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Versions: 00 01 02 03 04 05 06 07 RFC 6219

Network Working Group                                              X. Li
Internet-Draft                                                   M. Chen
Intended status: Informational                                    C. Bao
Expires: August 13, 2009                                        H. Zhang
                                                                   J. Wu
                                       CERNET Center/Tsinghua University
                                                        February 9, 2009


   Prefix-specific and Stateless Address Mapping (IVI) for IPv4/IPv6
                       Coexistence and Transition
                        draft-xli-behave-ivi-01

Status of this Memo

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   This Internet-Draft will expire on August 13, 2009.

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Abstract

   This document presents the concept and practice of the prefix-
   specific and stateless address mapping mechanism (IVI) for IPv4/IPv6
   coexistence and transition.  In this scheme, subsets of the IPv4
   addresses are embedded in prefix-specific IPv6 addresses and these
   IPv6 addresses can therefore communicate with the global IPv6
   networks directly and can communicate with the global IPv4 networks
   via stateless gateways.  The IVI scheme supports the end-to-end
   address transparency and incremental deployment.  This document is a
   comprehensive report on the IVI design and its deployment in large
   scale public networks.

   Version 01 of the IVI document is a simplified version of version 00
   to present the main concepts and recent practice of the IVI
   translation scheme.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terms and Abbreviations  . . . . . . . . . . . . . . . . . . .  5
   3.  The IVI Translation Algorithm  . . . . . . . . . . . . . . . .  6
     3.1.  Address Mapping  . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Routing and Forwarding . . . . . . . . . . . . . . . . . .  8
     3.3.  Network-layer Header Translation . . . . . . . . . . . . .  9
     3.4.  Transport-layer Header Translation . . . . . . . . . . . . 10
     3.5.  Fragmentation and MTU Handling . . . . . . . . . . . . . . 11
     3.6.  ICMP Handling  . . . . . . . . . . . . . . . . . . . . . . 11
     3.7.  Application Layer Gateway  . . . . . . . . . . . . . . . . 11
   4.  The IVI DNS Configuration  . . . . . . . . . . . . . . . . . . 11
     4.1.  DNS Configuration for the IVI6(i) Addresses  . . . . . . . 11
     4.2.  DNS Configuration for the IVIG46(i) Addresses  . . . . . . 12
   5.  The Advanced IVI translation Algorithm . . . . . . . . . . . . 12
     5.1.  IPv4 Address Multiplexing  . . . . . . . . . . . . . . . . 12
     5.2.  IVI NAT464 . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.3.  IVI Multicast  . . . . . . . . . . . . . . . . . . . . . . 13
   6.  IVI Host Operation . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  IVI Address Assignment . . . . . . . . . . . . . . . . . . 13
     6.2.  IPv6 Source Address Selection  . . . . . . . . . . . . . . 14
   7.  The IVI Implementation . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Linux Implementation . . . . . . . . . . . . . . . . . . . 14
     7.2.  Testing Environment  . . . . . . . . . . . . . . . . . . . 14
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 15
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   12. Appendix A. The IVI gateway configuration example  . . . . . . 16
   13. Appendix B. The traceroute results . . . . . . . . . . . . . . 17
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 19
     14.2. Informative References . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
















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1.  Introduction

   This document presents the concept and practice of the prefix-
   specific and stateless address mapping mechanism (IVI) for IPv4/IPv6
   coexistence and transition.

   The experiences for the IPv6 deployment in the past 10 years strongly
   indicate that for a successful transition, the IPv6 hosts need to
   communicate with the global IPv4 networks [JJI07].  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 the IPv4 address depletion problem makes
   the dual-stack approach inapplicable [COUNT].  The tunneled
   architectures can link the IPv6 islands cross IPv4 networks, but they
   cannot help the communication between two address families [RFC3056]
   [RFC5214] [RFC4380].  The translation architectures can relay the
   communications for the hosts located in IPv4 and IPv6 networks, but
   the current implementation of this kind of architecture is not
   scalable and it cannot maintain the end-to-end address transparency
   [RFC2766] [RFC3142] [RFC4966] [RFC2775].

