[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 RFC 4388

Dynamic Host Configuration Working Group                     Rich Woundy
INTERNET DRAFT                                             Comcast Cable

                                                             Kim Kinnear
                                                           Cisco Systems

                                                              March 2003
                                                  Expires September 2003


                            DHCP Lease Query
                   <draft-ietf-dhc-leasequery-05.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   A DHCP server contains considerable authoritative information
   concerning the IP addresses it has leased to DHCP clients.  Other
   processes and devices, many that already send and receive DHCP format
   packets, sometimes need to access this information.  The leasequery
   protocol is designed to give these processes and devices a
   lightweight way to access information that may be critical to their
   operation.




Woundy & Kinnear         Expires September 2003                 [Page 1]

Internet Draft             DHCP Lease Query                   March 2003


1.  Introduction

   A DHCP server contains considerable authoritative information con-
   cerning the IP addresses it has leased to DHCP clients.  Other
   processes and devices, many that already send and receive DHCP format
   packets, sometimes need to access this information.  The leasequery
   protocol is designed to give these processes and devices a light-
   weight way to access information that may be critical to their opera-
   tion.

   For example, access concentrators that act as DHCP relay agents some-
   times derive information important to their operation by extracting
   data out of the DHCP packets they forward, a process known as "glean-
   ing".  Unfortunately, the typical access concentrator loses its
   gleaned information when the access concentrator is rebooted or is
   replaced.  This memo proposes that when gleaned DHCP information is
   not available, the access concentrator/relay agent can obtain the
   location information directly from the DHCP server(s) using the new
   lightweight DHCPLEASEQUERY message.

   To continue this example in more depth, in many broadband access net-
   works, the access concentrator needs to associate an IP address lease
   to the correct endpoint location, which includes knowledge of the
   host hardware address, the port or virtual circuit that leads to the
   host, and/or the hardware address of the intervening subscriber
   modem.  This is particularly important when one or more IP subnets
   are shared among many ports, circuits, and modems.  Representative
   cable and DSL environments are depicted in Figures 1 and 2 below.


           +--------+     +---------------+
           |  DHCP  |     |  DOCSIS CMTS  |
           | Server |-...-|  or DVB INA   |-------------------
           +--------+     | (Relay Agent) |      |          |
                          +---------------+  +------+    +------+
                                             |Modem1|    |Modem2|
                                             +------+    +------+
                                                |         |    |
                                            +-----+  +-----+ +-----+
                                            |Host1|  |Host2| |Host3|
                                            +-----+  +-----+ +-----+

               Figure 1: Cable Environment for DHCPLEASEQUERY








Woundy & Kinnear         Expires September 2003                 [Page 2]

Internet Draft             DHCP Lease Query                   March 2003




           +--------+     +---------------+
           |  DHCP  |     |  DSL Access   |     +-------+
           | Server |-...-| Concentrator  |-...-| DSLAM |
           +--------+     | (Relay Agent) |     +-------+
                          +---------------+      |     |
                                           +------+   +------+
                                           |Modem1|   |Modem2|
                                           +------+   +------+
                                              |        |    |
                                          +-----+  +-----+ +-----+
                                          |Host1|  |Host2| |Host3|
                                          +-----+  +-----+ +-----+

               Figure 2: DSL Environment for DHCPLEASEQUERY



   Knowledge of this location information can benefit the access concen-
   trator in several ways:

      1. The access concentrator can forward traffic to the access net-
         work using the correct access network port, down the correct
         virtual circuit, through the correct modem, to the correct
         hardware address.

      2. The access concentrator can perform IP source address verifica-
         tion of datagrams received from the access network.  The verif-
         ication may be based on the datagram source hardware address,
         the incoming access network port, the incoming virtual circuit,
         and/or the transmitting modem.

      3. The access concentrator can encrypt datagrams which can only be
         decrypted by the correct modem, using mechanisms such as [BPI]
         or [BPI+].

   The access concentrator in this example obtains the location informa-
   tion primarily from "gleaning" information from DHCP server responses
   sent through the relay agent.  When location information is not
   available from "gleaning", e.g.  due to reboot, the access concentra-
   tor can query the DHCP server(s) for location information using the
   DHCPLEASEQUERY message defined in this document.

   The DHCPLEASEQUERY message is a new DHCP message type transmitted
   from a DHCP relay agent to a DHCP server.  A DHCPLEASEQUERY-aware
   relay agent sends the DHCPLEASEQUERY message when it needs to know
   the location of an IP endpoint.  The DHCPLEASEQUERY-aware DHCP server



Woundy & Kinnear         Expires September 2003                 [Page 3]

Internet Draft             DHCP Lease Query                   March 2003


   replies with a DHCPLEASEKNOWN, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN
   message. The DHCPLEASEACTIVE response to a DHCPLEASEQUERY message
   allows the relay agent to determine the IP endpoint location, and the
   remaining duration of the IP address lease.  The DHCPLEASEKNOWN is
   similar to a DHCPLEASEACTIVE message but indicates that there is no
   currently active lease on the resultant IP address.  The DHCPLEASEUN-
   KNOWN message indicates that the DHCP server has no knowledge of the
   information specified in the query (e.g., IP address, MAC address, or
   client-id option).

   The DHCPLEASEQUERY message does not presuppose a particular use for
   the information it returns -- it is simply designed to return infor-
   mation for which the DHCP server is an authoritative source to a
   client which requests that information.  It is designed to make it
   straightforward for processes and devices which already interpret
   DHCP packets to access information from the DHCP server.


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 [RFC 2119].

   This document uses the following terms:

      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
        DHCP relay agent functionality.

      o "DHCP client"

        A DHCP client is an Internet host using DHCP to obtain confi-
        guration parameters such as a network address.

      o "DHCP relay agent"

        A DHCP relay agent is a third-party agent that transfers BOOTP
        and DHCP messages between clients and servers residing on dif-
        ferent subnets, per [RFC 951] and [RFC 1542].

      o "DHCP server"

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



Woundy & Kinnear         Expires September 2003                 [Page 4]

Internet Draft             DHCP Lease Query                   March 2003


      o "downstream"

        Downstream is the direction from the access concentrator towards
        the broadband subscriber.

      o "gleaning"

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

      o "location information"

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

      o "MAC address"

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

      o "reservation"

        At times it is convenient for an administrator to assign a fixed
        IP address to a particular DHCP client.  The DHCP server must be
        configured with this DHCP client to IP address mapping, typi-
        cally using the MAC address as the way to identify the client. A
        reservation defines a mapping between a client and an IP address
        but doesn't establish or record a lease binding for the IP
        address.  The DHCP client to IP address mapping, configured in
        the DHCP server, is called a reservation for the purposes of
        this document.

      o "primary DHCP server"

        The primary DHCP server in a DHCP Failover environment is con-
        figured to provide primary service to a set of DHCP clients for
        a particular set of subnet address pools.

      o "secondary DHCP server"

        The secondary DHCP server in a DHCP Failover environment is con-
        figured to act as backup to a primary server for a particular
        set of subnet address pools.



