCPLEASEQUERYDONE


7.2.2.  dhcp-message

   The dhcp-message option (option 56) from Section 9.9 of [RFC2132]
   requires additional definition for use in the context of a
   DHCPBULKLEASEQUERY.

   The format of the NVT ASCII message in the dhcp-message option is
   specified to have the first three characters appear in a constrained
   format.  The first three characters MUST be numeric (base 10)
   characters.

   Encoded in these first three characters is the decimal number
   corresponding to a variety of status codes defined below.

   The motivation for this constraint of the existing dhcp-message
   option is to reduce the number of top-level options used by this
   document.

   The status code returned in the dhcp-message option allows greater
   detail to be returned regarding the status of a DHCPBULKLEASEQUERY
   request.  While specified in the Bulk Leasequery document, this
   additional specification of the DHCPv4 dhcp-message option may well
   be valuable in other circumstances.  In those circumstances its scope
   should be explicitly defined.

   This option has two possible scopes when used with Bulk Leasequery,
   depending on the context in which it appears. It refers to the
   information in a single Leasequery reply if the value of the dhcp-
   message-type is DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED.  It refers to
   the message stream related to an entire request if the value of the
   dhcp-message-type is DHCPLEASEQUERYDONE.

   The code for this option is 56. The length of this option is at least
   3 octets.








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       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-code  |  option-len   | left-number   | middle-number |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | right-number  |    status-message (if any)   ...              .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         option-code     56.

         option-len      3 + length of status-message (which may be 0).

         left-number     NVT ASCII encoded characters representing the
         middle-number   base-10 value of the status code, taken
         right-number    from the table below.

         status-message  An optional NVT ASCII encoded text string
                         suitable for display to an end user, which
                         MUST NOT be null-terminated.  It SHOULD
                         start with an NVT ASCII space.



     Name    status-code Description
     ----    ----------- -----------
     Success         000 Success.  Also signaled by absence of
                         dhcp-message option.

     UnspecFail      001 Failure, reason unspecified.

     QueryTerminated 002 Indicates that the server is unable to
                         perform a query or has prematurely terminated
                         the query for some reason (which should be
                         communicated in the text message).

     MalformedQuery  003 The query was not understood.

     NotAllowed      004 The query or request was understood but was
                         not allowed in this context.


   A dhcp-message option MAY appear in the options field of a DHCPv4
   message.  If the dhcp-message option does not appear, it is assumed
   that the operation was successful.  The dhcp-message option SHOULD
   NOT appear in a message which is successful unless there is some text
   string that needs to be communicated to the requestor.




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7.2.3.  base-time

   The base-time option is the current time the message was created to
   be sent by the DHCPv4 server to the requestor of the Bulk Leasequery.
   This MUST be an absolute time. All of the other time based options in
   the reply message are relative to this time, including the dhcp-
   lease-time [RFC2132] and client-last-transaction-time [RFC4388].
   This time is in the context of the DHCPv4 server.

   This is an integer in network byte order.

   The code for this option is TBD. The length of this option is 4
   octets.

                       DHCPv4 Server
       Code   Len        Base Time
      +-----+-----+-----+-----+-----+-----+
      | TBD |  4  |  t1 |  t2 |  t3 |  t4 |
      +-----+-----+-----+-----+-----+-----+



7.2.4.  start-time-of-state

   The start-time-of-state option allows the receiver to determine the
   time at which the IP address transitioned into its current state.

   This MUST NOT be an absolute time.  This MUST NOT be an absolute
   number of seconds since Jan 1, 1970.  Instead, this MUST be an
   integer number of seconds in the past from the time specified in the
   base-time option in the same message that the IP address transitioned
   into its current state.  In the same way that the IP Address Lease
   Time option (option 51) encodes a lease time which is a number of
   seconds into the future from the time the message was sent, this
   option encodes a value which is a number of seconds into the past
   from the base-time option included in the same message.

   This is an integer in network byte order.

   The code for this option is TBD. The length of this option is 4
   octets.

                     Seconds in the past
       Code   Len      from base-time
      +-----+-----+-----+-----+-----+-----+
      | TBD |  4  |  t1 |  t2 |  t3 |  t4 |
      +-----+-----+-----+-----+-----+-----+




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7.2.5.  query-start-time

   The query-start-time option allows the requestor to specify a start
   query time to the DHCPv4 server. If specified, only bindings that
   have changed on or after the query-start-time should be included in
   the response to the query.

   This MUST be an absolute time.

   This MUST be a time in the context of the DHCPv4 server.  In the
   absence of information to the contrary, the requestor SHOULD assume
   that the time context of the DHCPv4 server is identical to the time
   context of the requestor.

   It SHOULD NOT be a time in the context of the requestor.

   This is an integer in network byte order.

   The code for this option is TBD. The length of this option is 4
   octets.

                         DHCPv4 Server
       Code   Len      query-start-time
      +-----+-----+-----+-----+-----+-----+
      | TBD |  4  |  t1 |  t2 |  t3 |  t4 |
      +-----+-----+-----+-----+-----+-----+


7.2.6.  query-end-time

   The query-end-time option allows the requestor to specify an end
   query time to the DHCPv4 server. If specified, only bindings that
   have changed on or before the query-end-time should be included in
   the response to the query.

   This MUST be an absolute time.

   This MUST be a time in the context of the DHCPv4 server.  In the
   absence of information to the contrary, the requestor SHOULD assume
   that the time context of the DHCPv4 server is identical to the time
   context of the requestor.

   It SHOULD NOT be a time in the context of the requestor.

   This is an integer in network byte order.

   The code for this option is TBD. The length of this option is 4
   octets.



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                         DHCPv4 Server
       Code   Len       query-end-time
      +-----+-----+-----+-----+-----+-----+
      | TBD |  4  |  t1 |  t2 |  t3 |  t4 |
      +-----+-----+-----+-----+-----+-----+


7.2.7.  dhcp-state

   The dhcp-state option allows greater detail to be returned than
   allowed by the DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types.

   The code for this option is TBD. The length of this option is 1
   octet.

       0                   1                   2
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Code      |    Length     |    State      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Code     The suboption code (TBD).

        Length   The suboption length, 1 octet.

        State    The State of the IP address.

      Value  State
      -----  -----
        1   AVAILABLE   Address is available to local DHCPv4 server
        2   ACTIVE      Address is assigned to a DHCPv4 client
        3   EXPIRED     Lease has expired
        4   RELEASED    Lease has been released by DHCPv4 client
        5   ABANDONED   Server or client flagged address as unusable
        6   RESET       Lease was freed by some external agent
        7   REMOTE      Address is available to a remote DHCPv4 server
        8   TRANSITIONING Address is moving between states

   Note that some of these states may be transient and may not appear in
   normal use.   A DHCPv4 server MUST implement at least the AVAILABLE
   and ACTIVE states, and SHOULD implement at least the ABANDONED and
   RESET states.

