path: root/doc/rfc/rfc6219.txt

Internet Engineering Task Force (IETF)                             X. Li
Request for Comments: 6219                                        C. Bao
Category: Informational                                          M. Chen
ISSN: 2070-1721                                                 H. Zhang
                                                                   J. Wu
                                                  CERNET Center/Tsinghua
                                                              University
                                                                May 2011


   The China Education and Research Network (CERNET) IVI Translation
   Design and Deployment for the IPv4/IPv6 Coexistence and Transition

Abstract

   This document presents the China Education and Research Network
   (CERNET)'s IVI translation design and deployment for the IPv4/IPv6
   coexistence and transition.

   The IVI is a prefix-specific and stateless address mapping mechanism
   for "an IPv6 network to the IPv4 Internet" and "the IPv4 Internet to
   an IPv6 network" scenarios.  In the IVI design, subsets of the ISP's
   IPv4 addresses are embedded in the ISP's IPv6 addresses, and the
   hosts using these IPv6 addresses can therefore communicate with the
   global IPv6 Internet directly and can communicate with the global
   IPv4 Internet via stateless translators.  The communications can
   either be IPv6 initiated or IPv4 initiated.  The IVI mechanism
   supports the end-to-end address transparency and incremental
   deployment.  The IVI is an early design deployed in the CERNET as a
   reference for the IETF standard documents on IPv4/IPv6 stateless
   translation.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6219.




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Copyright Notice

   Copyright (c) 2011 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 ....................................................3
      1.1. Analysis of IPv4-IPv6 Translation Mechanisms ...............3
      1.2. CERNET Translation Requirements ............................4
   2. Terms and Abbreviations .........................................6
   3. The IVI Translation Algorithm ...................................6
      3.1. Address Format .............................................8
      3.2. Routing and Forwarding .....................................9
      3.3. Network-Layer Header Translation ..........................10
      3.4. Transport-Layer Header Translation ........................11
      3.5. Fragmentation and MTU Handling ............................11
      3.6. ICMP Handling .............................................11
      3.7. Application Layer Gateway .................................12
   4. The IVI DNS Configuration ......................................12
      4.1. DNS Configuration for the IVI6(i) Addresses ...............12
      4.2. DNS Service for the IVIG6(i) Addresses ....................12
   5. The Advanced IVI Translation Functions .........................12
      5.1. IVI Multicast .............................................12
   6. IVI Host Operation .............................................13
      6.1. IVI Address Assignment ....................................13
      6.2. IPv6 Source Address Selection .............................13
   7. The IVI Implementation .........................................14
      7.1. Linux Implementation ......................................14
      7.2. Testing Environment .......................................14
   8. Security Considerations ........................................14
   9. Contributors ...................................................15
   10. Acknowledgments ...............................................15
   Appendix A. The IVI Translator Configuration Example ..............16
   Appendix B. The traceroute Results ................................17
   11. References ....................................................19
      11.1. Normative References .....................................19
      11.2. Informative References ...................................20



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1.  Introduction

   This document presents the CERNET IVI translation design and
   deployment for the IPv4/IPv6 coexistence and transition.  In Roman
   numerals, the "IV" stands for 4, and "VI" stands for 6, so "IVI"
   stands for the IPv4/IPv6 translation.

   The experiences with IPv6 deployment in the past 10 years indicate
   that the ability to communicate between IPv4 and IPv6 address
   families would be beneficial.  However, the current transition
   methods do not fully support this requirement [RFC4213].  For
   example, dual-stack hosts can communicate with both the IPv4 and IPv6
   hosts, but single-stack hosts can only communicate with hosts in the
   same address family.  While the dual-stack approach continues to work
   in many cases even in the face of IPv4 address depletion [COUNT],
   there are situations where it would be desirable to communicate with
   a device in another address family.  Tunneling-based architectures
   can link the IPv6 islands across IPv4 networks, but they cannot
   provide communication between the two different address families
   [RFC3056] [RFC5214] [RFC4380].  Translation can relay communications
   for hosts located in IPv4 and IPv6 networks, but the current
   implementation of this kind of architecture is not scalable, and it
   cannot maintain end-to-end address transparency [RFC2766] [RFC3142]
   [RFC4966] [RFC2775].

