DHC Working Group                                            P. Kurapati
Internet-Draft                                                R. Desetti
Expires: January 14, April 29, 2010                                         B. Joshi
                                               Infosys Technologies Ltd.
                                                           July 13,
                                                        October 26, 2009

               DHCPv4 Leasequery by relay agent remote ID
             draft-ietf-dhc-leasequery-by-remote-id-02.txt
             draft-ietf-dhc-leasequery-by-remote-id-03.txt

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Abstract

   Some Relay Agents extract lease information from the DHCP message
   exchanged between the client and DHCP server.  This lease information
   is used by relay agents for various purposes like antispoofing,
   prevention of flooding.  RFC 4388 defines a mechanism for relay
   agents to retrieve the lease information from the DHCP server as and
   when this information is lost.  Existing leasequery mechanism is data
   driven which means that a relay agent can initiate the leasequery
   only when it starts receiving data from/to the clients.  In certain
   scenarios, this model is not scalable.  This document first looks at
   issues in existing mechanism and then proposes a new query type,
   query by remote ID, to address these issues.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6  5
   3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  8  7
   4.  Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 10  9
     4.1.  Information Acquisition before Data Starts . . . . . . . . 10  9
     4.2.  Lessen Negative Caching  . . . . . . . . . . . . . . . . . 10  9
     4.3.  Antispoofing in 'Fast Path'  . . . . . . . . . . . . . . . 10  9
   5.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . . 11 10
   6.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 13 11
     6.1.  Sending the DHCPLEASEQUERY Message . . . . . . . . . . . . 13 11
     6.2.  Receiving the DHCPLEASEQUERY Message . . . . . . . . . . . 14 12
     6.3.  Responding to the DHCPLEASEQUERY Message . . . . . . . . . 14 12
     6.4.  Determining the IP address to be used in response  . . . . 14 12
     6.5.  Building a DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN, DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Messages  . . . . . . . . . . . . . . . . . 15 13
     6.6.  Sending a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message  . . . . . . . . . . . . . . . . . 17 15
     6.7.  Receiving a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message  . . . . . . . . . . . . . . . . . 17 15
     6.8.  Receiving No Response to the DHCPLEASEQUERY Message  . . . 18 15
     6.9.  Lease Binding Data Storage Requirements  . . . . . . . . . 18 15
     6.10. Using the DHCPLEASEQUERY Message with Multiple DHCP
           Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 18 16
   7.  RFC 4388 Considerations  . . . . . . . . . . . . . . . . . . . 19 17
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20 18
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21 19
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22 20
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 21
     11.1. Normative Reference  . . . . . . . . . . . . . . . . . . . 23 21
     11.2. Informative Reference  . . . . . . . . . . . . . . . . . . 23 21
   Appendix A.  Why a New Leasequery is Required? . . . . . . . . . . 24 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 25

1.  Introduction

   DHCP relay agents snoop DHCP messages and append relay agent
   information option before relaying it to the configured DHCP Servers.
   In this process, some relay agents also glean the lease information
   sent by the server and maintain this locally.  This information is
   used for prevention of spoofing attempts from the clients and also
   sometimes used to install routing information.  When relay agent
   reboots, this information is lost.  RFC 4388 [RFC4388] has defined a
   mechanism to retrieve this lease information from the DHCP server.
   The existing query types defined by RFC 4388 [RFC4388] are data
   driven.  When client initiates data, based on the source MAC/IP
   address, relay agent can query the server about the lease
   information.  These mechanisms do not scale well when there are
   thousands of clients connected to the relay agent.  In data driven
   model, DHCP Leasequery does not provide all the active Lease
   informations associated with a given connection/circuit [consolidated
   information] which will result into an inefficient anti-spoofing.  It
   also has to contend with considerable resources for negative caching
   specially under spoof attacks.

   We need a mechanism for relay agent to retrieve the consolidated
   lease information for a given connection/circuit before traffic is
   initiated by the clients.

