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rfc:rfc4388

Network Working Group R. Woundy Request for Comments: 4388 Comcast Cable Category: Standards Track K. Kinnear

                                                         Cisco Systems
                                                         February 2006
       Dynamic Host Configuration Protocol (DHCP) Leasequery

Status of This Memo

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

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 A Dynamic Host Configuration Protocol version 4 (DHCPv4) server is
 the authoritative source of IP addresses that it has provided to
 DHCPv4 clients.  Other processes and devices that already make use of
 DHCPv4 may need to access this information.  The leasequery protocol
 provides these processes and devices a lightweight way to access IP
 address information.

Woundy & Kinnear Standards Track [Page 1] RFC 4388 DHCP Leasequery February 2006

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................5
 3. Background ......................................................7
 4. Design Goals ....................................................7
    4.1. Broadcast ARP Is Undesirable ...............................7
    4.2. SNMP and LDAP Are Not Appropriate ..........................8
    4.3. DHCP Relay Agent Functionality Is Common ...................8
    4.4. DHCP Servers Are a Reliable Source of Location
         Information ................................................9
    4.5. Minimal Additional Configuration Is Required ...............9
 5. Protocol Overview ...............................................9
 6. Protocol Details ...............................................12
    6.1. Definitions Required for DHCPLEASEQUERY Processing ........12
    6.2. Sending the DHCPLEASEQUERY Message ........................14
    6.3. Receiving the DHCPLEASEQUERY Message ......................15
    6.4. Responding to the DHCPLEASEQUERY Message ..................16
    6.5. Receiving a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, or
         DHCPLEASEUNKNOWN Message ..................................20
    6.6. Receiving No Response to the DHCPLEASEQUERY Message .......21
    6.7. Lease Binding Data Storage Requirements ...................22
    6.8. Using the DHCPLEASEQUERY Message with Multiple
         DHCP Servers ..............................................23
 7. Security Considerations ........................................23
 8. IANA Considerations ............................................24
 9. Acknowledgements ...............................................24
 10. References ....................................................25
    10.1. Normative References .....................................25
    10.2. Informative References ...................................25

1. Introduction

 A DHCPv4 server contains considerable authoritative information
 concerning the IP addresses it has leased to DHCP clients.  Sometimes
 devices or other processes may need access to this information.  In
 some cases, these devices or processes already have the capability to
 send and receive DHCP packets, and so the leasequery protocol is
 designed to give these processes and devices a low-overhead way to
 access such information.
 For example, access concentrators that act as DHCP relay agents
 sometimes derive information important to their operation by
 extracting data out of the DHCP packets they forward, a process known
 as "gleaning".  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

Woundy & Kinnear Standards Track [Page 2] RFC 4388 DHCP Leasequery February 2006

 location information directly from the DHCP server(s) using the
 DHCPLEASEQUERY message.
 To continue this example in more depth, 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
 Knowledge of this location information can benefit the access
 concentrator in several ways:
    1.  The access concentrator can forward traffic to the access
        network using the correct access network port, down the
        correct virtual circuit, through the correct modem, to the
        correct hardware address.

Woundy & Kinnear Standards Track [Page 3] RFC 4388 DHCP Leasequery February 2006

    2.  The access concentrator can perform IP source address
        verification of datagrams received from the access network.
        The verification 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 that can only be
        decrypted by the correct modem, using mechanisms such as [BPI]
        or [BPI+].
 The access concentrator in this example obtains the 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., because the access concentrator
 has rebooted, the access concentrator 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
 replies with a DHCPLEASEUNASSIGNED, 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 DHCPLEASEUNASSIGNED is similar to a DHCPLEASEACTIVE message, but
 indicates that there is no currently active lease on the resultant IP
 address but that this DHCP server is authoritative for this IP
 address.  The DHCPLEASEUNKNOWN message indicates that the DHCP server
 has no knowledge of the information specified in the query (e.g., IP
 address, MAC address, or Client-identifier option).
 The DHCPLEASEQUERY message does not presuppose a particular use for
 the information it returns -- it is simply designed to return
 information for which the DHCP server is an authoritative source to a
 client that requests that information.  It is designed to make it
 straightforward for processes and devices that already interpret DHCP
 packets to access information from the DHCP server.
 This document specifies an extension specifically to the DHCPv4
 protocol [RFC2131].  Given the nature of the DHCPv6 protocol
 [RFC3315], there is no effective way to make the DHCPLEASEQUERY
 message interaction common between DHCPv4 and DHCPv6 even should the
 desire to do so exist.

