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Versions: 00 01 02 03 04 05 06 07 draft-ietf-dhc-dhcp4o6-saddr-opt

Softwire WG                                                    I. Farrer
Internet-Draft                                       Deutsche Telekom AG
Updates: RFC7568 (if approved)                                    Q. Sun
Intended status: Standards Track                                  Y. Cui
Expires: August 5, 2017                                           L. Sun
                                                     Tsinghua University
                                                        February 1, 2017


                DHCPv4 over DHCPv6 Source Address Option
                draft-fsc-softwire-dhcp4o6-saddr-opt-07

Abstract

   DHCPv4 over DHCPv6 [RFC7341] describes a mechanism for dynamically
   configuring IPv4 over an IPv6-only network.  For DHCPv4 over DHCPv6
   to function with some IPv4-over-IPv6 softwire mechanisms and
   deployment scenarios, the operator must learn the /128 IPv6 address
   that the client will use as the source of IPv4-in-IPv6 tunnel.  This
   address, in conjunction with the IPv4 address and the Port Set ID
   allocated to the DHCP 4o6 client are used to create a binding table
   entry in the softwire tunnel concentrator.  This memo defines two
   DHCPv6 options used to communicate the source tunnel IPv6 address
   between the DHCP 4o6 client and server.  It also describes a method
   for configuring the client with the IPv6 address of the border router
   so that the softwire can be established.  It is designed to work in
   conjunction with the IPv4 address allocation process.

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/.

   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 August 5, 2017.







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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   4.  Solution Overview . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Provisioning the BR Address . . . . . . . . . . . . . . .   4
   5.  IPv6/IPv4 Binding Message Flow  . . . . . . . . . . . . . . .   4
   6.  DHCPv6 Options  . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  DHCPv4 over DHCPv6 Source Address Hint Option . . . . . .   6
       6.1.1.  Client Option Validation Behavior . . . . . . . . . .   6
     6.2.  DHCPv4 over DHCPv6 Source Address Option  . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Deterministic IPv4-over-IPv6 transition technologies require that
   elements are pre-configured with binding rules for routing traffic to
   clients.  This places a constraint on the location of the client's
   tunnel endpoint: The tunnel endpoint has to be a pre-determined
   prefix which is usually be configured on the home gateway device.
   [RFC7597] describes a DHCPv6 based mechanism for provisioning such
   deterministic softwires.

   A dynamic provisioning model, such as using DHCPv4 over DHCPv6
   [RFC7341] allows much more flexibility in the location of the IPv4-
   over-IPv6 tunnel endpoint, as the IPv6 address is dynamically



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   signalled back to the service provider so that the corresponding
   tunnel configuration in the border router (BR) can be created.  The
   DHCP 4o6 client and tunnel client could be run on end devices
   attached to any routable IPv6 prefix allocated to an end-user,
   located anywhere within an arbitrary home network topology.  Dynamic
   allocation also helps to optimize IPv4 resource usage as only clients
   which are currently active are allocated IPv4 addresses.

   This document describes a mechanism for dynamically provisioning
   softwires created using DHCPv4 over DHCPv6 (DHCP 4o6), including
   provisioning the client with the address of the softwire border
   router (BR) and informing the service provider of client's binding
   between the dynamically allocated IPv4 address and Port Set ID and
   the IPv6 address that the softwire Initiator will use for accessing
   IPv4-over-IPv6 services.

   It is used with DHCP 4o6 message flows to communicate the binding
   over the IPv6-only network.  The service provider can then use this
   binding information to provision other functional elements in their
   network accordingly, e.g. using the client's binding information to
   synchronise the binding table in the border router.

2.  Applicability

   The mechanism described in this document is only suitable for use for
   provisioning softwire clients via DHCP 4o6.  The options described
   here are only applicable within the DHCP 4o6 message exchange
   process.  Current softwire technologies suitable for extending to
   incorporate DHCPv4 over DHCPv6 with dynamic IPv4 address leasing
   include [RFC7597] and [RFC7596].

3.  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].

4.  Solution Overview

   The solution in this document is intended for the dynamic
   establishment of IPv4-over-IPv6 softwires.  DHCP 4o6 [RFC7341]
   supports dynamically allocating (shared) IPv4 address.  For a
   softwire to be successfully created, the IPv4 address has to be
   linked to the client's IPv6 tunnel source address.  Within this
   process, the DHCP 4o6 client uses a DHCPv6 option to signal its
   tunnel source IPv6 address to the DHCP 4o6 server so that the
   operator's provisioning system can create the binding and configure
   the tunnel concentrator accordingly.



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   Two new DHCPv6 options are defined in this memo:
   OPTION_DHCP4O6_SADDR_HINT and OPTION_DHCP4O6_SADDR.  They are
   intended to be used alongside the normal DHCPv4 IPv4 address
   allocation message flow in the context of DHCP 4o6.  If a DHCP 4o6
   client supports this mechanism, it MUST include the code of
   OPTION_DHCP4O6_SADDR_HINT in the Option Request Option (ORO)
   [RFC3315] when requesting IPv4 configuration through DHCP 4o6.

