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Versions: 00 01 02 03 04 05 06 07

Network Working Group                                       M. Boucadair
Internet-Draft                                              C. Jacquenet
Intended status: Standards Track                                  Orange
Expires: October 20, 2017                                       T. Reddy
                                                                   Cisco
                                                          April 18, 2017


        DHCP Options for Network-Assisted Multipath TCP (MPTCP)
                      draft-boucadair-mptcp-dhc-07

Abstract

   Because of the lack of Multipath TCP (MPTCP) support at the server
   side, some service providers now consider a network-assisted model
   that relies upon the activation of a dedicated function called MPTCP
   Conversion Point (MCP).  Network-assisted MPTCP deployment models are
   designed to facilitate the adoption of MPTCP for the establishment of
   multi-path communications without making any assumption about the
   support of MPTCP by the communicating peers.  MCPs located in the
   network are responsible for establishing multi-path communications on
   behalf of endpoints, thereby taking advantage of MPTCP capabilities
   to achieve different goals that include (but are not limited to)
   optimization of resource usage (e.g., bandwidth aggregation), of
   resiliency (e.g., primary/backup communication paths), and traffic
   offload management.

   This document focuses on the explicit deployment scheme where the
   identity of the MPTCP Conversion Point(s) is explicitly configured on
   connected hosts.  This document specifies DHCP (IPv4 and IPv6)
   options to configure hosts with Multipath TCP (MPTCP) parameters.

Requirements Language

   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].

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.




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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 October 20, 2017.

Copyright Notice

   Copyright (c) 2017 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.  DHCPv6 MPTCP Option . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . .   6
   4.  DHCPv4 MPTCP Option . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  DHCPv4 Client Behavior  . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . .   9
     7.2.  DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  DHCP Server Configuration Guidelines . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12








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1.  Introduction

   One of the promising deployment scenarios for Multipath TCP (MPTCP,
   [RFC6824]) is to enable a Customer Premises Equipment (CPE) that is
   connected to multiple networks (e.g., DSL, LTE, WLAN) to optimize the
   usage of such resources.  This deployment scenario relies on MPTCP
   Conversion Points (MCPs) located on both the CPE and network sides
   (Figure 1).  The latter plays the role of traffic concentrator.  An
   MCP terminates the MPTCP sessions established from a CPE, before
   redirecting traffic into a legacy TCP session.  Further Network-
   Assisted MPTCP deployment and operational considerations are
   discussed in [I-D.nam-mptcp-deployment-considerations].

  +------------+        _--------_    +----------------+
  |            |       (    LTE   )   |                |
  |   CPE      +=======+          +===+  Backbone      |
  |  (MCP)     |       (_        _)   |   Network      |
  |            |         (_______)    |+--------------+|
  |            |       IP Network #1  || Concentrator ||------> Internet
  |            |                      ||    (MCP)     ||
  |            |                      |+--------------+|
  |            |       IP Network #2  |                |
  |            |        _--------_    |                |
  |            |       (    DSL    )  |                |
  |            +=======+           +==+                |
  |            |       (_        _)   |                |
  +-----+------+        (_______)     +----------------+
        |
  ---- LAN ----
        |
    end-nodes

                 Figure 1: "Network-Assisted" MPTCP Design

   This document focuses on the explicit mode that consists in
   configuring explicitly the reachability information of the MCP on a
   host.  Concretely, the explicit mode has several advantages, e.g.,:

   o  It does not impose any specific constraint on the location of the
      MCP.  For example, the MCP can be located in any access network,
      located upstream in the core network, or located in a data canter
      facility.

   o  Tasks required for activating the explicit mode are minimal.  In
      particular, this mode does not require any specific routing and/or
      forwarding policies for handling outbound packets other than
      ensuring that an MCP is reachable from a CPE, and vice versa
      (which is straightforward IP routing policy operation).



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   o  The engineering effort to change the location of an MCP for some
      reason (e.g., to better accommodate dimensioning constraints, to
      move the MCP to a data canter, to enable additional MCP instances
      closer to the customer premises, etc.) is minimal

   o  An operator can easily enforce strategies for differentiating the
      treatment of MPTCP connections that are directly initiated by an
      MPTCP-enabled host connected to an MCP if the explicit mode is
      enabled.  Typically, an operator may decide to offload MPTCP
      connections originated by an MPTCP-enabled terminal from being
      forwarded through a specific MCP, or decide to relay them via a
      specific MCP.  Such policies can be instructed to the MCP.
      Implementing such differentiating behavior if the implicit mode is
      in use may be complex to achieve.