   The dhcp-state option SHOULD contain ACTIVE when it appears in a
   DHCPLEASEACTIVE message.  A DHCPv4 server MAY choose to not send a
   dhcp-state option in a DHCPLEASEACTIVE message, and a requestor
   SHOULD assume that the dhcp-state is ACTIVE if no dhcp-state option



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   appears in a DHCPLEASEACTIVE message.

   The reference to local and remote relate to possible use in an
   environment that includes multiple servers cooperating to provide an
   increased availability solution.  In this case, an IP address with
   the state of AVAILABLE is available to the local server, while one
   with the state of REMOTE is available to a remote server.  Usually,
   an IP address which is AVAILABLE on one server would be REMOTE on any
   remote server.  The TRANSITIONING state is also likely to be useful
   in multiple server deployments, where sometimes one server must
   interlock a state change with one or more other servers.  Should a
   Bulk Leasequery need to send information concerning the state of the
   IP address during this period, it SHOULD use the TRANSITIONING state,
   since the IP address is likely to be neither ACTIVE or AVAILABLE.

   There is no requirement for the state of an IP address to transition
   in a well defined way from state to state.  To put this another way,
   you cannot draw a simple state transition graph for the states of an
   IP address and the requestor of a Leasequery MUST NOT depend on one
   certain state always following a particular previous state.  In
   general, every state can (at times) follow every other state.

7.2.8.  data-source

   The data-source option contains information about the source of the
   data in a DHCPLEASEACTIVE or a DHCPLEASEUNASSIGNED message.  It is
   used when there are two or more servers who might have information
   about a particular IP address binding.  Frequently two servers work
   together to provide an increased availability solution for the DHCPv4
   service, and in these cases, both servers will respond to Bulk
   Leasequery requests for the same IP address.

   The data contained in this option will allow an external process to
   better discriminate between the information provided by each of the
   servers servicing this IPv4 address.

   The code for this option is TBD. The length of this option is 1
   octet.













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         0                   1                   2
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |     Code      |    Length     |     Flags     |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Code     The suboption code (TBD).

          Length   The suboption length, 1 octet.

          Flags    The Source information for this message.

                      0 1 2 3 4 5 6 7
                     +-+-+-+-+-+-+-+-+
                     |    MBZ      |R|
                     +-+-+-+-+-+-+-+-+

                     R:  REMOTE flag

                          remote = 1
                          local = 0

                     MBZ:  MUST BE ZERO (reserved for future use)

   The REMOTE flag is used to indicate where the most recent change of
   state (or other interesting change) concerning this IPv4 address took
   place.  If the value is local, then the change took place on the
   server from which this message was transmitted.  If the value is
   remote, then the change took place on some other server, and was made
   known to the server from which this message was transmitted.

   If this option was requested and it doesn't appear, the the requestor
   SHOULD consider that the data-source was local.

7.2.9.  Virtual Subnet Selection Type and Information

   All of the (sub)options defined in [VpnId] carry identical payloads,
   consisting of a type and additional VSS (Virtual Subnet Selection)
   information.  The existing table is extended (see below) with a new
   type 254 to allow specification of a type code which indicates that
   all VPN's are to be used to process the Bulk Leasequery.









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          Type     VSS Information format:
          ----     -----------------------
           0       NVT ASCII VPN identifier
           1       RFC2685 VPN-ID
           2-253   Not Allowed
    NEW -> 254     All VPN's (wildcard).
           255     Global, default VPN.



7.3.  Connection and Transmission Parameters

   DHCPv4 servers that support Bulk Leasequery SHOULD listen for
   incoming TCP connections on the DHCPv4 server port 67.
   Implementations MAY offer to make the incoming port configurable, but
   port 67 MUST be the default.  Requestors SHOULD make TCP connections
   to port 67, and MAY offer to make the destination server port
   configurable.

   This section presents a table of values used to control Bulk
   Leasequery behavior, including recommended defaults.  Implementations
   MAY make these values configurable.



     Parameter             Default  Description
     ------------------------------------------
     BULK_LQ_CONN_TIMEOUT      30 secs  Leasequery connection timeout
     BULK_LQ_QUERY_TIMEOUT     30 secs  Leasequery query timeout
     BULK_LQ_MAX_CONNS         10       Max Leasequery TCP connections
     BULK_LQ_MAX_CONN_RETRY    60 secs  Max Leasequery retry timeout
     BULK_LQ_DATA_TIMEOUT      30 secs  Leasequery data timeout



8.  Requestor Behavior


8.1.  Connecting and General Processing

   A requestor attempts to establish a TCP connection to a DHCPv4 server
   in order to initiate a Leasequery exchange.  The requestor SHOULD be
   prepared to abandon the connection attempt after
   BULK_LQ_CONN_TIMEOUT.  If the attempt fails, the requestor MAY retry.
   Retries MUST use an exponential backoff timer, increasing the
   interval between attempts up to BULK_LQ_MAX_CONN_RETRY.




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   If Bulk Leasequery is terminated prematurely by a DHCPLEASEQUERYDONE
   with a dhcp-message status-code 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 MUST use an exponential backoff timer, increasing the
   interval between attempts up to BULK_LQ_MAX_CONN_RETRY.

   Messages from the DHCPv4 server come as multiple responses to a
   single DHCPBULKLEASEQUERY message.  Thus, each DHCPBULKLEASEQUERY
   request MUST have a xid (transaction-id) unique on the connection on
   which it is sent, and all of the messages which come as a response to
   it all contain the same xid as the request.  It is the xid which
   allows the data-streams of two different DHCPBULKLEASEQUERY requests
   to be demultiplexed by the requestor.

   A requestor MAY send a DHCPBULKLEASEQUERY request to a DHCPv4 server
   and immediately close the transmission side of its TCP connection,
   and then read the resulting response messages from the DHCPv4 server.
   This is not required, and the usual approach is to leave both sides
   of the TCP connection up until at least the conclusion of the Bulk
   Leasequery.

8.2.  Forming a Bulk Leasequery

   Bulk Leasequery is designed to create a connection which will
   transfer the state of some subset (or possibly all) of the IP address
   bindings to the requestor from  DHCPv4 server.  The DHCPv4 server
   will send all of the requested IPv4 address bindings across this
   connection with minimal delay after it receives the request.  In this
   context, "all IP address binding information" means information about
   all IPv4 addresses configured within the DHCPv4 server which meet the
   specified query criteria.  For some query criteria, this may include
   IP address binding information for IP addresses which may not now
   have or ever had have an association with a specific DHCPv4 client.