Woundy & Kinnear Standards Track [Page 4] RFC 4388 DHCP Leasequery February 2006

 The DHCPLEASEQUERY message was the result of a set of specific real-
 world implementation needs that appeared many years after the DHCPv4
 protocol was in wide use.  Furthermore, at the time of this writing,
 the DHCPv6 protocol has yet to be widely deployed.  The needs of
 access concentrators in yet to be determined DHCPv6 deployment
 scenarios are difficult to estimate.  If a DHCPLEASEQUERY-like
 function is necessary in DHCPv6, many of the ideas of this document
 will probably be applicable, while others may not.  We have been
 cautioned against designing protocol capabilities for which there is
 only an imagined consumer, and that is all that exists today in the
 realm of DHCPLEASEQUERY for DHCPv6.
 Thus, this document applies only to DHCPv4, and for clarity we have
 not appended DHCPv4 to every appearance of several common terms.  In
 this document, all references to IP addresses should be taken to mean
 IPv4 addresses, and all references to DHCP servers and DHCP clients
 should be taken to mean DHCPv4 servers and DHCPv4 clients.

2. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].
 This document uses the following terms:
      o "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
        configuration parameters such as a network address.
      o "DHCP relay agent"
        A DHCP relay agent is a third-party agent that transfers
        Bootstrap Protocol (BOOTP) and DHCP messages between clients
        and servers residing on different subnets, per [RFC951] and
        [RFC1542].

Woundy & Kinnear Standards Track [Page 5] RFC 4388 DHCP Leasequery February 2006

      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
        concentrator to forward traffic to a broadband-accessible
        host.  This information includes knowledge of the host
        hardware address, the port or virtual circuit that leads to
        the host, and/or the hardware address of the intervening
        subscriber modem.
      o "MAC address"
        In the context of a DHCP packet, a MAC address consists of the
        following fields: hardware type "htype", hardware length
        "hlen", and client hardware address "chaddr".
      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 that requires restart of the server.
      o "upstream"
        Upstream is the direction from the broadband subscriber
        towards the access concentrator.

Woundy & Kinnear Standards Track [Page 6] RFC 4388 DHCP Leasequery February 2006

3. Background

 The focus of this document is to enable processes and devices that
 wish to access information from the DHCP server in a lightweight and
 convenient manner.  It is especially appropriate for processes and
 devices that 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
 Interactive Network Adapters (INAs) [EUROMODEM], and DSL Access
 Concentrators.
 The DHCPLEASEQUERY message is an extension to the DHCP protocol
 [RFC2131].
 The DHCPLEASEQUERY message is a query message only and does not
 affect the state of the IP address or the binding information
 associated with it.

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 that 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 Address Resolution
 Protocol (ARP) Request [RFC826], and observe the origin and contents
 of the ARP Reply, to reconstruct 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),

Woundy & Kinnear Standards Track [Page 7] RFC 4388 DHCP Leasequery February 2006

    2.  the burden on the numerous subscriber hosts to receive and
        process the broadcast, and
    3.  the ease by which a malicious host can misrepresent itself as
        the IP endpoint.

4.2. SNMP and LDAP Are Not Appropriate

 Access concentrator implementations typically do not have Simple
 Network Management Protocol (SNMP) management client interfaces nor
 Lightweight Directory Access Protocol (LDAP) client interfaces
 (although they typically do include SNMP management agents).  This is
 one reason why this document does not leverage the proposed DHCP
 Server MIB [DHCPMIB].
 The DHCP Server MIB effort [DHCPMIB] grew out of traffic engineering
 and troubleshooting activities at large DHCP installations, and is
 primarily intended as a method of gathering performance statistics
 about servers the load presented to them.
 Despite the presence in the proposed DHCPv4 server MIB of objects
 that report configuration and status information, the MIB is intended
 to provide more generic, server-wide aggregated or summarized data.
 DHCPLEASEQUERY is intended to provide detailed, specific information
 about individual leases at a level that would be difficult or
 impossible to shoehorn into a MIB.
 From an implementation standpoint, the DHCPLEASEQUERY message is not
 required to be supported by all DHCPv4 servers.  Since it appears
 that defining optional MIB objects and objects for optional features
 in a MIB is discouraged, trying to support DHCPLEASEQUERY
 functionality optionally through a MIB would be similarly discouraged
 from an SNMP MIB standpoint.

