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rfc:rfc6148

Internet Engineering Task Force (IETF) P. Kurapati Request for Comments: 6148 Juniper Networks Updates: 4388 R. Desetti Category: Standards Track B. Joshi ISSN: 2070-1721 Infosys Technologies Ltd.

                                                         February 2011
            DHCPv4 Lease Query by Relay Agent Remote ID

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 defines a mechanism for relay
 agents to retrieve the lease information from the DHCP server 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 to and from the clients.  In
 certain scenarios, this model is not scalable.  This document first
 looks at issues in the existing mechanism and then proposes a new
 query type, query by Remote ID, to address these issues.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6148.

Kurapati, et al. Standards Track [Page 1] RFC 6148 Query by Remote ID February 2011

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 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.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Kurapati, et al. Standards Track [Page 2] RFC 6148 Query by Remote ID February 2011

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................4
 3. Motivation ......................................................6
 4. Protocol Details ................................................7
    4.1. Sending the DHCPLEASEQUERY Message .........................7
    4.2. Responding to the DHCPLEASEQUERY Message ...................8
    4.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message .....8
    4.4. Determining the IP Address to Be Used in Response ..........9
    4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message ......9
    4.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message ....9
    4.7. Receiving No Response to the DHCPLEASEQUERY Message .......10
    4.8. Lease-Binding Data Storage Requirements ...................10
    4.9. Using the DHCPLEASEQUERY Message with Multiple
         DHCP Servers ..............................................10
 5. RFC 4388 Considerations ........................................11
 6. Security Considerations ........................................11
 7. Acknowledgments ................................................11
 8. References .....................................................12
    8.1. Normative References ......................................12
    8.2. Informative References ....................................12

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, lease query does not provide the full and consolidated
 active lease information 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,
 especially 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.

Kurapati, et al. Standards Track [Page 3] RFC 6148 Query by Remote ID February 2011

            +--------+
            |  DHCP  |     +--------------+
            | Server |-...-|    DSLAM     |
            |        |     |  Relay Agent |
            +--------+     +--------------+
                              |        |
                          +------+   +------+
                          |Modem1|   |Modem2|
                          +------+   +------+
                             |        |    |
                          +-----+  +-----+ +-----+
                          |Node1|  |Node2| |Node3|
                          +-----+  +-----+ +-----+
                               Figure 1
 For example, when a DSLAM (Digital Subscriber Line Access
 Multiplexer) 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",
 "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 node using DHCP to obtain
    configuration parameters such as a network address.

Kurapati, et al. Standards Track [Page 4] RFC 6148 Query by Remote ID February 2011

 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 node that returns configuration
    parameters to DHCP clients.
 o  Fast path
    Fast path refers to data transfer that happens through a network
    processor or an Application Specific Integrated Circuit (ASIC)
    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 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
    Slow path refers to data transfer that happens through the control
    plane.  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.

Kurapati, et al. Standards Track [Page 5] RFC 6148 Query by Remote ID February 2011

3. Motivation

 Consider an 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.  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 to a single port using DHCP, 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: the 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
 required.
 The existing query types necessitate a data-driven approach: the
 lease queries can only be performed when the access concentrator
 receives data.  This results in
 o  increased outage time for clients
 o  excessive negative caching, consuming a lot of resources under a
    spoofing attack
 o  antispoofing being done in the slow path instead of the fast path

Kurapati, et al. Standards Track [Page 6] RFC 6148 Query by Remote ID February 2011

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.  The Remote ID is globally unique in the 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 will remain available to the access concentrator
 after reboot.
 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 lease query defined in this document will mostly be used by
 access concentrators, but it may also be used by other authorized
 elements in the network.  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:

Kurapati, et al. Standards Track [Page 7] RFC 6148 Query by Remote ID February 2011

 o  There MUST be a Relay Agent Information option (option 82) with
    only a Remote ID sub-option (sub-option 2) in the DHCPLEASEQUERY
    message.
 o  The Parameter Request List option [RFC2132] MUST be populated by
    the access concentrator with the Associated-IP option code.  The
    giaddr field and other option codes listed in the Parameter
    Request List option are set as explained in Section 6.2 of
    RFC 4388 [RFC4388].
 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 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:
 o  DHCPLEASEUNKNOWN
    The DHCPLEASEUNKNOWN message indicates that the client associated
    with the Remote ID sub-option 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. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message

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

Kurapati, et al. Standards Track [Page 8] RFC 6148 Query by Remote ID February 2011

 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].
 All other options specified in the Parameter Request 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
 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.

4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message

 The server unicasts the DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message
 to the address specified in the giaddr field of the 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 message as well as the Relay

Kurapati, et al. Standards Track [Page 9] RFC 6148 Query by Remote ID February 2011

 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 the 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 document brings is the removal of periodic
 lease queries generated from negative caching caused by
 DHCPLEASEUNKNOWN messages.  Since the information obtained through
 query by Remote ID is complete, there is no need to attempt 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 is 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 efficiently, 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 is handled in the same way it is done in RFC 4388
 [RFC4388].

Kurapati, et al. Standards Track [Page 10] RFC 6148 Query by Remote ID February 2011

5. RFC 4388 Considerations

 This document is compatible with RFC 4388-based [RFC4388]
 implementations, which means that a client that supports this
 extension can work with a server not supporting this document,
 provided it uses RFC 4388-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 a Remote ID.  In that case,
    the query will still be recognized as a 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
    message 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 inherits the security concerns present in the original
 lease query protocol specification (RFC 4388 [RFC4388]).
 This specification introduces one additional issue, beyond those
 described in RFC 4388 [RFC4388].  A query by Remote ID will result in
 the server replying with consolidated lease-binding information.
 Such a query, if done from an unauthorized source, may lead to a leak
 of lease-binding information.  It is critical to deploy
 authentication techniques mentioned in RFC 3118 [RFC3118] to prevent
 such unauthorized lease queries.

7. Acknowledgments

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

Kurapati, et al. Standards Track [Page 11] RFC 6148 Query by Remote ID February 2011

8. References

8.1. Normative References

 [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]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
            Extensions", RFC 2132, March 1997.
 [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
            RFC 3046, January 2001.
 [RFC3118]  Droms, R., Ed. and W. Arbaugh, Ed., "Authentication for
            DHCP Messages", RFC 3118, June 2001.

8.2. Informative References

 [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.

Kurapati, et al. Standards Track [Page 12] RFC 6148 Query by Remote ID February 2011

Authors' Addresses

 Pavan Kurapati
 Juniper Networks
 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/

Kurapati, et al. Standards Track [Page 13]

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