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Network Working Group                                       N. Matsuhira
Internet-Draft                                           Fujitsu Limited
Intended status: Informational                              June 1, 2019
Expires: December 3, 2019


   Multiple IPv4 - IPv6 address mapping encapsulation - fixed prefix
                               (M46E-FP)
                       draft-matsuhira-m46e-fp-06

Abstract

   This document specifies Multiple IPv4 - IPv6 address mapping
   encapsulation - fixed prefix (M46E-FP) specification.  M46E-FP makes
   backbone network to IPv6 only.  And also, M46E-FP can stack many IPv4
   networks, i.e. the networks using same IPv4 (private) addresses,
   without interdependence.

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/.

   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 December 3, 2019.

Copyright Notice

   Copyright (c) 2019 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



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   (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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Architecture of M46E-FP  . . . . . . . . . . . . . . . . . . .  3
   3.  Basic Network Configuration  . . . . . . . . . . . . . . . . .  5
   4.  Basic Function of M46E-FP  . . . . . . . . . . . . . . . . . .  6
     4.1.  IPv4 over IPv6 Encapsulation / Decapsulation . . . . . . .  6
     4.2.  M46A architecture  . . . . . . . . . . . . . . . . . . . .  7
     4.3.  Route Advertisement  . . . . . . . . . . . . . . . . . . .  8
   5.  Stacking IPv4 Networks . . . . . . . . . . . . . . . . . . . .  9
   6.  Redundancy of M46E-FP  . . . . . . . . . . . . . . . . . . . .  9
   7.  Example of M46E-FP Operation . . . . . . . . . . . . . . . . . 10
     7.1.  Basic M46E-FP Operation  . . . . . . . . . . . . . . . . . 10
     7.2.  M46E-FP Operation with plane ID  . . . . . . . . . . . . . 12
   8.  Characteristic . . . . . . . . . . . . . . . . . . . . . . . . 15
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     11.2. References . . . . . . . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17





















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1.  Introduction

   This document provides Multiple IPv4 - IPv6 address maping
   encapsulation - fixed prefix (M46E-FP) specification.

   The basic strategy for IPv6 deployment is dual stack.  Viewing this
   strategy from operational side, operation cost of dual stack is
   higher than single stack operation.  Viewing from future, IPv6 only
   operation is more reasonable rather than IPv4 only operation.
   Therefore IPv6 only operation is desired.

   M46E-FP makes backbone network to IPv6 only and privide IPv4
   connectivities.  And also, M46E-FP can stack many IPv4 networks, i.e.
   the networks using same IPv4 (private) address, without
   interdependence.


2.  Architecture of M46E-FP

   IP address contain two information, one is locator information, and
   another is identifier information.  This is basic architecture of
   internet protocol, and also the Internet, and no difference between
   IPv4 and IPv6.

   Locater is a information related "Where", and indentifier is a
   information related "Who".  That mean, IP address's semantics is
   "Where's Who" meaning.  Host is identified whole IP address
   information, that is "Where's Who", however route to the host is
   identified just locator information in IP address, that is "Where".
   See Figure 1.


        |<------ IP address ------------------>|
        |<----- Locator ----->|<--Identifier-->|
               (Where )             (Who)
        +---------------------+----------------+
        |                     |                |
        +---------------------+----------------+


                                 Figure 1

   In IPv4 address space, some host has IPv4 address, which consist n
   bits length identifier and 32 - n bits locator.  In Where's Who
   representation, 32 - n bits "Where" and n bits "Who".

   Keeping such "Where's Who" relation, IPv4 address can be represent as
   IPv6 address by expanding "Where" information from 32 - n bits to 128



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   - n bits.  Expanding " Where" information, IPv4 address can be mapped
   to IPv6 address.  Figure 2 shows such expanding.



    |<------------------------ 128 bits ----------------------------->|
    |<-------------------- 96 bits ------------------->|<-- 32 bits ->|
    |                                                          :      |
    |                                                          :      |
    |                                                  +-------:------+
    |                                                  | IPv4 address |
    |                                                  +-------:------+
    |                                                  |<-Loc->:<-ID->|
    |                                                  | 32-n  :  n   |
    |                                                  | bits  : bits |
    |                                                  |       :      |
    +--------------------------------------------------+-------:------+
    |       M46A prefix (no IPv4 network plane ID)     | IPv4 address |
    +--------------------------------------------------+-------:------+
    |                                                          :      |
    |<------------- Locator (128 - n bits ) ------------------>:<-ID->|
    |                                                          :  n   |
    |                                                          : bits |