   o  Multiple MCPs can be supported to service the same CPE, e.g., an
      MCP can be enabled for internal services (to optimize the delivery
      of some operator-specific services) while another MCP may be
      solicited for external services (e.g., access to the Internet).
      The explicit mode allows the deployment of such scenario owing to
      the provisioning of an MCP selection policy table that relies upon
      the destination IP prefixes to select the MCP to involve for an
      ongoing MPTCP connection, for instance.

   o  Because the MCP's reachability information is explicitly
      configured on the CPE, means to guarantee successful inbound
      connections can be enabled in the CPE to dynamically discover the
      external IP address that has been assigned for communicating with
      remote servers, instruct the MCP to maintain active bindings so
      that incoming packets can be successfully redirected towards the
      appropriate CPE, etc.

   o  Troubleshooting and root cause analysis may be facilitated in the
      explicit mode since faulty key nodes that may have caused a
      service degradation are known.  Because of the loose adherence to
      the traffic forwarding and routing polices, troubleshooting a
      service degradation that is specific to multi-access serviced
      customers should first investigate the behavior of the involved
      MCP.

   This document defines DHCPv4 [RFC2131] and DHCPv6 [RFC3315] options
   that can be used to configure hosts with MCP IP addresses.

   This specification assumes an MCP is reachable through one or
   multiple IP addresses.  As such, a list of IP addresses can be
   returned in the DHCP MPTCP option.  Also, it assumes the various
   network attachments provided to an MPTCP-enabled CPE are managed by
   the same administrative entity.



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2.  Terminology

   This document makes use of the following terms:

   o  Multipath Conversion Point (MCP): a function that terminates a
      transport flow and relays all data received over it over another
      transport flow.  This element is located upstream in the network.
      One or multiple MCPs can be deployed in the network side to assist
      MPTCP-enabled devices to establish MPTCP connections via available
      network attachments.

      On the uplink path, the MCP terminates the MPTCP connections
      [RFC6824] received from its customer-facing interfaces and
      transforms these connections into legacy TCP connections [RFC0793]
      towards upstream servers.

      On the downlink path, the MCP turns the legacy server's TCP
      connection into MPTCP connections towards its customer-facing
      interfaces.
   o  DHCP refers to both DHCPv4 [RFC2131] and DHCPv6 [RFC3315].
   o  DHCP client denotes a node that initiates requests to obtain
      configuration parameters from one or more DHCP servers.
   o  DHCP server refers to a node that responds to requests from DHCP
      clients.

3.  DHCPv6 MPTCP Option

3.1.  Format

   The DHCPv6 MPTCP option can be used to configure a list of IPv6
   addresses of an MCP.

   The format of this option is shown in Figure 2.  As a reminder, this
   format follows the guidelines for creating new DHCPv6 options
   (Section 5.1 of [RFC7227]).
















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       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     OPTION_V6_MPTCP           |         Option-length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                         ipv6-address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                         ipv6-address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 2: DHCPv6 MPTCP option

   The fields of the option shown in Figure 2 are as follows:

   o  Option-code: OPTION_V6_MPTCP (TBA, see Section 7.1)
   o  Option-length: Length of the 'MCP IP Address(es)' field in octets.
      MUST be a multiple of 16.
   o  MCP IPv6 Addresses: Includes one or more IPv6 addresses [RFC4291]
      of the MCP to be used by the MPTCP client.

      Note, IPv4-mapped IPv6 addresses (Section 2.5.5.2 of [RFC4291])
      are allowed to be included in this option.

   To return more than one MCPs to the requesting DHCPv6 client, the
   DHCPv6 server returns multiple instances of OPTION_V6_MPTCP.  Some
   guidelines for DHCP servers are elaborated in Appendix A.

3.2.  DHCPv6 Client Behavior

   Clients MAY request option OPTION_V6_MPTCP, as defined in [RFC3315],
   Sections 17.1.1, 18.1.1, 18.1.3, 18.1.4, 18.1.5, and 22.7.  As a
   convenience to the reader, we mention here that the client includes
   requested option codes in the Option Request Option.

   The DHCPv6 client MUST be prepared to receive multiple instances of
   OPTION_V6_MPTCP; each instance is to be treated separately as it
   corresponds to a given MCP: there are as many MCPs as instances of
   the OPTION_V6_MPTCP option.





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   If an IPv4-mapped IPv6 address is received in OPTION_V6_MPTCP, it
   indicates that the MCP has the corresponding IPv4 address.

   The DHCPv6 client MUST silently discard multicast and host loopback
   addresses [RFC6890] conveyed in OPTION_V6_MPTCP.

