DHC Working Group                                            P. Kurapati
Internet-Draft                                     Juniper Networks Ltd.
Updates: 4388 (if approved)                                   R. Desetti
Expires: April 11, 2011
Intended status: Standards Track                                B. Joshi
Expires: May 20, 2011                          Infosys Technologies Ltd.
                                                         October 8,
                                                       November 16, 2010

              DHCPv4 lease query by Relay Agent Remote ID


   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 defines a mechanism for relay
   agents to retrieve the lease information from the DHCP server as and
   when this information is lost.  The existing lease query mechanism is
   data driven, which means that a relay agent can initiate the lease
   query 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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  Sending the DHCPLEASEQUERY Message . . . . . . . . . . . .  9
     4.2.  Responding to the DHCPLEASEQUERY Message . . . . . . . . . 10
     4.3.  Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message . . 10
     4.4.  Determining the IP address to be used in response  . . . . 11
     4.5.  Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message  . . 11
           Message  . . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.7.  Receiving No Response to the DHCPLEASEQUERY Message  . . . 12
     4.8.  Lease Binding Data Storage Requirements  . . . . . . . . . 12
     4.9.  Using the DHCPLEASEQUERY Message with Multiple DHCP
           Servers  . . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  RFC 4388 Considerations  . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  Normative Reference  . . . . . . . . . . . . . . . . . . . 17
     9.2.  Informative Reference  . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18

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- data
   driven model, lease query does not provide the full and 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|
                            +------+   +------+
                               |        |    |
                            +-----+  +-----+ +-----+
                            |Node1|  |Node2| |Node3|
                            +-----+  +-----+ +-----+

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

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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

   o  "DHCP client"

   A DHCP client is an Internet node 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

   o  "DHCP server"

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

   o  "Fast path"

   Data transfer that happens through a 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

   o  "Location information"

   Location information is information needed by the access concentrator
   to forward traffic to a broadband-accessible node.  This information
   includes knowledge of the node's hardware address, the port or
   virtual circuit that leads to the node, 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 that happens through the control plane.  Typically this
   has very limited buffers to store data and the speeds are very low
   compared to the 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.  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 the fast path.  The access
   concentrator keeps track of only one list of IP addresses: list of IP
   addresses that are assigned by the DHCP servers; 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

   The existing query types

   o  necessitate a data-driven approach: the lease queries can only be
      performed 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

4.  Protocol Details

   This section talks about the protocol details for query by Remote ID.
   Most of the message handling is similar to RFC 4388 [RFC4388] and
   this section highlights only the differences.  Readers are advised to
   go through RFC 4388 [RFC4388] before going through this section for
   complete understanding of the protocol.

   When used in this document, the unqualified term "DHCPLEASEQUERY"
   indicates 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 node connected to the access
   concentrator.  This  The Remote ID is globally unique in the network. network and is
   configured per circuit/connection in the relay agent.

   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 initiates (for each connection/circuit) a DHCP lease
   query by Remote ID as defined in this section.  For this query, the
   requester supplies an option 82 that includes only a Remote ID sub-
   option in the DHCPLEASEQUERY message.  The Remote ID is normally pre-
   provisioned in the access concentrator per circuit/connection and
   hence the same will remain available to the access concentrator after

   The DHCP server MUST reply with a DHCPLEASEACTIVE message if there is
   an active lease corresponding to the Remote ID that is present in the
   DHCPLEASEQUERY message.  Otherwise, the server MUST reply with a
   DHCPLEASEUNKNOWN message.  Servers that do not implement DHCP lease
   query 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  There MUST be a Relay Agent Information option (option 82) with
      only a Remote ID sub-option (sub-option 2) in the DHCPLEASEQUERY

   o  The Parameter Request List option [RFC2132] MUST be populated by
      the access concentrator with the Associated-IP option. option code.  The
      giaddr field and other
      options option codes listed in Parameter Request
      List option are set as explained in section 6.2 of RFC 4388

   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

   The DHCPLEASEQUERY message SHOULD be sent to a DHCP server that 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:


   The DHCPLEASEUNKNOWN message indicates that the client associated
   with the Remote ID suboption of the DHCPLEASEQUERY message is not
   allocated any lease or it is not managed by the server.


   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.


   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 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.  This is intended for
   maintaining backwards compatibility with RFC 4388 [RFC4388].

   For all

   All other options that are specified in the Parameter Request List,
   the processing is same List [RFC2132]
   are processed as mentioned in section 6.4.2 of RFC 4388 [RFC4388].

   In a DHCPLEASEUNKNOWN response message, the DHCP server MUST echo the
   Option 82 received in the DHCPLEASEQUERY message.  No other option is
   included in the message.

4.4.  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

   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.


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


   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 the Relay Agent
   Information option 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 Remote ID sub-option of the DHCPLEASEQUERY
   message.  The access concentrator MAY store this information for
   future use.  However, another DHCPLEASEQUERY message to the same DHCP
   server SHOULD NOT be attempted with the same Remote ID sub-option.

   For lease query by Remote ID, the impact of negative caching is
   greatly reduced as the response leads to "definitive" information on
   all the nodes connected behind the connection.  Note that in case of
   the data-driven approach [RFC4388], a node spoofing several IP
   addresses can lead to negative caching of greater magnitude.  Another
   important change that this draft brings is the removal of periodic
   lease queries generated from negative caching caused by
   DHCPLEASEUNKNOWN.  Since the information obtained through query by
   Remote ID is complete, there is no need of attempting lease query
   again for the same connection.

4.7.  Receiving No Response to the DHCPLEASEQUERY Message

   The condition of an access concentrator receiving no response to a
   DHCPLEASEQUERY message 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].

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  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.

6.  Security Considerations

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

7.  IANA Considerations

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

8.  Acknowledgments

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

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.

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

Authors' Addresses

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

   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

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

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

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