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
 network 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

Woundy & Kinnear Standards Track [Page 8] RFC 4388 DHCP Leasequery February 2006

 does not persist across access concentrator reboots (due to lack of
 stable storage), and almost never persists across concentrator
 replacements.

4.4. DHCP Servers Are 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
 single IP subnet extends behind many broadband modems).  DHCP servers
 participate in all IP lease transactions (and therefore in all
 location information updates) with DHCP clients, whereas access
 concentrators sometimes miss some important lease transactions.
 An access concentrator can be configured with the IP addresses of
 multiple different DHCP servers, 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 readers a concrete feel for how the message might be used.
 The access concentrator initiates all DHCPLEASEQUERY message
 conversations.  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
 public 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.
 This query will then be answered by returning the information current
 when this client's lease was last granted or renewed, allowing the
 access concentrator to forward the IP datagram.

Woundy & Kinnear Standards Track [Page 9] RFC 4388 DHCP Leasequery February 2006

 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 must 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 SHOULD be the IP address with the
 latest client-last-transaction-time associated with the client
 described by the MAC address or Client-identifier option.
 The DHCP servers that implement this protocol always send a response
 to the DHCPLEASEQUERY message: either a DHCPLEASEUNASSIGNED,
 DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN.  The reasons why a
 DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN message
 might be generated are explained in the specific query regimes,
 below.
 Servers that do not implement the DHCPLEASEQUERY message SHOULD
 simply not respond.
 The DHCPLEASEQUERY message can support three query regimes:  A server
 that implements the DHCPLEASEQUERY message must implement all 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
      information that it has on the most recent client to have been
      assigned that IP address.
      The DHCP server replies with a DHCPLEASEUNASSIGNED or
      DHCPLEASEACTIVE message if the IP address in the DHCPLEASEQUERY
      message 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 DHCPLEASEUNKNOWN message if
      the server does not have definitive information concerning the
      address in the DHCPLEASEQUERY message.
    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
      information that it has on the IP address most recently accessed
      by a client with that MAC address.  In addition, it may supply
      additional IP addresses that have been associated with that MAC
      address in different subnets.  Information about these bindings

Woundy & Kinnear Standards Track [Page 10] RFC 4388 DHCP Leasequery February 2006

      can then be found using the Query by IP Address, described
      above.
      The DHCP server replies with a DHCPLEASEACTIVE message if the
      MAC address in the DHCPLEASEQUERY message corresponds to a MAC
      address with an active lease on an IP address in this server.
      The server replies with a DHCPLEASEUNKNOWN message if the server
      does not presently have an active lease by a client with this
      MAC address in this DHCP server.
    o Query by Client-identifier option:
      For this query, the requester supplies only a Client-identifier
      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-identifier.  In
      addition, it may supply additional IP addresses that have been
      associated with Client-identifier 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 DHCPLEASEACTIVE message if the
      Client-identifier in the DHCPLEASEQUERY message currently has an
      active lease on an IP address in this DHCP server.  The server
      replies with a DHCPLEASEUNKNOWN message if the server does not
      have an active lease by a client with this Client-identifier.
 For many DHCP servers, the query by IP address is likely to be the
 most efficient form of leasequery.  This is the form of
 DHCPLEASEQUERY that SHOULD be used if possible.
 The DHCPLEASEUNASSIGNED or DHCPLEASEACTIVE message reply must always
 contain the IP address in the "ciaddr" field.  The DHCPLEASEACTIVE
 message SHOULD contain the physical 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 [RFC3046].  The access
 concentrator uses the "chaddr" field and Relay Agent Information
 option to construct location information, which can be cached on the
 access concentrator until lease expiration.
 Any DHCP server that supports the DHCPLEASEQUERY message SHOULD save
 the information from the most recent Relay Agent Information option
 (option 82) [RFC3046] associated with every IP address that it
 serves.  It is assumed that most clients that generate the
 DHCPLEASEQUERY message will ask for the Relay Agent Information

