Unified IPv4-in-IPv6 Softwire CPE
draft-ietf-softwire-unified-cpe-00

Softwire WG                                                 M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                               I. Farrer
Expires: September 12, 2013                             Deutsche Telekom
                                                          March 11, 2013

                   Unified IPv4-in-IPv6 Softwire CPE
                   draft-ietf-softwire-unified-cpe-00

Abstract

   Transporting IPv4 packets encapsulated in IPv6 is a common solution
   to the problem of IPv4 service continuity over IPv6-only provider
   networks.  A number of differing functional approaches have been
   developed for this, each having their own specific characteristics.
   As these approaches share a similar functional architecture and use
   the same data plane mechanisms, this memo describes a specification
   whereby a single CPE can interwork with all of the standardized and
   proposed approaches to providing encapsulated IPv4 in IPv6 services.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on September 12, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Rationale . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  IPv4 Service Continuity Architectures: A 'Big Picture'
       Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Functional Elements . . . . . . . . . . . . . . . . . . .   4
     2.2.  Required Provisoning Information  . . . . . . . . . . . .   6
   3.  Unified Softwire CPE Behaviour  . . . . . . . . . . . . . . .   6
     3.1.  IPv4 Address Functional Requirements  . . . . . . . . . .   7
     3.2.  Generic CPE Bootstrapping Logic . . . . . . . . . . . . .   7
     3.3.  Customer Side DHCP Based Provisioning . . . . . . . . . .   9
     3.4.  Forwarding Action by the Customer End-Node  . . . . . . .  11
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   IPv4 service continuity is one of the major technical challenges
   which must be considered during IPv6 migration.  Over the past few
   years, a number of different approaches have been developed to assist
   with this problem.  These approaches, or modes, exist in order to
   meet the particular deployment, scaling, addressing and other
   requirements of different service provider's networks.  Section 2 of
   this document describes these approaches in more detail.

   A common feature shared between all of the differing modes is the
   integration of softwire tunnel end-point functionality into the CPE
   router.  Due to this inherent data plane similarity, a single CPE may
   be capable of supporting several different approaches.  Users may
   also wish to configure a specific mode of operation.

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   A service provider's network may also have more than one mode enabled
   in order to support diverse CPE client functionality, during
   migration between modes or where services require specific supporting
   softwire architectures.

   For softwire based services to be successfully established, it is
   essential that the customer end-node, the service provider end-node
   and provisioning systems are able to indicate their capabilities and
   preferred mode of operation.

   This memo describes the logic required by both the CPE tunnel end-
   node and the service provider's provisioning infrastructure so that
   softwire services can be provided in mixed-mode environments.

1.1.  Rationale

   The following rationale has been adopted for this document:

   (1)  Describe the functionality of each the different solution modes
      and provide clear distinctions between them

   (2)  Simplify solution migration paths: Define unified CPE behavior,
      allowing for smooth migration between the different modes

   (3)  Deterministic CPE co-existence behavior: Specify the behavior
      when several modes co-exist in the CPE

   (4)  Deterministic service provider co-existence behavior: Specify
      the behavior when several modes co-exist in the service providers
      network

   (5)  Re-usability: Maximize the re-use of existing functional blocks
      including tunnel end-points, port restricted NAPT44, forwarding
      behavior, etc.

   (6)  Solution agnostic: Adopt neutral terminology and avoid (as far
      as possible) overloading the document with solution-specific terms

   (7)  Flexibility: Allow operators to compile CPE software only for
      the mode(s) necessary for their chosen deployment context(s)

   (8)  Simplicity: Provide a model that allows operators to only
      implement the specific mode(s) that they require without the
      additional complexity of unneeded modes.