Woundy & Kinnear         Expires September 2003                 [Page 5]

Internet Draft             DHCP Lease Query                   March 2003


      o "stable storage"

        Every DHCP server is assumed to have some form of what is called
        "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 server failure which
        requires restart of the server.

      o "upstream"

        Upstream is the direction from the broadband subscriber towards
        the access concentrator.


3.  Background

   The focus of this document is to enable processes and devices which
   wish to access information from the DHCP server in a lightweight and
   convenient manner.  It is especially appropriate for processes and
   devices which already interpret DHCP packets.

   One important motivating example is that the DHCPLEASEQUERY message
   allows access concentrators to send DHCPLEASEQUERY messages to DHCP
   servers, to obtain location information of broadband access network
   devices.

   This document assumes that many access concentrators have an embedded
   DHCP relay agent functionality. Typical access concentrators include
   DOCSIS Cable Modem Termination Systems (CMTSs) [DOCSIS], DVB Interac-
   tive Network Adapters (INAs) [EUROMODEM], and DSL Access Concentra-
   tors.

   The DHCPLEASEQUERY message is an optional extension to the DHCP pro-
   tocol [RFC 2131].

   In a DHCP Failover environment [FAILOVER], the DHCPLEASEQUERY message
   can be sent to the primary or secondary DHCP server. In order for the
   secondary DHCP server to answer DHCPLEASEQUERY messages, the primary
   DHCP server must send "interesting options" (such as the relay-
   agent-information option [RFC 3046]) in Failover BNDUPD messages to
   the secondary DHCP server, as recommended by section 7.1.1 of [FAIL-
   OVER].

   The DHCPLEASEQUERY message is a query message only, and does not
   affect the state of the IP address or the binding information associ-
   ated with it.





Woundy & Kinnear         Expires September 2003                 [Page 6]

Internet Draft             DHCP Lease Query                   March 2003


4.  Design Goals

   The goal of this document is to provide a lightweight mechanism for
   processes or devices to access information contained in the DHCP
   server.  It is designed to allow processes and devices which already
   process and interpret DHCP messages to access this information in a
   rapid and lightweight manner.

   Some of this information might be acquired in a different way, and
   the following sections discuss some of these alternative approaches.


4.1.  Broadcast ARP is Undesirable

   The access concentrator can transmit a broadcast ARP Request [RFC
   826], and observe the origin and contents of the ARP Reply, to recon-
   struct the location information.

   The ARP mechanism is undesirable for three reasons:

      1. the burden on the access concentrator to transmit over multiple
         access ports and virtual circuits (assuming that IP subnets
         span multiple ports or virtual circuits),

      2. the burden on the numerous subscriber hosts to receive and pro-
         cess the broadcast, and

      3. the ease by which a malicious host can misrepresent itself as
         the IP endpoint.


4.2.  SNMP and LDAP Client Functionality is Lacking

   Access concentrator implementations typically do not have SNMP
   management client interfaces nor LDAP client interfaces (although
   they typically do include SNMP management agents).  This is a primary
   reason why this document does not leverage the proposed DHCP Server
   MIB [DHCPMIB].


4.3.  DHCP Relay Agent Functionality is Common

   Access concentrators commonly act as DHCP relay agents.  Furthermore,
   many access concentrators already glean location information from
   DHCP server responses, as part of the relay agent function.

   The gleaning mechanism as a technique to determine the IP addresses
   valid for a particular downstream link is preferred over other



Woundy & Kinnear         Expires September 2003                 [Page 7]

Internet Draft             DHCP Lease Query                   March 2003


   mechanisms (ARP, SNMP, LDAP) because of the lack of additional net-
   work traffic, but sometimes gleaning information can be incomplete.
   The access concentrator usually cannot glean information from any
   DHCP unicast (i.e.  non-relayed) messages due to performance reasons.
   Furthermore, the DHCP-gleaned location information often does not
   persist across access concentrator reboots (due to lack of stable
   storage), and almost never persists across concentrator replacements.


4.4.  DHCP Servers as a Reliable Source of Location Information

   DHCP servers are the most reliable source of location information for
   access concentrators, particularly when the location information is
   dynamic and not reproducible by algorithmic means (e.g.  when a sin-
   gle IP subnet extends behind many broadband modems).  DHCP servers
   participate in all IP lease transactions (and therefore in all loca-
   tion information updates) with DHCP clients, whereas access concen-
   trators sometimes miss some important lease transactions.

   In a DHCP Failover environment [FAILOVER], the access concentrator
   can query either the primary or secondary DHCP server, so that no one
   DHCP server is a single point of failure.


4.5.  Minimal Additional Configuration is Required

   Access concentrators can usually query the same set of DHCP servers
   used for forwarding by the relay agent, thus minimizing configuration
   requirements.


5.  Protocol Overview

   In the following discussion of the DHCPLEASEQUERY message, the client
   of the message is assumed to be an access concentrator.  Note that
   access concentrators are not the only allowed (or required) consumers
   of the information provided by the DHCPLEASEQUERY message, but they
   do give reader a concrete feel for how the message might be used.

   The access concentrator initiates all DHCPLEASEQUERY message conver-
   sations.  This document assumes that the access concentrator gleans
   location information in its DHCP relay agent function.  However, the
   location information is usually unavailable after the reboot or
   replacement of the access concentrator.

   Suppose the access concentrator is a router, and further suppose that
   the router receives an IP datagram to forward downstream to the pub-
   lic broadband access network.  If the location information for the



Woundy & Kinnear         Expires September 2003                 [Page 8]

Internet Draft             DHCP Lease Query                   March 2003


   downstream next hop is missing, the access concentrator sends one or
   more DHCPLEASEQUERY message(s), each containing the IP address of the
   downstream next hop in the "ciaddr" field.

