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Versions: 00 01

intarea Working Group                                              L. Li
Internet-Draft                                                    Y. Cui
Intended status: Standards Track                                  C. Liu
Expires: September 27, 2017                                        J. Wu
                                                     Tsinghua University
                                                                F. Baker

                                                       J. Palet Martinez
                                                       Consulintel, S.L.
                                                          March 26, 2017


              DHCPv6 Options for Discovery NAT64 Prefixes
              draft-li-intarea-nat64-prefix-dhcp-option-01

Abstract

   Several IPv6 transition mechanisms require the usage of stateless or
   stateful translators (commonly named as NAT64) able to allow IP/ICMP
   communication between IPv4 and IPv6 networks.

   Those translators are using either a default Well-Known Prefix (WKP),
   and/or one or several additional Network Specific Prefix (NSP), which
   need to be configured into the nodes willing to use the translator.
   Different translators will likely have different IPv6 prefixes, to
   attract traffic to the correct translator.  Thus, an automatic
   translator prefix discovery method is necessary.

   This document defines a DHCPv6-based method to inform DHCPv6 clients
   the set of IPv6 and IPv4 prefixes it serves.  This DHCPv6 option can
   be used by several transition mechanisms such as SIIT, 464XLAT, EAM.

Status of This Memo

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

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

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

   This Internet-Draft will expire on September 27, 2017.



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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
   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  New DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  NAT64 Prefix List Option Format . . . . . . . . . . . . .   4
     3.2.  NAT64 Prefix Option Format  . . . . . . . . . . . . . . .   4
   4.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Message Flow Illustration . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Stateless IP/ICMP Translation (SIIT) [RFC7915] describes the basic
   translation mechanism (NAT64), which is actually used as the base for
   most of the related translation protocols.

   Stateful NAT64 [RFC6146] describes how to allow IPv6-only clients to
   contact IPv4 servers using unicast UDP, TCP or ICMP.

   464XLAT [RFC6877] describes an IPv4-over-IPv6 solution as one
   technique for IPv4 service extension and encouragement of IPv6
   deployment.  The 464XLAT architecture uses IPv4/IPv6 translation,
   described in [RFC6144], and standardized in [RFC6052], [RFC7915], and
   [RFC6146].  It encourages the IPv6 transition by making IPv4 service
   reachable across IPv6-only networks and providing IPv6 and IPv4
   connectivity to single-stack IPv4 or IPv6 servers and peers.  In the



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   464XLAT architecture, the CLAT (customer-side NAT46 translator) must
   determine which of potentially several PLAT (provider-side NAT64
   translator) IPv6 prefix to use in order to send a packet to the PLAT
   with connectivity to its destination.

   [RFC7050] describes a mechanism to learn the PLAT-side IPv6 prefix
   for protocol translation by DNS64 [RFC6147].  Although it supports
   multiple PLAT-side prefix by responding with multiple AAAA records to
   a DNS64 query, it does not support mapping IPv4 prefixes to IPv6
   prefix, which would be required, for example, if one PLAT has
   connectivity to the general Internet following a default route,
   another has connectivity to a BGP peer, and a third has connectivity
   to a network using private addressing [RFC1918].  Therefore, in the
   scenario with multiple PLATs, [RFC7050] does not directly support
   destination-based IPv4 routing among PLATs; instead, the DNS64
   database must contain equivalent information.  It also requires the
   additional deployment of DNS64 service in customer-side networks,
   which is not required in 464XLAT deployment.  Indeed, this scenario,
   which may become very common in wired access networks, has not even
   been considered by [RFC7051].

   464XLAT is in fact, a usage case of Stateful NAT64.

   Explicit Address Mappings for Stateless IP/ICMP Translation [RFC7757]
   extends SIIT with an Explicit Address Mapping (EAM) algorithm to
   facilitate stateless IP/ICMP translation between arbitrary (non-
   IPv4-translatable) IPv6 endpoints and IPv4.