2.  IPv4 Service Continuity Architectures: A 'Big Picture' Overview

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   The solutions which have been proposed within the Softwire WG can be
   categorized into three main functional approaches, differentiated by
   the amount and type of state that the service provider needs to
   maintain within their network:

   (1)  Full stateful approach (DS-Lite, [RFC6333]): Requires per-
      session state to be maintained in the Service Provider's network.
   (2)  Binding approach (e.g., Lightweight 4over6 (Lw4o6) [I-D.cui-
      softwire-b4-translated-ds-lite][I-D.ietf-softwire-public-4over6]
      or MAP 1:1 [I-D.ietf-softwire-map] ): Requires a single per-
      subscriber state (or a few) to be maintained in the Service
      Provider's network.
   (3)  Full stateless approach (MAP, [I-D.ietf-softwire-map]): Does not
      require per-session or per-subscriber state to be maintained in
      the Service Provider's network.

   All these approaches share a similar architecture, with a tunnel
   endpoint located in the CPE and a remote tunnel endpoint.  All use
   IPv6 as the transport protocol for the delivery of an IPv4
   connectivity service using an IPv4-in-IPv6 encapsulation scheme
   [RFC2473].

   Several cases can be envisaged:

   1.  The CPE is complied to support only one mode: No issue is raised
       by this case.
   2.  The CPE supports several modes but only one mode is explicitly
       configured: No issue is raised by this case.
   3.  The CPE supports several modes but no mode is explicitly enabled:
       the CPE will need additional triggers to decide which mode to
       activate.
   4.  The CPE supports several modes and several modes are configured:
       the CPE will need additional triggers to decide which mode to
       activate.

   As this document describes a provisioning profile whereby a single
   CPE could be capable of supporting any, or multiple modes, the
   customer should not be required to have any knowledge of the
   capabilities and configuration of their CPE, or of their service
   provider's network.

   The service provider, however, may have only a single mode enabled,
   or may have multiple modes, but with one preferred mode.  For this
   reason, it is necessary to approach the configuration of CPEs from
   the standpoint of the service provider's network capabilities.

2.1.  Functional Elements

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   The functional elements for each of the solution modes are listed in
   Table 1:

                +---------+---------------+--------------+
                |    Mode | Customer side | Network side |
                +---------+---------------+--------------+
                | DS-Lite |       B4      |     AFTR     |
                |   Lw4o6 |      lwB4     |    lwAFTR    |
                |     MAP |     MAP CE    |    MAP BR    |
                +---------+---------------+--------------+

                       Table 1: Functional Elements

   Table 2 describes each functional element:

   +----------------+--------------------------------------------------+
   |     Functional | Description                                      |
   |        Element |                                                  |
   +----------------+--------------------------------------------------+
   |             B4 | An IPv4-in-IPv6 tunnel endpoint; the B4 creates  |
   |                | a tunnel to a pre-configured remote tunnel       |
   |                | endpoint.                                        |
   |           AFTR | Provides both an IPv4-in-IPv6 tunnel endpoint    |
   |                | and a NAT44 function implemented in the same     |
   |                | node.                                            |
   |           lwB4 | A B4 which supports port-restricted IPv4         |
   |                | addresses. An lwB4 MAY also provide a NAT44      |
   |                | function.                                        |
   |         lwAFTR | An IPv4-in-IPv6 tunnel endpoint which maintains  |
   |                | per-subscriber address binding. Unlike the AFTR, |
   |                | it MUST NOT perform a NAPT44 function.           |
   |         MAP CE | A B4 which supports port-restricted IPv4         |
   |                | addresses. It MAY be co-located with a NAT44. A  |
   |                | MAP CE forwards IPv4-in-IPv6 packets using       |
   |                | provisioned mapping rules to derive the remote   |
   |                | tunnel endpoint.                                 |
   |         MAP BR | An IPv4-in-IPv6 tunnel endpoint. A MAP BR        |
   |                | forwards IPv4-in-IPv6 packets following pre-     |
   |                | configured mapping rules.                        |
   +----------------+--------------------------------------------------+

                  Table 2: Required Element Functionality

   Table 3 identifies features required by the customer end-node.