Woundy & Kinnear Standards Track [Page 11] RFC 4388 DHCP Leasequery February 2006

 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 helpful.
 A server that implements DHCPLEASEQUERY SHOULD also save the
 information on the most recent Vendor class identifier, option 60,
 associated with each IP address, since this option is also likely 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 [RFC2131] and [RFC2132].  See also Section 8, IANA
 Considerations.
    1.  The message type option (option 53) from [RFC2132] requires
        four new values: one for the DHCPLEASEQUERY message itself and
        one for each of its three possible responses
        DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, DHCPLEASEUNKNOWN.  The
        values of these message types are shown below in an extension
        of the table from section 9.6 of [RFC2132]:
                       Value   Message Type
                       -----   ------------
                         10    DHCPLEASEQUERY
                         11    DHCPLEASEUNASSIGNED
                         12    DHCPLEASEUNKNOWN
                         13    DHCPLEASEACTIVE
    2.  There is a new option, the client-last-transaction-time:
        client-last-transaction-time
        This option allows the receiver to determine the time of the
        most recent access of the client.  It is particularly useful
        when DHCPLEASEACTIVE messages from two different DHCP servers
        need to be compared, although it can be useful in other
        situations.  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.

Woundy & Kinnear Standards Track [Page 12] RFC 4388 DHCP Leasequery February 2006

        This MUST NOT be an absolute time.  This MUST NOT be an
        absolute number of seconds since Jan. 1, 1970.  Instead, this
        MUST be an integer number of seconds in the past from the time
        the DHCPLEASEACTIVE 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 that is a number of seconds into the future from the time
        the message was sent, this option encodes a value that is a
        number of seconds into the past from when the message was
        sent.
        The code for the this option is 91.  The length of the this
        option is 4 octets.
            Code   Len      Seconds in the past
           +-----+-----+-----+-----+-----+-----+
           |  91 |  4  |  t1 |  t2 |  t3 |  t4 |
           +-----+-----+-----+-----+-----+-----+
    3.  There in a second new option, the associated-ip option:
        associated-ip
        This option is used to return all of the IP addresses
        associated with the DHCP client specified in a particular
        DHCPLEASEQUERY message.
        The code for this option is 92.  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
           +-----+-----+-----+-----+-----+-----+-----+-----+--
           |  92 |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  ...
           +-----+-----+-----+-----+-----+-----+-----+-----+--

Woundy & Kinnear Standards Track [Page 13] RFC 4388 DHCP Leasequery February 2006

6.2. Sending the DHCPLEASEQUERY Message

 The DHCPLEASEQUERY message is typically sent by an access
 concentrator.  The DHCPLEASEQUERY message uses the DHCP message
 format as described in [RFC2131], and uses message number 10 in the
 DHCP Message 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 the DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN
     message from the DHCP server.
     Note that this use of the giaddr is consistent with the
     definition of giaddr in [RFC2131], where the giaddr is always
     used as the return address of the DHCP response message.  In some
     (but not all) contexts in RFC 2131, the giaddr is used as the
     "key" to access the appropriate address pool.  The DHCPLEASEQUERY
     message is one of those cases where the giaddr MUST NOT be used
     as such a "key".
   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 SHOULD
     return the same options it would return for a DHCPREQUEST message
     that didn't contain a DHCPLEASEQUERY message, which includes
     those mandated by Section 4.3.1 of [RFC2131] as well as any
     options that the server was configured to always return to a
     client.
 Additional details concerning different query types are:
    o Query by IP address:
      The values of htype, hlen, and chaddr MUST be set to zero.
      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.

Woundy & Kinnear Standards Track [Page 14] RFC 4388 DHCP Leasequery February 2006

    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.
      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 zero.
 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).
 Any device expecting to use a DHCPLEASEQUERY message SHOULD ensure
 that the Relay Agent Info option that it uses contains information
 that unambiguously identifies the device.