   However, since IPv4 and IPv6 are different protocols with different
   addressing structure, the translation mechanism is still necessary
   for the communication between the two address families.  There are
   several ways to implement the translation.  One is the stateless IP/
   ICMP translation algorithm (SIIT), which provides a mechanism for the
   translation between IPv4 and IPv6 packet headers (including ICMP
   headers) without requiring any per-connection state.  But, SIIT does
   not specify the address assignment and routing scheme [RFC2766].  For
   example, when SIIT is used for the IPv4 mapped IPv6 addresses
   [::FFFF:ipv4-addr/96] and IPv4 compatible IPv6 addresses [::ipv4-
   address/96]), these addresses violate the aggregation nature of the
   IPv6 routing [RFC4291].  The other translation mechanism is NAT-PT,
   which has serious technical and operational difficulties and IETF has
   reclassified it from proposed standard to historic status.  But in
   the same document, it suggested that a revised, possibly restricted
   version of NAT-PT can be a suitable solution for the communication
   between IPv4 and IPv6 hosts [RFC4966].  Recently, several mechanisms
   are proposed in this direction, for example NAT64 translates the IPv4
   server address by adding or removing a /96 prefix, and translates the
   IPv6 client address by installing mappings in the normal NAT manner
   [I-D.bagnulo-behave-nat64].

   In this document, we follow the basic specification of SIIT, but we
   define the address assignment and routing scheme (IVI).  Our IVI
   mechanism is related to SIIT and NAT-PT, but differs from them
   significantly.  First, it is stateless in both the IPv4-to-IPv6
   mapping direction, as well as in the IPv6-to-IPv4 mapping direction.



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   Secondly, it supports address transparency.  Thirdly, it supports
   both client-server applications and the peer-to-peer applications
   cross IPv4 and IPv6 address families without using NAT-traversal
   techniques.  Finally, it can satisfy most of the basic and advanced
   requirements for the IPv4 to IPv4 transition as specified by the
   Internet Drafts [I-D.v6ops-nat64-pb-statement-req].


2.  Terms and Abbreviations

   The following terms and abbreviations are used in this document:

   IVI: IV means 4 and VI means 6 in Roman representation, so IVI means
   mapping and translation between IPv4 and IPv6.

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

   IPG4: An address set containing all IPv4 addresses, the addresses in
   this set are mainly used by IPv4 hosts at the current stage.

   IPS4(i): A subset of IPG4 allocated to ISP(i).

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

   IPG6: An address set containing all IPv6 addresses.

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

   IVIG46(i): A subset of IPS6(i), an image of IPG4 in IPv6 address
   family via IVI mapping rule.

   IVI6(i): A subset of IVIG46(i), an image of IVI4(i) in IPv6 address
   family via IVI mapping rule.

   IVI gateway: The mapping and translation gateway between IPv4 and
   IPv6 based on IVI scheme.

   IVI DNS: Providing IVI Domain Name Service (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].







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3.  The IVI Translation Algorithm

   The IVI is a prefix-specific and stateless address mapping scheme
   which can be carried out by individual ISPs.  This is to say a subset
   of the ISPs IPv6 network can communicate with the IPv4 Internet and
   the IPv4 Internet can communicate with the subset of the ISPs IPv6
   network

   IVI mapping and translation mechanism is implemented in an IVI
   gateway which connects to both the ISP's IPv4 and IPv6 networks.  The
   IP header and ICMP header translation algorithms similar to the ones
   in SIIT are implemented in the IVI gateway [RFC2765].

   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, which is the image of the totality
   of the global IPv4 addresses.

   Each provider can borrow a portion of its IPv4 addresses and maps
   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.

   The packets generated from the global IPv4 addresses and sent to IVI4
   (the IPv4 image of the special IPv6 addresses) are routed to the IPv4
   interface of the IVI gateway via the IPv4 routing protocol and the
   packets generated from the special IPv6 addresses and sent to IPG46
   (the image of the global IPv4 addresses) are routed to the IPv6
   interface of the IVI gateway via the IPv6 routing protocol.  The
   processes in both directions are symmetric.  In addition, the special
   IPv6 addresses can communicate with the global IPv6 networks.

   The IVI scheme related issues, for example the IVI DNS, the IPv4
   addresses multiplexing, the IVI multicast, etc. can be solved without
   involving any major change in the current Internet protocol.

3.1.  Address Mapping

   The IVI address mapping is defined based on individual ISP's prefix
   as shown in the following figure.









