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Network Working Group                                             C. Bao
Internet-Draft                                                     X. Li
Intended status: Informational                                   Y. Zhai
Expires: August 1, 2017                                         W. Shang
                                                  CERNET Center/Tsinghua
                                                              University
                                                        January 28, 2017


               dIVI: Dual-Stateless IPv4/IPv6 Translation
                        draft-xli-behave-divi-07

Abstract

   This document presents the concepts and the implementations of
   address-sharing dual-stateless IPv4/IPv6 translation (dIVI).

   The dIVI is an extension of 1:1 stateless IPv4/IPv6 translation with
   features of IPv4 address sharing and dual translation.  The major
   benefits of those extensions are using public IPv4 addresses more
   effectively and removing the requirements of DNS64 and ALG, without
   loosing the stateless, end-to-end address transparency and
   bidirectional-initiated communications.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 1, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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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.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminologies  . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Port Mapping Algorithm and Address Format Extension  . . . . .  5
     4.1.  Port Mapping Algorithm . . . . . . . . . . . . . . . . . .  5
     4.2.  Address Format Extensions  . . . . . . . . . . . . . . . .  6
     4.3.  Stateless Translation Algorithm with Address Sharing . . .  7
     4.4.  Partial-state Translation Algorithm with Address
           Sharing  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Dual Stateless Translation . . . . . . . . . . . . . . . . . .  7
     5.1.  Header Translation and MTU Handling  . . . . . . . . . . .  8
     5.2.  Port Mapping Algorithm in CPE  . . . . . . . . . . . . . .  8
   6.  Implementation Considerations  . . . . . . . . . . . . . . . .  8
     6.1.  Host implementation  . . . . . . . . . . . . . . . . . . .  9
     6.2.  Port Mapping in the Core Translator  . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Address Format and Workflow Examples  . . . . . . . . 11
     A.1.  The address-sharing host on an IPv6 network initiates
           communication  . . . . . . . . . . . . . . . . . . . . . . 12
     A.2.  A host in the IPv4 Internet initiates communication  . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13














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1.  Introduction

   The experiences for the IPv6 deployment in the past 10 years strongly
   indicate that for a successful transition, the communication between
   IPv4 and IPv6 address families should be supported.

   Recently, the stateless and stateful IPv4/IPv6 translation methods
   are developed and became the IETF standards.  The original stateless
   IPv4/IPv6 translation (stateless 1:1 IVI) is scalable, maintains the
   end-to-end address transparency and support both IPv6 initiated and
   IPv4 initiated communications [RFC6052], [RFC6144], [RFC6145],
   [RFC6147], [RFC6219].  But it can not use the IPv4 addresses
   effectively.  The stateful IPv4/IPv6 translation can share the IPv4
   addresses among IPv6 hosts, but it only supports IPv6 initiated
   communication [RFC6052], [RFC6144], [RFC6145], [RFC6146], [RFC6147].
   In addition, both stateless and stateful IPv4/IPv6 translation
   technologies require the application layer gateway (ALG) for the
   applications which embed IP address literals.

   In this document, we present concepts and the implementations of the
   dual-stateless IPv4/IPv6 translation (dIVI).  The dIVI can solve the
   IPv4 address sharing and the ALG problems mentioned above, though
   still keeps the stateless, end-to-end address transparency and
   supporting of both IPv6 initiated and IPv4 initiated communications.
   The dIVI is in the family of stateless IPv4/IPv6 translation, along
   with IVI and dIVI-PD [I-D.xli-behave-divi-pd].  These techniques are
   used for the following scenarios with second translation extension
   defined in [RFC6144].

   o  Scenario 1: IPv4 hosts via an IPv6 network to the IPv4 Internet.

   o  Scenario 2: The IPv4 Internet via an IPv6 network to IPv4 hosts.

   o  Scenario 5: An IPv6 network via an IPv4 network to IPv4 hosts.

   o  Scenario 6: IPv4 hosts via an IPv4 network to an IPv6 network.