6.3. Receiving the DHCPLEASEQUERY Message

 A server that implements the DHCPLEASEQUERY message MUST implement
 all three query regimes: query by IP address, query by MAC address,
 and query by Client-identifier.
 A DHCPLEASEQUERY message MUST have a non-zero giaddr.  The
 DHCPLEASEQUERY message MUST have exactly one of the following: a
 non-zero ciaddr, a non-zero htype/hlen/chaddr, or a Client-identifier
 option.
 The DHCP server that receives a DHCPLEASEQUERY message MUST base its
 response on the particular data item used in the query.

Woundy & Kinnear Standards Track [Page 15] RFC 4388 DHCP Leasequery February 2006

 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
 restrict the processing of the query in any way, and MUST NOT be used
 locate a subnet to which the ciaddr (if any) must belong.
 Note that this use of the giaddr is consistent with the definition of
 giaddr in [RFC2131], where the giaddr is always used as the return
 address of the DHCP response message.  In some (but not all) contexts
 in RFC 2131, the giaddr is used as the "key" to access the
 appropriate address pool.  The DHCPLEASEQUERY message is one of those
 cases where the giaddr MUST NOT be used as such a "key".

6.4. Responding to the DHCPLEASEQUERY Message

 There are three possible responses to a DHCPLEASEQUERY message:
    o DHCPLEASEUNASSIGNED
      The server MUST respond with a DHCPLEASEUNASSIGNED message if
      this server has information about the IP address, but there is
      no active lease for the IP address.  The DHCPLEASEUNASSIGNED
      message is only returned for a query by IP address, and
      indicates that the server manages this IP address, but there is
      no currently active lease on this IP address.
    o DHCPLEASEUNKNOWN
      The DHCPLEASEUNKNOWN message indicates that the server does not
      manage the IP address or the client specified in the
      DHCPLEASEQUERY message does not currently have a lease on an IP
      address.
      When responding with a DHCPLEASEUNKNOWN, the DHCP server MUST
      NOT include other DHCP options in the response.
    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 knows that there is an active
      lease by that client for that IP address.
      The server MUST respond with a DHCPLEASEACTIVE message when the
      IP address returned in the "ciaddr" field is currently leased.

Woundy & Kinnear Standards Track [Page 16] RFC 4388 DHCP Leasequery February 2006

6.4.1. Determining the IP address about 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 about 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, #3).  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
 DHCPLEASEUNASSIGNED 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 that 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
 DHCPLEASEQUERY message are non-zero).  This client matching approach
 will, for the purposes of this section, be described as "Client-
 identifier or MAC address".
 If the "ciaddr" field is zero in a DHCPLEASEQUERY message, then the
 IP address placed in the "ciaddr" field of a 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 that fulfills this criteria,
 then it MUST be placed in the "ciaddr" field of the 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.

Woundy & Kinnear Standards Track [Page 17] RFC 4388 DHCP Leasequery February 2006

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

6.4.2. Building a DHCPLEASEUNASSIGNED or DHCPLEASEACTIVE Message Once

      the "ciaddr" Field Is Set
 Once the "ciaddr" field of the DHCPLEASEUNASSIGNED is set, the
 processing for a DHCPLEASEUNASSIGNED message is complete.  No other
 options are returned for the DHCPLEASEUNASSIGNED message.
 For the DHCPLEASEACTIVE message, the rest of the processing largely
 involves returning information about the IP address specified in the
 "ciaddr" field.
 The IP address in the "ciaddr" field of the DHCPLEASEUNASSIGNED or
 DHCPLEASEACTIVE message MUST be one for which this server is
 responsible (or a DHCPLEASEUNKNOWN message would be have already been
 returned early in the processing described in the previous section).
 The MAC address of the DHCPLEASEACTIVE message MUST be set to the
 values that identify the client associated with the IP address in the
 "ciaddr" field of the DHCPLEASEUNASSIGNED message.
 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 DHCPLEASEACTIVE message.
 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 MUST be returned in the associated-ip option, whether or
 not 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 DHCPLEASEACTIVE message 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).
 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 and these times are not