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

                                 Figure 1

   For example, when a DSLAM acting as a Relay Agent is rebooted, it
   should query the server for the lease information for all the
   connections/circuits.  Also, as shown in the above figure, there
   could be multiple clients on one DSL circuit.  Relay agent should get
   the lease information of all the clients connected to a DSL circuit.
   This is possible by introducing a new query type based on the Remote
   Id sub-option of Relay Agent Information option.  This document talks
   about the motivation for the new query type and the method to do the
   same.

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[RFC951] and
   RFC1542[RFC1542].

   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  "fast path"

   Data transfer which happens through Network Processor or an ASIC
   which are programmed to forward the data at very high speeds.

   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  "slow path"

   Data transfer which happens through the control plane.  Typically
   this has very limited buffers to store data and the speeds are very
   low compared to fast path data transfer.

   o  "upstream"

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

3.  Motivation

   Consider a typical access concentrator (e.g., DSLAM) working also as
   a DHCP relay agent.  "Fast path" and "slow path" generally exist in
   most networking boxes.  Fast path processing is done in network
   processor or an ASIC (Application Specific Integrated Circuit).  Slow
   path processing is done in a normal processor.  As much as possible,
   regular data handling code should be in fast path.  Slow path
   processing should be reduced as it may become a bottleneck.

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

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

   After a deep analysis, we found that the three existing query types
   supported by RFC 4388[RFC4388] do not provide effective and efficient
   antispoofing for the above scenario and a new mechanism is required.

   The existing query types

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

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

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

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

4.  Design Goals

   The goal of this document is to provide a lightweight mechanism for
   access concentrator to retrieve lease information available in the
   DHCP server.  The mechanism SHOULD also support an access
   concentrator to retrieve consolidated lease information for a
   connection/circuit.

4.1.  Information Acquisition before Data Starts

   Existing data driven approach by RFC 4388 [RFC4388] means that the
   lease queries can only be done when access concentrator receives
   data.  If an approach exists to initiate lease queries even before
   the calls come up, then it will be more effective.  For antispoofing,
   packets need to be dropped until it gets the lease information from
   DHCP server.  If access concentrator finishes the lease queries
   before it start receiving data, then there is no need to drop
   legitimate packets.  So, effectively outage time may be reduced.  The
   lease queries should help in retrieving lease information even before
   the data starts flowing and should be independent of data traffic.

4.2.  Lessen Negative Caching

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

4.3.  Antispoofing in 'Fast Path'

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

5.  Protocol Overview

   RFC 3046 [RFC3046] defines two sub-options for Relay Agent
   Information option.  Sub-option 1 corresponds to circuit ID which
   identifies the local circuit of the access concentrator.  This sub-
   option is unique to the relay agent.  Sub-option 2 corresponds to
   remote ID which identifies the remote host end of the circuit.  This
   is globally unique in the network.

   This document defines a new query type based on remote ID sub-option.
   Suppose that the access concentrator (e.g., DSLAM) lost the lease
   information when it was rebooted.  When the access concentrator comes
   up, it would initiate a DHCPLEASEQUERY message for each connection/
   circuit containing the Relay Agent Information option [RFC3046] with
   sub-option remote ID.  DHCP server must return an IP address in the
   ciaddr if it has any record of the client described by the remote ID.
   In the absence of specific configuration information to the contrary,
   it SHOULD be the IP address with the latest client-last-transaction-
   time associated with the client described by the remote ID.  The DHCP
   servers that implement this document always send a response
   (DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE,
   (DHCPLEASEACTIVE or DHCPLEASEUNKNOWN) to the DHCPLEASEQUERY message.
   The reasons why a DHCPLEASEUNASSIGNED,
   DHCPLEASEACTIVE, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message might
   be generated are explained in the specific query regimes below.
   Servers that do not implement the DHCPLEASEQUERY based on remote ID
   message SHOULD simply not respond.