   An alternative approach is to send in a DHCPLEASEQUERY message with
   the "ciaddr" field empty and the MAC address (i.e., "htype", "hlen",
   and "chaddr" fields) with a valid MAC address or a Client-identifier
   option (option 61) appearing in the options area.  In this case, the
   DHCP server SHOULD return an IP address in the "ciaddr" if it has any
   record of the client described by the Client-identifier or MAC
   address. In the absence of specific configuration information to the
   contrary (see Section 6.4) it MUST be the IP address most recently
   used by the client described by the MAC address or Client-identifier
   option (or the client described by both, if both appear).

   The DHCP servers that implement this protocol always send a response
   to the DHCPLEASEQUERY message: either a DHCPLEASEKNOWN, DHCPLEASEAC-
   TIVE or DHCPLEASEUNKNOWN (or in some cases, DHCPUNIMPLEMENTED). The
   reasons why a DHCPLEASEKNOWN, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN
   message might be generated are explained in the specific query
   regimes, below.

   Servers which do not implement the DHCPLEASEQUERY message fall into
   two classes.  Those that simply do not know about the DHCPLEASEQUERY
   message will simply not respond to it, so clients which send the
   DHCPLEASEQUERY message MUST be prepared to deal with this behavior.
   Servers which are aware of the DHCPLEASEQUERY message but do not
   implement it SHOULD respond with a DHCPUNIMPLEMENTED message but MAY
   simply not respond.

   The DHCPLEASEQUERY message can support three query regimes:

      o Query by IP address:

        For this query, the requester supplies only an IP address in the
        DHCPLEASEQUERY message.  The DHCP server will return any infor-
        mation that it has on the most recent client to have been
        assigned that IP address.

        The DHCP server replies with a DHCPLEASEKNOWN or DHCPLEASEACTIVE
        message if the IP address in the DHCPLEASEQUERY message
        corresponds to an IP address about which the server has defini-
        tive information (ie., it is authorized to lease this IP
        address).  The server replies with a DHCPLEASEUNKNOWN message if
        the server does not have definitive information concerning the
        address in the DHCPLEASEQUERY message.

        A server which implements the DHCPLEASEQUERY message MUST



Woundy & Kinnear         Expires September 2003                 [Page 9]

Internet Draft             DHCP Lease Query                   March 2003


        implement this capability.

      o Query by MAC address:

        For this query, the requester supplies only a MAC address in the
        DHCPLEASEQUERY message.  The DHCP server will return any infor-
        mation that it has on the IP address most recently accessed by a
        client with that MAC address.  In addition, it may supply addi-
        tion IP addresses which have been associated with that MAC
        address in different subnets.  Information about these bindings
        can then be found using the Query by IP Address, described
        above.

        The DHCP server replies with a DHCPLEASEKNOWN or DHCPLEASEACTIVE
        message if the MAC address in the DHCPLEASEQUERY message
        corresponds to an IP address about which the server has defini-
        tive information (ie., it is authorized to lease this IP
        address).  The server replies with a DHCPLEASEUNKNOWN message if
        the server does not have definitive information concerning the
        MAC address in the DHCPLEASEQUERY message.

        A server which implements the DHCPLEASEQUERY message SHOULD
        implement this capability.  If it does not, it SHOULD respond
        with a DHCPUNIMPLEMENTED message when it receives a query by MAC
        address.

      o Query by Client-identifier option:

        For this query, the requester supplies only a client-id option
        in the DHCPLEASEQUERY message.  The DHCP server will return any
        information that it has on the IP address most recently accessed
        by a client with that client-id.  In addition, it may supply
        addition IP addresses which have been associated with client-id
        in different subnets.  Information about these bindings can then
        be found using the Query by IP Address, described above.

        The DHCP server replies with a DHCPLEASEKNOWN or DHCPLEASEACTIVE
        message if the client-id in the DHCPLEASEQUERY message
        corresponds to an IP address about which the server has defini-
        tive information (ie., it is authorized to lease this IP
        address).  The server replies with a DHCPLEASEUNKNOWN message if
        the server does not have definitive information concerning the
        client-id in the DHCPLEASEQUERY message.

        A server which implements the DHCPLEASEQUERY message SHOULD
        implement this capability.  If it does not, it SHOULD respond
        with a DHCPUNIMPLEMENTED message when it receives a query by
        Client-identifier option address.



Woundy & Kinnear         Expires September 2003                [Page 10]

Internet Draft             DHCP Lease Query                   March 2003


   Generally, the query by IP address is likely to be the most efficient
   and widely implemented form of leasequery, and it SHOULD be used if
   at all possible.  Use of the other two query formats SHOULD be minim-
   ized, as they can potentially place a large load on some servers.

   The DHCPLEASEKNOWN or DHCPLEASEACTIVE message reply MUST always con-
   tain the IP address in the ciaddr field and SHOULD contains the phy-
   sical address of the IP address lease owner in the "htype", "hlen",
   and "chaddr" fields. The Parameter Request List (option 55) can be
   used to request specific options to be returned about the IP address
   in the ciaddr.  The reply often contains the time until expiration of
   the lease, and the original contents of the Relay Agent Information
   option [RFC 3046].  The access concentrator uses the "chaddr" and
   Relay Agent Information option to construct location information,
   which can be cached on the access concentrator until lease expira-
   tion.

   Any DHCP server which supports the DHCPLEASEQUERY message SHOULD save
   the information from the most recent Relay Agent Information option
   (option 82) [RFC 3046] associated with every IP address which it
   serves. It is assumed that most clients which generate the DHCPLEASE-
   QUERY message will ask for the Relay Agent Information option (option
   82) in the Parameter Request List (option 55), and so supporting the
   DHCPLEASEQUERY message without having the Relay Agent Information
   option around to return to the client is likely to be less than help-
   ful.

   A server which implements DHCPLEASEQUERY SHOULD also save the infor-
   mation on the most recent Vendor class identifier, option 60, associ-
   ated with each IP address, since this option is also a likely candi-
   date to be requested by clients sending the DHCPLEASEQUERY message.