                                 Figure 2

   IPv4 address space contain private address, that is non globally
   unique IP address.  If some identifier which distinguish private
   address can introduce in IPv6 address space, we can treate IPv4
   private address as different address in IPv6 address space.  This
   document define such identifier as "IPv4 network plane ID".  "IPv6
   network plane ID" can provide VPN (Virtual Private Network) like
   service.

   That is M46A. In M46E-FP address, "Where" information's bit length is
   128 -n bits, and "Who" information's bit length is n bits.  Figure 3
   shows summary of IPv4 address and M46E-FP address relation.













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    |<------------------------ 128 bits ----------------------------->|
    |<-------------------- 96 bits ------------------->|<-- 32 bits ->|
    |                                                          :      |
    |                                                          :      |
    |                                                  +-------:------+
    |                                                  | IPv4 address |
    |                                                  +-------:------+
    |                                                  |<-Loc->:<-ID->|
    |                                                  | 32-n  :  n   |
    |                                                  | bits  : bits |
    |                                                  |       :      |
    +--------------------------------------------------+-------:------+
    |       M46A prefix (no IPv4 network plane ID)     | IPv4 address |
    +--------------------------------------------------+-------:------+
    |                                                          :      |
    |                                                          :      |
    |    96 - m bits        |          m bits          |     32 bits  |
    +-----------------------+--------------------------+-------:------+
    |      M46A prefix      |  IPv4 network plane ID   | IPv4 address |
    +-----------------------+--------------------------+-------:------+
    |<------------- Locator (128 - n bits ) ------------------>:<-ID->|
    |                                                          :  n   |
    |                                                          : bits |


                                 Figure 3


3.  Basic Network Configuration

   Figure 4 shows network configuration with M46E-FP.  The network
   consists of three parts.  Backbone network, stub network, and
   M46E-FP.

   Backbone network is operated with IPv6 only.  Stub network has three
   cases.  IPv4 only, Dual Stack (both IPv4 and IPv6), and IPv6 only.

   M46E-FP connects backbone network and stub network in case IPv4 still
   works in that stub network.  If stub network is IPv6 only, M46E-FP is
   not needed.

   Campus network, corporate network, ISP and datacenter network are the
   example for such network.








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    /---------------------------------------------------\
    |                                                   |
    |                  Backbone Network                 |
    |                    (IPv6 only)                    |
    |                                                   |
    \---------------------------------------------------/
          |                    |                |
      +-------+            +-------+            |
      |M46E-FP|            |M46E-FP|            |
      +-------+            +-------+            |
          |                    |                |
    /--------------\   /--------------\   /--------------\
    |              |   |              |   |              |
    | Stub Network |   | Stub Network |   | Stub Network |
    | (IPv4 only)  |   | (Dual Stack) |   | (IPv6 only)  |
    |              |   |              |   |              |
    \--------------/   \--------------/   \--------------/

                                 Figure 4


4.  Basic Function of M46E-FP

   M46E-FP has mainly two function.  One is IPv4 over IPv6 Encapsulation
   / Decapsulation, and another is advertise route for stub network.

4.1.  IPv4 over IPv6 Encapsulation / Decapsulation

   M46E-FP encapsulates IPv4 packet to IPv6 from stub network to
   backbone network, and decapsulates IPv6 packet to IPv4 from backbone
   network to stub network.  Figure 5 shows such movement.