   This document proposes a method for the translator (NAT64) IPv6
   prefix discovery based on DHCPv6, which is widely deployed and
   supported in customer networks.  It defines two new DHCPv6 options
   for use by a DHCPv6 client to discover the translator IPv6
   prefix(es).  Also, the proposed mechanism can deal with the scenario
   with multiple independent DNS64 databases supporting separate
   translators.

2.  Requirements Language

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

3.  New DHCPv6 Option








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3.1.  NAT64 Prefix List Option Format

   The NAT64 Prefix List Option is a container for NAT64 Prefix
   Option(s).  A NAT64 Prefix List Option MAY contain multiple NAT64
   Prefix Options.

   The format of the NAT64 Prefix List Option is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   OPTION_NAT64_PREFIX_LIST    |       option-length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                      NAT64_PREFIX-options                     +
   |                        (see Figure 2)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Format of NAT64 Prefix List Option

   o  option-code: OPTION_NAT64_PREFIX_LIST (TBA1)

   o  option-length: length of NAT64_PREFIX-options, specified in
      octets.

   o  NAT64_PREFIX-options: one or more OPTION_NAT64_PREFIX options.

3.2.  NAT64 Prefix Option Format

   The NAT64 Prefix Option is encapsulated in the NAT64 Prefix List
   Option.  This option allows the mapping of destination IPv4 address
   ranges (contained in the IPv4 Prefix List) to a NAT64 IPv6 prefix.
   If there is more than one such prefix, each prefix comes in its own
   option, with its associated IPv4 prefix list.  In this way, the
   DHCPv6 client can select the NAT64 with the corresponding destination
   IPv4 address.

   The format of the NAT64 Prefix Option is:













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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     OPTION_NAT64_PREFIX      |         option-length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         NAT64-Type           |         NAT64-prelen           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         NAT64-prefix                          |
   |                       (variable length)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         NAT64-suffix                          |
   |                       (variable length)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                         (optional)                            .
   .              IPv4 Prefix List (variable length)               .
   .                       (see Figure 3)                          .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: Format of NAT64 Prefix Option

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  IPv4-prelen  |            IPv4 Prefix (32 bits)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    (cont.)    |  IPv4-prelen  |     IPv4 Prefix (32 bits)     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      IPv4 Prefix (cont.)      |             ...               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: Format of IPv4 Prefix List field

   o  option-code: OPTION_NAT64_PREFIX (TBA2)

   o  type-field: NAT64-Type (TBA3)

   o  option-length: 4 + length of NAT64-prefix + length of NAT64-suffix
      + length of IPv4 Prefix List, specified in octets.

   o  NAT64-prelen: length of NAT64-prefix, in octets.  The values
      allowed are: 4, 5, 6, 7, 8 or 12, as indicated in Section 2.2 of
      [RFC6052].

   o  NAT64-prefix: The NAT64 IPv6 prefix to be used by the DHCPv6
      client for the IPv6 address synthesis.  MUST follow the
      specifications of [RFC6052].



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   o  NAT64-suffix: The NAT64 suffix to be used by the DHCPv6 client for
      the IPv6 address synthesis, specified in Section 2.2 of [RFC6052].
      The length of this field, in octets is 12 - NAT64-prelen.  Not
      used in case of using the WKP (i.e., 64:ff9b::/96) or any other
      NSP (Network-Specific Prefix) which a length of 96 bits (/96).

   o  IPv4 Prefix List: This is an optional field.  The format of the
      IPv4 Prefix List is shown in Figure 3.  It is a list of zero or
      more IPv4 Prefixes.  Each entry is formed by IPv4-prelen and IPv4
      Prefix.  The total length of the field is 5*number of IPv4
      prefixes.

   o  IPv4-prelen: The length of the IPv4 Prefix.

   o  IPv4 Prefix: The destination-based IPv4 Prefix.  The length is 4
      octets.