6.  Protocol Details


6.1.  Definitions required for DHCPLEASEQUERY processing

   The operation of the DHCPLEASEQUERY message requires the definition
   of the following new and extended values for the DHCP packet beyond
   those defined by [RFC 2131] and [RFC 2132].  See also Section 8, IANA
   considerations.

      1. The message type option (option 53) from [RFC 2132] requires
         five new values:  The DHCPLEASEQUERY message itself and its
         three possible responses DHCPLEASEKNOWN, DHCPLEASEACTIVE,
         DHCPLEASEUNKNOWN, and DHCPUNIMPLEMENTED.  The values of these
         message types are shown below in a reproduction of the table



Woundy & Kinnear         Expires September 2003                [Page 11]

Internet Draft             DHCP Lease Query                   March 2003


         from [RFC 2132]:


                    Value   Message Type
                    -----   ------------
                      1     DHCPDISCOVER
                      2     DHCPOFFER
                      3     DHCPREQUEST
                      4     DHCPDECLINE
                      5     DHCPACK
                      6     DHCPNAK
                      7     DHCPRELEASE
                      8     DHCPINFORM
                      TBD   DHCPLEASEQUERY
                      TBD   DHCPLEASEKNOWN
                      TBD   DHCPLEASEUNKNOWN
                      TBD   DHCPLEASEACTIVE
                      TBD   DHCPUNIMPLEMENTED




      2. There is a new bit defined in the "flags" field of the DHCP
         packet (see Section 1, Figure 1 and Table 1 of [RFC 2131]).  It
         is called the R: RESERVATION flag.  The revised Figure 2 from
         [RFC 2131] is show here:


                                             1 1 1 1 1 1
                         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         |B|R|           MBZ             |
                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         B:  BROADCAST flag
                         R:  RESERVATION FLAG

                         MBZ:  MUST BE ZERO (reserved for future use)

                         Revised Figure 2 from RFC2131:
                         Format of the 'flags' field



      3. There is a new option, the client-last-transaction-time:

         client-last-transaction-time




Woundy & Kinnear         Expires September 2003                [Page 12]

Internet Draft             DHCP Lease Query                   March 2003


         This option allows the receiver to determine the time of the
         most recent access of the client.  It is particularly useful
         when DHCPLEASEKNOWN messages from two different DHCP servers
         need to be compared, although it can be useful in other situa-
         tions.  The value is a duration in seconds from the current
         time into the past when this IP address was most recently the
         subject of communication between the client and the DHCP
         server.

         This MUST NOT be an absolute time.  This MUST NOT be an abso-
         lute number of seconds since Jan 1, 1970.  Instead, this MUST
         be an integer number of seconds in the past from the time the
         DHCPLEASEKNOWN message is sent that the client last dealt with
         this server about this IP address.  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 when the message was sent.

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


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


      4. There in a second new option, the associated-ip option:

         associated-ip

         This option is used to return all of the IP addresses associ-
         ated with the DHCP client specified in a particular DHCPLEASE-
         QUERY message.

         The code for this option is TBD.  The minimum length for this
         option is 4 octets, and the length MUST always be a multiple of
         4.


             Code   Len         Address 1               Address 2
            +-----+-----+-----+-----+-----+-----+-----+-----+--
            | TBD |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  ...
            +-----+-----+-----+-----+-----+-----+-----+-----+--





Woundy & Kinnear         Expires September 2003                [Page 13]

Internet Draft             DHCP Lease Query                   March 2003


6.2.  Sending the DHCPLEASEQUERY Message

   The DHCPLEASEQUERY message is typically sent by an access concentra-
   tor.  The DHCPLEASEQUERY message uses the DHCP message format as
   described in [RFC 2131], and uses message number TBD in the DHCP Mes-
   sage Type option (option 53).  The DHCPLEASEQUERY message has the
   following pertinent message contents:

      o The giaddr MUST be set to the IP address of the requester (i.e.
        the access concentrator).  The giaddr is independent of the
        "ciaddr" field to be searched -- it is simply the return address
        of for the DHCPLEASEKNOWN or DHCPLEASEUNKNOWN message from the
        DHCP server.

      o The Parameter Request List option (option 55) SHOULD be set to
        the options of interest to the requester.  The interesting
        options are likely to include the IP Address Lease Time option
        (option 51), the Relay Agent Information option (option 82) and
        possibly the Vendor class identifier option (option 60).  In the
        absence of a Parameter Request List option, the server will
        return the same options it would return for a DHCPREQUEST mes-
        sage which didn't contain a DHCPLEASEQUERY message, which
        includes those mandated by [RFC 2131, Section 4.3.1] as well as
        any options which the server was configured to always return to
        a client.

      o The Reservation bit in the "flags" field of the DHCP packet (see
        [RFC 2131] and Section 6.1 of this document) is not used when
        sending a DHCPLEASEQUERY message.

   Additional details concerning different query types are:

      o Query by IP address:

        The values of htype, hlen, and chaddr MUST be set to 0.

        The "ciaddr" field MUST be set to the IP address of the lease to
        be queried.

        The Client-identifier option (option 61) MUST NOT appear in the
        packet.

      o Query by MAC address:

        The values of htype, hlen, and chaddr MUST be set to the value
        of the MAC address to search for.

        The "ciaddr" field MUST be set to zero.



Woundy & Kinnear         Expires September 2003                [Page 14]

Internet Draft             DHCP Lease Query                   March 2003


        The Client-identifier option (option 61) MUST NOT appear in the
        packet.

      o Query by Client-identifier option:

        There MUST be a Client-identifier option (option 61) in the
        DHCPLEASEQUERY message.

        The "ciaddr" field MUST be set to zero.

        The values of htype, hlen, and chaddr MUST be set to 0.

   The DHCPLEASEQUERY message SHOULD be sent to a DHCP server which is
   known to possess authoritative information concerning the IP address.
   The DHCPLEASEQUERY message MAY be sent to more than one DHCP server,
   and in the absence of information concerning which DHCP server might
   possess authoritative information concerning the IP address, it
   SHOULD be sent to all DHCP servers configured for the associated
   relay agent (if any are known).

6.3.  Receiving the DHCPLEASEQUERY Message

   A DHCPLEASEQUERY message MUST have a non-zero giaddr.  The DHCPLEASE-
   QUERY message MUST have exactly one of:  a non-zero ciaddr, a non-
   zero "htype"/"hlen"/"chaddr", or a Client-identifier.