     +--------+------------+       +----------+--------+------------+
     |IPv4 Hdr|    Data    |  -->  | IPv6 Hdr |IPv4 Hdr|    Data    |
     +--------+------------+       +----------+--------+------------+

     +--------+------------+       +----------+--------+------------+
     |IPv4 Hdr|    Data    |  <--  | IPv6 Hdr |IPv4 Hdr|    Data    |
     +--------+------------+       +----------+--------+------------+


    /-------------------\  +-------+  /-----------------------------\
    |   Stub Network    |--|M46E-FP|--|       Backbone Network      |
    |      (IPv4)       |  +-------+  |         (IPv6 only)         |
    \-------------------/             \-----------------------------/

                                 Figure 5



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   M46E-FP MUST support tunnel MTU discovery [RFC1853].  When
   encapsulated IPv6 Packet size exceed path MTU and inner IPv4 packet
   have the Don't Fragment bit is set, M46E-FP MUST return ICMP
   Destination unreachable message with Type3 Code4, fragmentation
   needed and DS set [RFC0792].

   In case IPv6, M46E-FP just relays IPv6 packet.


     +----------+------------+       +----------+------------+
     | IPv6 Hdr |    data    |  -->  | IPv6 Hdr |    data    |
     +----------+------------+       +----------+------------+

     +----------+------------+       +----------+------------+
     | IPv6 Hdr |    data    |  <--  | IPv6 Hdr |    data    |
     +----------+------------+       +----------+------------+


    /---------------------\  +-------+  /--------------------\
    |    Stub Network     |--|M46E-FP|--|  Backbone Network  |
    |        (IPv6)       |  +-------+  |   (IPv6 only)      |
    \--------------------/             \---------------------/

                                 Figure 6

   By IPv4 over IPv6 function, M46E-FP make backbone network to IPv6
   only.

4.2.  M46A architecture

   M46A is a IPv6 address used in outer IPv6 header which encapsulate
   IPv4 packet by M46E-FP.  M46A is described in M46A
   [I-D.draft-matsuhira-m46a].

   Figure 7 shows M46A address architecture


    |      96 - m bits      |          m bits          |     32 bits  |
    +-----------------------+--------------------------+--------------+
    |      M46A  prefix     |  IPv4 network plane ID   | IPv4 address |
    +-----------------------+--------------------------+--------------+

                                 Figure 7

   M46A consists of three parts as follows.






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   M46A prefix

      M46A prefix.  This value is fixed value and preconfigured to all
      M46E-FP in the networks.

   IPv4 network plane ID

      IPv4 network plane ID is an identifier of IPv4 network stack over
      IPv6 backbone network.  This value is preconfigured depend on the
      M46E-FP belong which IPv4 network plane.  For more detail see
      Section 5.

   IPv4 address

      IPv4 address in inner IPv4 packet.

   M46A is resolved copying IPv4 address in inner IPv4 packet, and
   preconfigured values, M46A prefix and IPv4 network plane ID.

4.3.  Route Advertisement

   M46E-FP converts stub network's IPv4 route to M46E-FP IPv6 route and
   advertises to backbone network.  And reverse direction, M46E-FP
   converts M46E-FP IPv6 route to IPv4 route, that advertises other IPv4
   stub networks.

   The IPv4 route for stub network is map to M46E-FP IPv6 route one to
   one, so number of route of IPv4 is same as number of route of M46E-FP
   IPv6 route.  Total number of route is same as when backbone network
   operate dual stack, without M46E-FP.

   In stub network, usual dynamic routing protocol for IPv4 and IPv6 can
   be used such as RIPv2 [RFC2453], RIPng [RFC2080], OSPFv2 [RFC2328],
   OSPFv3 [RFC2740] and IS-IS [RFC1195][RFC5308].  Similarly, in
   backbone network, usual dynamic routing protocol for IPv6 can be used
   such as RIPng [RFC2080], OSPFv3 [RFC2740] and IS-IS [RFC5308] .

   If want using default route, default M46E-FP advertise the route
   [M46E-FP address prefix/( 96 - m )] as default route.  If want using
   different default route by IPv4 network plane ID, default M46E-FP in
   IPv4 network plane #1 advertise the route [ M46E-FP address prefix +
   IPv4 network plane ID #1 / 96] as default route.  Figure 10 in
   Section 7 show the example using default route.








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5.  Stacking IPv4 Networks

   M46E-FP can provide VPN like service to stub networks by using
   different IPv4 network plane ID value.