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     | 0                 |32 |40                   |72             127|
     ------------------------------------------------------------------
     |                   |FF |                     |                  |
     ------------------------------------------------------------------
     |<-  IPv6 prefix  ->|   |<-  IPv4 address   ->|<- zero padding ->|


                       Figure 1: IVI Address Mapping

   where bit 0 to bit 31 are the prefix of ISP(i)'s /32 (e.g.
   IPS6=2001:DB8::/32), bit 32 to bit 39 are all one's as the identifier
   of IVI, bit 40 to bit 71 are embedded global IPv4 space (IPG4)
   presented in hexadecimal format. (e.g. 2001:DB8:ff00::/40).  Because
   this mapping is 1-to-1 defined by the IVI mapping rule, it is
   stateless and it has feature of end-to-end address transparency.

   (1) The ISP(i) uses a subset of ISP4(i) defined as IVI4(i), and maps
   it into IPv6 as IVI6(i).  The IVI6(i) is physically used by IPv6
   hosts inside ISP(i)'s IPv6 network and the IVI4(i) cannot be used by
   IPv4 hosts.  Therefore, IVI6(i) is the special IPv6 address block
   which can communicate with both address families.

   (2) Based on the above mapping rule, the ISP(i) uses a subset of
   ISP6(i) defined as IVIG46(i), and maps it into IPv4 as IPG4.  The
   IVIG46(i) is virtually used by global IPv4 hosts and it cannot be
   used by IPv6 hosts, except the portion of IVI6(i).

   The mapping of the different address sets and the relations are shown
   in the following figure.


                |<-------IPG4--------------------->|
                |        |<----IPS4(i)----->|      |
                |           |<-IVI4(i)->|          |
                |           |           |          |
                |           |    /\     |          |
                |           |    ||     |          |
                |           | mapping   |          |
                |           |    ||     |          |
                |           |    \/     |          |
                |           |           |          |
                |           |<-IVI6(i)->|          |
                |<------IPG46(i)------------------>|
          |<--------IPS6(i)------------------------------>|
      |<-----------IPG6-------------------------------------------->|






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                  Figure 2: IVI Address Mapping Relation

   The address reachability matrix of the IPv4, IVI, non-IVI and IPv6 is
   shown in the following figure.


                              IPG4    IVI     non-IVI     IPG6
                        ---------------------------------------
            IPG4       |       OK      OK        NO        NO
            IVI        |       OK      OK        OK        OK
            non-IVI    |       NO      OK        OK        OK
            IPG6       |       NO      OK        OK        OK



                     Figure 3: IVI Reachability Matrix

   where IVI4(i) and IVI6(i) are representing the same entities in IPv4
   and IPv6 address families, respectively.  Similarly, IPG4 and
   IVIG46(i) are representing the same entities in IPv4 and IPv6 address
   families, respectively.  In addition, IVI4(i) is a subset of IPG4 and
   IVI6(i) is a subset of IVIG46(i).

   In addition, depending on the implementation scope of the IVI
   gateway, IVIG46(i) block can also be defined as 2001:DB8:FFFF::/48,
   2001:DB8:ABCD:FF00::/56 or 2001:DB8:ABCD:FFFF::/64, etc.  A special
   case is to define IVIG46(i)=2001:DB8:XXXX:XXXX:XXXX:XXXX::/96, then
   the mapping rule is similar to the method of translating the IPv4
   server address proposed in [I-D.bagnulo-behave-nat64].

3.2.  Routing and Forwarding

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


    /-----\                                                     /-----\
   (ISP's  )  ----192.168.1.2  ------------- 2001:DB8::2----   (ISP's  )
   (IPv4   )--|R1|-------------|IVI gateway|------------|R2|---(IPv6   )
   (network)  ----  192.168.1.1-------------2001:DB8::1 ----   (network)
    \-----/                                                     \-----/


                           Figure 4: IVI Routing

   where

   (1) Router R1 has IPv4 route of IVI4(i)/k (k is the prefix length of



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   IVI4(i)) with next-hop equals to 192.168.1.1 and this route is
   distributed to global IPv4 networks with proper aggregation.

   (2) Router R2 has IPv6 route of IVIG46(i)/40 with next-hop equals to
   2001:DB8::1 and this route is distributed to global IPv6 networks
   with proper aggregation.

   (3) IVI gateway has IPv6 route of IVI6(i)/(40+k) with next hop equals
   to 2001:DB8::2.  IVI gateway also has IPv4 default route 0.0.0.0/0
   with next hop equals to 192.168.1.2 .