1.1.  Analysis of IPv4-IPv6 Translation Mechanisms

   Since IPv4 and IPv6 are different protocols with different addressing
   structures, a translation mechanism is necessary for communication
   between endpoints using different address families.  There are
   several ways to implement the translation.  One is the Stateless IP/
   ICMP Translation Algorithm (SIIT) [RFC2765], which provides a
   mechanism for translation between IPv4 and IPv6 packet headers
   (including ICMP headers) without requiring any per-connection state.
   However, SIIT does not specify the address assignment and routing
   scheme [RFC2766].  For example, SIIT uses IPv4-mapped IPv6 addresses
   [::ffff:ipv4-addr/96] and IPv4-compatible IPv6 addresses
   [::ipv4-address/96] for the address mapping, but these addresses
   violate the aggregation principle of IPv6 routing [RFC4291].  The
   other translation mechanism is Network Address Translation - Protocol
   Translation (NAT-PT), which has serious technical and operational
   difficulties; the IETF has reclassified it from Proposed Standard to
   Historic status [RFC4966].

   In order to solve the technical difficulties in NAT-PT, the issues
   and the possible workarounds are:





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   1.  NAT-PT disrupts all protocols that embed IP addresses (and/or
       ports) in packet payloads.  There is little that can be done
       about this, other than using Application Layer Gateways (ALGs) or
       preferring protocols that transport DNS names instead of
       addresses.

   2.  Loss of end-to-end address transparency may occur.  End-to-end
       address transparency implies a global address space, the ability
       to pass packets unaltered throughout the network, and the ability
       to use source and destination addresses as unique labels
       [RFC2775].  A reversible, algorithmic mapping can restore some of
       this transparency.  However, it is still not possible to ensure
       that all nodes in the existing Internet support such reversible
       mappings.

   3.  The states maintained in the translator cause scalability,
       multihoming, and load-sharing problems.  Hence, a stateless
       translation scheme is preferred.

   4.  Loss of information due to incompatible semantics between IPv4
       and IPv6 versions of headers and protocols may occur.  A partial
       remedy to this is the proper attention to the details of the
       protocol translation, for example, the error-codes mapping
       between ICMP and ICMPv6.  However, some semantic differences
       remain.

   5.  The DNS is tightly coupled with the translator and lack of
       address mapping persistence discussed in Section 3.3 of
       [RFC4966].  Hence, the DNS should be decoupled from the
       translator.

   6.  Support for referrals is difficult in NAT-PT, given that
       translated addresses may leak outside the network where these
       addresses have a meaning.  Stateless translation, algorithmic
       address mappings, and the decoupling of DNS from the translation
       process can help the handling of referrals.  Nevertheless, it is
       still possible that an address-based referral is passed to
       someone who cannot employ it.  For instance, an IPv6-only node
       may pass a referral based on an IPv6 address to a node that only
       understands IPv4.

1.2.  CERNET Translation Requirements

   The China Education and Research Network has two backbones using
   different address families.  The CERNET is IPv4-only [CERNET] and
   CERNET2 is IPv6-only [CNGI-CERNET2], which fit in "an IPv6 network to
   the IPv4 Internet" and "the IPv4 Internet to an IPv6 network"
   scenarios in the IETF BEHAVE working group definition [BEHAVE]



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   [RFC6144].  In order to make CERNET2 communicate with the IPv4
   Internet, we designed the IVI mechanism and installed IVI translators
   between the CERNET and CERNET2.

   The requirements of the IVI mechanism are:

   1.  It should support both IPv6-initiated and IPv4-initiated
       communications for the IPv6 clients/servers in "an IPv6 network".

   2.  It should follow current IPv4 and IPv6 routing practice without
       increasing the global routing table size in both address
       families.

   3.  It should be able to be deployed incrementally.

   4.  It should be able to use IPv4 addresses effectively due to the
       IPv4 address depletion problem.

   5.  It should be stateless to achieve scalability.

   6.  The DNS function should be decoupled from the translator.

   The specific IVI design presented in this document can satisfy the
   above requirements, with the following notes:

   1.  It restricts the IPv6 hosts to use a subset of the addresses
       inside the ISP's IPv6 block.  Therefore, IPv6 autoconfiguration
       cannot be used for these IPv6 hosts.  Manual configuration or
       autoconfiguration via stateful DHCPv6 is required.

   2.  It defines a one-to-one mapping between IPv4 addresses and IPv6
       addresses; hence, the IPv4 addresses cannot be used efficiently.
       However, the IVI6 addresses can be used both for IPv6 clients and
       IPv6 servers.  Due to this limitation, we suggest using IVI6
       addresses for servers.

