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Versions: (draft-kurapati-dhc-leasequery-by-remote-id) 00 01 02 03 04 05 06 07 08 09 RFC 6148

DHC Working Group                                            P. Kurapati
Internet-Draft                                     Juniper Networks Ltd.
Expires: December 9, 2010                                     R. Desetti
                                                                B. Joshi
                                               Infosys Technologies Ltd.
                                                            June 7, 2010


               DHCPv4 Leasequery by relay agent remote ID
             draft-ietf-dhc-leasequery-by-remote-id-05.txt

Abstract

   Some Relay Agents extract lease information from the DHCP messages
   exchanged between the client and DHCP server.  This lease information
   is used by relay agents for various purposes like antispoofing and
   prevention of flooding.  RFC 4388 [RFC4388] defines a mechanism for
   relay agents to retrieve the lease information from the DHCP server
   as and when this information is lost.  The 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.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 9, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Sending the DHCPLEASEQUERY Message . . . . . . . . . . . .  8
     4.2.  Responding to the DHCPLEASEQUERY Message . . . . . . . . .  9
     4.3.  Determining the IP address to be used in response  . . . .  9
     4.4.  Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE message . . 10
     4.5.  Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message  . . 10
     4.6.  Receiving a  DHCPLEASEACTIVE or DHCPLEASEUNKNOWN
           Message  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.7.  Receiving No Response to the DHCPLEASEQUERY Message  . . . 11
     4.8.  Lease Binding Data Storage Requirements  . . . . . . . . . 11
     4.9.  Using the DHCPLEASEQUERY Message with Multiple DHCP
           Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  RFC 4388 Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     9.1.  Normative Reference  . . . . . . . . . . . . . . . . . . . 16
     9.2.  Informative Reference  . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17















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1.  Introduction

   DHCP relay agents snoop DHCP messages and append a relay agent
   information option before relaying them to the configured DHCP
   Server.  In this process, some relay agents also glean the lease
   information sent by the server and maintain this locally.  This
   information is used to prevent spoofing attempts from clients and
   also sometimes to install routing information.  When a 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 a client sends data upstream, the relay agent can query
   the server about the related lease information, based on the source
   MAC/IP address.  These mechanisms do not scale well when there are
   thousands of clients connected to the relay agent.  In the data-
   driven model, DHCP Leasequery does not provide the full, consolidated
   active Lease informations associated with a given connection/circuit
   which will result in inefficient anti-spoofing.  The relay agent also
   has to contend with considerable resources for negative caching
   specially under spoofing attacks.

   We need a mechanism for a relay agent to retrieve the consolidated
   lease information for a given connection/circuit before upstream
   traffic is sent 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.  The 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 the Relay Agent Information option.  This



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   document talks about the motivation for the new query type and the
   method to perform it.

















































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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 RFC 951 [RFC951] and RFC 1542
   [RFC1542].

   o  "DHCP server"

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

   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



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   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.
































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3.  Motivation

   Consider a typical access concentrator (e.g., DSLAM) working also as
   a DHCP relay agent.  A "Fast path" and a "slow path" generally exist
   in most networking boxes.  Fast path processing is done in a network
   processor or an ASIC (Application Specific Integrated Circuit).  Slow
   path processing is done in a normal processor.  As much as possible,
   regular data forwarding should be done in the 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 from
   DHCP negotiations for antispoofing and other purposes.  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; upstream traffic from all other IP addresses
   is dropped.  If a client starts its data transfer after its DHCP
   negotiations have been gleaned by the 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 the 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 a 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 the access concentrator receives data.  This results in
      increased outage time for clients

   o  results in excessive negative caching, consuming a lot of
      resources under a spoofing attack

   o  results in antispoofing being done in the slow path instead of the
      fast path




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4.  Protocol Details

   This section talks about the protocol details for query by relay
   agent remote id.  Most of the message handlings are similar to RFC
   4388 [RFC4388] and this section highlights only the differences.
   Reader is advised to go through RFC 4388 [RFC4388] before going
   through this section for complete understanding of the protocol.