   Note that the routes described above can be learned/inserted by
   dynamic routing protocols in the IVI gateway neighboring (IGP) or
   peering (BGP) 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, there will be no affect to
   the global IPv4 and IPv6 routing tables [RFC4632].

   Since IVI gateway is stateless, it can support multi-homing when same
   prefix is used.

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

3.3.  Network-layer Header Translation

   IPv4 [RFC791] [RFC0791] and IPv6 [RFC2460] are different protocols
   with different network layer header format, the translation of the
   IPv4 and IPv6 headers must be performed [MVB98] [RFC2765] as shown in
   the following figures.




















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       -------------------------------------------------------------
       IPv4 Field             Translated to IPv6
       -------------------------------------------------------------
       Version (0x4)          Version (0x6)
       IHL                    discarded
       Type of Service        discarded
       Total Length           Payload Length = Total Length -IHL * 4
       Identification         discarded
       Flags                  discarded
       Offset                 discarded
       Time to Live           Hop Limit
       Protocol               Next Header
       Header Checksum        discarded
       Source Address         IVI address mapping
       Destination Address    IVI address mapping
       Options                discarded
       -------------------------------------------------------------


       Figure 5: IPv4 to IPv6 Header translation based on IVI scheme


       -------------------------------------------------------------
       IPv6 Field             Translated to IPv4 Header
       -------------------------------------------------------------
       Version (0x6)          Version (0x4)
       Traffic Class          discarded
       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 6: IPv6 to IPv4 Header translation based on IVI scheme

3.4.  Transport-layer Header Translation

   Since the TCP and UDP headers [RFC0793] [RFC0768] consist of check
   sums which include the IP header, the recalculation and updating of
   the transport-layer headers MUST be performed [RFC2765].






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3.5.  Fragmentation and MTU Handling

   When the packet is translated by the IVI gateway, 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
   fragmentation field in the IPv4 headers are necessary, which is
   performed in the IVI gateway according to SIIT [RFC2765].

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 IVIG46(i).  Since ICMP
   translation is important to the path MTU discovery, the inverse
   mapping for unmapped addresses is defined in this document.  In the
   current prototype, a pseudo IPv4 address is generated.  This prevents
   translated ICMP messages from being discarded due to unknown or
   private IP source.  A small IPv4 address block should be reserved to
   identify the non-IVI mapped IPv6 addresses.

3.7.  Application Layer Gateway

   Due to the features of 1-to-1 address mapping and stateless, IVI can
   support most of the existing applications, such as HTTP, SSH, Telnet
   and Microsoft Remote Desktop Protocol.  However, some applications
   are designed such that IP addresses are used to identify application-
   layer entities (e.g.  FTP).  In these cases, application layer
   gateway (ALG) is unavoidable, but it can be integrated into the IVI
   gateway.


4.  The IVI DNS Configuration

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

4.1.  DNS Configuration for the IVI6(i) Addresses

   For providing authoritative DNS service for IVI4(i) and IVI6(i), each
   host name will both have an A record and an 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 gateway.






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4.2.  DNS Configuration for the IVIG46(i) Addresses

   For resolving the IVI IPv6-mapped global IPv4 space (IVIG46(i)), each
   ISP must provide customized IVI DNS service for the IVI6(i) hosts.
   The IVI DNS server is in dual stack environment.  When the IVI6(i)
   host queries an AAAA record for an IPv4 only domain name, the IVI DNS
   server will query the A record and map it to IVIG46(i) with ISP's
   IPv6 prefix and return an AAAA record to the IVI6(i) host.


5.  The Advanced IVI translation Algorithm

5.1.  IPv4 Address Multiplexing

   Since public-IPv4 address is a scarce resource, the effective use of
   the IPv4 address is important for the IVI scheme.  The multiplexing
   techniques are temporal multiplexing and transport port multiplexing.

   The IVI6 can be temporally multiplexed inside the ISP(i)'s /32.  This
   is to say that the ISP can dynamically assign IVI6(i) to an end
   system when it requests the IPv4 communication service and release
   the IVI6(i) when the communication is finished.  For temporal
   multiplexing, the features of stateless and end-to-end address
   transparency are maintained.

   To further increase the utilization ratio of the public IPv4
   addresses, the port multiplexing inside the ISP(i)'s /32 can be
   deployed [RFC2766] [RFC4966].  This is to say that a single IPv4
   address (IVI4(i)) can be used for multiple IVI6(i) addresses.  The
   mapping scheme is to use the least significant bits in the IVI6(i) to
   define the multiple mapping and combine the transport-layer port
   number to perform uniquely the mapping from IVI4(i) to IVI6(i).