   3.  An ALG is still required for any applications that embed
       address(es) in the payload.

   4.  Some issues with end-to-end transparency, address referrals, and
       incompatible semantics between protocol versions still remain, as
       discussed above.

   The IVI is an early design deployed in the CERNET for the stateless
   translation.  The IETF standard IPv4-IPv6 stateless and stateful
   translation mechanisms are defined in [RFC6144], [RFC6052],
   [RFC6145], [RFC6146], and [RFC6147].




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2.  Terms and Abbreviations

   The following terms and abbreviations are used in this document:

   ISP(i):  A specific Internet service provider "i".

   IVIG4:  The global IPv4 address space.

   IPS4(i):  A subset of IVIG4 allocated to ISP(i).

   IVI4(i):  A subset of IPS4(i); the addresses in this set will be
      mapped to IPv6 via the IVI mapping mechanism and used by IPv6
      hosts of ISP(i).

   IPG6:  The global IPv6 address space.

   IPS6(i):  A subset of IPG6 allocated to ISP(i).

   IVIG6(i):  A subset of IPS6(i), and an image of IVIG4 in the IPv6
      address family via the IVI mapping mechanism.  It is defined as
      the IPv4-converted address in [RFC6144].

   IVI6(i):  A subset of IVIG6(i) and an image of IVI4(i) in the IPv6
      address family via the IVI mapping mechanism.  It is defined as
      the IPv4-translatable address in [RFC6144].

   IVI translator:  The mapping and translation gateway between IPv4 and
      IPv6 based on the IVI mechanism.

   IVI DNS:  Providing the IVI Domain Name System (DNS).

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL", when
   they appear in this document, are to be interpreted as described in
   [RFC2119].

3.  The IVI Translation Algorithm

   The IVI is a prefix-specific and stateless address mapping scheme
   that can be carried out by individual ISPs.  In the IVI design,
   subsets of the ISP's IPv4 addresses are embedded in the ISP's IPv6
   addresses, and the hosts using these IPv6 addresses can therefore
   communicate with the global IPv6 Internet directly and can
   communicate with the global IPv4 Internet via stateless translators.
   The communications can either be IPv6 initiated or IPv4 initiated.






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   The IVI mapping and translation mechanism is implemented in an IVI
   translator that connects between "an IPv6 network" and the IPv4
   Internet via the ISP's IPv4 network, as shown in the following
   figure.

            ------                        -----           ------
          /  The   \       -----        /  An   \       /  The   \
         |  IPv4    |-----|Xlate|------|  IPv6   |-----|  IPv6    |
          \Internet/       -----        \Network/       \Internet/
            ------                        -----           ------
                           <===>

    Figure 1: The Scenarios: "An IPv6 Network to the IPv4 Internet" and
                  "the IPv4 Internet to an IPv6 Network"

   In order to perform the translation function between IPv4 and IPv6
   addresses, the translator needs to represent the IPv4 addresses in
   IPv6 and the IPv6 addresses in IPv4.

   To represent the IPv4 addresses in IPv6, a unique, prefix-specific,
   and stateless mapping scheme is defined between IPv4 addresses and
   subsets of IPv6 addresses, so each provider-independent IPv6 address
   block (usually a /32) will have a small portion of IPv6 addresses
   (for example, /40 defined by PREFIX), which is the image of the
   totality of the global IPv4 addresses, as shown in the following
   figure.  The SUFFIX is all zeros.

                            +-+-+-+-+-+-+
                            |  IVIG4    |
                            +-+-+-+-+-+-+
                                 ||
                                \  /
                                 \/
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |  PREFIX      | IPv4 addr |  SUFFIX            |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

             Figure 2: Representing the IPv4 Addresses in IPv6













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   To represent the IPv6 addresses in IPv4, each provider can borrow a
   portion of its IPv4 addresses and map them into IPv6 based on the
   above mapping rule.  These special IPv6 addresses will be physically
   used by IPv6 hosts.  The original IPv4 form of the borrowed addresses
   is the image of these special IPv6 addresses, and it can be accessed
   by the IPv4 Internet, as shown in the following figure.  The SUFFIX
   can either be all zeros, or some other value for future extensions.