   The query regime is described below:

   o  Query by Agent Remote ID sub-option:

   For this query, the requester supplies only a option 82 which will
   include only an Agent Remote ID sub-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 Agent
   Remote ID.  In addition, it SHOULD supply any additional IP addresses
   that have been associated with Agent Remote ID in different subnets.
   Information about these bindings can then be found using the Query by
   IP Address, as described in RFC 4388[RFC4388].

   The DHCP server MUST reply with a DHCPLEASEACTIVE message if the
   Agent Remote ID in the DHCPLEASEQUERY message currently has an active
   lease on an IP address in this DHCP server.  The server MUST reply
   with a DHCPLEASEUNASSIGNED if it has information of the said remote
   ID but no lease is assigned for the same.  The server MAY keep track
   of the remote ID values for which it has currently active leases as
   well as any which it has served in  Otherwise, the past but for which it has no
   currently active leases.  The server
   MUST reply with a DHCPLEASEUNKNOWN message if it has no information of the said remote
   ID. message.

6.  Protocol Details

   In this section, DHCPLEASEQUERY message refers to DHCPLEASEQUERY
   message with query by remote ID.

6.1.  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[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 the return address of the
      DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE,
      DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message from the DHCP server.
      Note that this use of the giaddr is consistent with the definition
      of giaddr in RFC2131[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. to allocate to a client is
      selected based on 'giaddr'.

   o  The Parameter Request List option (option 55) SHOULD be set to the
      options of interest to the requester.  It MUST include the Relay
      Agent Information option (option 82).  The other interesting
      options are likely to include the IP Address Lease Time option
      (option 51), 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, Parameter Request List
      option (option 55), 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 Agent Remote ID sub-option:

      *  There MUST be a Relay Agent Information option (option 82) with
         only Agent Remote ID sub-option (sub-option 2) 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 Client-identifier option (option 61) MUST NOT appear in the
         packet.

   The DHCPLEASEQUERY message SHOULD be sent to a DHCP server which is
   known to possess authoritative information concerning the remote ID.
   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 remote ID, 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 giaddr.  The
   DHCPLEASEQUERY message MUST have a zero ciaddr, a zero htype/hlen/
   chaddr, and no Client-identifier option.  The DHCPLEASEQUERY message
   MUST have a relay agent option 82 with only remote ID sub-option.

6.3.  Responding to the DHCPLEASEQUERY Message

   There are three two possible responses to a DHCPLEASEQUERY message:

   o  DHCPLEASEUNASSIGNED

   The server MUST respond with a DHCPLEASEUNASSIGNED message if this
   server has information about the remote ID, but there is no
   associated active lease.  The DHCPLEASEUNASSIGNED indicates that the
   server manages the IP address allocation for the given remote ID, but
   there is no currently active lease.

   o  DHCPLEASEUNKNOWN

   The DHCPLEASEUNKNOWN message indicates that the client specified in
   the DHCPLEASEQUERY message is not allocated any lease or it is not
   managed by the server.

   o  DHCPLEASEACTIVE

   The DHCPLEASEACTIVE message indicates that the server not only knows
   the client specified in the DHCPLEASEQUERY message, but also knows
   that there is an active lease for that client.

6.4.  Determining the IP address to be used in response

   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 (RFC 4388[RFC4388], Section 6.1, #3).  This is
   the only information returned not directly associated with the IP
   address in the "ciaddr" field.

   The client's identity is any client that has proffered an identical
   Agent Remote ID (if the option 82 with Agent Remote ID sub-option
   appears in DHCPLEASEQUERY message).  This client matching approach
   will, for the purposes of this section, be described as "remote ID".

   The IP address placed in the "ciaddr" field of a DHCPLEASEACTIVE
   message MUST be the IP address with the latest client-last-
   transaction-time associated with the client described by the remote
   ID 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 Remote ID, 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.