   +--------------+----------------+-----------------+-----------------+
   |   Functional |  IPv4-in-IPv6  | Port-restricted | Port-restricted |
   |      Element |     tunnel     |       IPv4      |      NAT44      |

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   |              |    endpoint    |                 |                 |
   +--------------+----------------+-----------------+-----------------+
   |           B4 |      Yes       |       N/A       |        No       |
   |         lwB4 |      Yes       |       Yes       |     Optional    |
   |     MAP-E CE |      Yes       |       Yes       |     Optional    |
   +--------------+----------------+-----------------+-----------------+

                        Table 3: Supported Features

2.2.  Required Provisoning Information

   Table 4 identifies the provisioning information required for each
   solution mode.

         +---------+---------------------------------------------+
         |    Mode | Provisioning Information                    |
         +---------+---------------------------------------------+
         | DS-Lite | Remote IPv4-in-IPv6 Tunnel Endpoint Address |
         |   Lw4o6 | Remote IPv4-in-IPv6 Tunnel Endpoint Address |
         |         | IPv4 Address                                |
         |         | Port Set                                    |
         |   MAP-E | Mapping Rules                               |
         |         | MAP Domain Parameters                       |
         +---------+---------------------------------------------+

                     Table 4: Provisioning Information

   Note: MAP Mapping Rules are translated into the following
   configuration parameters: Set of remote IPv4-in-IPv6 tunnel endpoint
   addresses, IPv4 address and port set.

     Note: Required provisioning information for each mode may also
           be represented as follows:
     DS-Lite: - Remote IPv4-in-IPv6 Tunnel Endpoint
       Lw4o6: - DS-Lite set of provisioning information
              - IPv4 address
              - Port set
       MAP-E: - Lw4o6 set of provisioning information
              - Forwarding mapping rules

3.  Unified Softwire CPE Behaviour

   This section specifies a unified CPE behavior capable of supporting
   any one, or combination of, the three modes.

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3.1.  IPv4 Address Functional Requirements

   The following two requirements must be met by the functional
   elements:

   Full IPv4 Address Assingment  All the aforementioned modes MUST be
      designed to allow either a full or a shared IPv4 address to be
      assigned to a customer end-node.  DS-Lite and MAP-E fulfill this
      requirement.  With minor changes, the
      [I-D.cui-softwire-b4-translated-ds-lite] specification can be
      updated to assign full IPv4 addresses.

   Customer End-Node NAT  A NAT function within the customer end-node is
      not required for DS-Lite, while it is optional for both MAP-E and
      Lw4o6.  When NAT is enabled for MAP-E or Lw4o6, the customer end-
      node NAT MUST be able to restrict the external translated source
      ports to the set of ports that it has been provisioned with.

3.2.  Generic CPE Bootstrapping Logic

   The generic provisioning logic is designed to meet the following
   requirements:

   o  When several service continuity modes are supported by the same
      CPE, it MUST be possible to configure a single mode for use.

   o  For each network attachment, the end-node MUST NOT activate more
      than one mode.

   o  The CPE MAY be configured by a user or via remote device
      management means (e.g., DHCP, TR-069).

   o  A network which supports one or several modes MUST return valid
      configuration data enabling requesting devices to unambiguously
      select a single mode to use for attachment.

   o  A CPE which supports only one mode or it is configured to enable
      only mode MUST ignore any configuration parameter which is not
      required for the mode it supports.

   This section sketches a generic algorithm to be followed by a CPE
   supporting one or more of the modes listed above.  Based on the
   retrieved information, the CPE will determine which mode to activate.

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   (1)  If a given mode is enabled (DS-Lite, Lw4o6 or MAP-E), the CPE
      MUST be configured with the required provisioning information
      listed in Table 4.  If all of the required information is not
      available locally, the CPE MUST use available provisioning means
      (e.g., DHCP) to retrieve the missing configuration data.