             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |  PREFIX      |   |IVI4|  |  SUFFIX            |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                                  ||
                                 \  /
                                  \/
                                -+-+-+
                                |IVI4|
                                -+-+-+

             Figure 3: Representing the IPv6 Addresses in IPv4

3.1.  Address Format

   The IVI address format is defined based on an individual ISP's IPv6
   prefix, as shown in the following figure

     | 0                 |32 |40                   |72             127|
     ------------------------------------------------------------------
     |                   |ff |                     |                  |
     ------------------------------------------------------------------
     |<-     PREFIX        ->|<-  IPv4 address   ->|   <- SUFFIX ->   |

                       Figure 4: IVI Address Mapping

   where bit 0 to bit 31 are the prefix of ISP(i)'s /32 (e.g., using
   document IPv6 address IPS6=2001:db8::/32) in the CERNET
   implementation, bit 32 to bit 39 are all ones as the identifier of
   the IVI addresses, and bit 40 to bit 71 are embedded global IPv4
   space (IVIG4), presented in hexadecimal format (e.g.,
   2001:db8:ff00::/40).  Note that based on the IVI mapping mechanism,
   an IPv4 /24 is mapped to an IPv6 /64, and an IPv4 /32 is mapped to an
   IPv6 /72.

   The IETF standard for the address format is defined in [RFC6052].








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3.2.  Routing and Forwarding

   Based on the IVI address mapping rule, routing is straightforward, as
   shown in the following figure

    /-----\                                                     /-----\
   ( ISP's )   --  192.0.2.2    -----------  2001:db8::2 --    ( ISP's )
   ( IPv4  )--|R1|-------------| IVI Xlate |------------|R2|---( IPv6  )
   (network)   --    192.0.2.1  ----------- 2001:db8::1  --    (network)
    \-----/                                                     \-----/
       |                                                           |
       |                                                           |
   The IPv4 Internet                                   The IPv6 Internet

                           Figure 5: IVI Routing

   where

   1.  IVI Xlate is a special dual-stack router, with two interfaces,
       one to the IPv4 network and the other to the IPv6 network (it is
       also possible to have a single interface configured with both
       IPv4 and IPv6 addresses).  IVI Xlate can support dynamic routing
       protocols in IPv4 and IPv6 address families.  In the above
       configuration, the static routing configuration can be used.

   2.  Router R1 has an IPv4 route for IVI4(i)/k (k is the prefix length
       of IVI4(i)) with the next hop equal to 192.0.2.1, and this route
       is distributed to the Internet with proper aggregation.

   3.  Router R2 has an IPv6 route for IVIG6(i)/40 with the next hop
       equal to 2001:db8::1, and this route is distributed to the IPv6
       Internet with proper aggregation.

   4.  The IVI translator has an IPv6 route for IVI6(i)/(40+k) with the
       next hop equal to 2001:db8::2.  The IVI translator also has an
       IPv4 default route 0.0.0.0/0 with the next hop equal to
       192.0.2.2.

   Note that the routes described above can be learned/inserted by
   dynamic routing protocols (IGP or BGP) in the IVI translator peering
   with R1 and R2.

   Since both IVI4(i) and IVI6(i) are aggregated to IPS4(i) and IPS6(i)
   in ISP(i)'s border routers, respectively, they will not affect the
   global IPv4 and IPv6 routing tables [RFC4632].

   Since the IVI translation is stateless, it can support multihoming
   when the same prefix is used for multiple translators.



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   Since the IVI translation can be implemented independently in each
   ISP's network, it can be incrementally deployed in the global
   Internet.

3.3.  Network-Layer Header Translation

   IPv4 [RFC0791] and IPv6 [RFC2460] are different protocols with
   different network-layer header formats; the translation of the IPv4
   and IPv6 headers MUST be performed according to SIIT [RFC2765],
   except for the source and destination addresses in the header, as
   shown in the following figures.