   A DHCPLEASEQUERY specified in this document specifies a lease query
   by remote ID unless otherwise specified.

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

   This document defines a new query type based on the 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 (for each connection/circuit) a dhcp
   lease query by remote-id as defined in this section.  For this query,
   the requester supplies only an option 82 which will include only an
   Agent Remote ID sub-option in the DHCPLEASEQUERY message.

   The DHCP server MUST reply with a DHCPLEASEACTIVE message if there is
   an active lease corresponding to the agent remote-ID that is present
   in the DHCPLEASEQUERY message.  Otherwise, the server MUST reply with
   a DHCPLEASEUNKNOWN message.  Servers that do not implement
   DHCPLEASEQUERY based on remote ID SHOULD simply not respond.

4.1.  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 RFC 2131 [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 and Parameter Request List option" are set as explained
      in section 6.2 of RFC 4388 [RFC4388].

   o  There MUST be a Relay Agent Information option (option 82) with
      only Agent Remote ID sub-option (sub-option 2) in the
      DHCPLEASEQUERY message.





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   o  The "ciaddr" field MUST be set to zero.

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

   o  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).

4.2.  Responding to the DHCPLEASEQUERY Message

   There are two possible responses to a DHCPLEASEQUERY message:

   o  DHCPLEASEUNKNOWN

   The DHCPLEASEUNKNOWN message indicates that the client associated
   with the agent remote-ID suboption of 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.

4.3.  Determining the IP address to be used in response

   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.




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4.4.  Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE message

   In a DHCPLEASEUNKNOWN response message, the DHCP server MUST echo the
   Option 82 received in the DHCPLEASEQUERY message.  No other options
   are returned for these messages.

   A DHCPLEASEACTIVE message is built by populating information
   pertaining to the client associated with the IP address specified in
   the "ciaddr" field.

   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.

   For all other options that are specified in Parameter Request List,
   the processing is same as mentioned in section 6.4.2 of RFC 4388
   [RFC4388].

4.5.  Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message

   The server unicasts the DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message
   to the address specified in giaddr field of DHCPLEASEQUERY message.

4.6.  Receiving a  DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message

   When a DHCPLEASEACTIVE message is received in response to the
   DHCPLEASEQUERY message, it means that there is currently an active
   lease associated with the remote-id in the 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 DHCPLEASEUNKNOWN message is received by an access concentrator
   that 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 MAY store this
   information for future use.  However, a DHCPLEASEQUERY SHOULD NOT be
   attempted with the same Remote ID sub-option.

   For leasequery by remote-id, the impact of negative caching is
   greatly reduced as the response leads to "definitive" information on



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   all the hosts connected behind the connection.  Note that in the case
   of data-driven approach [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 connection.

4.7.  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].

4.8.  Lease Binding Data Storage Requirements

   Implementation Note:

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

4.9.  Using the DHCPLEASEQUERY Message with Multiple DHCP Servers

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
























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5.  RFC 4388 Considerations

   This document is compatible with RFC 4388 [RFC4388] based
   implementations, which means that a client that 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].  Implementers extending
   RFC 4388 [RFC4388] implementations 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.  Although it would be possible to return
      DHCPLEASEUNASSIGNED in case of a query by 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.






















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6.  Security Considerations

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














































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7.  IANA Considerations

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















































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8.  Acknowledgments

   Copious amounts of text in this document are derived from RFC 4388
   [RFC4388].  Kim kinnear, Damien Neil, Stephen Jacob and Alfred Hoenes
   provided valuable feedback on this document














































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9.  References

9.1.  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.

9.2.  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.

























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Authors' Addresses

   Pavan Kurapati
   Juniper Networks Ltd.
   Embassy Prime Buildings, C.V.Raman Nagar
   Bangalore  560 093
   India

   Email: kurapati@juniper.net
   URI:   http://www.juniper.net/


   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/





















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