   The DHCP server which receives a DHCPLEASEQUERY message MUST base its
   response on the particular data item used in the query.

   The giaddr is used only for the destination address of any generated
   response and, while required, is not otherwise used in generating the
   response to the DHCPLEASEQUERY message.  It MUST NOT be used to res-
   trict the processing of the query in any way, and MUST NOT be used
   locate a subnet to which the ciaddr (if any) must belong.

6.4.  Responding to the DHCPLEASEQUERY Message

   There are four possible responses to a DHCPLEASEQUERY message:

      o DHCPLEASEKNOWN

        The server MUST respond with a DHCPLEASEKNOWN message if this
        server has information about the IP address or client in ques-
        tion, but there is no active lease for the IP address or client
        specified in the query.  If the query was by IP address, then
        the DHCPLEASEKNOWN message indicates that this server manages
        this IP address. In the case where a client was specified either
        by Client-identifier or MAC address, then the DHCPLEASEKNOWN



Woundy & Kinnear         Expires September 2003                [Page 15]

Internet Draft             DHCP Lease Query                   March 2003


        message indicates that the client is known to the DHCP server,
        and was the most recent client associated with a particular IP
        address.

        For any type of query, if the client specified in the DHCPLEASE-
        KNOWN message has a reservation for the IP address specifed in
        the ciaddr, then the server MUST set the R (reservation) bit in
        the DHCPLEASEKNOWN message.

      o DHCPLEASEUNKNOWN

        The DHCPLEASEKNOWN message indicates that the server knows noth-
        ing about the IP address or client specified in the DHCPLEASE-
        QUERY message.

        The server MUST response with a DHCPLEASEKNOWN message when this
        server has no information about the IP address or client speci-
        fied in the DHCPLEASEQUERY message.

        When responding with a DHCPLEASEUNKNOWN, the DHCP server SHOULD
        NOT include other DHCP options in the response.  The R (reserva-
        tion) bit MUST NOT be set in the "flags" field of the DHCP
        packet.

      o DHCPLEASEACTIVE

        The DHCPLEASEACTIVE message indicates that the server not only
        knows about the IP address and client specified in the
        DHCPLEASEACTIVE message but also that there is an active lease
        by that client for that IP address.

        In some cases, the DHCP server MAY be configured to return a
        DHCPLEASEACTIVE message when there is no active lease but when
        there is a reservation by the specified client for the IP
        address in the "ciaddr" field of the DHCPLEASEACTIVE message.  A
        server would be so configured when it was desired that the
        access concentrator would allow access to IP addresses which are
        not DHCP clients.  In this case the DHCP server SHOULD NOT place
        an IP Address Lease Time (option 51) in the DHCPLEASEACTIVE mes-
        sage, allowing the access concentrator to determine that this is
        a DHCPLEASEACTIVE message for an IP address without a currently
        active lease.

        The server MUST respond with a DHCPLEASEACTIVE message when the
        IP address returned in the "ciaddr" field is currently leased.
        If the client returned in the DHCPLEASEACTIVE message has a
        reservation for that IP address recorded in the DHCP server,
        then the R (reservation) bit MUST be set in the "flags" field of



Woundy & Kinnear         Expires September 2003                [Page 16]

Internet Draft             DHCP Lease Query                   March 2003


        the DHCP packet.

      o DHCPUNIMPLEMENTED

        The DHCPUNIMPLEMENTED response to the DHCPLEASEQUERY message
        indicates that the particular form of DHCPLEASEQUERY used is not
        implemented in this DHCP server. It may mean that the DHCPLEASE-
        QUERY message as a whole is not implemented by this DHCP server
        although it is usually used to indicate that a query by Client-
        identifier or MAC address is not implemented by a DHCP server
        that otherwise supports a DHCPLEASEQUERY by IP address.

        The DHCPUNIMPLEMENTED message can apply to any unimplemented
        messages, and MAY be used to respond to messages other than
        DHCPLEASEQUERY.

6.4.1.  Determining the IP address to which to respond

   Since the response to a DHCPLEASEQUERY request can only contain full
   information about one IP address -- the one that appears in the
   "ciaddr" field -- determination of which IP address to which to
   respond is a key issue. Of course, the values of additional IP
   addresses for which a client has a lease must also be returned in the
   associated-ip option (Section 6.1, #4).  This is the only information
   returned not directly associated with the IP address in the "ciaddr"
   field.

   In the event that an IP address appears in the "ciaddr" field of a
   DHCPLEASEQUERY message, if that IP address is one managed by the DHCP
   server, then that IP address MUST be set in the "ciaddr" field of a
   DHCPLEASEKNOWN message.

   If the IP address is not managed by the DHCP server, then a
   DHCPLEASEUNKNOWN message must be returned.

   If the "ciaddr" field of the DHCPLEASEQUERY is zero, then the
   DHCPLEASEQUERY message is a query by Client-identifier or MAC
   address. In this case, the client's identity is any client which has
   proffered an identical Client-identifier option (if the Client-
   identifier option appears in the DHCPLEASEQUERY message), or an
   identical MAC address (if the MAC address fields in the DHCPLEASE-
   QUERY message are non-zero).  This client matching approach will, for
   the purposes of this section, be described as "Client-identifier or
   MAC address".

   The Reservations bit (the R bit) has no meaning in the DHCPLEASEQUERY
   message and is used only to indicate the existence of a reservation
   in a DHCPLEASEKNOWN or DHCPLEASEACTIVE message.



Woundy & Kinnear         Expires September 2003                [Page 17]

Internet Draft             DHCP Lease Query                   March 2003


   If the "ciaddr" field is zero in a DHCPLEASEQUERY message, then the
   IP address placed in the "ciaddr" field of the DHCPLEASEKNOWN or
   DHCPLEASEACTIVE message MUST be that of an IP address for which the
   client that most recently used the IP address matches the Client-
   identifier or MAC address specified in the DHCPLEASEQUERY message.

   If there is only a single IP address which fulfills this criteria,
   then it MUST be placed in the "ciaddr" field of the DHCPLEASEKNOWN or
   DHCPLEASEACTIVE message.

   In the case where more than one IP address has been accessed by the
   client specified by the MAC address or Client-identifier option, then
   the DHCP server MUST return the IP address returned to the client in
   the most recent transaction with the client unless the DHCP server
   has been configured by the server administrator to use some other
   preference mechanism.

