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

Dynamic Host Configuration Working Group                     Rich Woundy
INTERNET DRAFT                                               Kim Kinnear
                                                           Cisco Systems

                                                           November 2000
                                                        Expires May 2001


                            DHCP Lease Query
                   <draft-ietf-dhc-leasequery-00.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 (2000). All Rights Reserved.

Abstract

   Access concentrators that act as DHCP relay agents need to determine
   the endpoint locations of IP addresses across public broadband access
   networks such as cable, DSL, and wireless networks.  Because ARP
   broadcasts are undesirable in public networks, many access
   concentrator implementations "glean" location information from DHCP
   messages forwarded by its relay agent function.  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 obtains the location information directly



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   from the DHCP server(s) using a new, lightweight DHCPLEASEQUERY
   message.


1.  Introduction

   In many broadband access networks, 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




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

               Figure 2: DSL Environment for DHCPLEASEQUERY




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   Knowledge of this location information benefits the access concentra-
   tor 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 premise of this document is that the access concentrator obtains
   this location information 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 concentrator can query the DHCP server(s) for location
   information using the DHCPLEASEQUERY message.  The DHCPLEASEQUERY
   mechanism is the focus of this document.

   The DHCPLEASEQUERY message is a new DHCP message type transmitted
   from a DHCP relay agent to a DHCP server.  The DHCPLEASEQUERY-aware
   relay agent sends the DHCPLEASEQUERY message when it needs to know
   the location of an IP endpoint.  The DHCPLEASEQUERY-aware DHCP server
   replies with a DHCPACK or DHCPNAK message.  The DHCPACK response to a
   DHCPLEASEQUERY message allows the relay agent to determine the IP
   endpoint location, and the remaining duration of the IP address
   lease.


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.



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        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.

      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 "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



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        set of subnet address pools.

      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 access concentrators to send
   DHCPLEASEQUERY messages to DHCP servers, to obtain location informa-
   tion 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]. Unlike previous DHCP message types, the DHCP relay
   agent originates and sends the DHCPLEASEQUERY message to the DHCP
   server, and processes the reply from the DHCP server (a DHCPACK or
   DHCPNAK).

   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) in Failover BNDUPD messages to the secon-
   dary DHCP server, as recommended by section 7.1.1 of [FAILOVER].

   The DHCPLEASEQUERY message is a query message only, and does not
   affect the state of the IP address lease.


4.  Design Goals

   The core requirement of this document is to provide a lightweight



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   mechanism for access concentrator implementations to obtain location
   information for broadband access network devices.  The specifics of
   the broadband environment that drove the approach of this document
   follow.


   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] nor leverage the proposed DHCP LDAP schema
   [DHCPSCHEMA].


   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
   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



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   persist across access concentrator reboots (due to lack of stable
   storage), and almost never persists across concentrator replacements.


   4.4.  DHCP Servers Are Most 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

   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
   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.

   The DHCP servers that implement this protocol always sends a response
   to the DHCPLEASEQUERY message: either a DHCPACK or DHCPNAK. The DHCP
   server replies to the DHCPLEASEQUERY message with a DHCPACK message
   if the "ciaddr" corresponds to an IP address about which the server
   has definitive information (i.e., it is authorized to lease this IP
   address).  The server replies with a DHCPNAK message if the server
   does not have definitive location information concerning the lease



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   implied by the "ciaddr".  Note that non-DHCPLEASEQUERY-literate DHCP
   servers are expected to drop the DHCPLEASEQUERY message silently.

   The DHCPACK message reply contains the physical address of the IP
   address lease owner in the "htype", "hlen", and "chaddr" fields.  The
   reply often contains the time until expiration of the lease, and the
   original contents of the Relay Agent Information option [RELAYAGEN-
   TINFO].  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 expiration.

   Any DHCP server which supports the DHCPLEASEQUERY message SHOULD save
   the information from the most recent Relay Agent Information option
   [RELAYAGENTINFO] associated with every IP address which it serves.