6.5.  Building a DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN, DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Messages

   DHCPLEASEUNASSIGNED and

   For a DHCPLEASEUNKNOWN messages are created alike
   except for message type. message, DHCP server MUST echo the received
   Option 82 available in DHCPLEASEQUERY in the response.  No other
   options are returned for these messages. this message.  With that the processing for
   a
   DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN message is complete.

   For the DHCPLEASEACTIVE message, the rest of the processing largely
   involves returning information about the IP address specified in the
   "ciaddr" field.

   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 DHCPLEASEACTIVE 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 Agent Remote
   ID, then the list of all those 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 then the DHCP server MUST return this option
   in the DHCPLEASEACTIVE message with its value equal to the time
   remaining until lease expiration.

   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.  DHCP server SHOULD return these options (when
   requested) with the remaining time until renewal or rebinding,
   respectively.

   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 access concentrator when
   specified in the Parameter Request List of the DHCPLEASEQUERY
   message.  Any option not on this list SHOULD NOT be returned to an
   access concentrator, even if requested by that access concentrator.

   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.

6.6.  Sending a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message

   The server expects a giaddr in the DHCPLEASEQUERY message, and
   unicasts the DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message to the
   giaddr.

6.7.  Receiving a DHCPLEASEUNASSIGNED, DHCPLEASEACTIVE, 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 Relay Agent
   Information option information included in the packet to refresh its
   location information for this IP address.  An access concentrator is
   likely to query by IP address for all the IP addresses specified in
   the associated-ip option in the response, if any, at this point in
   time.

   When a DHCPLEASEUNASSIGNED message is received in response to the
   DHCPLEASEQUERY message, it means that there is currently no active
   lease associated with the client specified by remote ID in the DHCP
   server, but that this server does in fact manage the IP address
   allocation for the client specified by remote ID.  Access
   Concentrator MAY store this information for future use.

   When a DHCPLEASEUNKNOWN message is received by an access concentrator
   that has had sent out a DHCPLEASEQUERY message, it means that the DHCP
   server does not have definitive information concerning the DHCP
   client specified in the Agent Remote ID sub-option of the
   DHCPLEASEQUERY message.  The Access Concentrator access concentrator MAY store this
   information for future use.  However, a DHCPLEASEQUERY SHOULD NOT be
   attempted with the same Remote ID sub-option.

   In both the cases above, su-option.

   For leasequry by remote-id, the impact of negative caching is greatly
   reduced as the leasequery by remote-id the response leads to "definitive" and
   complete information on all
   the hosts connected through a behind the connection.  Note that in the case of
   RFC 4388 [RFC4388], a host spoofing several IP addresses can lead to
   negative caching of greater magnitude.  Another important change this
   draft brings is the removal of "periodic" leasequeries generated from
   negative caching caused by DHCPLEASEUNKNOWN.  Since the information
   obtained through query by remote-id is complete, there is no need of
   attempting leasequery again for the same remote-id.

6.8.  Receiving No Response to the DHCPLEASEQUERY Message

   When an access concentrator receives no response to a DHCPLEASEQUERY
   message, it should be handled in the same manner as suggested in RFC
   4388 [RFC4388].

6.9.  Lease Binding Data Storage Requirements

   IMPLEMENTATION:

   To generate replies for a lease query by remote-id effeciently, a
   DHCP server should index the lease binding data structures using
   remote-id.

6.10.  Using the DHCPLEASEQUERY Message with Multiple DHCP Servers

   This scenario should be handled in the same way it is done in RFC
   4388 [RFC4388].