4.  DHCPv4 MPTCP Option

4.1.  Format

   The DHCPv4 MPTCP option can be used to configure a list of IPv4
   addresses of an MCP.  The format of this option is illustrated in
   Figure 3.

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Code         |     Length    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | List-Length   |   List of     |
      +-+-+-+-+-+-+-+-+    MPTCP      |
      /      MCP IPv4 Addresses       /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ---
      | List-Length   |   List of     |   |
      +-+-+-+-+-+-+-+-+    MPTCP      |   |
      /      MCP IPv4 Addresses       /   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
      .             ...               . Optional
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
      | List-Length   |   List of     |   |
      +-+-+-+-+-+-+-+-+    MPTCP      |   |
      /      MCP IPv4 Addresses       /   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ---


                       Figure 3: DHCPv4 MPTCP option

   The fields of the option shown in Figure 3 are as follows:

   o  Code: OPTION_V4_MPTCP (TBA, see Section 7.2);
   o  Length: Length of all included data in octets.  The minimum length
      is 5.
   o  List-Length: Length of the "List of MCP IPv4 Addresses" field in
      octets; MUST be a multiple of 4.
   o  List of MCP IPv4 Addresses: Contains one or more IPv4 addresses of
      the MCP to be used by the MPTCP client.  The format of this field
      is shown in Figure 4.
   o  OPTION_V4_MPTCP can include multiple lists of MCP IPv4 addresses;
      each list is treated separately as it corresponds to a given MCP.



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      When several lists of MCP IPv4 addresses are to be included,
      "List-Length" and "MCP IPv4 Addresses" fields are repeated.

      0     8     16    24    32    40    48
      +-----+-----+-----+-----+-----+-----+--
      |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 | ...
      +-----+-----+-----+-----+-----+-----+--
           IPv4 Address 1          IPv4 Address 2 ...

   This format assumes that an IPv4 address is encoded as a1.a2.a3.a4.

            Figure 4: Format of the List of MCP IPv4 Addresses

   OPTION_V4_MPTCP is a concatenation-requiring option.  As such, the
   mechanism specified in [RFC3396] MUST be used if OPTION_V4_MPTCP
   exceeds the maximum DHCPv4 option size of 255 octets.

   Some guidelines for DHCP servers are elaborated in Appendix A.

4.2.  DHCPv4 Client Behavior

   To discover one or more MCPs, the DHCPv4 client MUST include
   OPTION_V4_MPTCP in a Parameter Request List Option [RFC2132].

   The DHCPv4 client MUST be prepared to receive multiple lists of MCP
   IPv4 addresses in the same OPTION_V4_MPTCP; each list is to be
   treated as a separate MCP instance.

   The DHCPv4 client MUST silently discard multicast and host loopback
   addresses [RFC6890] conveyed in OPTION_V4_MPTCP.

5.  Security Considerations

   The security considerations in [RFC2131] and [RFC3315] are to be
   considered.

   MPTCP-related security considerations are discussed in [RFC6824].

   Means to protect the MCP against Denial-of-Service (DoS) attacks must
   be enabled.  Such means include the enforcement of ingress filtering
   policies at the boundaries of the network.  In order to prevent
   exhausting the resources of the MCP by creating an aggressive number
   of simultaneous subflows for each MPTCP connection, the administrator
   should limit the number of allowed subflows per host for a given
   connection.

   Attacks outside the domain can be prevented if ingress filtering is
   enforced.  Nevertheless, attacks from within the network between a



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   host and an MCP instance are yet another actual threat.  Means to
   ensure that illegitimate nodes cannot connect to a network should be
   implemented.

   Traffic theft is also a risk if an illegitimate MCP is inserted in
   the path.  Indeed, inserting an illegitimate MCP in the forwarding
   path allows to intercept traffic and can therefore provide access to
   sensitive data issued by or destined to a host.  To mitigate this
   threat, secure means to discover an MCP (for non-transparent modes)
   should be enabled.

6.  Privacy Considerations

   Generic privacy-related considerations are discussed in [RFC7844].

   The MCP may have access to privacy-related information (e.g.,
   International Mobile Subscriber Identity (IMSI), link identifier,
   subscriber credentials, etc.).  The MCP must not leak such sensitive
   information outside an administrative domain.