   To form the Bulk query, a DHCPv4 request is constructed with a dhcp-
   message-type of DHCPBULKLEASEQUERY. The query SHOULD have a dhcp-
   parameter-request-list to inform the DHCPv4 server which DHCPv4
   options are of interest to the requestor sending the
   DHCPBULKLEASEQUERY message.  The dhcp-parameter-request-list in a
   DHCPBULKLEASEQUERY message SHOULD contain the codes for base-time,
   dhcp-lease-time, start-time-of-state, and client-last-transaction-
   time.

   A DHCPBULKLEASEQUERY request is constructed of one of a series of
   primary queries and the optional addition of one or more qualifiers
   to those primary queries.




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   The possible primary queries are listed below.  Each
   DHCPBULKLEASEQUERY request MUST consist of only one of these primary
   queries.

      o Query by MAC address

        In a Query by MAC address, the chaddr, htype, and hlen of the
        DHCPv4 packet are filled in with the values requested.

      o Query by Client-Id

        In a Query by Client-Id, the dhcp-client-id option containing
        the requested value is included in the DHCPBULKLEASEQUERY
        request.

      o Query by Remote-Id

        In a Query by Remote-Id, the remote-id sub-option of the relay-
        agent-information option containing the requested value is
        included in the DHCPBULKLEASEQUERY request.

      o Query by Relay-Id

        In a Query by Relay-Id, the relay-id sub-option [RelayId] of the
        relay-agent-information option containing the requested value is
        included in the DHCPBULKLEASEQUERY request.

      o Query for All Configured IP Addresses

        A Query for All Configured IP addresses is signaled by the
        absence of any other primary query.

   There are three qualifiers which can be applied to any of the above
   primary queries.  These qualifiers can appear individually or
   together in any combination, but only one of each can appear.

   o Query Start Time

     Inclusion of the query-start-time option specifies that only IP
     address bindings which have changed on or after the time specified
     in the query-start-time option should be returned.

   o Query End Time

     Inclusion of the query-end-time option specifies that only IP
     address bindings which have changed on or before the time specified
     in the query-end-time option should be returned.




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   o VPN Id

     If no vpn-id option appears in the DHCPBULKLEASEQUERY, the default
     VPN is used to search to satisfy the query specified by the
     DHCPBULKLEASEQUERY. Using the vpn-id option [VpnId] allows the
     requestor to specify a single VPN other than the default VPN.  In
     addition, the vpn-id option has been extended as part of this
     document to allow specification that all configured VPN's be
     searched in order to satisfy the query specified in the
     DHCPBULKLEASEQUERY.

     In all cases, any message returned from a DHCPBULKLEASEQUERY
     request containing information about an IP address for other than
     the default VPN MUST contain a vpn-id option in the message.

   Both of the query-start-time and query-end-time options (if they
   appear) MUST be in the time context of the DHCPv4 server to which the
   Bulk Leasequery is directed.  In the absence of information to the
   contrary, the requestor SHOULD assume that the time context on the
   DHCPv4 server is identical to the time context on the requestor.  In
   the event that previous operations have determined that the time
   context on the DHCPv4 server to which the Bulk Leasequery is
   addressed differs from the time context of the requestor, the time
   context of the DHCPv4 server MUST be used.

   Use of the query-start-time or the query-end-time options or both can
   serve to reduce the amount of data transferred over the TCP
   connection by a considerable amount.

   If the TCP connection becomes blocked while the requestor is sending
   its query, the requestor SHOULD be prepared to terminate the
   connection after BULK_LQ_QUERY_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.

8.3.  Processing Bulk Replies

   The requestor attempts to read a DHCPv4 Leasequery message from the
   TCP connection.  If the stream of replies becomes blocked, the
   requestor SHOULD be prepared to terminate the connection after
   BULK_LQ_DATA_TIMEOUT, and MAY begin retry processing if configured to
   do so.

   A single Bulk Leasequery can and usually will result in a large
   number of replies.  The requestor MUST be prepared to receive more
   than one reply with an xid matching a single DHCPBULKLEASEQUERY
   message from a single DHCPv4 server. If the xid in the received



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   message does not match an outstanding DHCPBULKLEASEQUERY message, the
   requestor MUST close the TCP connection.

   If a response message does not contain a DHCPv4 server-identifier
   option (option 54), then the server-identifier option from the
   previous message should be used.  Thus, the DHCPv4 server MUST send
   the server-identifier option in the first response message, and MAY
   send it in subsequent response message for the same request.

   The response messages generated by a DHCPBULKLEASEQUERY request are:

      o DHCPLEASEQUERYDONE

        A response of DHCPLEASEQUERYDONE indicates that the server has
        completed its response to the query, and that no more messages
        will be sent in response to the DHCPBULKLEASEQUERY. More details
        will sometimes be available in the received dhcp-message option
        in the DHCPLEASEQUERYDONE message. If there is no dhcp-message
        option in the DHCPLEASEQUERYDONE message, then the query
        completed successfully.

        Note that a query which returned no data, that is a
        DHCPBULKLEASEQUERY request followed by a DHCPLEASEQUERYDONE
        response, is considered a successful query in that no errors
        occurred during the processing.  It is not considered an error
        to have no information to return to a DHCPBULKLEASEQUERY
        request.

      o DHCPLEASEACTIVE

        A Bulk Leasequery will generate DHCPLEASEACTIVE messages
        containing binding data for bound IP addresses which match the
        specified query criteria. The IP address which is bound to a
        DHCPv4 client will appear in the ciaddr field of the
        DHCPLEASEACTIVE message.  The message may contain a non-zero
        chaddr, htype, and hlen and possibly additional options.

      o DHCPLEASEUNASSIGNED

        Some queries will also generate DHCPLEASEUNASSIGNED messages for
        IP addresses which match the query criteria.  These messages
        indicate that the IP address was not currently bound to any
        DHCPv4 client.  The IP address to which this message refers will
        appear in the ciaddr field of the DHCPLEASEUNASSIGNED message.
        A DHCPLEASEUNASSGINED message MAY also contain information about
        the last DHCPv4 client that was bound to this IP address. The
        message may contain a non-zero chaddr, htype, and hlen and
        possibly additional options.



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      o DHCPLEASEUNKNOWN

        The DHCPLEASEUNKNOWN message MUST NOT appear in a response to a
        Bulk Leasequery.

   The requestor MUST NOT assume that there is any inherent order in the
   IP address binding information that is sent in response to a
   DHCPBULKLEASEQUERY.  While the base-time will tend to increase
   monotonically (as it is the current time on the DHCPv4 server), the
   actual time that any IP address binding information changed is
   unrelated to the base-time.