5.2.  IVI NAT464

   The IVI scheme can support the IPv4 over IPv6 service (NAT464), i.e.
   a stub IPv4 network can be connected to an IVI gateway to reach the
   IPv6 network and via another IVI gateway to reach the global IPv4
   network [RFC4925]

   A more interesting scenario is to integrate the functions of the
   first IVI gateway into the end-system.  In this case, the application
   softwares are IPv4-based and there is no need to have ALG support in
   the IVI gateway when it is communicating with IPv4 hosts.







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5.3.  IVI Multicast

   The IVI scheme can support IPv4/IPv6 communication of the protocol-
   independent specific-source sparse-mode multicast (PIM SSM) [RFC3171]
   [RFC3569] [RFC4607].

   (1) The IVI group address mapping rule: 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.


          -------------------------------------------------------
          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 7: IVI Multicast Group Address Mapping

   (2) The IVI multicast source address selection: The source address in
   IPv6 has to be IVI6(i) in order to perform reverse path forwarding
   (RPF) as required by PIM-SM.

   (3) The multicast protocol: The inter operation of PIM-SM for address
   families IPv4 and IPv6 can either be implemented via the application
   layer gateway or via the static join based on IGMPv3 and MLDv2 in
   IPv4 and IPv6, respectively.

   The Any Source Multicast (ASM) cannot be supported in the cross
   address-family environment, since IPv6 does not support the MSDP
   [RFC4611], and IPv4 does not support the embedded RP [RFC3956].


6.  IVI Host Operation

6.1.  IVI Address Assignment

   The IVI6 address has special format (for example IVI4=202.38.114.1/32
   and IVI6=2001:250:ffca:2672:0100::0/72), therefore, the stateless
   IPv6 address autoconfiguration cannot be used.  However, the IVI6 can
   be assigned to the IPv6 end system via manual configuration.  It is
   also possible to do stateful autoconfiguration via DHCPv6.







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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 work around is to use IVI6(i) as the default IPv6
   address of the host.  The long-term solution requires that the
   application be able to select the source addresses for different
   services.


7.  The IVI Implementation

7.1.  Linux Implementation

   The IVI translation algorithm presented in this document is
   implemented in the Linux OS and the source code can be downloaded
   [LINUX].  The example of the configuration is shown in Appendix A.

   The IVI DNS Configuration for the IVIG46(i) Addresses presented in
   this document can be downloaded [DNS].

7.2.  Testing Environment

   The IVI gateway based on the Linux implementation has been deployed
   between [CERNET] (IPv4 and partially dual-stack) and [CNGI-CERNET2]
   (pure IPv6) since March 2006.  The pure IPv6 web servers using IPv6
   addresses (IVI) behind IVI gateway can be accessed by the IPv4 hosts
   [IVI4], and also by the global IPv6 hosts [IVI6].

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

   The IVI6 manual configuration and the 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 scheme (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, the specific security issues for the IVI gateway
   implementation should be studied and addressed during the development
   of the IVI mechanisms.




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9.  IANA Considerations

   This memo adds no new IANA considerations.

   Note to RFC Editor: This section will have served its purpose if it
   correctly tells IANA that no new assignments or registries are
   required, or if those assignments or registries are created during
   the RFC publication process.  From the author's perspective, it may
   therefore be removed upon publication as an RFC at the RFC Editor's
   discretion.


10.  Contributors

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

   The authors would like to acknowledge the following contributors who
   provided helpful inputs concerning the IVI concept: Bill Manning,
   David Ward, Lixia Zhang, Jun Murai and Fred Baker.


11.  Acknowledgments

   The authors thank to the funding supports of the CERNET, CNGI-
   CERNET2, CNGI Research and Development, China "863" and China "973"
   projects.























