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Internet Engineering Task Force (IETF)                       P. KurapatiRequest for Comments: 6148                              Juniper NetworksUpdates:4388                                                 R. DesettiCategory: Standards Track                                       B. JoshiISSN: 2070-1721                                Infosys Technologies Ltd.                                                           February 2011DHCPv4 Lease Query by Relay Agent Remote IDAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6148.Kurapati, et al.             Standards Track                    [Page 1]

RFC 6148                   Query by Remote ID              February 2011Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 2011Table of Contents1. Introduction ....................................................32. Terminology .....................................................43. Motivation ......................................................64. Protocol Details ................................................74.1. Sending the DHCPLEASEQUERY Message .........................74.2. Responding to the DHCPLEASEQUERY Message ...................84.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message .....84.4. Determining the IP Address to Be Used in Response ..........94.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message ......94.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message ....94.7. Receiving No Response to the DHCPLEASEQUERY Message .......104.8. Lease-Binding Data Storage Requirements ...................10      4.9. Using the DHCPLEASEQUERY Message with Multiple           DHCP Servers ..............................................105.RFC 4388 Considerations ........................................116. Security Considerations ........................................117. Acknowledgments ................................................118. References .....................................................128.1. Normative References ......................................128.2. Informative References ....................................121.  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 byRFC 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 inRFC 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, perRFC 951 [RFC951] andRFC 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 20113.  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 byRFC 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 pathKurapati, et al.             Standards Track                    [Page 6]

RFC 6148                   Query by Remote ID              February 20114.  Protocol Details   This section talks about the protocol details for query by Remote ID.   Most of the message handling is similar toRFC 4388 [RFC4388], and   this section highlights only the differences.  Readers are advised to   go throughRFC 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 inRFC 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 inSection 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 withRFC 4388 [RFC4388].   All other options specified in the Parameter Request List [RFC2132]   are processed as mentioned inSection 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 RelayKurapati, 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 inRFC 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 inRFC 4388   [RFC4388].Kurapati, et al.             Standards Track                   [Page 10]

RFC 6148                   Query by Remote ID              February 20115.RFC 4388 Considerations   This document is compatible withRFC 4388-based [RFC4388]   implementations, which means that a client that supports this   extension can work with a server not supporting this document,   provided it usesRFC 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 toRFC 4388 [RFC4388].  Implementers extendingRFC 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 byRFC 4388 [RFC4388].   oSection 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 inRFC 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 inRFC 3118 [RFC3118] to prevent   such unauthorized lease queries.7.  Acknowledgments   Copious amounts of text in this document are derived fromRFC 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 20118.  References8.1.  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 2011Authors' 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]