       -------------------------------------------------------------
       IPv4 Field             Translated to IPv6
       -------------------------------------------------------------
       Version (0x4)          Version (0x6)
       IHL                    discarded
       Type of Service        Traffic Class
       Total Length           Payload Length = Total Length - 20
       Identification         discarded
       Flags                  discarded
       Offset                 discarded
       TTL                    Hop Limit
       Protocol               Next Header
       Header Checksum        discarded
       Source Address         IVI address mapping
       Destination Address    IVI address mapping
       Options                discarded
       -------------------------------------------------------------

                 Figure 6: IPv4-to-IPv6 Header Translation

       -------------------------------------------------------------
       IPv6 Field             Translated to IPv4 Header
       -------------------------------------------------------------
       Version (0x6)          Version (0x4)
       Traffic Class          Type of Service
       Flow Label             discarded
       Payload Length         Total Length = Payload Length + 20
       Next Header            Protocol
       Hop Limit              TTL
       Source Address         IVI address mapping
       Destination Address    IVI address mapping
       -                      IHL = 5
       -                      Header Checksum recalculated
       -------------------------------------------------------------

                 Figure 7: IPv6-to-IPv4 Header Translation



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   The IETF standard for IP/ICMP translation is defined in [RFC6145],
   which contains updated technical specifications.

3.4.  Transport-Layer Header Translation

   Since the TCP and UDP headers [RFC0793] [RFC0768] consist of
   checksums that include the IP header, the recalculation and updating
   of the transport-layer headers MUST be performed.  Note that SIIT
   does not recalculate the transport-layer checksum, since checksum-
   neutral IPv6 addresses are used in SIIT [RFC2765].

   The IETF standard for transport-layer header translation is defined
   in [RFC6145], which contains updated technical specifications.

3.5.  Fragmentation and MTU Handling

   When the packet is translated by the IVI translator, due to the
   different sizes of the IPv4 and IPv6 headers, the IVI6 packets will
   be at least 20 bytes larger than the IVI4 packets, which may exceed
   the MTU of the next link in the IPv6 network.  Therefore, the MTU
   handling and translation between IPv6 fragmentation headers and the
   fragmentation field in the IPv4 headers are necessary; this is
   performed in the IVI translator according to SIIT [RFC2765].

   The IETF standard for fragmentation and MTU handling is defined in
   [RFC6145], which contains updated technical specifications.

3.6.  ICMP Handling

   For ICMP message translation between IPv4 and IPv6, IVI follows the
   ICMP/ICMPv6 message correspondence as defined in SIIT [RFC2765].
   Note that the ICMP message may be generated by an intermediate router
   whose IPv6 address does not belong to IVIG6(i).  Since ICMP
   translation is important to the path MTU discovery and
   troubleshooting, the IPv4 representation of the non-IVIG6 addresses
   in the ICMP packets is required.  In the current IVI prototype, a
   small IPv4 address block is used to identify the non-IVIG6 addresses.
   This prevents translated ICMP messages from being discarded due to
   unknown or private IP sources.

   The IETF standard for IP/ICMP translation is defined in [RFC6145],
   which contains updated technical specifications.









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3.7.  Application Layer Gateway

   Due to the features of 1-to-1 address mapping and stateless
   operation, IVI can support most of the existing applications, such as
   HTTP, Secure SHell (SSH), and Telnet.  However, some applications are
   designed such that IP addresses are used to identify application-
   layer entities (e.g., FTP).  In these cases, an Application Layer
   Gateway (ALG) is unavoidable, and it can be integrated into the IVI
   translator.

   The discussion of the use of ALGs is in [RFC6144].

4.  The IVI DNS Configuration

   The DNS [RFC1035] service is important for the IVI mechanism.

4.1.  DNS Configuration for the IVI6(i) Addresses

   For providing authoritative DNS service for IVI4(i) and IVI6(i), each
   host name will have both an A record and a AAAA record pointing to
   IVI4(i) and IVI6(i), respectively.  Note that the same name always
   points to a unique host, which is an IVI6(i) host, and it has IVI4(i)
   representation via the IVI translator.

4.2.  DNS Service for the IVIG6(i) Addresses

   For resolving the IPv6 form of the global IPv4 space (IVIG6(i)), each
   ISP must provide customized IVI DNS service for the IVI6(i) hosts.
   The IVI DNS server MUST be deployed in a dual-stack environment.
   When the IVI6(i) host queries a AAAA record for an IPv4-only domain
   name, the IVI DNS will query the AAAA record first.  If the AAAA
   record does not exist, the IVI DNS will query the A record and map it
   to IVIG6(i), and return a AAAA record to the IVI6(i) host.  The
   technical specifications for this process are defined in [RFC6147].

5.  The Advanced IVI Translation Functions

5.1.  IVI Multicast

   The IVI mechanism can support IPv4/IPv6 communication of Protocol
   Independent Multicast - Source-Specific Multicast (PIM-SSM) [RFC5771]
   [RFC3569] [RFC4607].