   The communication of parameters between the client and server is a
   two-way process: OPTION_DHCP4O6_SADDR_HINT is optionally used by the
   DHCP 4o6 server to indicate to the client a preferred IPv6 prefix for
   binding the received IPv4 configuration and sourcing tunnel traffic.
   This may be necessary if there are multiple IPv6 prefixes in use in
   the customer network (e.g.  ULAs), or if the specific IPv4-over-IPv6
   transition mechanism requires the use of a particular prefix for any
   reason.  When the client has selected an IPv6 address to bind the
   IPv4 configuration to, it passes the address back to the DHCP 4o6
   server using OPTION_DHCP4O6_SADDR.

4.1.  Provisioning the BR Address

   To configure a softwire, the initiator also requires the IPv6 address
   of the BR.  Section 4.2 of [RFC7598] defines option 90
   (OPTION_S46_BR) for this purpose, but mandates that the option can
   only be used when encapsulated within one of the softwire container
   options: OPTION_S46_CONT_MAPE, OPTION_S46_CONT_MAPT or
   OPTION_S46_CONT_LW.  From Section 3 of [RFC7598]:

      "Softwire46 DHCPv6 clients that receive provisioning options that
      are not encapsulated in container options MUST silently ignore
      these options."

   This document updates [RFC7598] to remove this restriction for DHCPv6
   option 90 (OPTION_S46_BR) allowing it to appear directly within the
   list of options in the client's ORO request and directly within
   subsequent messages sent by the DHCPv6 server.

5.  IPv6/IPv4 Binding Message Flow

   The following diagram shows the client/server message flow and how
   the options defined in this document are used.  In each step, the
   relevant DHCPv4 message is given above the arrow and the relevant
   options below the arrow.  All the DHCPv4 messages here are
   encapsulated in DHCPv4-query or DHCPv4-response messages, and those
   options are included in the 'options' field of the DHCPv4-query or
   DHCPv4-response message.





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        DHCP 4o6                                              DHCP 4o6
         Client                                                Server
           |                DHCPDISCOVER (DHCPv4)                 |
    Step 1 |----------------------------------------------------->|
           |               ORO with OPTION_S46_BR,                |
           |          OPTION_DHCP4O6_SADDR_HINT(DHCPv6)           |
           |                                                      |
           |                 DHCPOFFER (DHCPv4)                   |
    Step 2 |<-----------------------------------------------------|
           |     OPTION_S46_BR, OPTION_DHCP4O6_SADDR_HINT         |
           |    (cipv6-prefix-hint with service provider's        |
           |              preferred prefix) (DHCPv6)              |
           |                                                      |
           |                 DHCPREQUEST (DHCPv4)                 |
    Step 3 |----------------------------------------------------->|
           |                  OPTION_S46_BR,                      |
           |    OPTION_DHCP4O6_SADDR (cipv6-bound-prefix with     |
           |     client's bound /128 IPv6 address) (DHCPv6)       |
           |                                                      |
           |                   DHCPACK (DHCPv4)                   |
    Step 4 |<-----------------------------------------------------|
           |                    OPTION_S46_BR,                    |
           |    OPTION_DHCP4O6_SADDR (cipv6-bound-prefix with     |
           |      client's bound /128 IPv6 prefix) (DHCPv6)       |
           |                                                      |


                      IPv6/IPv4 Binding Message Flow

   A client attempting dynamic softwire configuration includes the
   option code for OPTION_BR_PREFIX, OPTION_DHCP4O6_SADDR_HINT in the
   DHCPv6 ORO in all DHCPv4-query messages it sends.

   When a DHCP 4o6 Server replies with a DHCPOFFER message, it SHOULD
   include OPTION_S46_BR.  It MAY also include
   OPTION_DHCP4O6_SADDR_HINT, which is used to indicate a preferred
   prefix that the client should use to bind IPv4 configuration to.  If
   this option is received, the client MUST perform a longest prefix
   match between cipv6-prefix-hint and all prefixes/addresses in use on
   the device.  If a match is found, the selected prefix MUST then be
   used to bind the received IPv4 configuration to and source the tunnel
   from.  If no match is found, or the client doesn't receive
   OPTION_DHCP4O6_SADDR_HINT the client MAY select any valid IPv6
   address to use as the tunnel source.

   Once the client has selected which prefix it will use, it MAY use
   either an existing IPv6 address that is already configured on an
   interface, or create a new address specifically for use as the



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   softwire source address (e.g. using an Interface Identifier
   constructed as per Section 6 of [RFC7597]).  If a new address is
   being created, the client MUST complete configuration of the new
   address, performing duplicate address detection (if required) before
   proceeding to Step 3.