   If, after all of the above processing, no value is set in the
   "ciaddr" field of the DHCPLEASEKNOWN or DHCPLEASEACTIVE message, then
   a DHCPLEASEUNKNOWN message MUST be returned instead.

6.4.2.  Building a DHCPLEASEKNOWN or DHCPLEASEACTIVE message once the
"ciaddr" field is set

   Once the "ciaddr" field of the DHCPLEASEKNOWN or DHCPLEASEACTIVE mes-
   sage is set, the rest of the processing largely involves returning
   information about the IP address specified in the "ciaddr" field.

   If the IP address in the "ciaddr" field of the DHCPLEASEKNOWN or
   DHCPLEASEACTIVE message is currently leased by the client specified
   in the Client-identifier or MAC address returned in the DHCPLEASE-
   KNOWN or DHCPLEASEACTIVE message, then the message MUST be a
   DHCPLEASEACTIVE message, otherwise it MUST be a DHCPLEASEKNOWN mes-
   sage.

   It MAY be possible to configure a DHCP server to return a
   DHCPLEASEACTIVE message even though the IP address specified in the
   "ciaddr" field is not currently leased if there is a reservation for
   that IP address by the client specified in the Client-identifier or
   MAC address fields of the DHCPLEASEACTIVE message.  In this case,
   there MUST NOT be an IP Address Lease Time option (option 51) in the
   packet.

   The R (reservation) bit must be set in the "flags" field if the IP
   address in the "ciaddr" field is reserved for the client returned in
   the MAC address or Client-identifier option.

   The IP address in the "ciaddr" field of the DHCPLEASEKNOWN or



Woundy & Kinnear         Expires September 2003                [Page 18]

Internet Draft             DHCP Lease Query                   March 2003


   DHCPLEASEACTIVE message MUST be one for which this server is respon-
   sible (or a DHCPLEASEUNKNOWN message would be have already been
   returned early in the processing described in the previous section).

   The MAC address of the DHCPLEASEKNOWN or DHCPLEASEACTIVE message MUST
   be set to the values which identify the client associated with the IP
   address in the "ciaddr" field of the DHCPLEASEKNOWN message.  This
   may be derived from a real DHCP client or from reservation informa-
   tion configured into the DHCP server.

   If the Client-identifier option (option 61) is specified in the
   Parameter Request List option (option 55), then the Client-identifier
   (if any) of the client associated with the IP address in the "ciaddr"
   field SHOULD be returned in the DHCPLEASEKNOWN or DHCPLEASEACTIVE
   message. This may be derived from a real DHCP client, or from reser-
   vation information configured into the DHCP server.

   In the case where more than one IP address has been involved in a
   DHCP message exchange with the client specified by the MAC address
   and/or Client-identifier option, then the list of all of the IP
   addresses SHOULD be returned in the associated-ip option (option
   TBD), if that option was requested as part of the Parameter Request
   List option.

   If the IP Address Lease Time option (option 51) is specified in the
   Parameter Request List and if there is a currently valid lease for
   the IP address specified in the ciaddr, then the DHCP server MUST
   return this option in the DHCPLEASEKNOWN with its value equal to the
   time remaining until lease expiration.  If there is no valid lease
   for the IP address, then the server MUST NOT return the IP Address
   Lease Time option (option 51).

   If there is no currently valid lease on the IP address in the
   "ciaddr" field, and if the "ciaddr" in the DHCPLEASEKNOWN message is
   currently reserved for the client specified by the client-id or MAC
   address, then the DHCP server MAY synthesize an IP Address Lease Time
   option for the DHCPLEASEKNOWN message if configured to do so.  Typi-
   cally the value of this option would itself be a configuration param-
   eter of the DHCP server.

   A request for the Renewal (T1) Time Value option or the Rebinding
   (T2) Time Value option in the Parameter Request List of the
   DHCPLEASEQUERY message MUST be handled like the IP Address Lease Time
   option is handled.  If there is a valid lease, then the DHCP server
   SHOULD return these options (when requested) with the remaining time
   until renewal or rebinding, respectively.  If there is not currently
   a valid lease for this IP address, the DHCP server MUST NOT return
   these options.



Woundy & Kinnear         Expires September 2003                [Page 19]

Internet Draft             DHCP Lease Query                   March 2003


   If the Relay Agent Information (option 82) is specified in the Param-
   eter Request List and if the DHCP server has saved the information
   contained in the most recent Relay Agent Information option, the DHCP
   server MUST include that information in a Relay Agent Information
   option in the DHCPLEASEKNOWN.

   The DHCPLEASEKNOWN or DHCPLEASEACTIVE message SHOULD include the
   values of all other options not specifically discussed above that
   were requested in the Parameter Request List of the DHCPLEASEQUERY
   message.  The DHCP server uses information from its lease binding
   database to supply the DHCPLEASEKNOWN or DHCPLEASEACTIVE option
   values.  The values of the options that were returned to the DHCP
   client would generally be preferred, but in the absence of those,
   options that were sent in DHCP client requests would be acceptable.

   In order to accommodate DHCPLEASEQUERY messages sent to a DHCP Fail-
   over secondary server [FAILOVER] when the primary server is down, the
   primary server MUST communicate the Relay Agent Information option
   (option 82) values to the secondary server via the DHCP Failover
   BNDUPD messages.

6.4.3.  Sending a DHCPLEASEKNOWN, DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN
message

   The server expects a giaddr in the DHCPLEASEQUERY message, and uni-
   casts the DHCPLEASEKNOWN, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message
   to the giaddr. If the giaddr field is zero, then the DHCP server MUST
   NOT reply to the DHCPLEASEQUERY message.

6.5.  Receiving a DHCPLEASEKNOWN, DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN
Message

   When a DHCPLEASEACTIVE message is received in response to the
   DHCPLEASEQUERY message it means that there is a currently active
   lease for this IP address in this DHCP server.  The access concentra-
   tor SHOULD use the information in the htype, hlen, and chaddr fields
   of the DHCPLEASEACTIVE as well as any Relay Agent Information option
   information included in the packet to refresh its location informa-
   tion for this IP address.