   There will be 2^24 group addresses for IPv4 SSM.  The corresponding
   IPv6 SSM group addresses can be defined as shown in the following
   figure.





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          -------------------------------------------------------
          IPv4 Group Address          IPv6 Group Address
          -------------------------------------------------------
          232.0.0.0/8                 ff3e:0:0:0:0:0:f000:0000/96
          232.255.255.255/8           ff3e:0:0:0:0:0:f0ff:ffff/96
          -------------------------------------------------------

               Figure 8: IVI Multicast Group Address Mapping

   The source address in IPv6 MUST be IVI6(i) in order to perform
   Reverse Path Forwarding (RPF) as required by PIM - Sparse Mode
   (PIM-SM).

   The interoperation of PIM-SM for IPv4 and IPv6 address families can
   either be implemented via an Application Layer Gateway or via static
   joins based on IGMPv3 and Multicast Listener Discovery Version 2
   (MLDv2) in IPv4 and IPv6, respectively.

6.  IVI Host Operation

6.1.  IVI Address Assignment

   The IVI6 address has a special format (for example, IVI4=192.0.2.1/32
   and IVI6=2001:db8:ffc0:2:100::/72); therefore, stateless IPv6 address
   autoconfiguration cannot be used.  However, the IVI6 can be assigned
   to the IPv6 end system via manual configuration or stateful
   autoconfiguration via DHCPv6.

   o  For the manual configuration, the host needs to configure the IVI6
      address and the corresponding prefix length, as well as the
      default gateway address and the DNS resolver address.

   o  For the DHCPv6 configuration, the DHCPv6 will assign the IVI6
      address and the DNS resolver address to the host.  The router in
      the subnet should enable router advertisement (RA), since the
      default gateway is learned from the router.

6.2.  IPv6 Source Address Selection

   Since each IPv6 host may have multiple addresses, it is important for
   the host to use an IVI6(i) address to reach the global IPv4 networks.
   The short-term workaround is to use IVI6(i) as the default source
   IPv6 address of the host, defined as the policy table in [RFC3484].
   The long-term solution requires that the application should be able
   to select the source addresses for different services.






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7.  The IVI Implementation

7.1.  Linux Implementation

   An implementation of IVI exists for the Linux operating system.  The
   source code can be downloaded from [LINUX].  An example of how to
   configure an IVI deployment is shown in Appendix A.

   The IVI DNS source code for the IVIG6(i) addresses presented in this
   document can be downloaded from [DNS].

7.2.  Testing Environment

   The IVI translator based on the Linux implementation has been
   deployed between [CERNET] (IPv4-only) and [CNGI-CERNET2] (IPv6-only)
   since March 2006.  The pure-IPv6 web servers using IVI6 addresses
   [2001:250:ffca:2672:100::] behind the IVI translator can be accessed
   by the IPv4 hosts [TEST4], and also by the global IPv6 hosts [TEST6].
   The pure-IPv6 clients using IVI6 addresses behind the IVI translator
   can access IPv4 servers on the IPv4 Internet.

   Two traceroute results are presented in Appendix B to show the
   address mapping of the IVI mechanism.

   IVI6 manual configuration and DHCPv6 configuration of the IPv6 end
   system have also been tested with success.

8.  Security Considerations

   This document presents the prefix-specific and stateless address
   mapping mechanism (IVI) for the IPv4/IPv6 coexistence and transition.
   The IPv4 security and IPv6 security issues should be addressed by
   related documents of each address family and are not included in this
   document.

   However, there are several issues that need special considerations,
   specifically (a) IPsec and its NAT traversal, (b) DNS Security
   Extensions (DNSSEC), and (c) firewall filter rules.

   o  IPsec and its NAT traversal: Since the IVI scheme maintains end-
      to-end address transparency, IPsec could work with or without NAT
      traversal techniques.

   o  DNSSEC: DNSSEC verification will be terminated at the IVI DNS for
      the "A record to AAAA record" translation.  It would be fine to
      have a translation in a local IVI DNS server that also verifies





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      DNSSEC, or in the host, if the host both translates the DNS entry
      and again verifies DNSSEC validity.  The DNSSEC discussion is in
      [RFC6147].

   o  Firewall filter rules: Since the IVI scheme maintains the end-to-
      end address transparency and there is a unique mapping between
      IPv4 and IPv6 addresses, the firewall filter rule can therefore be
      implemented for one address family, or mapped to another address
      family and implemented in that address family.  However, the
      current IPv6 routers may only support the access-list or uRPF
      (unicast Reverse Path Forwarding) for the prefix length shorter
      than /64; there may a practical constraint for the construction of
      such rules.