Woundy & Kinnear Standards Track [Page 18] RFC 4388 DHCP Leasequery February 2006

 yet in the past, then the DHCP server SHOULD return these options
 (when requested) with the remaining time until renewal or rebinding,
 respectively.  If these times are already in the past, or if there is
 not currently a valid lease for this IP address, the DHCP server MUST
 NOT return these options.
 If the Relay Agent Information (option 82) is specified in the
 Parameter Request List, then the information contained in the most
 recent Relay Agent Information option received from the relay agent
 associated with this IP address MUST be included in the
 DHCPLEASEACTIVE message.
 The 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 and that are
 acceptable to return based on the list of "non-sensitive options",
 discussed below.
 DHCP servers SHOULD be configurable with a list of "non-sensitive
 options" that can be returned to the client when specified in the
 Parameter Request List of the DHCPLEASEQUERY message.  Any option not
 on this list SHOULD NOT be returned to a client, even if requested by
 that client.
 The DHCP server uses information from its lease binding database to
 supply the 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 some cases, the Relay Agent Information option in an incoming
 DHCPREQUEST packet is used to help determine the options returned to
 the DHCP client that sent the DHCPREQUEST.  When responding to a
 DHCPLEASEQUERY message, the DHCP server MUST use the saved Relay
 Agent Information option just like it did when responding to the DHCP
 client in order to determine the values of any options requested by
 the DHCPLEASEQUERY message.  The goal is to return the same option
 values to the DHCPLEASEQUERY as those that were returned to the
 DHCPDISCOVER or DHCPREQUEST from the DHCP client (unless otherwise
 specified, above).
 In the event that two servers are cooperating to provide a high-
 availability DHCP server, as supported by [RFC2131], they would have
 to communicate some information about IP address bindings to each
 other.  In order to properly support the DHCPLEASEQUERY message,
 these servers MUST ensure that they communicate the Relay Agent
 Information option information to each other in addition to any other
 IP address binding information.

Woundy & Kinnear Standards Track [Page 19] RFC 4388 DHCP Leasequery February 2006

6.4.3. Sending a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, or

      DHCPLEASEUNKNOWN Message
 The server expects a giaddr in the DHCPLEASEQUERY message, and
 unicasts the DHCPLEASEUNASSIGNED, 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 DHCPLEASEUNASSIGNED, 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
 concentrator 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 information for this IP address.
 When a DHCPLEASEUNASSIGNED 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, but that this
 server does in fact manage that IP address.  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 caching could be as simple as simply
 setting a bit saying that a response was received from a server that
 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 existence.
 In either case, when a DHCPLEASEUNASSIGNED or DHCPLEASEACTIVE message
 is received in response to a DHCPLEASEQUERY message, it means that
 the DHCP server that responded is a DHCP server that 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
 that 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
 message.  If there is no IP address in the "ciaddr" field of the
 DHCPLEASEQUERY message, then a DHCPLEASEUNKNOWN message means that

Woundy & Kinnear Standards Track [Page 20] RFC 4388 DHCP Leasequery February 2006

 the DHCP server does not have definitive information concerning the
 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, but only for a
 relatively short lifetime, approximately 5 minutes.
 Having cached this information, the access concentrator SHOULD only
 infrequently direct a DHCPLEASEQUERY message to a DHCP server that
 responded to a DHCPLEASEQUERY message for a particular "ciaddr" field
 with a DHCPLEASEUNKNOWN.

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 DHCPLEASEUNASSIGNED,
     DHCPLEASEACTIVE, or DHCPLEASEUNKNOWN was 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
 DHCPLEASEQUERY 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 that utilizes the DHCPLEASEQUERY message
 SHOULD attempt to resend DHCPLEASEQUERY messages to servers that 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 that 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 70
 seconds.
 In practice, this approach would probably best be handled by a per-
 server timer that is restarted whenever a response to a
 DHCPLEASEQUERY message is received, and expires after one 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.