   When a DHCPLEASEKNOWN message is received in response to the
   DHCPLEASEQUERY message that means that there is no currently active
   lease for the IP address present in the DHCP server.  In this case,
   the access concentrator SHOULD cache this information in order to
   prevent unacceptable loads on the access concentrator and the DHCP
   server in the face of a malicious or seriously compromised device
   downstream of the access concentrator.  This cacheing could be as
   simple as simply setting a bit saying that a response was received



Woundy & Kinnear         Expires September 2003                [Page 20]

Internet Draft             DHCP Lease Query                   March 2003


   from a server which knew about this IP address but that there was no
   current lease.  This would of course need to be cleared when the
   access concentrator next "gleaned" that a lease for this IP address
   came into existance.

   If the R (reservation) bit is set in the "flags" field of the
   DHCPLEASEKNOWN message, it means that a reservation exists in the
   DHCP server for the IP address and associated client.  The access
   concentrator MAY be configured to allow the client access even though
   no currently outstanding lease is in place for this

   In either case, when a DHCPLEASEKNOWN or DHCPLEASEACTIVE message is
   received in response to a DHCPLEASEQUERY message, it means that the
   DHCP server which responded is a DHCP server which manages the IP
   address present in the ciaddr, and the Relay Agent SHOULD cache this
   information for later use.

   When a DHCPLEASEUNKNOWN message is received by an access concentrator
   which has sent out  a DHCPLEASEQUERY message, it means that the DHCP
   server contacted supports the DHCPLEASEQUERY message but that the
   DHCP server does not have definitive information concerning the IP
   address contained in the "ciaddr" field of the DHCPLEASEQUERY mes-
   sage.  If there is no IP address in the "ciaddr" field of the
   DHCPLEASEQUERY message, then a DHCPLEASEUNKNOWN message means that
   the DHCP server does not have definitive information concerning the
   any DHCP client specified in the "hlen", "htype", and "chaddr" fields
   or the Client-identifier option of the DHCPLEASEQUERY message.

   The access concentrator SHOULD cache this information, and only
   infrequently direct a DHCPLEASEQUERY message to a DHCP server that
   responded to a DHCPLEASEQUERY message for a particular "ciaddr" field
   with a DHCPLEASEUNKNOWN.

   When a DHCPUNIMPLEMENTED message is received by an access concentra-
   tor, it means that the particular aspect of DHCPLEASEQUERY processing
   requested is not implemented in the responding server.  It may or may
   not be the case that other aspects of DHCPLEASEQUERY processing are
   not implemented in that server.

6.6.  Receiving no response to the DHCPLEASEQUERY Message

   When an access concentrator receives no response to a DHCPLEASEQUERY
   message, there are several possible reasons:

      o The DHCPLEASEQUERY or a corresponding DHCPLEASEKNOWN,
        DHCPLEASEACTIVE or DHCPLEASEUNKNOWN were lost during transmis-
        sion or the DHCPLEASEQUERY arrived at the DHCP server but it was
        dropped because the server was too busy.



Woundy & Kinnear         Expires September 2003                [Page 21]

Internet Draft             DHCP Lease Query                   March 2003


      o The DHCP server doesn't support DHCPLEASEQUERY.

   In the first of the cases above, a retransmission of the DHCPLEASE-
   QUERY would be appropriate, but in the second of the two cases, a
   retransmission would not be appropriate.  There is no way to tell
   these two cases apart (other than, perhaps, because of a DHCP
   server's response to other DHCPLEASEQUERY messages indicating that it
   does or does not support the DHCPLEASEQUERY message).

   An access concentrator which utilizes the DHCPLEASEQUERY message
   SHOULD attempt to resend DHCPLEASEQUERY messages to servers which do
   not respond to them using a backoff algorithm for the retry time that
   approximates an exponential backoff.  The access concentrator SHOULD
   adjust the backoff approach such that DHCPLEASEQUERY messages do not
   arrive at a server which is not otherwise known to support the
   DHCPLEASEQUERY message at a rate of more than approximately one
   packet every 10 seconds, and yet (if the access concentrator needs to
   send DHCPLEASEQUERY messages) not less than one DHCPLEASEQUERY per
   minute.

   In practice this approach would probably best be handled by a per-
   server timer that backs off exponentially to once a minute, and a
   per-message backoff timer that also backs off to once a minute.  The
   per-server timer would start off expired, and in the expired state
   only one DHCPLEASEQUERY message would be queued for the associated
   server.  This DHCPLEASEQUERY message would be sent with the backoff
   quickly moving to once a minute until a DHCPLEASEACTIVE, DHCPLEASE-
   KNOWN, or DHCPLEASEUNKNOWN message reply was received.  Whenever one
   of these messages is received, the per-server timer is reset, and
   whenever the per-server timer has not expired, more than one indivi-
   dual DHCPLEASEQUERY messages can be outstanding to the DHCP server at
   one time.  It is recommended that this number be limited to a rela-
   tively small number, for example, 100 or 200, to avoid swamping the
   DHCP server.  Each of these messages should have its own per-message
   retry timer.  This would retransmit each message and backoff as dis-
   cussed above. In the event the per-server timer goes off, then all
   outstanding messages SHOULD be dropped except for a single DHCPLEASE-
   QUERY message which is used to poll the server until such time as
   another DHCPLEASEACTIVE, DHCPLEASEKNOWN, or DHCPLEASEUNKNOWN message
   is received.

6.7.  Using the DHCPLEASEQUERY message in a failover environment

   When using the DHCPLEASEQUERY message in an environment where multi-
   ple DHCP server may contain authoritative information about the same
   IP address (such as when failover [FAILOVER] is operating), there
   could be some difficulty in deciding which results are the most use-
   ful if two servers respond with DHCPLEASEKNOWN messages to the same



Woundy & Kinnear         Expires September 2003                [Page 22]

Internet Draft             DHCP Lease Query                   March 2003


   query.

   In this case, the client-last-transaction-time can be used to decide
   which server has more recent information concerning the IP address
   returned in the "ciaddr" field.

7.  Security Considerations

   Access concentrators that use DHCP gleaning, refreshed with
   DHCPLEASEQUERY messages, will maintain accurate location information.
   Location information accuracy ensures that the access concentrator
   can forward data traffic to the intended location in the broadband
   access network, can perform IP source address verification of
   datagrams from the access network, and can encrypt traffic which can
   only be decrypted by the intended access modem (e.g.  [BPI] and
   [BPI+]).  As a result, the access concentrator does not need to
   depend on ARP broadcasts across the access network, which is suscep-
   tible to malicious hosts which masquerade as the intended IP end-
   points.  Thus, the DHCPLEASEQUERY message allows an access concentra-
   tor to provide considerably enhanced security.