   The DHCPLEASEQUERYDONE message always ends a successful
   DHCPBULKLEASEQUERY request and any unsuccessful DHCPBULKLEASEQUERY
   requests not terminated by a dropped connection. After receiving
   DHCPLEASEQUERYDONE from a server, the requestor MAY close the TCP
   connection to that server if no other DHCPBULKLEASEQUERY is
   outstanding on that TCP connection.

   The DHCPv4 Leasequery protocol [RFC4388] uses the associated-ip
   option as an indicator that multiple bindings were present in
   response to a single DHCPv4 client based query.  For Bulk Leasequery,
   a separate message is returned for each binding, and so the
   associated-ip option is not used.

8.4.  Processing Time Values in Leasequery messages

   Bulk Leasequery requests may be made to a DHCPv4 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 Bulk Leasequery response, and in the situation where
   multiple DHCPv4 servers are queried, the situation becomes even more
   complex.

   If the requestor of a Bulk Leasequery is saving the data returned in
   some form, it has a requirement to store a variety of time values,
   and some of these will be time in the context of the requestor and
   some will be time in the context of the DHCPv4 server.

   When receiving a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message from
   the DHCPv4 server, the message will contain a base-time option.  The
   time contained in this base-time option is in the context of the
   DHCPv4 server.  As such, it is an ideal time to save and use as input
   to a DHCPBULKLEASEQUERY in the query-start-time or query-end-time
   options, should the requestor need to ever issue a DHCPBULKLEASEQUERY
   message using those options as part of the query.

   In addition to saving the base-time for possible future use in a



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   query-start-time option, the base-time is used as part of the
   conversion of the other times in the Leasequery message to values
   which are meaningful in the context of the requestor.

   The requestor SHOULD use the base-time values received in Bulk
   Leasequery messages to develop a value which represents the clock
   skew between the DHCPv4 server and the requestor.  In theory this
   clock skew would simply be the difference between the first base-time
   value and the current time on the requestor when the message
   containing the base-time value was received.  However, there may be
   transmission delays at the beginning or end or along the TCP
   connection, and so the actual clock skew may not be the same as any
   individual difference between a base-time value and the current time
   of the requestor.

   Moreover, in systems whose clocks are synchronized, perhaps using
   NTP, the clock skew will usually be zero, which is not only
   acceptable, but desired.

   The requestor SHOULD smooth the value which it uses as the clock skew
   by continuously examining the instantaneous value developed from the
   base-time of each message received from a DHCPv4 server and using
   this instantaneous value of clock skew to make small adjustments to
   the existing value of the clock skew.  Thus, the clock skew will vary
   only slowly and one slow message will not completely distort a large
   number of future time calculations.

   Given the value of the clock skew on the requestor, the requestor
   SHOULD bring all of the times in the DHCPLEASEACTIVE and
   DHCPLEASEUNASSIGNED messages into the context of the requestor.
   Except for the base-time value, the times in the Leasequery message
   are all relative to the base-time.  These relative times SHOULD first
   be converted into absolute times in the context of the DHCPv4 server
   using the base-time value.  Once this stage is complete, the absolute
   times that result SHOULD be brought into the context of the requestor
   by applying the calculated clock skew to each of the absolute times.

   After all of this processing, the times are in the context of the
   requestor.

   An alternative might appear to be to leave all of the times in the
   context of the DHCPv4 server, and if the requestor is dealing with
   only one DHCPv4 server at a time, this is an accurate and effective
   approach.  However, if the requestor is dealing with DHCPLEASEACTIVE
   and DHCPLEASEUNASSIGNED messages from two or more different DHCPv4
   servers, then in order to make any sense of them, the times from each
   server SHOULD be converted into the time of the requestor.




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   Since various transmission and processing delays may occur, a time
   converted into the requestor's context may be accurate to only a few
   seconds, at best.  This is rarely an issue in the larger context of
   the use of the information derived from a Bulk Leasequery request.
   However, time comparison is an important factor in determining which
   update to the address binding information for a particular IPv4
   address is the most recent and therefore worth remembering.  The next
   section discusses the issue of comparing two updates in some detail,
   but a key aspect of that comparison is a comparison of the times in
   the two messages.

   The requestor SHOULD consider times converted into its context as
   effectively equivalent if they are within a small number of seconds
   of each other.  The precise number depends on the particular
   implementation involved, but 4 to 8 seconds is probably a good
   starting point.  Thus, if two times are 3 seconds apart after
   conversion to the requestor's context they should be considered the
   same for purposes of comparison with each other.

8.5.  Querying Multiple Servers

   A Bulk Leasequery requestor MAY be configured to attempt to connect
   to and query from multiple DHCPv4 servers in parallel.  The DHCPv4
   Leasequery specification [RFC4388] includes a discussion about
   reconciling binding data received from multiple DHCPv4 servers.

   In addition, the algorithm in the Section 8.6 should be used.

8.6.  Making Sense Out of Multiple Responses Concerning a Single IPv4
Address

   Any requestor of an Bulk Leasequery MUST be prepared for multiple
   responses to arrive for a particular IPv4 address from multiple
   different DHCPv4 servers. The following algorithm SHOULD be used to
   decide if the information just received is more up to date (i.e.,
   better) than the best existing information.  In the discussion below,
   the information that is received from a DHCPv4 server about a
   particular IPv4 address is termed a "record".  The times used in the
   algorithm below SHOULD have been converted into the requestor's
   context and the time comparisons SHOULD be performed in a manner
   consistent with the information in Section 8.4.

      o If both the existing and the new record contain client-last-
        transaction-time information, the record with the later client-
        last-transaction-time is considered better.

      o If one of the records contains client-last-transaction-time
        information and the other one doesn't, then compare the client-



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        last-transaction-time in the record that contains it against the
        other record's start-time-of-state.  The record with the later
        time is considered better.

      o If neither record contains client-last-transaction-time
        information, compare their start-time-of-state information.  The
        record with the later start-time-of-state is considered better.

      o If none of the comparisons above yield a clear answer as to
        which record is later, then compare the value of the REMOTE flag
        from the data-source option for each record.

        If the values of the REMOTE flag are different between the two
        records, the record with the REMOTE flag value of local is
        considered better.

   The above algorithm does not necessarily determine which record is
   better.  In the event that the algorithm is inconclusive with regard
   to a record which was just received by the requestor, the requestor
   SHOULD use additional information in the two records to make a
   determination as to which record is better.

8.7.  Multiple Queries to a Single Server over One Connection

   Bulk Leasequery requestors may need to make multiple queries in order
   to recover binding information.  A requestor MAY use a single
   connection to issue multiple queries to a server willing to support
   them. Each query MUST have a unique xid.