   If backbone network operator provide IPv4 privates network service to
   Organization A, backbone network operator sets IPv4 network plane ID
   value =1 to the M46E-FP which connects stub network of organization
   A. If there are five stub network of organization A, backbone network
   operator sets same IPv4 network plane ID = 1, to five M46E-FPs which
   connect stub network of organization A. If there are one hundred stub
   network of organization B, backbone network operator sets same IPv4
   network plane ID = 2, to one hundred M46E-FPs which connect stub
   network of organization B. If a new stub network in organization B
   join, backbone network operator configures same IPv4 network plane ID
   = 2, to the new stub network only, which connect stub network of
   organization B, and no configuration is needed to one hundred M46E-
   FPs which are already connected.

   Such configuration, that means same stub network group to same IPv4
   network plane ID value, is simple and easy to understand, so, it is
   expected that possibility of misconfiguration is very low.  And also,
   number of configuration is minimum, that mean, number of
   configuration is same as number of stub networks, and add new stub
   network, configure to new one only.

   Describe above, M46E-FP can provide VPN like service, for example,
   Intranet or extranet.  And, after IPv4 global address running out,
   some service provider may want to reuse IPv4 private address.
   M46E-FP can provide such IPv4 private address networks over single
   IPv6 backbone network.  By M46E-FP, some service providers may reuse
   IPv4 private address.


6.  Redundancy of M46E-FP

   M46E-FP brings no limit for redundancy.  Figure 8 shows such example
   in case two connection between backbone network and stub network.
   Number of link between backbone network and stub network is not
   limited, and different type of link can be used, for example, for
   wire and wireless.

   Configuration of M46E-FPs, which connect same stub network, is same.
   That mean same M46E-FP prefix and same IPv4 network plane ID value.







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    /---------------------------------------------------\
    |                                                   |
    |                  Backbone Network                 |
    |                    (IPv6 only)                    |
    |                                                   |
    \---------------------------------------------------/
          |         |                  |         |
      +-------+ +-------+          +-------+ +-------+
      |M46E-FP| |M46E-FP|          |M46E-FP| |M46E-FP|
      +-------+ +-------+          +-------+ +-------+
          |         |                  |         |
    /---------------------\      /---------------------\
    |                     |      |                     |
    |    Stub Network     |      |    Stub Network     |
    |    (IPv4 only)      |      |    (Dual Stack)     |
    |                     |      |                     |
    \---------------------/      \---------------------/

                                 Figure 8


7.  Example of M46E-FP Operation

7.1.  Basic M46E-FP Operation

   Figure 9 shows M46E-FP operation which does not use IPv4 network
   plane ID.  In this example, two stub network is connected to backbone
   network via M46E-FP.  One stub network is 10.1.1.0/24 sub network,
   and the other is 10.1.2.0/24 sub network.

   When M46E-FP receives IPv4 route advertisement, then M46E-FP convert
   this IPv4 route to IPv6 route by address resolution to M46E-FP
   address, and advertise this IPv6 route to backbone network.  When
   M46E-FP receives IPv6 route advertisements, then M46E-FP converts
   this IPv6 route to IPv4 route if this IPv6 route is match M46E-FP
   address ( same prefix with M46E-FP), and advertise this IPv4 route to
   stub network.

   In this example.  IPv4 route, 10.1.1.0/24 is converted to IPv6 route,
   <M46E-FPprefix>:10.1.1.0/120,and IPv4 route, 10.1.2.0/24 is converted
   to IPv6 route, <M46E-FPprefix>:10.1.2.0/120 at M46E-FP from stub
   network to backbone network.  And, from backbone network to stub
   network, IPv6 route, <M46E-FPprefix>:10.1.1.0/120 is converted to
   IPv4 route, 10.1.1.0/24, and IPv6 route, <M46E-FPprefix>:10.1.2.0/120
   is converted to IPv4 route, 10.1.2.0/24.