2.  Applicability

   The address sharing dual stateless IPv4/IPv6 translation (dIVI) is
   shown in the following figure.









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                                                   -----     ------
                                                .-|CPE.0|---|Host.0|
                                               /   -----     ------
           ------                   -----     |
         /  The   \    ------     /  An   \   |    -----     ------
        |   IPv4   |--| 1:N  |---|   IPv6  |------|CPE.1|---|Host.1|
         \Internet/   | XLAT |    \Network/   |    -----     ------
           ------      ------       -----     |
                                              |\   -----     ------
                                              |  -|CPE.2|---|Host.2|
                                              |    -----     ------
                                              |         ......
                                               \   -----     ------
                                                 -|CPE.K|---|Host.K|
                                                   -----     ------
                                                        ......

                              Figure 1: dIVI

   Where

   o  The 1:N XLAT (first translator) is the IPv4/IPv6 translator
      perform stateless 1:N translation between the IPv4 Internet and an
      IPv6 network.

   o  The CPE.0 to CPE.K (second translators) are 1:1 IPv6/IPv4
      translators/IPv6 routers which also perform port mapping function
      for Host.x when it is communicating with the IPv4 Internet with
      IPv4 address sharing.

   o  The Host.1 to Host.N are the dual-stack hosts.

   The IPv6 network routes the IPv6 more specific routes of the IPv4-
   translatable addresses (longer than /64) defined in Section 5 of this
   document to corresponding CPEs.  In the case of prefix delegation
   (shorter than /64), the dual stateless IPv4/IPv6 translation with
   prefix delegation (dIVI-pd) defined in [I-D.xli-behave-divi-pd] can
   be used.


3.  Terminologies

   This document uses the terminologies defined in [RFC6144].

   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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4.  Port Mapping Algorithm and Address Format Extension

4.1.  Port Mapping Algorithm

   The dual stateless IPv4/IPv6 translation (dIVI) uses the port mapping
   algorithm defined in [I-D.bcx-behave-address-fmt-extension].

   For given sharing ratio (R) and the maximum number of continue ports
   (M), the generalized modulus algorithm is defined as

   1.  The port number (P) of a given PSID (K) is composed of

       P = R*M*j + M*K + i

       Where
       o PSID: K=0 to R-1
       o Port range index: j = (1024/M)/R to ((65536/M)/R)-1, if the
       well-known port numbers (0-1023) are excluded.
       o Port continue index: i=0 to M-1

   2.  The PSID (K) of a given port number (P) is determined by

       K = (floor(P/M)) % R

       Where
       o % is modular operator
       o floor(arg) is a function returns the largest integer not
       greater than arg

   3.  The well-known port number (0-1023) can be used, if additional
       port mapping rule is defined.

   For example, for R=128, M=4

              Port range-1             | Port rang-2             | Port
    -------------------------------------------------------------------
    PSID=0   | 1024, 1025, 1026, 1027, | 1536, 1537, 1538, 1539, | 2048
    PSID=1   | 1028, 1029, 1030, 1031, | 1540, 1541, 1542, 1543, | ....
    PSID=2   | 1032, 1033, 1034, 1035, | 1544, 1545, 1546, 1547, | ....
    PSID=3   | 1036, 1037, 1038, 1039, | 1548, 1549, 1550, 1551, | ....
    ...
    PSID=127 | 1532, 1533, 1534, 1535, | 2044, 2045, 2046, 2047, | ....

                             Figure 2: Example







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4.2.  Address Format Extensions

   The dual stateless IPv4/IPv6 translation (dIVI) uses the address
   format extension defined in [I-D.bcx-behave-address-fmt-extension].

    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-|
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |32|     prefix    |v4(32)         | u | PSID  | 0             | Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |40|     prefix        |v4(24)     | u |(8)| PSID | 0          | Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |48|     prefix            |v4(16) | u | (16)  | PSID | 0      | Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |56|     prefix                |(8)| u |  v4(24)   | PSID | 0  | Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |64|     prefix                    | u |   v4(32)      |PSID |0| Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                         Figure 3: Address Format

   Where PL designates the prefix length.