   Except for the issues discussed above, we have not found special
   security problems introduced by the IVI translation in our
   experiments.

9.  Contributors

   The authors would like to acknowledge the following contributors in
   the different phases of the IVI development: Ang Li, Yuncheng Zhu,
   Junxiu Lu, Yu Zhai, Wentao Shang, Weifeng Jiang, and Bizheng Fu.

   The authors would like to acknowledge the following contributors, who
   provided helpful inputs concerning the IVI concept: Bill Manning,
   David Ward, Elwyn Davies, Lixia Zhang, Jun Murai, Fred Baker, Jari
   Arkko, Ralph Droms, Tony Hain, and Kevin Yin.

10.  Acknowledgments

   The authors thank the following for funding support: the CERNET,
   CNGI-CERNET2, CNGI Research and Development, and the China "863" and
   China "973" projects.

















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Appendix A.  The IVI Translator Configuration Example

   #!/bin/bash
   # open forwarding
   echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
   echo 1 > /proc/sys/net/ipv4/conf/all/forwarding

   # config route for IVI6 = 2001:db8:ffc0:2:0::/64,
   #                  IVI4 = 192.0.2.0/24

   # configure IPv6 route
   route add -A inet6 2001:db8:ffc0:2:0::/64 \
   gw 2001:da8:aaae::206 dev eth0

   # config mapping for      source-PF = 2001:db8::/32
   # config mapping for destination-PF = 2001:db8::/32

   # for each mapping, a unique pseudo-address (10.0.0.x/8)
   # should be configured.
   # ip addr add 10.0.0.1/8 dev eth0

   # IPv4-to-IPv6 mapping: multiple mappings can be done via multiple
   # commands.
   # mroute IVI4-network IVI4-mask pseudo-address interface \
   # source-PF destination-PF
   /root/mroute 192.0.2.0 255.255.255.0 10.0.0.1 \
   eth0 2001:db8:: 2001:db8::

   # IPv6-to-IPv4 mapping
   # mroute6 destination-PF destination-PF-pref-len
   /root/mroute6 2001:db8:ff00:: 40

                    Figure 9: IVI Configuration Example


















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Appendix B.  The traceroute Results

   ivitraceroute 202.38.108.2

   1  202.112.0.65 6 ms 2 ms 1 ms
   2  202.112.53.73 4 ms 6 ms 12 ms
   3  202.112.53.178 1 ms 1 ms 1 ms
   4  202.112.61.242 1 ms 1 ms 1 ms
   5  192.0.2.100 1 ms 1 ms 1 ms
   6  192.0.2.102 1 ms 1 ms 1 ms
   7  192.0.2.103 2 ms 2 ms 2 ms
   8  192.0.2.104 2 ms 2 ms 2 ms
   9  192.0.2.105 4 ms 4 ms 3 ms
   10 202.38.108.2 2 ms 3 ms 3 ms

                     Figure 10: ivitraceroute Results

   Note that the non-IVIG6 addresses are mapped to IPv4 document address
   192.0.2.0/24.
































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   ivitraceroute6 www.mit.edu

   src_ivi4=202.38.97.205 src_ivi6=2001:da8:ffca:2661:cd00::
   dst_host=www.mit.edu
   dst_ip4=18.7.22.83 dst_ivig=2001:da8:ff12:716:5300::

   traceroute to 2001:da8:ff12:716:5300:: (2001:da8:ff12:716:5300::),
   30 hops max, 40 byte packets to not_ivi