   (2)  If the CPE supports several modes, but no mode is explicitly
      enabled, the CPE MUST use available provisioning means (e.g.,
      DHCP) to retrieve available configuration parameters and use the
      availability of individual parameters to ascertain which
      functional mode to configure:

      (2.1)  If only a Remote IPv4-in-IPv6 Tunnel Endpoint is received,
            the CPE MUST proceed as follows:

      (2.1)

            (2.1.1)  IPv4-in-IPv6 tunnel endpoint initialization is
                     defined in [RFC6333].
            (2.1.2)  Outbound IPv4 packets are forwarded to the next hop
                     as specified in Section 3.4.

      (2.3)  If a Remote IPv4-in-IPv6 Tunnel Endpoint, an IPv4 Address
            and optionally a Port Set are received, the CPE MUST behave
            as follows:

      (2.3)

            (2.2.1)  IPv4-in-IPv6 tunnel endpoint initialization is
                     similar to the B4 [RFC6333].
            (2.2.2)  When NAPT44 is required (e.g., because the CPE is a
                     router), a NAPT44 module is enabled.
            (2.2.3)  The tunnel endpoint address is selected from the
                     native IPv6 addresses configured on the CPE.  No
                     particular considerations are required to be taken
                     into account to generate the Interface Identifier.
            (2.2.4)  When a port set is provisioned, the external source
                     ports MUST be restricted to the provisioned set of
                     ports.
            (2.2.5)  After translation, outbound IPv4 packets are
                     forwarded to the next hop as specified in
                     Section 3.4.

      (2.6)  If Mapping Rule(s) are received, the CPE MUST behave as
            follows:

      (2.6)

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            (2.3.1)  IPv4-in-IPv6 tunnel endpoint initialization is
                     similar to the B4 [RFC6333].
            (2.3.2)  The tunnel endpoint is assigned with an IPv6
                     address which includes an IPv4 address.  The MAP
                     Interface Identifier is based on the format
                     specified in Section 2.2 of [RFC6052].
            (2.3.3)  When NAPT44 is required (e.g., because the CPE is a
                     router), a NAPT44 module is enabled.
            (2.3.4)  When a port set is provisioned, the external source
                     port MUST be restricted to the provisioned set of
                     ports.
            (2.3.5)  After translation, outbound IPv4 packets then
                     forwarded to the next hop as specified in
                     Section 3.4.

3.3.  Customer Side DHCP Based Provisioning

      [DISCUSSION NOTE:

      1.  This section will be updated to reflect the consensus from DHC
          WG.

      2.  As it is proposed that OPTION_MAP would be used for all new
          softwire provisioning, should we rename OPTION_MAP to
          OPTION_SW (incl.  the associated sub-options)?]

      ]

   DHCP-based configuration SHOULD be implemented by the customer end-
   node using the following two DHCP options:

   OPTION_AFTR_NAME    [RFC6334] Provides the FQDN for the remote IPv4
                       -in-IPv6 tunnel end-point.

   OPTION_MAP          [I-D.ietf-softwire-map-dhcp] Provides
                       IPv4-related configuration for binding mode and/
                       or mapping rules for stateless mode (including
                       MAP parameters such as offset, domain prefix,
                       etc.).  OPTION_MAP_BIND is a sub-option used to
                       convey an IPv4 address (for example, encoded as
                       an IPv4-mapped IPv6 address [RFC4291]).  This
                       address is used when binding mode is enabled.
                       The receipt of OPTION_MAP_BIND is an implicit
                       indication to the customer side device to operate
                       in binding, rather than stateless mode.

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   The customer end-node uses the DHCP Option Request Option (ORO) to
   request either one or both of these options depending on which modes
   it is capable of and configured to support.

   The DHCP option(s) sent in the response allow the service provider to
   inform the customer end-node which operating mode to enable.

   The following table shows the different DHCP options (and sub-
   options) that the service provider can supply in a response.