   The PSID prefix length (Q) is encoded in the last octet (bits 120-
   127) to indicate the number of ports can be used.  When Q=0, the
   extended address format will become the address format defined in
   [RFC6052].  The relations between Q, the sharing ratio (R), the
   maximum continue port range (M) and the number of ports can be shown
   in the following figure.

                  Q   Ratio  |  Maximum M  | # of Ports
                 ------------------------------------------
                  0    1:1         65,536     65,536
                  1    1:2         32,786     32,786
                  2    1:4         16,384     16,384
                  3    1:8          8,192      8,192
                  4    1:16         4,096      4,096
                  5    1:32         2,048      2,048
                  6    1:64         1,024      1,024
                  7    1:128          512        512
                  8    1:256          256        256
                  9    1:512          128        128
                 10    1:1,024         64         64
                 11    1:2,048         32         32
                 12    1:4,096         16         16
                 ------------------------------------------

                           Figure 4: Port Range



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4.3.  Stateless Translation Algorithm with Address Sharing

   For the stateless translation, the IPv6 nodes are required to follow
   the port number range defined by the extended IPv4-translatable
   address format when communicating with the IPv4 Internet.  The port
   number handling algorithm is:

   o  If the packets are from the IPv4 Internet to an IPv6 network, the
      IPv4 source addresses are translated to the IPv4-converted
      addresses and the source port numbers are unchanged before and
      after translation; the IPv4 destination addresses are translated
      to the extended IPv4-translatable addresses based on the
      destination port number and the destination port numbers are
      unchanged before and after translation.  Note that this means that
      only a specific IPv6 node can receive the packets for a specific
      port number.

   o  If the packets are from an IPv6 network to the IPv4 Internet, the
      IPv6 source addresses and the source port numbers are checked, if
      the source port number matches the port number range defined by
      the extended IPv4-translatable address format, the IPv6 source
      addresses (which are the IPv4-translatable addresses) are
      translated to the IPv4 addresses and the source port numbers are
      unchanged before and after translation; the destination IPv6
      addresses (which are the IPv4-converted addresses) are translated
      to the IPv4 destination addresses and the destination port numbers
      are unchanged before and after translation.  However, if the
      source port number does not match the port number range defined by
      the extended IPv4-translatable address format, the packets will be
      dropped.

4.4.  Partial-state Translation Algorithm with Address Sharing

   Stateless translation requires that IPv6 nodes generate source port
   number in the range defined by the extended IPv4-translatable
   address.  If this condition does not hold, the partial-state
   translation algorithm can be used, which can map the random source
   port number to the extended IPv4-translatable address defined source
   port number range.  Due to the requirement of the states in the
   translator for the port mapping (no states required for the address
   mapping), it is named partial state.  The technical details of the
   port mapping state maintaining algorithm is an implementation issue
   (see Section 6.2).


5.  Dual Stateless Translation

   In general dual stateful IPv4/IPv6 translations (IPv4-IPv6-IPv4) are



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   considered harmful, since the two translators cannot synchronize the
   parameter to translate the IPv4 address to its original format.
   However, the dual stateless IPv4/IPv6 translation (IPv4-IPv6-IPv4)
   can translate the IPv4 address to its original format based on
   algorithm.  There are several reasons for using dual stateless IPv4/
   IPv6 translation.

   o  The second translator (CPE) performs the port-set mapping
      algorithm discussed in Section 4.1, therefore, there is no need to
      modify the host with IPv4 address sharing.

   o  ALG cannot be developed for some applications, or has not been
      developed during the early transition stage.

   o  DNS64 is not allowed (due to DNSSec, etc.).

   o  All the IPv6 packet processing tools (routing, policy based
      routing, packet filtering, traffic shaping based on layer 3 and
      layer 4 can be used for dual stateless translation, while new
      tools are required for encapsulation and tunneling.