Woundy & Kinnear Standards Track [Page 21] RFC 4388 DHCP Leasequery February 2006

 All DHCPLEASEQUERY messages SHOULD use the exponential backoff
 algorithm specified in Section 4.1 of [RFC2131].
 Thus, in the initial state, the per-server timer is expired, and a
 single DHCPLEASEQUERY message is queued for each server.  After the
 first response to a DHCPLEASEQUERY message, the per-server timer is
 started.  At that time, multiple DHCPLEASEQUERY messages can be sent
 in parallel to the DHCP server, though the total number SHOULD be
 limited to 100 or 200, to avoid swamping the DHCP server.  Each of
 these messages uses the [RFC2131] exponential backoff algorithm.
 Every time a response to any of these messages is received, the per-
 server timer is reset and starts counting again up to one minute.  In
 the event the per-server timer goes off, then all outstanding
 messages SHOULD be dropped except for a single DHCPLEASEQUERY message
 that is used to poll the server at approximately 64-second intervals
 until such time as another (or the first) response to the
 DHCPLEASEQUERY is received.
 In the event that there is no DHCPLEASEQUERY traffic for one minute,
 then the per-server timer will expire.  After that time, there will
 only be one DHCPLEASEQUERY message allowed to be outstanding to that
 server until a response to that message is received.

6.7. Lease Binding Data Storage Requirements

 DHCP server implementations that implement the DHCPLEASEQUERY
 capability MUST save the most recent Relay Agent Information option
 from the most recent DHCPREQUEST packet for two reasons.  First, it
 is almost certain to be requested by in the dhcp-parameter-request-
 list option in any DHCPLEASEQUERY request.  Second, the saved Relay
 Agent Information option may be necessary to determine the value of
 other options given to the DHCP client, if these are requested by the
 dhcp-parameter-request list in the DHCPLEASEQUERY request.
 This is a list of the information that is required to successfully
 implement
    o relay-agent-info option from client packet: MUST store with
      binding.
    o client-last-transaction-time of last client interaction: MUST
      store with binding.
    o vendor-class-id: SHOULD store with binding.
 These data storage requirements are minimally larger than those
 required for normal operation of the DHCP protocol, as required to
 properly implement [RFC2131].

Woundy & Kinnear Standards Track [Page 22] RFC 4388 DHCP Leasequery February 2006

6.8. Using the DHCPLEASEQUERY Message with Multiple DHCP Servers

 When using the DHCPLEASEQUERY message in an environment where
 multiple DHCP servers may contain authoritative information about the
 same IP address (such as when two DHCP servers are cooperating to
 provide a high-availability DHCP service), multiple, possibly
 conflicting, responses might be received.
 In this case, some information in the response packet SHOULD be used
 to decide among the various responses.  The client-last-transaction-
 time (if it is available) 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 that 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
 susceptible to malicious hosts that masquerade as the intended IP
 endpoints.  Thus, the DHCPLEASEQUERY message allows an access
 concentrator to provide considerably enhanced security.
 DHCP servers SHOULD prevent exposure of location information
 (particularly the mapping of hardware address to IP address lease,
 which can be an invasion of broadband subscriber privacy) by
 employing the techniques detailed in [RFC3118], "Authentication for
 DHCP Messages".
 This RFC describes how a DHCP client interacts with a DHCP server.
 Access concentrators that send the DHCPLEASEQUERY message are
 essentially DHCP clients for the purposes of the DHCPLEASEQUERY
 message, even though they perform the functions of a DHCP relay agent
 as well.  Thus, [RFC3118] is an appropriate mechanism for
 DHCPLEASEQUERY messages.
 Since [RFC3118] discusses the normal DHCP client interaction,
 consisting of a DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK, it
 is necessary to transpose the operations described in [RFC3118] to
 the DHCPLEASEQUERY domain.  The operations described in [RFC3118] for

Woundy & Kinnear Standards Track [Page 23] RFC 4388 DHCP Leasequery February 2006

 DHCPDISCOVER are performed for DHCPLEASEQUERY, and the operations
 described for DHCPOFFER are performed for DHCPLEASEUNASSIGNED,
 DHCPLEASEACTIVE, and DHCPLEASEUNKNOWN messages.
 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 DHCPLEASEUNASSIGNED,
 DHCPLEASEACTIVE, 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 transmitting one DHCPLEASEQUERY message (excluding
 message retries) per legitimate broadband access network IP address
 after a reboot event.
 DHCP servers supporting the DHCPLEASEQUERY message SHOULD ensure that
 they cannot be successfully attacked by being flooded with large
 quantities of DHCPLEASEQUERY messages in a short time.
 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 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.