   +---------------------------+------------+------------+-------------+
   |               DHCP Option | Stateful   | Binding    | Stateless   |
   |                           | Mode       | Mode       | Mode        |
   +---------------------------+------------+------------+-------------+
   |          OPTION_AFTR_NAME | Yes        | Yes        | Optional    |
   |           OPTION_MAP_BIND | No         | Yes        | No          |
   |           OPTION_MAP_RULE | No         | No         | Yes         |
   |     OPTION_MAP_PORTPARAMS | No         | Optional   | Optional    |
   +---------------------------+------------+------------+-------------+

                 Table 5: DHCP Option Provisioning Matrix

   The customer side device MUST interpret the received DHCP
   configuration parameters according to the logic defined in
   Section 3.2:

   o  If only OPTION_AFTR_NAME is received, then the device MUST operate
      in stateful mode

   o  If both OPTION_AFTR_NAME and OPTION_MAP_BIND are received then the
      device MUST operate in binding mode

   o  If one or more OPTION_MAP_RULE options are received, then the
      customer side device MUST operate in stateless mode

   o  If both OPTION_AFTR_NAME and OPTION_MAP_RULE(s) are received, then
      the customer side device MUST operate as a MAP CE.
      OPTION_AFTR_NAME provides the FQDN of the MAP BR.

   o  If OPTION_MAP_PORTPARAMS is received as a sub-option to either
      OPTION_MAP_BIND or OPTION_MAP_RULE, then NAPT44 MUST be configured
      using the supplied port-set for external translated source ports.

   From the service providers side, the following rule MUST be followed:

   o  The DHCP server MUST NOT send both OPTION_MAP_BIND and
      OPTION_MAP_RULE in a single OPTION_MAP response.

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3.4.  Forwarding Action by the Customer End-Node

   For all modes, the longest prefix match algorithm MUST be enforced to
   forward outbound IPv4 packets.

   Specifically, this algorithm will:

   o  Always return the address of the AFTR for the DS-Lite mode.

   o  Always return the address of the lwAFTR for the binding mode.

   o  Return the next hop according to the pre-configured mapping rules
      for the stateless mode (i.e., MAP-E).

4.  Security Considerations

   Security considerations discussed in Section 7 of
   [I-D.ietf-softwire-stateless-4v6-motivation] and Section 11 of
   [RFC6333] should be taken into account.

5.  IANA Considerations

   This document does not require any action from IANA.

6.  Acknowledgements

   Many thanks to T.  Tsou, S.  Perrault, S.  Sivakumar, O.  Troan, W.
   Dec, M.  Chen, for their review and comments.

   Special thanks to S.  Krishnan for the suggestions and guidance.

7.  References

7.1.  Normative References

   [I-D.cui-softwire-b4-translated-ds-lite]
              Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
              Farrer, "Lightweight 4over6: An Extension to the DS-Lite
              Architecture", draft-cui-softwire-b4-translated-ds-lite-11
              (work in progress), February 2013.

   [I-D.ietf-softwire-map-dhcp]
              Mrugalski, T., Troan, O., Dec, W., Bao, C.,
              leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options
              for Mapping of Address and Port", draft-ietf-softwire-map-
              dhcp-03 (work in progress), February 2013.

   [I-D.ietf-softwire-map]

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              Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S., and
              T. Murakami, "Mapping of Address and Port with
              Encapsulation (MAP)", draft-ietf-softwire-map-04 (work in
              progress), February 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

7.2.  Informative References

   [I-D.ietf-softwire-public-4over6]
              Cui, Y., Wu, J., Wu, P., Vautrin, O., and Y. Lee, "Public
              IPv4 over IPv6 Access Network", draft-ietf-softwire-
              public-4over6-05 (work in progress), February 2013.

   [I-D.ietf-softwire-stateless-4v6-motivation]
              Boucadair, M., Matsushima, S., Lee, Y., Bonness, O.,
              Borges, I., and G. Chen, "Motivations for Carrier-side
              Stateless IPv4 over IPv6 Migration Solutions", draft-ietf-
              softwire-stateless-4v6-motivation-05 (work in progress),
              November 2012.

   [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
              Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
              RFC 6334, August 2011.

Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes
   France

   Email: mohamed.boucadair@orange.com

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   Ian Farrer
   Deutsche Telekom
   Germany

   Email: ian.farrer@telekom.de

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