5.1.  Header Translation and MTU Handling

   The general header and ICMP translation specifications are defined in
   [RFC6145].

   Special MTU and fragmentation actions must be taken in the case of
   dual translation.

5.2.  Port Mapping Algorithm in CPE

   The port mapping algorithm is straightforward.  The port mapping
   device maintains a database of allowed port numbers defined by the
   extended IPv4-translatable address format.  If the packets from the
   host contains the source port number which do not match the port
   number range defined by the extended IPv4-translatable address
   format, the CPE will map the source port number to an allowed one and
   keep the record in the database for mapping back the returning
   packets and all the packets in the same session.

   The port number database can be refreshed via the corresponding
   transport layer flags for TCP or via timeout for UDP sessions.


6.  Implementation Considerations






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6.1.  Host implementation

   For the wireless mobile Internet environment, it is not difficult to
   modify the operating system of the mobile device, therefore it
   possible to integrate the port mapping algorithm and the second IPv4/
   IPv6 translation function in the mobile device, which is an IPv6-only
   host to the network and has a dual-stack socket API for the
   applications running on this host.

6.2.  Port Mapping in the Core Translator

   The port mapping can be performed in the core translator, in this
   case, there is no need to have the second translator (CPE.x) and no
   need to modify the IPv6 host for the port restriction requirements.


7.  Security Considerations

   There are no security considerations in this document.


8.  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.


9.  Acknowledgments

   The authors would like to acknowledge the following contributors in
   the different phases of the address-sharing IVI and dIVI development:
   Maoke Chen, Hong Zhang, Weifeng Jiang, Yuncehng Zhu and Guoliang Han.

   The authors would like to acknowledge the following contributors who
   provided helpful inputs: Dan Wing, Fred Baker, Dave Thaler, Randy
   Bush, Kevin Yin, Wojciech Dec and Rajiv Asati.


10.  References






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10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <http://www.rfc-editor.org/info/rfc2473>.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              DOI 10.17487/RFC6052, October 2010,
              <http://www.rfc-editor.org/info/rfc6052>.

   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, DOI 10.17487/RFC6144,
              April 2011, <http://www.rfc-editor.org/info/rfc6144>.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, DOI 10.17487/RFC6145, April 2011,
              <http://www.rfc-editor.org/info/rfc6145>.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
              April 2011, <http://www.rfc-editor.org/info/rfc6146>.

   [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,
              DOI 10.17487/RFC6147, April 2011,
              <http://www.rfc-editor.org/info/rfc6147>.

   [RFC6219]  Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
              China Education and Research Network (CERNET) IVI
              Translation Design and Deployment for the IPv4/IPv6
              Coexistence and Transition", RFC 6219, DOI 10.17487/
              RFC6219, May 2011,
              <http://www.rfc-editor.org/info/rfc6219>.

10.2.  Informative References

   [I-D.bcx-behave-address-fmt-extension]
              Bao, C. and X. Li, "Extended IPv6 Addressing for Encoding
              Port Range", draft-bcx-behave-address-fmt-extension-09
              (work in progress), January 2016.



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   [I-D.xli-behave-divi-pd]
              Sun, Q., Asati, R., Xie, C., Li, X., Dec, W., and C. Bao,
              "dIVI-pd: Dual-Stateless IPv4/IPv6 Translation with Prefix
              Delegation", draft-xli-behave-divi-pd-01 (work in
              progress), September 2011.


Appendix A.  Address Format and Workflow Examples

   The prefix we selected is 2001:da8:a4a6::/48.  The formats of the
   IPv4-converted address and the IPv4-translatable address are:

                           IPv4-converted address
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |PL| 0-------------32--40--48--56--64--72--80--88--92--104-112-120-|
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |48|     prefix            |v4(16) | u | (16)  |      0            |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                           IPv4-translatable address
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |PL| 0-------------32--40--48--56--64--72--80--88--92--104-112-120-|
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
    |48|     prefix            |v4(16) | u | (16)  |PSID|    0     | Q |
    +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                         Figure 5: Address format

   The sharing ratio R=16, so the PSID has 4 bits (Q=4) and each PSID
   can have (4096-1024/16)= 4032 concurrent port numbers to use.  The
   continue port range M=4, so each PSID will have 1008 available port
   range.