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     /-------------\  +-----+  /------------\  +-----+  /-------------\
     |Stub Network |  |     |  | Backbone   |  |     |  |Stub Network |
     |(10.1.1.0/24)|--|M46E |--| Network    |--|M46E |--|(10.1.2.0/24)|
     |             |  | -FP |  |(IPv6 only) |  | -FP |  |             |
     \-------------/  +-----+  \------------/  +-----+  \-------------/

    [10.1.1.0/24] ---> [<M46A prefix>:10.1.1.0/120] ---> [10.1.1.0/24]
    [10.1.2.0/24] <--- [<M46A prefix>:10.1.2.0/120] <--- [10.1.2.0/24]


     +---------+----+       +---------+----+----+      +---------+----+
     | data    |IPv4|  -->  | data    |IPv4|IPv6| -->  | data    |IPv4|
     +---------+----+       +---------+----+----+      +---------+----+
     src: 10.1.1.1       src: <M46A prefix>:10.1.1.1     src: 10.1.1.1
     dst: 10.1.2.1       dst: <M46A prefix>:10.1.2.1     dst: 10.1.2.1

                                 Figure 9

   Figure 10 shows the example using default route.  Default route is
   useful in case most packets are routed same path.  Typically, access
   network is one of the example.  Although using default route,
   communication between stub networks can be done.  Communication
   between host 10.1.1.1 and host 10.1.2.1 can be done inside in access
   network, and does not pass over default M46E-FP.



























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                               /------------\
                               |            |
     /-------------\  +-----+  |            |  +-----+  /-------------\
     |  Backbone   |  |     |  | Access     |  |     |  |Stub Network |
     |  Network    |--|M46E |--| Network    |--|M46E |--|(10.1.1.0/24)|
     |             |  | -FP |  |(IPv6 only) |  | -FP |  |             |
     \-------------/  +-----+  |            |  +-----+  \-------------/
                     (default) |      <--[<M46A prefix>:10.1.1.0/120]
                [<M46A prefix>/96] -->      |
                               |            |
                               |            |  +-----+  /-------------\
                               |            |  |     |  |Stub Network |
                               |            |--|M46E |--|(10.1.2.0/24)|
                               |            |  | -FP |  |             |
                               |            |  +-----+  \-------------/
                               |      <--[<M46A prefix>:10.1.2.0/120]
                               |            |
                               |            |
                               |            |  +-----+  /-------------\
                               |            |  |     |  |Stub Network |
                               |            |--|M46E |--|(10.1.3.0/24)|
                               |            |  | -FP |  |             |
                               |            |  +-----+  \-------------/
                               |      <--[<M46A prefix>:10.1.3.0/120]
                               |            |
                               \------------/


                                 Figure 10

7.2.  M46E-FP Operation with plane ID

   Figure 11 shows M46E-FP operation which uses IPv4 network plane ID.
   In this example, there are two planes, and two stub network in each
   plane is connected to backbone network via M46E-FP.  In each plane,
   one stub network is 10.1.1.0/24 sub network, and the other is
   10.1.2.0/24 sub network, that means same IPv4 address is used in
   different plane.

   When M46E-FP receives IPv4 route advertisements, then M46E-FP
   converts this IPv4 route to IPv6 route by address resolution to
   M46E-FP address, and advertise this IPv6 route to backbone network.
   When M46E-FP receives IPv6 route advertisements, then M46E-FP
   converts this IPv6 route to IPv4 route if this IPv6 route is match
   M46E-FP address ( same prefix with M46E-FP), and advertises this IPv4
   route to stub network.

   In this example in plane #1.  IPv4 route, 10.1.1.0/24 is converted to



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   IPv6 route, <M46E-FPprefix><#1>:10.1.1.0/120,and IPv4 route,
   10.1.2.0/24 is converted to IPv6 route, <M46E-FPprefix><#1>:10.1.2.0/
   120 at M46E-FP from stub network to backbone network.  And, from
   backbone network to stub network, IPv6 route, <M46E-
   FPprefix><#1>:10.1.1.0/120 is converted to IPv4 route, 10.1.1.0/24,
   and IPv6 route, <M46E-FPprefix><#1>:10.1.2.0/120 is converted to IPv4
   route, 10.1.2.0/24.

   And also, In this example in plane #2.  IPv4 route, 10.1.1.0/24 is
   converted to IPv6 route, <M46E-FPprefix><#2>:10.1.1.0/120,and IPv4
   route, 10.1.2.0/24 is converted to IPv6 route, <M46E-
   FPprefix><#2>:10.1.2.0/120 at M46E-FP from stub network to backbone
   network.  And, from backbone network to stub network, IPv6 route,
   <M46E-FPprefix><#2>:10.1.1.0/120 is converted to IPv4 route,
   10.1.1.0/24, and IPv6 route, <M46E-FPprefix><#2>:10.1.2.0/120 is
   converted to IPv4 route, 10.1.2.0/24.