6.  Protocol Details


6.1.  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 values of htype, hlen, and chaddr MUST be set to 0.  This
        DHCP message is used for querying on IP address, not on hardware
        address or DHCP client ID.

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

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

      o The Parameter Request List SHOULD be set to the options of
        interest to the requestor.  The interesting options are likely
        to include the IP Address Lease Time option (option 51) and the
        Relay Agent Information option (82).

   The access concentrator SHOULD ensure that the ciaddr mentioned in
   the DHCPLEASEQUERY message is a local subnet of the interface speci-
   fied for the client.




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   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).

6.2.  Receiving the DHCPLEASEQUERY Message

   A DHCPLEASEQUERY message MUST have a non-zero ciaddr and MUST have a
   non-zero giaddr.  The DHCP server which receives a DHCPLEASEQUERY
   message MUST base its response (if any) on the IP address represented
   by the ciaddr in the DHCPLEASEQUERY message.  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.

6.3.  Responding to the DHCPLEASEQUERY Message

   The DHCP server MUST respond to a DHCPLEASEQUERY message with a
   DHCPACK message if the ciaddr corresponds to an IP address which is
   managed by the DHCP server.

   The DHCP server SHOULD respond to a DHCPLEASEQUERY message with a
   DHCPACK if the ciaddr corresponds to an IP address about which the
   DHCP server has definitive information, even if the ciaddr does not
   correspond to an IP address which might be dynamically allocated by
   the DHCP server -- for example, a statically allocated IP address
   which is known to be reserved for a particular device by the DHCP
   server.

   The DHCP server MUST respond to the DHCPLEASEQUERY with a DHCPNAK if
   the DHCP server supports the DHCPLEASEQUERY message but does not have
   definitive information concerning the IP address in the ciaddr.  When
   responding with a DHCPNAK, the DHCP server SHOULD NOT include other
   DHCP options in the response.

   A DHCP server which does not support the DHCPLEASEQUERY message MUST
   NOT respond to the DHCPLEASEQUERY message.

   When responding to a DHCPLEASEQUERY message with a DHCPACK:

      o If the IP Address Lease Time (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 DHCPACK with its value equal to
        the time remaining until lease expiration.  If there is no valid



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        lease for the IP address, then the server MUST NOT return the IP
        Address Lease Time option (option 51).  This allows the reques-
        tor (i.e.  the access concentrator) to determine if there is
        currently a valid lease for the IP address as well as the time
        until the lease expiration.

        A request for the Renewal (T1) Time Value option or the Rebind-
        ing (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.

      o If the DHCP server has information about the most recent device
        associated with the IP address specified in the ciaddr, then the
        DHCP server MUST encode the physical address of that device in
        the htype, hlen, and chaddr fields.  Otherwise, the values of
        htype, hlen, and chaddr MUST be set to 0 in the DHCPACK.  If the
        IP Address Lease Time (option 51) is returned in the DHCPACK
        (indicating a currently valid lease by some device for this IP
        address), the DHCP server MUST encode the physical address of
        the device which owns the lease in the htype, hlen, and chaddr
        fields.

      o If the Relay Agent Information (option 82) is specified in the
        Parameter 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 DHCPACK.

        In environments with non-DHCP-enabled devices, when the DHCP
        server knows the network access information (perhaps through
        server configuration), the DHCP server MAY generate its own
        Relay Agent Information option value in the DHCPACK; in such
        cases, the DHCP server MUST generate an option value that the
        access concentrator can process.

      o The DHCPACK 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 the lease binding database to
   supply the DHCPACK option values.

   In order to accommodate DHCPLEASEQUERY messages sent to a DHCP Fail-
   over secondary server [FAILOVER] when the primary server is down, the



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   primary server MUST communicate the Relay Agent Information option
   (82) values to the secondary server via the DHCP Failover BNDUPD mes-
   sages.