   DHCP servers SHOULD prevent exposure of location information (partic-
   ularly the mapping of hardware address to IP address lease, which can
   be an invasion of broadband subscriber privacy) by leveraging DHCP
   authentication [RFC 3118].  With respect to authentication, the
   access concentrator acts as the "client".  The use of "Authentication
   Protocol 0" (using simple unencoded authentication token(s) between
   the access concentrator and the DHCP server) is straightforward.
   Alternatively, use of IPsec would also be a way to ensure security
   between the relay agent and the DHCP server.

   Access concentrators SHOULD minimize potential denial of service
   attacks on the DHCP servers by minimizing the generation of
   DHCPLEASEQUERY messages.  In particular, the access concentrator
   should employ negative cacheing (i.e.  cache both DHCPLEASEKNOWN and
   DHCPLEASEUNKNOWN responses to DHCPLEASEQUERY messages) and ciaddr
   restriction (i.e.  don't send a DHCPLEASEQUERY message with a ciaddr
   outside of the range of the attached broadband access networks).
   Together, these mechanisms limit the access concentrator to transmit-
   ting one DHCPLEASEQUERY message (excluding message retries) per legi-
   timate broadband access network IP address after a reboot event.

   In some environments it may be appropriate to configure a DHCP server
   with the IP addresses of the relay agents for which it may respond to
   DHCPLEASEQUERY messages, thereby allowing it to respond only to to
   requests from only a handful of relay agents.  This does not provide
   any true security, but may be useful to thwart unsophisticated
   attacks of various sorts.



Woundy & Kinnear         Expires September 2003                [Page 23]

Internet Draft             DHCP Lease Query                   March 2003


8.  IANA Considerations

   IANA has assigned seven values and one bit position for this docu-
   ment. See Section 6.1 for details.  There are five new messages
   types, which are the value of the message type option (option 53)
   from [RFC 2132].  The value for DHCPLEASEQUERY is TBD, the value for
   DHCPLEASEKNOWN is TBD, the value for DHCPLEASEACTIVE is TBD, the
   value for DHCPLEASEUNKNOWN is TBD and the value for DHCPUNIMPLEMENTED
   is TBD.  There is a new bit defined for the "flags" field of the DHCP
   packet (see Section 1, Figure 1 and Table 1 of [RFC 2131]).  The flag
   is called "R: RESERVATION flag", and its value is TBD.  Finally,
   there are two new DHCP option defined; the client-last-transaction-
   time option -- option code TBD, and the associated-ip option --
   option code TBD.

9.  Acknowledgments

   Jim Forster, Joe Ng, Guenter Roeck, and Mark Stapp contributed
   greatly to the initial creation of the DHCPLEASEQUERY message.

   Patrick Guelat suggested several improvements to support static IP
   addressing.


10.  References


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

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

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

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

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

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

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



Woundy & Kinnear         Expires September 2003                [Page 24]

Internet Draft             DHCP Lease Query                   March 2003


   [RFC 3118] Droms, R., Arbaugh, W., "Authentication for DHCP Mes-
      sages", RFC 3118, June 2001.

   [BPI] CableLabs, "Baseline Privacy Interface Specification", SP-BPI-
      I02-990319, March 1999, available at http://www.cablemodem.com/.

   [BPI+] CableLabs, "Baseline Privacy Plus Interface Specification",
      SP-BPI+-I04-000407, April 2000, available at
      http://www.cablemodem.com/.

   [DHCPMIB] Hibbs, R., Waters, G., "Dynamic Host Configuration Protocol
      (DHCP) Server MIB", draft-ietf-dhc-server-mib-06.txt, February
      2002.

   [DOCSIS] CableLabs, "Data-Over-Cable Service Interface Specifica-
      tions:  Cable Modem Radio Frequency Interface Specification SP-
      RFI-I05-991105", November 1999.

   [EUROMODEM] ECCA, "Technical Specification of a European Cable Modem
      for digital bi-directional communications via cable networks",
      Version 1.0, May 1999.

   [FAILOVER] Droms, R., Kinnear, K., Stapp, M., Volz, B., Gonczi, S.,
      Rabil, G., Dooley, M., Kapur, A., "DHCP Failover Protocol",
      draft-ietf-dhc-failover-10.txt, January 2002.



11.  Author's information


      Rich Woundy
      Comcast Cable
      27 Industrial Ave.
      Chelmsford, MA  01824

      Phone: (978) 244-4010

      EMail: richard_woundy@cable.comcast.com


      Kim Kinnear
      Cisco Systems
      250 Apollo Drive
      Chelmsford, MA  01824

      Phone: (978) 497-8000




Woundy & Kinnear         Expires September 2003                [Page 25]

Internet Draft             DHCP Lease Query                   March 2003



      EMail: kkinnear@cisco.com



12.  Intellectual Property Statement

The IETF takes no position regarding the validity or scope of any intel-
lectual property 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; neither does it represent that it has made any effort to
identify any such rights.  Information on the IETF's procedures with
respect to rights in standards-track and standards-related documentation
can be found in BCP-11.  Copies of claims of rights made available for
publication 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 implementors or users of this
specification can be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary rights
which may cover technology that may be required to practice this stan-
dard.  Please address the information to the IETF Executive Director.


13.  Full Copyright Statement

Copyright (C) The Internet Society (2003).  All Rights Reserved.

This document and translations of it may be copied and furnished to oth-
ers, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and dis-
tributed, in whole or in part, without restriction of any kind, provided
that the above copyright notice and this paragraph are included on all
such copies and derivative works.  However, this document itself may not
be modified in any way, such as by removing the copyright notice or
references to the Internet Society or other Internet organizations,
except as needed for the  purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet Stan-
dards process must be followed, or as required to translate it into
languages other than English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK



Woundy & Kinnear         Expires September 2003                [Page 26]

Internet Draft             DHCP Lease Query                   March 2003


FORCE DISCLAIMS 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 FIT-
NESS FOR A PARTICULAR PURPOSE.















































Woundy & Kinnear         Expires September 2003                [Page 27]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/