   In IPv6 space, address <M46E-FPprefix><#1>:10.1.1.1 and address
   <M46E-FPprefix><#2>:10.1.1.1 are different address, route <M46E-
   FPprefix><#1>:10.1.1.0/120 and route <M46E-FPprefix><#2>:10.1.1.0/120
   are different route, although in IPv4 space, address 10.1.1.1 in
   plane #1 and 10.1.1.1 in plane#2 are same address, route 10.1.1.0/24
   in plane#1 and route 10.1.1.0/24 in plane#2 are same route.




























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                              /------------\
  .......<plane#1>............|............|............................
  : /-------------\  +-----+  |            |  +-----+  /-------------\ :
  : | Stub Network|  |     |  |            |  |     |  | Stub Network| :
  : |(10.1.1.0/24)|--|M46E |--| Backbone   |--|M46E |--|(10.1.2.0/24)| :
  : |             |  | -FP |  | Network    |  | -FP |  |             | :
  : \-------------/  +-----+  |(IPv6 only) |  +-----+  \-------------/ :
  :...........................|............|...........................:
                              |            |
  ........<plane#2>...........|............|............................
  : /-------------\  +-----+  |            |  +-----+  /-------------\ :
  : | Stub Network|  |     |  |            |  |     |  | Stub Network| :
  : |(10.1.1.0/24)|--|M46E |--|            |--|M46E |--|(10.1.2.0/24)| :
  : |             |  | -FP |  |            |  | -FP |  |             | :
  : \-------------/  +-----+  |            |  +-----+  \-------------/ :
  :...........................|............|...........................:
                              \------------/


  <<plane #1>>

   [10.1.1.0/24]  --> [<M46A prefix><#1>:10.1.1.0/120] --> [10.1.1.0/24]
   [10.1.2.0/24]  <-- [<M46A prefix><#1>:10.1.2.0/120] <-- [10.1.2.0/24]

    +---------+----+       +---------+----+----+       +---------+----+
    | data    |IPv4|  -->  | data    |IPv4|IPv6|  -->  | data    |IPv4|
    +---------+----+       +---------+----+----+       +---------+----+
    src: 10.1.1.1      src: <M46A prefix><#1>:10.1.1.1    src: 10.1.1.1
    dst: 10.1.2.1      dst: <M46A prefix><#1>:10.1.2.1    dst: 10.1.2.1


  <<plane#2>>

   [10.1.1.0/24]  --> [<M46A prefix><#2>:10.1.1.0/120] --> [10.1.1.0/24]
   [10.1.2.0/24]  <-- [<M46A prefix><#2>:10.1.2.0/120] <-- [10.1.2.0/24]

    +---------+----+       +---------+----+----+      +---------+----+
    | data    |IPv4|  -->  | data    |IPv4|IPv6| -->  | data    |IPv4|
    +---------+----+       +---------+----+----+      +---------+----+
    src: 10.1.1.1      src: <M46A prefix><#2>:10.1.1.1    src: 10.1.1.1
    dst: 10.1.2.1      dst: <M46A prefix><#2>:10.1.2.1    dst: 10.1.2.1

                                 Figure 11

   Figure 12shows the example using default route with IPv4 network
   plane.  In this case, default M46E-FP may configure different by each
   IPv4 network plane.