   The server expects a giaddr in the DHCPLEASEQUERY message, and uni-
   casts the DHCPACK or DHCPNAK to the giaddr.  If the giaddr field is
   zero, then the DHCP server does not reply to the DHCPLEASEQUERY mes-
   sage.

6.4.  Receiving a DHCPACK or DHCPNAK response to the DHCPLEASEQUERY Mes-
sage

   When a DHCPACK message is received in response to the DHCPLEASEQUERY
   message and the DHCPACK has an IP Address Lease Time option value
   that is non-zero, it means that there is a currently active lease for
   this IP address in this DHCP server.  The access concentrator SHOULD
   use the information in the htype, hlen, and chaddr fields of the
   DHCPACK as well as any Relay Agent Information option information
   included in the packet to refresh its location information for this
   IP address.

   When a DHCPACK message is received in response to the DHCPLEASEQUERY
   message and the DHCPACK has no IP Address Lease Time option (though
   one was requested in the Parameter Request List), 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 con-
   centrator and the DHCP server in the face of a malicious or seriously
   compromised device downstream of the access concentrator.

   In either case, when a DHCPACK 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 DHCPNAK 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 not have definitive information concerning the IP address con-
   tained in the ciaddr of the DHCPLEASEQUERY message.  It doesn't
   manage this IP address.

   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 with a
   DHCPNAK.





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6.5.  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 DHCPACK or DHCPNAK were
        lost during transmission or the DHCPLEASEQUERY arrived at the
        DHCP server but it was dropped because the server was too busy.

      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
   supports 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 not 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.

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 [DHCPAUTH].  With respect to authentication, the



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   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.  The
   use of "Authentication Protocol 1" (using "delayed authentication")
   is under investigation, since it requires two message round trips.

   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 caching (i.e.  cache both DHCPACK and DHCPNAK
   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 transmitting one
   DHCPLEASEQUERY message (excluding message retries) per legitimate
   broadband access network IP address after a reboot event.

8.  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.

   Ralph Droms, Mark Stapp and Andy Sudduth contributed to making the
   draft more complete and helped add clarity.


9.  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.




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

   [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/.

   [DHCPAUTH] Droms, R., Arbaugh, W., "Authentication for DHCP Mes-
      sages", draft-ietf-dhc-authentication-14.txt, July 2000.

   [DHCPMIB] Hibbs, R., Waters, G., "Dynamic Host Configuration Protocol
      (DHCP) Server MIB", draft-ietf-dhc-server-mib-05.txt, November
      2000.

   [DHCPSCHEMA] Bennett, A., Volz, B., "DHCP Schema for LDAP", draft-
      ietf-dhc-schema-02.txt, March 2000.

   [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-08.txt, November 2000.

   [RELAYAGENTINFO] Patrick, M., "DHCP Relay Agent Information Option",
      draft-ietf-dhc-agent-options-12.txt, October 2000.


10.  Author's information


      Rich Woundy
      Kim Kinnear
      Cisco Systems
      250 Apollo Drive
      Chelmsford, MA  01824

      Phone: (978) 244-8000





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      EMail: rwoundy@cisco.com
             kkinnear@cisco.com



11.  Full Copyright Statement

Copyright (C) The Internet Society (2000).  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
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.

Open Issues

   These issues need to be resolved by the working group:


      1. May the DHCPLEASEQUERY message be sent by parties other than
         relay agents?

         [Resolved]  Sure, you can't stop them in any case.

      2. Should the DHCPLEASEQUERY message be extended to find lease
         information by physical address or by DHCP Client ID? This
         might be useful for non-router access concentrators.




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         [Resolved] There has been no working group interest in this
         aspect of the DHCPLEASEQUERY message, so it has been specifi-
         cally excluded.

      3. How can the DHCPLEASEQUERY message exchange be modified to lev-
         erage the better DHCP authentication protocol types?

         [Unresolved]











































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