7.  IANA Considerations

7.1.  DHCPv6 Option

   IANA is requested to assign the following new DHCPv6 Option Code in
   the registry maintained in http://www.iana.org/assignments/
   dhcpv6-parameters:

                               Option Name Value
                           --------------- -----
                           OPTION_V6_MPTCP TBA

7.2.  DHCPv4 Option

   IANA is requested to assign the following new DHCPv4 Option Code in
   the registry maintained in http://www.iana.org/assignments/bootp-
   dhcp-parameters/:

       Option Name Value Data length   Meaning
   --------------- ----- ------------- ---------------------------------
   OPTION_V4_MPTCP TBA   Variable; the Includes one or multiple lists of
                         minimum       MCP IP addresses; each list is
                         length is 5.  treated as a separate MCP.








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8.  Acknowledgements

   Many thanks to Olivier Bonaventure for the feedback on this document.
   Olivier suggested to define the option as a name but that design
   approach was debated several times within the dhc wg.

   Thanks to Dan Seibel, Bernie Volz, Niall O'Reilly, Simon Hobson, and
   Ted Lemon for the feedback on the dhc wg mailing list.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <http://www.rfc-editor.org/info/rfc2131>.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <http://www.rfc-editor.org/info/rfc2132>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3396]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
              Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
              DOI 10.17487/RFC3396, November 2002,
              <http://www.rfc-editor.org/info/rfc3396>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <http://www.rfc-editor.org/info/rfc4291>.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
              <http://www.rfc-editor.org/info/rfc6824>.







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   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153,
              RFC 6890, DOI 10.17487/RFC6890, April 2013,
              <http://www.rfc-editor.org/info/rfc6890>.

9.2.  Informative References

   [I-D.nam-mptcp-deployment-considerations]
              Boucadair, M., Jacquenet, C., Bonaventure, O., Henderickx,
              W., and R. Skog, "Network-Assisted MPTCP: Use Cases,
              Deployment Scenarios and Operational Considerations",
              draft-nam-mptcp-deployment-considerations-01 (work in
              progress), December 2016.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.

   [RFC7227]  Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
              S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
              BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
              <http://www.rfc-editor.org/info/rfc7227>.

   [RFC7844]  Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
              Profiles for DHCP Clients", RFC 7844,
              DOI 10.17487/RFC7844, May 2016,
              <http://www.rfc-editor.org/info/rfc7844>.

   [RFC7969]  Lemon, T. and T. Mrugalski, "Customizing DHCP
              Configuration on the Basis of Network Topology", RFC 7969,
              DOI 10.17487/RFC7969, October 2016,
              <http://www.rfc-editor.org/info/rfc7969>.

Appendix A.  DHCP Server Configuration Guidelines

   DHCP servers that support the DHCP MCP option can be configured with
   a list of IP addresses of the MCP(s).  If multiple IP addresses are
   configured, the DHCP server MUST be explicitly configured whether all
   or some of these addresses refer to:

   1.  the same MCP: the DHCP server returns multiple addresses in the
       same instance of the DHCP MCP option.

   2.  distinct MCPs : the DHCP server returns multiple lists of MCP IP
       addresses to the requesting DHCP client (encoded as multiple
       OPTION_V6_MPTCP or in the same OPTION_V4_MPTCP); each list refers
       to a distinct MCP.




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   Precisely how DHCP servers are configured to separate lists of IP
   addresses according to which MCP they refer to is out of scope for
   this document.  However, DHCP servers MUST NOT combine the IP
   addresses of multiple MCPs and return them to the DHCP client as if
   they were belonging to a single MCP, and DHCP servers MUST NOT
   separate the addresses of a single MCP and return them as if they
   were belonging to distinct MCPs.  For example, if an administrator
   configures the DHCP server by providing a Fully Qualified Domain Name
   (FQDN) for an MCP, even if that FQDN resolves to multiple addresses,
   the DHCP server MUST deliver them within a single server address
   block.

   DHCPv6 servers that implement this option and that can populate the
   option by resolving FQDNs will need a mechanism for indicating
   whether to query A records or only AAAA records.  When a query
   returns A records, the IP addresses in those records are returned in
   the DHCPv6 response as IPv4-mapped IPv6 addresses.

   Since this option requires support for IPv4-mapped IPv6 addresses, a
   DHCPv6 server implementation will not be complete if it does not
   query A records and represent any that are returned as IPv4-mapped
   IPv6 addresses in DHCPv6 responses.  The mechanism whereby DHCPv6
   implementations provide this functionality is beyond the scope of
   this document.

   For guidelines on providing context-specific configuration
   information (e.g., returning a regional-based configuration), and
   information on how a DHCP server might be configured with FQDNs that
   get resolved on demand, see [RFC7969].

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Christian Jacquenet
   Orange
   Rennes
   France

   Email: christian.jacquenet@orange.com





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   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com











































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