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                              /------------\
  .......<plane#1>............|............|............................
  : /-------------\  +-----+  |            |  +-----+  /-------------\ :
  : | Backbone    |  |     |  |            |  |     |  | Stub Network| :
  : | Network     |--|M46E |--| Access     |--|M46E |--|(10.1.1.0/24)| :
  : |             |  | -FP |  | Network    |  | -FP |  |             | :
  : \-------------/  +-----+  |(IPv6 only) |  +-----+  \-------------/ :
  :                 (default) |    <--[<M46A prefix><#1>:10.1.1.0/120] :
  :         [<M46A prefix><#1>/96] -->     |                           :
  :                           |            |                           :
  :                           |            |                           :
  :                           |            |  +-----+  /-------------\ :
  :                           |            |  |     |  | Stub Network| :
  :                           |            |--|M46E |--|(10.1.2.0/24)| :
  :                           |            |  | -FP |  |             | :
  :                           |            |  +-----+  \-------------/ :
  :                           |   <--[<M46A prefix><#1>:10.1.2.0/120]  :
  :...........................|............|...........................:
                              |            |
  .......<plane#2>............|............|............................
  : /-------------\  +-----+  |            |  +-----+  /-------------\ :
  : | Backbone    |  |     |  |            |  |     |  | Stub Network| :
  : | Network     |--|M46E |--|            |--|M46E |--|(10.1.1.0/24)| :
  : |             |  | -FP |  |            |  | -FP |  |             | :
  : \-------------/  +-----+  |            |  +-----+  \-------------/ :
  :                 (default) |    <--[<M46A prefix><#2>:10.1.1.0/120] :
  :         [<M46A prefix><#2>/96] -->     |                           :
  :                           |            |                           :
  :                           |            |                           :
  :                           |            |  +-----+  /-------------\ :
  :                           |            |  |     |  | Stub Network| :
  :                           |            |--|M46E |--|(10.1.2.0/24)| :
  :                           |            |  | -FP |  |             | :
  :                           |            |  +-----+  \-------------/ :
  :                           |   <--[<M46A prefix><#2>:10.1.2.0/120]  :
  :...........................|............|...........................:
                              |            |
                              \------------/


                                 Figure 12


8.  Characteristic

   M46E-FP has following useful characteristics.





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   o  Reduce backbone network operation cost with IPv6 single stack ( at
      least less than Dual Stack)

   o  Can allocate IPv4 address to stub networks, which used in backbone
      network before installing M46E-FP

   o  Less configuration

   o  No need for special protocol

   o  No dependent Layer 2 network

   o  Can Stack IPv4 Private networks

   o  Easy stop IPv4 operation in stub network for future ( just remove
      M46E-FP)

   o  Provide redundancy


9.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


10.  Security Considerations

   M46E-FP use automatic Encapsulation / Decapsulation technologies.
   Security consideration related tunneling technologies are discussed
   in RFC2893[RFC2893], RFC2267[RFC2267], etc.


11.  References

11.1.  Normative References

   [I-D.draft-matsuhira-m46a]
              Matsuhira, N., "Multiple IPv4 - IPv6 mapped IPv6 address",
              June 2019.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <http://www.rfc-editor.org/info/rfc792>.

   [RFC1853]  Simpson, W., "IP in IP Tunneling", RFC 1853, DOI 10.17487/



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              RFC1853, October 1995,
              <http://www.rfc-editor.org/info/rfc1853>.

   [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>.

11.2.  References

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <http://www.rfc-editor.org/info/rfc1195>.

   [RFC2080]  Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
              DOI 10.17487/RFC2080, January 1997,
              <http://www.rfc-editor.org/info/rfc2080>.

   [RFC2267]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", RFC 2267, DOI 10.17487/RFC2267,
              January 1998, <http://www.rfc-editor.org/info/rfc2267>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/
              RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [RFC2453]  Malkin, G., "RIP Version 2", STD 56, RFC 2453,
              DOI 10.17487/RFC2453, November 1998,
              <http://www.rfc-editor.org/info/rfc2453>.

   [RFC2740]  Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
              RFC 2740, DOI 10.17487/RFC2740, December 1999,
              <http://www.rfc-editor.org/info/rfc2740>.

   [RFC2893]  Gilligan, R. and E. Nordmark, "Transition Mechanisms for
              IPv6 Hosts and Routers", RFC 2893, DOI 10.17487/RFC2893,
              August 2000, <http://www.rfc-editor.org/info/rfc2893>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <http://www.rfc-editor.org/info/rfc5308>.









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Author's Address

   Naoki Matsuhira
   Fujitsu Limited
   17-25, Shinkamata 1-chome, Ota-ku
   Tokyo,   144-8588
   Japan

   Phone: +81-3-3735-1111
   Fax:
   Email: matsuhira@jp.fujitsu.com








































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