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12.  Appendix A. The IVI gateway configuration example

   IVI 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:da8:ffca:2661:cc00::/70,
   #                  IVI4 = 202.38.97.204/30

   # configure IPv6 route
   route add -A inet6 2001:da8:ffca:2661:cc00::/70 \
   gw 2001:da8:aaae::206 dev eth0

   # config mapping for      source-PF = 2001:da8::/32
   # config mapping for destination-PF = 2001:da8::/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 202.38.97.204 255.255.255.252 10.0.0.1 \
   eth0 2001:da8:: 2001:da8::

   # IPv6-to-IPv4 mapping
   # mroute6 destination-PF destination-PF-pref-len
   /root/mroute6 2001:da8:ff00:: 40



                                 Figure 8













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13.  Appendix B. The traceroute results

   ivitraceroute


   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  202.38.17.186 1 ms 1 ms 1 ms
      202.38   AS4538
   6  202.38.17.186 1 ms 1 ms 1 ms
      202.38   AS4538
   7  202.38.17.186 2 ms 2 ms 2 ms
      202.38   AS4538
   8  202.38.17.186 2 ms 2 ms 2 ms
      202.38   AS4538
   9  202.38.17.186 4 ms 4 ms 3 ms
      202.38   AS4538
   10 202.38.108.2 2 ms 3 ms 3 ms


                                 Figure 9

   Note that the non-IVI IPv6 addresses are mapped to 202.38.17.186,
   which is defined in this document (the first two sections are the
   IPv4 prefix of /16 of the IVI gateway interface and the last two
   sections are the autonomous system number 4538).





















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   ivitraceroute6


   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 10



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   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::).


14.  References

14.1.  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.

   [RFC2008]  Rekhter, Y. and T. Li, "Implications of Various Address
              Allocation Policies for Internet Routing", BCP 7,
              RFC 2008, October 1996.

   [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.

   [RFC3171]  Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
              "IANA Guidelines for IPv4 Multicast Address Assignments",
              BCP 51, RFC 3171, August 2001.

   [RFC3956]  Savola, P. and B. Haberman, "Embedding the Rendezvous
              Point (RP) Address in an IPv6 Multicast Address",
              RFC 3956, November 2004.



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   [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.

   [RFC4611]  McBride, M., Meylor, J., and D. Meyer, "Multicast Source
              Discovery Protocol (MSDP) Deployment Scenarios", BCP 121,
              RFC 4611, 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.

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

14.2.  Informative References

   [APNIC]    Ito, K., "Large IPv4 address space Usage trial for Future
              IPv6 Deployment", http://www.apnic.net/meetings/25/
              program/policy/ito-large-ipv4-trial.pdf  .

   [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 count down: http://penrose.uk6x.com/".

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

   [I-D.bagnulo-behave-nat64]
              Bagnulo, M., Matthews, P., and I. van Beijnum, "NAT64/
              DNS64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers",
              draft-bagnulo-behave-nat64-00 (work in progress),



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              June 2008.

   [I-D.v6ops-nat64-pb-statement-req]
              Bagnulo, M., Baker, F., and I. van Beijnum, "IPv4/IPv6
              Coexistence and Transition: Requirements for solutions",
              draft-ietf-v6ops-nat64-pb-statement-req-00 (work in
              progress), May 2008.

   [IVI4]     "Test homepage for the IVI4(i): http://202.38.114.1/".

   [IVI6]     "Test homepage  for the IVI6(i):
              http://[2001:250:ffca:2672:0100::0]/".

   [JJI07]    Joseph, D., Chuang, J., and I. Stocia, "Modeling the
              Adoption of new Network Architectures", EECS Department,
              University of California, Berkeley Tech. Rep. UCB/
              EECS-2007-41, April 2007.

   [JSG2008]  "A Report of Japaness Study Group on Internet's Smooth
              Transition to IPv6:
              http://www.soumu.go.jp/joho_tsusin/eng/pdf/080617_1.pdf",
              June 2008.

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

   [MVB98]    Fiuczynski, M., Lam, V., and B.  Bershad , "The design and
              implementation of an ipv6/ipv4 network address and
              protocol translator", Proceedings of the USENIX Annual
              Technical Conference (NO 98), June 1998.

   [RFC1744]  Huston, G., "Observations on the Management of the
              Internet Address Space", RFC 1744, December 1994.

   [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.

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

   [RFC4925]  Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire
              Problem Statement", RFC 4925, July 2007.

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



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              Historic Status", RFC 4966, July 2007.


Authors' Addresses

   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 62785983
   Email: xing@cernet.edu.cn


   Maoke Chen
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 62785983
   Email: mk@cernet.edu.cn


   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 62785983
   Email: congxiao@cernet.edu.cn


   Hong Zhang
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 62785983
   Email: neilzh@gmail.com








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   Jianping Wu
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 62785983
   Email: jianping@cernet.edu.cn











































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