8. IANA Considerations

 IANA has assigned six values for this document.  See Section 6.1 for
 details.  There are four new messages types, which are the value of
 the message type option (option 53) from [RFC2132].  The value for
 DHCPLEASEQUERY is 10, the value for DHCPLEASEUNASSIGNED is 11, the
 value for DHCPLEASEUNKNOWN is 12, and the value for DHCPLEASEACTIVE
 is 13.  Finally, there are two new DHCP option defined; the client-
 last-transaction-time option -- option code 91, and the associated-ip
 option -- option code 92.

9. Acknowledgements

 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.  Thomas Narten made many suggestions for improvements.
 Russ Housley pressed effectively for increased security capabilities,
 and Ted Hardie suggested ways to minimize undesired information
 leakage.  Bert Wijnen suggested we clarify our focus to DHCPv4 and

Woundy & Kinnear Standards Track [Page 24] RFC 4388 DHCP Leasequery February 2006

 distinguish our approach from that of the DHCP MIB.  R. Barr Hibbs,
 one of the authors of the DHCP MIB, supplied information to
 effectively distinguish that effort from DHCPLEASEQUERY.

10. References

10.1. Normative References

 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2131]   Droms, R., "Dynamic Host Configuration Protocol", RFC
             2131, March 1997.
 [RFC3046]   Patrick, M., "DHCP Relay Agent Information Option", RFC
             3046, January 2001.
 [RFC3118]   Droms, R. and W. Arbaugh, "Authentication for DHCP
             Messages", RFC 3118, June 2001.

10.2. Informative References

 [RFC826]    Plummer, D., "Ethernet Address Resolution Protocol: Or
             converting network protocol addresses to 48.bit Ethernet
             address for transmission on Ethernet hardware", STD 37,
             RFC 826, November 1982.
 [RFC951]    Croft, W. and J. Gilmore, "Bootstrap Protocol", RFC 951,
             September 1985.
 [RFC1542]   Wimer, W., "Clarifications and Extensions for the
             Bootstrap Protocol", RFC 1542, October 1993.
 [RFC2132]   Alexander, S. and R. Droms, "DHCP Options and BOOTP
             Vendor Extensions", RFC 2132, March 1997.
 [RFC3315]   Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
             and M. Carney, "Dynamic Host Configuration Protocol for
             IPv6 (DHCPv6)", RFC 3315, July 2003.
 [BPI]       SCTE Data Standards Subcommittee, "Data-Over-Cable
             Service Interface Specifications: DOCSIS 1.0 Baseline
             Privacy Interface Specification SCTE 22-2 2002", 2002,
             available at http://www.scte.org/standards/.

Woundy & Kinnear Standards Track [Page 25] RFC 4388 DHCP Leasequery February 2006

 [BPI+]      CableLabs, "Data-Over-Cable Service Interface
             Specifications: Baseline Privacy Plus Interface
             Specification CM-SP-BPI+_I12-050812", August 2005,
             available at http://www.cablemodem.com/.
 [DHCPMIB]   Hibbs, R., Waters, G., "Dynamic Host Configuration
             Protocol (DHCP) Server MIB", Work in Progress, February
             2004.
 [DOCSIS]    SCTE Data Standards Subcommittee, "Data-Over-Cable
             Service Interface Specifications: DOCSIS 1.0 Radio
             Frequency Interface Specification SCTE 22-1 2002", 2002,
             available at http://www.scte.org/standards/.
 [EUROMODEM] ECCA, "Technical Specification of a European Cable Modem
             for digital bi-directional communications via cable
             networks", Version 1.0, May 1999.

Authors' Addresses

 Rich Woundy
 Comcast Cable
 27 Industrial Ave.
 Chelmsford, MA  01824
 Phone: (978) 244-4010
 EMail: richard_woundy@cable.comcast.com
 Kim Kinnear
 Cisco Systems
 1414 Massachusetts Ave
 Boxborough, MA 01719
 Phone: (978) 936-0000
 EMail: kkinnear@cisco.com

Woundy & Kinnear Standards Track [Page 26] RFC 4388 DHCP Leasequery February 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Acknowledgement

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 Administrative Support Activity (IASA).

Woundy & Kinnear Standards Track [Page 27]

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