   1  2001:da8:ff0a:0:100::      0.304 ms 0.262 ms 0.190 ms
      10.0.0.1
   2  2001:da8:ffca:7023:fe00::  0.589 ms * *
      202.112.35.254
   3  2001:da8:ffca:7035:4900::  1.660 ms 1.538 ms 1.905 ms
      202.112.53.73
   4  2001:da8:ffca:703d:9e00::  0.371 ms 0.530 ms 0.459 ms
      202.112.61.158
   5  2001:da8:ffca:7035:1200::  0.776 ms 0.704 ms 0.690 ms
      202.112.53.18
   6  2001:da8:ffcb:b5c2:7d00::  89.382 ms 89.076 ms 89.240 ms
      203.181.194.125
   7  2001:da8:ffc0:cb74:9100::  204.623 ms 204.685 ms 204.494 ms
      192.203.116.145
   8  2001:da8:ffcf:e7f0:8300::  249.842 ms 249.945 ms 250.329 ms
      207.231.240.131
   9  2001:da8:ff40:391c:2d00::  249.891 ms 249.936 ms 250.090 ms
      64.57.28.45
   10 2001:da8:ff40:391c:2a00::  259.030 ms 259.110 ms 259.086 ms
      64.57.28.42
   11 2001:da8:ff40:391c:700::   264.247 ms 264.399 ms 264.364 ms
      64.57.28.7
   12 2001:da8:ff40:391c:a00::   271.014 ms 269.572 ms 269.692 ms
      64.57.28.10
   13 2001:da8:ffc0:559:dd00::   274.300 ms 274.483 ms 274.316 ms
      192.5.89.221
   14 2001:da8:ffc0:559:ed00::   274.534 ms 274.367 ms 274.517 ms
      192.5.89.237
   15 * * *
   16 2001:da8:ff12:a800:1900::  276.032 ms 275.876 ms 276.090 ms
      18.168.0.25
   17 2001:da8:ff12:716:5300::   276.285 ms 276.370 ms 276.214 ms
      18.7.22.83

                     Figure 11: ivitraceroute6 Results

   Note that all of the IPv4 addresses can be mapped to prefix-specific
   IPv6 addresses (for example, 18.7.22.83 is mapped to 2001:da8:ff12:
   716:5300::).



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11.  References

11.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2765]  Nordmark, E., "Stateless IP/ICMP Translation Algorithm
              (SIIT)", RFC 2765, February 2000.

   [RFC2766]  Tsirtsis, G. and P. Srisuresh, "Network Address
              Translation - Protocol Translation (NAT-PT)", RFC 2766,
              February 2000.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

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

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, August 2006.



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   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.

   [RFC5771]  Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for
              IPv4 Multicast Address Assignments", BCP 51, RFC 5771,
              March 2010.

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

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, April 2011.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6147]  Bagnulo, M., Sullivan, A., Matthews, P., and I. van
              Beijnum, "DNS64: DNS Extensions for Network Address
              Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
              April 2011.

11.2.  Informative References

   [BEHAVE]   "The IETF Behave Working Group Charter:
              http://datatracker.ietf.org/wg/behave/charter/".

   [CERNET]   "CERNET Homepage:
              http://www.edu.cn/english_1369/index.shtml".

   [CNGI-CERNET2]
              "CNGI-CERNET2 Homepage:
              http://www.cernet2.edu.cn/index_en.htm".

   [COUNT]    "IPv4 address countdown: http://penrose.uk6x.com/".

   [DNS]      "Source Code of the IVI DNS
              http://www.ivi2.org/IVI/src/ividns-0.1.tar.gz/".

   [LINUX]    "Source Code of the IVI implementation for Linux:
              http://linux.ivi2.org/impl/".





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   [RFC2775]  Carpenter, B., "Internet Transparency", RFC 2775,
              February 2000.

   [RFC3142]  Hagino, J. and K. Yamamoto, "An IPv6-to-IPv4 Transport
              Relay Translator", RFC 3142, June 2001.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC3569]  Bhattacharyya, S., Ed., "An Overview of Source-Specific
              Multicast (SSM)", RFC 3569, July 2003.

   [RFC4966]  Aoun, C. and E. Davies, "Reasons to Move the Network
              Address Translator - Protocol Translator (NAT-PT) to
              Historic Status", RFC 4966, July 2007.

   [TEST4]    "Test homepage for the IVI4(i): http://test4.ivi2.org".

   [TEST6]    "Test homepage for the IVI6(i): http://test6.ivi2.org",
              Available using IPv6 only.































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Authors' Addresses

   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN
   Phone: +86 10-62785983
   EMail: xing@cernet.edu.cn


   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN
   Phone: +86 10-62785983
   EMail: congxiao@cernet.edu.cn


   Maoke Chen
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN
   Phone: +86 10-62785983
   EMail: fibrib@gmail.com


   Hong Zhang
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN
   Phone: +86 10-62785983
   EMail: neilzh@gmail.com


   Jianping Wu
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN
   Phone: +86 10-62785983
   EMail: jianping@cernet.edu.cn






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