   A server MAY process more than one query at a time. A server that
   will not support more than one query at a time on a single connection
   MUST return a DHCPLEASEQUERYDONE message containing a dhcp-message
   option with a status-code of NotAllowed to the unsupported queries.
   Alternatively, a server that will not support more than one query at
   a time on a single connection MAY chose to simply read one query and
   only read any subsequent queries after processing of the current
   query is complete.

   A server that is willing to do so MAY interleave replies to the
   multiple queries within the stream of reply messages it sends.
   Requestors need to be aware that replies for multiple queries may be
   interleaved within the stream of reply messages.  Requestors that are
   not able to process interleaved replies (based on xid) MUST NOT send
   more than one query over a single connection prior to the completion
   of the previous query.  Requestors should be aware that servers are
   not required to process more than one query over a connection at a
   time, and that servers are likely to limit the rate at which they
   process queries from any one requestor.



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8.7.1.  Example

   This example illustrates what a series of queries and responses might
   look like.  This is only an example - there is no requirement that
   this sequence must be followed, or that requestors or servers must
   support parallel queries.

   In the example session, the client sends four queries after
   establishing a connection.  Query 1 returns no results; query 2
   returns 3 messages and the stream of replies concludes before the
   client issues any new query. Query 3 and query 4 overlap, and the
   server interleaves its replies to those two queries.


      Requestor                                Server
      ---------                                ------
      DHCPBULKLEASEQUERY xid 1 ----->
                               <-----       DHCPLEASEQUERYDONE xid 1
      DHCPBULKLEASEQUERY xid 2 ----->
                               <-----       DHCPLEASEACTIVE xid 2
                               <-----       DHCPLEASEACTIVE xid 2
                               <-----       DHCPLEASEACTIVE xid 2
                               <-----       DHCPLEASEQUERYDONE xid 2
      DHCPBULKLEASEQUERY xid 3 ----->
      DHCPBULKLEASEQUERY xid 4 ----->
                               <-----       DHCPLEASEACTIVE xid 4
                               <-----       DHCPLEASEACTIVE xid 4
                               <-----       DHCPLEASEACTIVE xid 3
                               <-----       DHCPLEASEACTIVE xid 4
                               <-----       DHCPLEASEUNASSIGNED xid 3
                               <-----       DHCPLEASEACTIVE xid 4
                               <-----       DHCPLEASEACTIVE xid 3
                               <-----       DHCPLEASEQUERYDONE xid 3
                               <-----       DHCPLEASEACTIVE xid 4
                               <-----       DHCPLEASEQUERYDONE xid 4


8.8.  Closing Connections

   Either the requestor or DHCPv4 server MAY close the TCP connection at
   any time.  The requestor MAY choose to retain the connection if it
   intends to issue additional queries or if other queries are currently
   using the connection.  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.





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9.  Server Behavior


9.1.  Accepting Connections

   Servers that implement DHCPv4 Bulk Leasequery listen for incoming TCP
   connections.  Port numbers are discussed in Section 7.3.  Servers
   MUST be able to limit the number of currently accepted and active
   connections.  The value BULK_LQ_MAX_CONNS SHOULD be the default;
   implementations MAY permit the value to be configurable.  Connections
   SHOULD be accepted and, if the number of connections is over
   BULK_LQ_MAX_CONNS, they SHOULD be closed immediately.

   Servers MAY restrict Bulk Leasequery connections and
   DHCPBULKLEASEQUERY messages to certain requestors.  Connections not
   from permitted requestors SHOULD be closed immediately, to avoid
   server connection resource exhaustion. Servers MAY restrict some
   requestors to certain query types.  Servers MAY reply to queries that
   are not permitted with the DHCPLEASEQUERYDONE message with a dhcp-
   message status of NotAllowed, or MAY simply close the connection.

   If the TCP connection becomes blocked while the server is accepting a
   connection or reading a query, it SHOULD be prepared to terminate the
   connection after an BULK_LQ_QUERY_TIMEOUT.  We make this
   recommendation to allow servers to control the period of time they
   are willing to wait before abandoning an inactive connection,
   independent of the TCP implementations they may be using.

9.2.  Replying to a Bulk Leasequery

   If the connection becomes blocked while the server is attempting to
   send reply messages, the server SHOULD be prepared to terminate the
   TCP connection after BULK_LQ_DATA_TIMEOUT.

   Every Bulk Leasequery request MUST be terminated by sending a final
   DHCPLEASEQUERYDONE message if such a message can be sent. The
   DHCPLEASEQUERYDONE message MUST have a dhcp-message status if the
   termination was other than successful, and SHOULD NOT contain a
   dhcp-message status if the termination was successful.

   If the DHCPv4 server encounters an error during processing of the
   DHCPBULKLEASEQUERY message, either during initial processing or later
   during the message processing, it SHOULD send a DHCPLEASEQUERYDONE
   containing a status dhcp-message option. It MAY close the connection
   after this error is signaled, but that is not required.

   If the server does not find any bindings satisfying a query, it MUST
   send a DHCPLEASEQUERYDONE.  It SHOULD NOT include a dhcp-message



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   option with a Success status unless there is a useful string to
   include in the dhcp-message option.  Otherwise, the server sends each
   binding's data in a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message.

   The response to a DHCPBULKLEASEQUERY may involve examination of
   multiple DHCPv4 IP address bindings maintained by the DHCPv4 server.
   The Bulk Leasequery protocol does not require any ordering of the IP
   addresses returned in DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED
   messages.

   A Bulk Leasequery response MUST contain no more than one message for
   each configured IP address in the DHCPv4 server.  In addition, a Bulk
   Leasequery may well take significant time between the beginning and
   end of the processing of all of the messages required to satisfy the
   Bulk Leasequery query.  During this time, the state of some of the IP
   addresses sent early in the response may change prior to the
   completion of the entire response to the Bulk Leasequery.  This is
   normal and expected -- there is no requirement for the entire
   response to a Bulk Leasequery to represent an instantaneous snapshot
   of the state of the IP address bindings of a DHCPv4 server.  Quite
   the contrary -- as the cursor moves through the IP addresses in
   whatever order is convenient to the DHCPv4 server, the state of IP
   addresses already examined can change and a DHCPv4 server MUST NOT
   try to examine IP addresses already scanned in an attempt to "keep
   up" with the ongoing state changes of all of the IP addresses.  To do
   so would make it difficult to meet the requirement to send only one
   message per IP address in response to a Bulk Leasequery and would
   also make it difficult to know when to finish the Bulk Leasequery.

   If the ciaddr, yiaddr, or siaddr is non-zero in a DHCPBULKLEASEQUERY
   request, the request must be terminated immediately by a
   DHCPLEASEQUERYDONE message with a dhcp-message status of
   MalformedQuery.