   OPTION_DHCP4O6_SADDR is used by the client to inform the DHCP 4o6
   Server which IPv6 address the IPv4 configuration has been bound to.
   The client MUST put the selected IPv6 softwire source address into
   this option and include it in the DHCPv4-response message when it
   sends the DHCPREQUEST message.

6.  DHCPv6 Options

6.1.  DHCPv4 over DHCPv6 Source Address Hint Option

         0                   1                   2                   3
         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_DHCP4O6_SADDR_HINT   |         option-length         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |cipv6-hintlen  |                                               |
        +-+-+-+-+-+-+-+-+          cipv6-prefix-hint                    .
        .                          (variable length)                    .
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   o  option-code: OPTION_DHCP4O6_SADDR_HINT (TBA1)
   o  option-length: 1 + length of cipv6-prefix-hint, specified in
      bytes.
   o  cipv6-hintlen: 8-bit field expressing the bit mask length of the
      IPv6 prefix specified in cipv6-prefix-hint.  Valid values are 0 to
      128.
   o  cipv6-prefix-hint: The IPv6 prefix indicating the preferred prefix
      for the client to bind the received IPv4 configuration to.  The
      length is (cipv6-hintlen + 7) / 8.  The field is padded on the
      right with zero bits up to the nearest octet boundary when cipv6-
      prefix-hint is not evenly divisible by 8.

   OPTION_DHCP4O6_SADDR_HINT is a singleton.  Servers MUST NOT send more
   than one instance of the OPTION_DHCP4O6_SADDR_HINT option.

6.1.1.  Client Option Validation Behavior

   On receipt of the OPTION_DHCP4O6_SADDR_HINT option, the client makes
   the following validation checks:

   o  The received cipv6-hintlen value is not larger than 128.



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   o  The received cipv6-hintlen value is not larger than the number of
      bytes sent in the cipv6-prefix-hint field. (e.g. the cipv6-hintlen
      is 128 but the cipv6-prefix-hint has only 8 bytes).

   For either of these cases the receiver MAY either discard the option
   and proceed to attempt configuration as if the option had not been
   received, or attempt to use the received values for the long prefix
   match anyway.

   The receiver MUST only use bits the cipv6-prefix-hint field up to the
   value specified in the cipv6-hintlen when performing the longest
   prefix match.  cipv6-prefix-hint bits beyond this value MUST be
   ignored.

6.2.  DHCPv4 over DHCPv6 Source Address Option

   The format of DHCPv4 over DHCPv6 Source address option is defined as
   follows:

         0                   1                   2                   3
         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_DHCP4O6_SADDR      |         option-length         |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        +                        cipv6-src-address                      +
        .                           (128 bits)                          .
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   o  option-code: OPTION_DHCP4O6_SADDR (TBA2)
   o  option-length: 16.
   o  cipv6-src-address: 16 bytes long; The IPv6 address that the client
      has bound the allocated IPv4 configuration to.

7.  Security Considerations

   Security considerations which are applicable to [RFC7341] are also
   applicable here.

8.  IANA Considerations

   IANA is requested to allocate a DHCPv6 option code for
   OPTION_DHCP4O6_SADDR_HINT and a DHCPv4 option code for
   OPTION_DHCP4O6_SADDR.






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9.  Acknowledgements

   The authors would like to thank Ted Lemon, Lishan Li and Tatuya
   Jinmei for their contributions and comments.

10.  References

10.1.  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>.

   [RFC7341]  Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
              Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport",
              RFC 7341, DOI 10.17487/RFC7341, August 2014,
              <http://www.rfc-editor.org/info/rfc7341>.

10.2.  Informative References

   [I-D.farrer-softwire-br-multiendpoints]
              Farrer, I. and Q. Sun, "Multiple BR Tunnel Endpoint
              Addresses", draft-farrer-softwire-br-multiendpoints-01
              (work in progress), July 2015.

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

   [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>.

   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the Dual-
              Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
              July 2015, <http://www.rfc-editor.org/info/rfc7596>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <http://www.rfc-editor.org/info/rfc7597>.






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   [RFC7598]  Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
              W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
              Configuration of Softwire Address and Port-Mapped
              Clients", RFC 7598, DOI 10.17487/RFC7598, July 2015,
              <http://www.rfc-editor.org/info/rfc7598>.

Authors' Addresses

   Ian Farrer
   Deutsche Telekom AG
   CTO-ATI, Landgrabenweg 151
   Bonn, NRW  53227
   Germany

   Email: ian.farrer@telekom.de


   Qi Sun
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-5822
   Email: sunqi.csnet.thu@gmail.com


   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn


   Linhui Sun
   Tsinghua University
   Beijing  100084
   P.R. China

   Phone: +86-10-6278-5822
   Email: lh.sunlinh@gmail.com









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