7.  RFC 4388 Considerations

   This document is compatible with RFC 4388 [RFC4388] based
   implementations which means that a client which supports this
   extension can work with a server not supporting this document
   provided it uses RFC 4388 [RFC4388] defined query types.  Also, a
   server supporting this document can work with a client not supporting
   this query type.  However, there are some changes that this document
   proposes with respect to RFC 4388 [RFC4388].  Implementors extending
   RFC 4388 [RFC4388] implementation to support this document, should
   take note of the following points:

   o  RFC 4388 [RFC4388] suggests that a DHCPLEASEUNASSIGNED is returned
      only in the case of 'query by IP address'.  All other query types
      will have a return message of either DHCPLEASEACTIVE or
      DHCPLEASEUNKNOWN'.  This document proposes that  Although it is possible to return
      DHCPLEASEUNASSIGNED can be returned for the in case of a query by remote ID. remote-id, in order to
      maintain compatibility with other similar query types (MAC and
      Client-id) a query by remote-id does not support a
      DHCPLEASEUNASSIGNED response.

   o  There may be cases where a query by IP address/MAC address/Client
      Identifier has an option 82 containing remote ID.  In that case,
      the query will still be recognized as query by IP address/MAC
      address/Client Identifier as specified by RFC 4388 [RFC4388].

   o  Section 6.4 of RFC 4388 [RFC4388] suggests that a DHCPLEASEUNKNOWN
      MUST NOT have any other option present.  But for a query by remote
      ID, option 82 MUST be present in the reply.

8.  Security Considerations

   This document does not introduce any new security concerns beyond
   those specified in the original leasequery protocol RFC 4388
   [RFC4388] specifications.

9.  IANA Considerations

   This document does not introduce any new namespaces for the IANA to
   manage.

10.  Acknowledgments

   Copious amounts of text in this document are derived from RFC 4388
   [RFC4388].  Kim kinnear provided valuable feedback on this document.

11.  References

11.1.  Normative Reference

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

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

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

11.2.  Informative Reference

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

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

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

Appendix A.  Why a New Leasequery is Required?

   The three existing query types supported by RFC 4388 do not provide
   effective and efficient antispoofing for the above scenario.

   o  Query by Client Identifier

   Query by Client Identifier is not possible because to use that access
   concentrator need to glean client identifier also but the whole issue
   is that we need leasequeries because the gleaned information was
   lost.  On the other hand, we can query by client identifier when
   client sends a DHCP request, but then there may not be any need for
   lease query as such -- regular gleaning may be enough.

   o  Query by IP Address

   RFC 4388 suggests that it is preferable to use Query by IP Address
   when getting downstream traffic.

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

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

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

   This approach may be acceptable if only legitimate traffic is
   received.  Consider the case when someone sends packets that uses
   spoofed IP addresses.  In that case, lease response will be
   DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN.  RFC 4388 suggests usage of
   negative caching in this regard (which involves additional
   resources).

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

   RFC 4388 suggests that if the access concentrator knows the network
   portion of the IP addresses that are assigned to its clients, then
   some amount of antispoofing can be done in fast path and some lease
   queries may be avoided.  But as indicated before, that information
   may not always be available to access concentrators.

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

   RFC 4388 says that DHCP server should be protected from being flooded
   with too many leasequery requests and access concentrator also should
   not send too many lease query messages at a time.  This would mean
   that legitimate clients may be excessively delayed getting their
   information in the face of antispoofing attacks.

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

   o  Query by MAC Address

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

   Although, query by MAC address is better than query by IP address in
   the above respect, it has a specific problem which is not shared by
   query by IP address.  For a query by MAC address, only two types of
   responses are possible: DHCPLEASEUNKNOWN and DHCPLEASEACTIVE;
   DHCPLEASEUNASSIGNED is not supported.  This is particularly
   troublesome when a DHCP server indeed has definitive information that
   no IP addresses are associated with the specified MAC address in the
   leasequery, but it is forced to respond with DHCPLEASEUNKNOWN instead
   of DHCPLEASEUNASSIGNED.  As we have seen above, unlike
   DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN requires periodic querying with
   DHCP server, an additional overhead.

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

   We conclude that existing lease query types are not appropriate to
   achieve effective and efficient antispoofing.

Authors' Addresses

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

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

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

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

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

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