   Any DHCPBULKLEASEQUERY which has more than one of the following
   primary query types specified MUST be terminated immediately by a
   DHCPLEASEQUERYDONE message with a dhcp-message status code of
   NotAllowed.

   The allowable queries in a DHCPBULKLEASEQUERY message are processed
   as follows.  Note that the descriptions of the primary queries below
   must constrained by the actions of any of the three qualifiers
   described subsequently as well.

   The following table discusses how to process the various queries.
   For information on how to identify the query, see the information in
   Section 8.2.




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      o Query by MAC address

        Every IP address which has a current binding to a DHCPv4 client
        which matches the chaddr, htype, and hlen in the
        DHCPBULKLEASEQUERY request MUST be returned in a DHCPLEASEACTIVE
        message.

      o Query by Client-Id

        Every IP address which has a current binding to a DHCPv4 client
        which matches the client-id option in the DHCPBULKLEASEQUERY
        request MUST be returned in a DHCPLEASEACTIVE message.

      o Query by Remote-Id

        Every IP address which has a current binding to a DHCPv4 client
        which matches the remote-id sub-option of the relay-agent-
        information option in the DHCPBULKLEASEQUERY request MUST be
        returned in a DHCPLEASEACTIVE message.

      o Query by Relay-Id

        Every IP address which has a current binding to a DHCPv4 client
        which matches the relay-id sub-option of the relay-agent-
        information option in the DHCPBULKLEASEQUERY request MUST be
        returned in a DHCPLEASEACTIVE message.

      o Query for All Configured IP Addresses

        A Query for All Configured IP addresses is signaled by the
        absence of any other primary query.  That is, if there is no
        value in the chaddr, hlen, htype, no client-id option, no
        remote-id sub-option or relay-id sub-option of the relay-agent-
        information option, then the request is a query for information
        concerning all configured IP addresses. In this case, every
        configured IP address which has a current binding to a DHCPv4
        client MUST be returned in a DHCPLEASEACTIVE message.  In
        addition, every configured IP address which does not have a
        current binding to a DHCPv4 client MUST be returned in a
        DHCPLEASEUNASSIGNED message.

        In this form of query, each configured IP address MUST be
        returned at most one time.  If the absence of qualifiers which
        restrict the number of IP addresses returned, every configured
        IP address MUST be returned exactly once.

   There are three qualifiers which can be applied to any of the above
   primary queries.  These qualifiers can appear individually or



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   together in any combination, but only one of each can appear.

   o Query Start Time

     If a query-start-time option appears in the DHCPBULKLEASEQUERY
     request, only IP address bindings which have changed on or after
     the time specified in the query-start-time option should be
     returned.

   o Query End Time

     If a query-end-time option appears in the DHCPBULKLEASEQUERY
     request, only IP address bindings which have changed on or before
     the time specified in the query-end-time option should be returned.

   o VPN Id

     If no vpn-id option appears in the DHCPBULKLEASEQUERY, the default
     VPN is used to satisfy the query.  A vpn-id option [VpnId] value
     other than the wildcard value (254) allows the requestor to specify
     a single VPN other than the default VPN.  In addition, the vpn-id
     option has been extended as part of this document to allow
     specification of a type 254 which indicates that all configured
     VPN's be searched in order to satisfy the primary query.

     In all cases, if the information returned in a DHCPLEASEACTIVE or
     DHCPLEASEUNASSIGNED message is for other than the default a vpn-id
     option MUST appear in the packet.

   The query-start-time and query-end-time qualifiers are used to
   constrain the amount of data returned by a Bulk Leasequery request by
   returning only IP addresses whose address bindings have changed in
   some way during the time window specified by the query-start-time and
   query-end-time.

   A DHCPv4 server SHOULD consider an address binding to have changed
   during a specified time window if either the client-last-
   transaction-time or the start-time-of-state of the address binding
   changed during that time window.

   A DHCPv4 server MAY always compare the address binding information
   for an IP address against a time window if it follows the following
   guidelines.  If there is no query-start-time, then the DHCPv4 server
   MUST assume the query-start-time is equivalent to a time prior to any
   time that resides in any IP address binding.  If there is no query-
   end-time, the DHCPv4 server MUST assume that the query-end-time is
   equivalent to a time that is later than any time that resides in any
   IP address binding.



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   Even if the query-start-time or query-end-time option value is being
   used to limit the amount of data flow from the DHCPv4 server to the
   requestor, there is no requirement placed on the DHCPv4 server to
   return address binding data in any order and certainly not in any
   order based on time.

   When the DHCPv4 server has no additional information to send to the
   requestor, it will send a DHCPLEASEQUERYDONE message.

9.3.  Building a Single Reply for Bulk Leasequery

   The DHCPv4 Leasequery [RFC4388] specification describes the initial
   construction of DHCPLEASEQUERY reply messages using the
   DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types in Section
   6.4.2.  All of the reply messages in Bulk Leasequery are similar to
   the reply messages for an IP address query.  Message transmission and
   framing for TCP is described in this document in Section 7.1.

   [RFC2131] and [RFC4388] specify that every response message MUST
   contain the server-identifier option.  However, that option will be
   the identical for every response from a particular DHCPBULKLEASEQUERY
   request.  Thus, the DHCPv4 server MUST include the server-identifier
   option in the first message sent in response to a DHCPBULKLEASEQUERY.
   It MAY include the server-identifier in later messages as well, but
   there is no requirement for it to do so.

   The message type of DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED is based
   on the value of the dhcp-state option.  If the dhcp-state option
   value is ACTIVE, then the message type is DHCPLEASEACTIVE, otherwise
   the message type is DHCPLEASEUNASSIGNED.

   In addition to the basic message construction described in [RFC4388],
   the following guidelines exist:

      1. If the dhcp-state option code appears in the dhcp-parameter-
         request-list, the DHCPv4 server SHOULD include a dhcp-state
         option whose value corresponds most closely to the state held
         by the DHCPv4 server for the IP address associated with this
         reply.  If the state is ACTIVE and the message being returned
         in DHCPLEASEACTIVE then the DHCPv4 server MAY choose to not
         send the dhcp-state option.  The requestor SHOULD assume that
         any DHCPLEASEACTIVE message arriving without a requested dhcp-
         state option has a dhcp-state of ACTIVE.

      2. If the base-time option code appears in the dhcp-parameter-
         request-list, the DHCPv4 server MUST include a base-time
         option, which is the current time in the DHCPv4 server's
         context and the time from which the start-time-of-state, dhcp-



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         lease-time, client-last-transaction-time, and other duration-
         style times are based upon.