   The host in the IPv4 Internet is 202.112.35.254 and the corresponding
   IPv4-converted address is 2001:da8:a4a6:ca70:23:fe00::

   The shared IPv4 address is 202.38.117.1 with sharing ratio 16, the
   corresponding IPv4-translatable addresses are

     PSID=0    2001:da8:a4a6:ca26:75:100::4
     PSID=1    2001:da8:a4a6:ca26:75:110::4
     PSID=2    2001:da8:a4a6:ca26:75:120::4
     PSID=3    2001:da8:a4a6:ca26:75:130::4
     PSID=4    2001:da8:a4a6:ca26:75:140::4
     PSID=5    2001:da8:a4a6:ca26:75:150::4
     PSID=6    2001:da8:a4a6:ca26:75:160::4
     PSID=7    2001:da8:a4a6:ca26:75:170::4
     PSID=8    2001:da8:a4a6:ca26:75:180::4



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     PSID=9    2001:da8:a4a6:ca26:75:190::4
     PSID=10   2001:da8:a4a6:ca26:75:1a0::4
     PSID=11   2001:da8:a4a6:ca26:75:1b0::4
     PSID=12   2001:da8:a4a6:ca26:75:1c0::4
     PSID=13   2001:da8:a4a6:ca26:75:1d0::4
     PSID=14   2001:da8:a4a6:ca26:75:1e0::4
     PSID=15   2001:da8:a4a6:ca26:75:1f0::4

A.1.  The address-sharing host on an IPv6 network initiates
      communication

   An address-sharing Host.0 (202.38.117.1) in an IPv6 network behind
   CPE initiates communication with Host 202.112.35.254:80 in the IPv4
   Internet

       On the Host.0
       Src#p= 202.38.117.1#1881 (random port)
       Dst#p= 202.112.35.254#80 (server port)

       On an IPv6 network
       Src#p= [2001:da8:a4a6:ca26:75:0100::4]#8192 (CPE mapped port)
       Dst#p= [2001:da8:a4a6:ca70:23:fe00::]#80 (server port)

       On the IPv4 Internet
       Src#p= 202.38.117.1#8192 (CPE mapped port)
       Dst#p= 202.112.35.254#80 (server port)

                       Figure 6: Workflow Example 1

   The returning packets reverse the Src and Dst, the CPE maps the "CPE
   mapped port (8192)" back to the original "random port (1881)".

A.2.  A host in the IPv4 Internet initiates communication

   A host 202.112.35.254 in the IPv4 Internet initiates communication to
   the address-sharing Host.0 (202.38.117.1#4096)















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       On the IPv4 Internet
       Src#p= 202.112.35.254#36567 (random port)
       Dst#p= 202.38.117.1#4096 (server port)

       On an IPv6 network
       Src#p= [2001:da8:a4a6:ca70:23:fe00::]#36567 (random port)
       Dst#p= [2001:da8:a4a6:ca26:75:0100::4]#4096 (server port)

       On the Host.0
       Src#p= 202.112.35.254#36567 (random port)
       Dst#p= 202.38.117.1#4096 (server port)

                       Figure 7: Workflow Example 2

   The returning packets reverse the Src and Dst.


Authors' Addresses

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

   Phone: +86 10-62785983
   Email: congxiao@cernet.edu.cn


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

   Phone: +86 10-62785983
   Email: xing@cernet.edu.cn


   Yu Zhai
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 10-62785983
   Email: jacky.zhai@gmail.com




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   Wentao Shang
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing  100084
   CN

   Phone: +86 10-62785983
   Email: wentaoshang@gmail.com











































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