      3. If the start-time-of-state option code appears in the dhcp-
         parameter-request-list, the DHCPv4 server MUST include a
         start-time-of-state option whose value represents the time at
         which the dhcp-state option's state became valid.

      4. If the dhcp-lease-time option code appears in the dhcp-
         parameter-request-list, the DHCPv4 server MUST include a dhcp-
         lease-time option for any state that has a time-out value
         associated with it, and not just appear in a DHCPLEASEACTIVE
         message.  Thus, the EXPIRED state which is sent in a
         DHCPLEASEUNASSIGNED message would have a dhcp-lease-time option
         in the message if the EXPIRED state represented a grace-period
         and would be changing state after the grace-period expired.

      5. If the data-source option code appears in the dhcp-parameter-
         request-list, the DHCPv4 server MUST include the data-source
         option in any situation where any of the bits would be non-
         zero.  Thus, in the absence of the data-source option, the
         assumption is that all of the flags were zero.

      6. If the client-last-transaction-time option code appears in the
         dhcp-parameter-request-list, The DHCPv4 server MUST include the
         client-last-transaction-time option in any situation where the
         information is available.

      7. If there is a dhcp-parameter-request-list in the initial
         DHCPBULKLEASEQUERY request, then it should be used for all of
         the replies generated by that request.  Some options can be
         sent from a DHCPv4 client to the server or from the DHCPv4
         server to a DHCPv4 client. Option 125 is such an option.  If
         the option code for one of these options appears in the dhcp-
         parameter-request-list, it SHOULD result in returning the value
         of the option sent by the DHCPv4 client to the server if one
         exists.

   Note that there may be other requirements for a reply to a
   DHCPBULKLEASEQUERY request discussed in Section 9.2.

9.4.  Multiple or Parallel Queries

   As discussed in Section 8.3, requestors may want to leverage an
   existing connection if they need to make multiple queries.  Servers
   MAY support reading and processing multiple queries from a single
   connection.  A server MUST NOT read more query messages from a
   connection than it is prepared to process simultaneously.



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   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 MAY close its end of the TCP connection after sending its
   last message, a DHCPLEASEQUERYDONE message in response to a query.
   Alternatively, the server MAY retain the connection and wait for
   additional queries from the requestor.  The server SHOULD be prepared
   to limit the number of connections it maintains, and SHOULD be
   prepared to close idle connections to enforce the limit.

   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
   status code in the dhcp-message option in a DHCPLEASEQUERYDONE
   message, including a message string indicating details of the reason
   for the abort.   If the server detects that the requesting end of the
   connection has been closed, the server MUST close its end of the
   connection after it has finished processing any outstanding requests.

   The server MUST send a DHCPLEASEQUERYDONE message at the end of the
   data returned from a Bulk Leasequery request.

10.  Security Considerations

   The "Security Considerations" section of [RFC2131] details the
   general threats to DHCPv4.  The DHCPv4 Leasequery specification
   [RFC4388] describes recommendations for the Leasequery protocol,
   especially with regard to relayed LEASEQUERY messages, mitigation of
   packet-flooding 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 DHCPv4 server's available TCP connection
   resources, such as SYN flooding attacks, 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 also can exhaust a
   server's pool of available connections.  We recommend that servers
   offer configuration to limit the sources of incoming connections,
   that they limit the number of accepted connections and the number of
   in-process queries from any one connection, and that they limit the



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   period of time during which an idle connection will be left open.

11.  IANA Considerations

   IANA is requested to assign the following new values for this
   document.  See Section 7.2 for details.

      1. A dhcp-message-type of 14 for DHCPBULKLEASEQUERY.

      2. A dhcp-message-type of 15 for DHCPLEASEQUERYDONE.

      3. An option code of TBD for base-time.

      4. An option code of TBD for start-time-of-state.

      5. An option code of TBD for query-start-time.

      6. An option code of TBD for query-end-time.

      7. An option code of TBD for data-source.

      8. An option code of TBD for dhcp-state.

      9. Values for dhcp-state:

           State
           -----
             1     AVAILABLE
             2     ACTIVE
             3     EXPIRED
             4     RELEASED
             5     ABANDONED
             6     RESET
             7     REMOTE
             8     TRANSITIONING


      10.Values for status code in a constrained dhcp-message option
         (option 53):


           Name    status-code
           ----    -----------
           Success         000
           UnspecFail      001
           QueryTerminated 002
           MalformedQuery  003
           NotAllowed      004



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      11.Addtional type field values for the Virtual Subnet Selection
         Type and Information [VpnId]:

                Type     VSS Information format:

                 0       NVT ASCII VPN identifier
                 1       RFC2685 VPN-ID
                 2-253   Not Allowed
          NEW -> 254     All VPN's.  (wildcard)
                 255     Global, default VPN.


12.  Acknowledgements

   This draft is a collaboration between the authors of draft-dtv-dhc-
   dhcpv4-bulk-leasequery-00.txt and draft-kkinnear-dhc-dhcpv4-bulk-
   leasequery-00.txt.  Both documents acknowledged that significant text
   as well as ideas were borrowed in whole or in part from the DHCPv6
   Bulk Leasequery draft [DHCPv6Bulk].


13.  References


13.1.  Normative References


   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
      Requirement Levels", RFC 2119, March 1997.

   [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
      March 1997.

   [RFC2132] Alexander, S., Droms, R., "DHCP Options and BOOTP Vendor
      Extensions", RFC 2132, March 1997.

   [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC
      3046, January 2001.

   [RFC4301] Kent, S., K. Seo, "Security Architecture for the Internet
      Protocol", RFC4301, December 2005.

   [RFC4388] Woundy, R., K. Kinnear, "Dynamic Host Configuration
      Protocol (DHCP) Leasequery", RFC 4388, February 2006.

   [RelayId] Stapp, M., "The DHCPv4 Relay Agent Identifier Suboption",
      draft-ietf-dhc-relay-id-suboption-04.txt, September 2008.




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   [VpnId] Kinnear, K., R. Johnson, M. Stapp and J. Kumarasamy, "Virtual
      Subnet Selection Options for DHCPv4 and DHCPv6" draft-ietf-dhc-
      vpn-option-09.txt, July 2008.

13.2.  Informative References


   [RFC951] Croft, B., Gilmore, J., "Bootstrap Protocol (BOOTP)", RFC
      951, September 1985.

   [RFC1542] Wimer, W., "Clarifications and Extensions for the Bootstrap
      Protocol", RFC 1542, October 1993.

   [RFC4614] Duke, M., R. Braden, W. Eddy, and E. Blanton, "A Roadmap
      for Transmission Control Protocol (TCP) Specification Documents",
      RFC 4614, September 2006.

   [DHCPv6Bulk] Stapp, M., "DHCPv6 Bulk Leasequery", draft-ietf-dhc-
      dhcpv6-bulk-leasequery-04.txt, October 2008.

14.  Authors' Addresses


      Kim Kinnear
      Cisco Systems
      1414 Massachusetts Ave.
      Boxborough, Massachusetts 01719

      Phone: (978) 936-0000

      EMail: kkinnear@cisco.com



      Bernie Volz
      Cisco Systems
      1414 Massachusetts Ave.
      Boxborough, Massachusetts 01719

      Phone: (978) 936-0000

      EMail: volz@cisco.com



      Neil Russell
      Cisco Systems
      1414 Massachusetts Ave.



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      Boxborough, Massachusetts 01719

      Phone: (978) 936-0000

      EMail: nrussell@cisco.com



      Mark Stapp
      Cisco Systems
      1414 Massachusetts Ave.
      Boxborough, Massachusetts 01719

      Phone: (978) 936-0000

      EMail: mjs@cisco.com



      Ramakrishna Rao DTV
      Infosys Technologies Ltd.
      44 Electronics City, Hosur Road
      Bangalore  560 100
      India

      EMail: ramakrishnadtv@infosys.com
      URI:   http://www.infosys.com/



      Bharat joshi
      Infosys Technologies Ltd.
      44 Electronics City, Hosur Road
      Bangalore  560 100
      India

      EMail: bharat_joshi@infosys.com
      URI:   http://www.infosys.com/



      Pavan Kurapati
      Infosys Technologies Ltd.
      44 Electronics City, Hosur Road
      Bangalore  560 100
      India





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      EMail: pavan_kurapati@infosys.com
      URI:   http://www.infosys.com/


15.  Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

16.  Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

17.  Acknowledgment

   Funding for the RFC Editor function is provided by the IETF



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   Administrative Support Activity (IASA).

18.  Appendix -- Why a New Leasequery is Required

   The three existing query types supported by [RFC4388] do not provide
   effective and efficient antispoofing for the scenario discussed in
   Section 3.

   o  Query by Client Identifier

   Query by Client Identifier is not possible because the DSLAM would
   need to glean the client-identifier.  This is not possible since if
   we are using a Leasequery, it is because the gleaned information was
   lost. On the other hand, we can query by client-identifier when
   client sends a DHCPv4 request, but then there may not be any need for
   Leasequery as such -- regular gleaning may be enough.

   o  Query by IP Address

   [RFC4388] suggests that it is preferable to use Query by IP Address
   when getting downstream traffic.

   Query by IP address is not very useful because because downstream
   traffic may not exist for the clients on a DSL port.  (In most
   Internet applications, downstream traffic exists only when a client
   sends upstream traffic).  In other words, the client will be denied
   service until it gets downstream traffic, which may never come.

   Query by IP address may be used for upstream traffic.  Then whenever
   an upstream packet comes whose IP address is unknown to the DSLAM, a
   lease query may be initiated.  A related question is what to do with
   that upstream traffic itself until lease query response comes?  If
   the traffic is dropped, we may be dropping legitimate traffic.  If
   the traffic is forwarded, we may be forwarding spoofed packets.  Once
   the lease response comes, subsequent traffic is handled depending on
   the response.  If a DHCPLEASEACTIVE response comes, the DSLAM will
   accept the traffic.  If a DHCPLEASEUNASSIGNED response comes, the
   DSLAM will drop the traffic corresponding to the IP address.  If a
   DHCPLEASEUNKNOWN response comes the DSLAM may drop the traffic
   corresponding to the IP address but will have to periodically send
   the lease query for that IP address again (additional overhead).  The
   process is triggered whenever an unknown IP address comes.

   Note that the DSLAM needs to keep track of 4 lists of IP addresses:
   (1) List of IP addresses for which it got DHCPLEASEACTIVE responses;
   (2) List of IP addresses for which it got DHCPLEASEUNASSIGNED
   responses; (3) List of IP addresses for which it got DHCPLEASEUNKNOWN
   responses; (4) All other IP addresses.



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   This approach may be acceptable if only legitimate traffic is
   received.  Consider the case when someone sends packets that uses
   spoofed IP addresses.  In that case, lease response will be
   DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN.  [RFC4388] suggests usage of
   negative caching in this regard (which involves additional
   resources).

   In a spoofing type of attack, negative caching information may grow
   considerably if attacker varies the source IP address.  For each such
   new source IP address, traffic will come to slow path, a new lease
   query needs to be initiated, response will be processed, and negative
   caching needs to be done.  That will mean using many resources for
   negative caching.

   [RFC4388] suggests that if the DSLAM knows the network portion of the
   IP addresses that are assigned to its clients, then some amount of
   antispoofing can be done in fast path and some lease queries may be
   avoided.  But as indicated before, that information may not always be
   available to DSLAMs.

   Effectively, antispoofing support involves considerable slow path
   processing and considerable resources tied for negative caching.

   [RFC4388] says that DHCPv4 server should be protected from being
   flooded with too many Leasequery requests and DSLAM also should not
   send too many lease query messages at a time.  This would mean that
   legitimate requestors may be excessively delayed getting their
   information in the face of antispoofing attacks.

   It is concluded that antispoofing is neither effective nor efficient
   with this query type.

   o  Query by MAC Address

   Query by MAC address can also be used in a way similar to query by IP
   address described above.  Indeed, query by MAC address may be better
   than query by IP address in one sense because of the possible
   presence of the associated-ip option in lease responses. (Note that
   associated-ip option does not appear in responses for query by IP
   address).  With associated-ip option DSLAM can get information not
   only about the IP address/MAC address that triggered the Leasequery
   but also about other IP addresses that are associated with the
   original MAC address.  That way, when traffic that uses the other IP
   addresses comes along, DSLAM is already prepared to deal with them.

   Although, query by MAC address is better than query by IP address in
   the above respect, it has a specific problem which is not shared by
   query by IP address.  For a query by MAC address, only two types of



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   responses are possible: DHCPLEASEUNKNOWN and DHCPLEASEACTIVE;
   DHCPLEASEUNASSIGNED is not supported.  This is particularly
   troublesome when a DHCPv4 server indeed has definitive information
   that no IP addresses are associated with the specified MAC address in
   the Leasequery, but it is forced to respond with DHCPLEASEUNKNOWN
   instead of DHCPLEASEUNASSIGNED.  As we have seen above, unlike
   DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN requires periodic querying with
   DHCPv4 server, an additional overhead.

   Moreover, query by MAC address also shares all other issues we
   discussed above for query by IP address.

   We conclude that existing Leasequery types are not appropriate to
   achieve effective and efficient antispoofing in the environment
   discussed.




































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