4.  Client Behavior

   The client requests the OPTION_NAT64_PREFIX_LIST option using the
   Option Request option (ORO) in every Solicit, Request, Renew, Rebind,
   and Information-request message.  The NAT64-Type field defines the
   mechanism being used.  If the DHCPv6 server includes the
   OPTION_NAT64_PREFIX_LIST option in its response, the DHCPv6 client
   may use the contained NAT64-prefix to translate the destination IPv4
   address into the destination IPv6 address.

   When receiving the OPTION_NAT64_PREFIX option with IPv4 Prefix List,
   the DHCPv6 client MUST record the received IPv6 prefix and the
   corresponding IPv4 prefixes in IPv4 Prefix List.  When receiving the
   OPTION_NAT64_PREFIX option without IPv4 Prefix List, the DHCPv6
   client MUST treat the IPv6 prefix and the default IPv4 prefix
   0.0.0.0/0 as one of the records.

   If the DHCPv6 client loses contact with the DHCPv6 server, the DHCPv6
   client SHOULD clear the prefix(es) it learned from the DHCPv6 server.

   When translating the destination IPv4 address into the destination
   IPv6 address, DHCPv6 client MUST search an IPv4 routing database
   using the longest-match-first rule and select the IPv6 prefix
   offering that IPv4 prefix.

   In order to make sure that the client has the right information, only
   a single container with all the current NAT64 Prefix List Option is
   allowed.  When a new one is received, the client MUST clear the
   previous NAT64 Prefix List Option information and use only the new
   one.




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5.  Message Flow Illustration

   The figure below shows an example of message flow for a Client
   learning IPv6 prefixes using DHCPv6.

   In this example, two IPv6 prefixes are provided by the DHCPv6 server.
   The first IPv6 prefix is 2001:db8:122:300::/56, the corresponding
   IPv4 prefixes are 192.0.2.0/24 and 198.51.100.0/24.  The second IPv6
   prefix is 2001:db8:122::/48, the corresponding IPv4 prefix is
   192.0.2.128/25.

   When the DHCPv6 client receives the packet with destination IPv4
   address 192.0.2.1, according to the rule of longest prefix match, the
   NAT64 with IPv6 prefix 2001:db8:122::/48 is chosen.  In the same way,
   the NAT64 with IPv6 prefix 2001:db8:122::/48 is chosen.




































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   +---------------+                                +-----------------+
   | DHCPv6 Client |                                |  DHCPv6 server  |
   +---------------+                                +-----------------+
        |            DHCPv6 query for IPv6 prefix            |
        |--------------------------------------------------->|
        |   ORO with OPTION_NAT64_PREFIX_LIST                |
        |                                                    |
        |   DHCPv6 response with:                            |
        |      NAT64PREFIX{                                  |
        |         NAT64-v6-pre = 2001:db8:122:300::/56       |
        |         NAT64-v4-pre = 192.0.2.0/24                |
        |         NAT64-v4-pre = 198.51.100.0/24}            |
        |      NAT64PREFIX{                                  |
        |         NAT64-v6-pre = 2001:db8:122::/48           |
        |         NAT64-v4-pre = 192.0.2.128/25}             |
        |<---------------------------------------------------|
        |                                                    |
        |
        |                     +-----------------+   +-----------------+
        |                     |     NAT64 1     |   |     NAT64 2     |
        |                     +-----------------+   +-----------------+
        |                        NAT64-v6-pre =        NAT64-v6-pre =
        |                    2001:db8:122:300::/56  2001:db8:122::/48
        |                        NAT64-v4-pre =        NAT64-v4-pre =
        |                        192.0.2.0/24          192.0.2.128/25
        |                        198.51.100.0/24             |
        |                              |                     |
        |       Dest IPv4 addr:        |                     |
        |        192.0.2.1             |                     |
        |       Dest IPv6 addr:        |                     |
        |  2001:db8:122:300::c000:201  |                     |
        |----------------------------->|                     |
        |                              |                     |
        |                                                    |
        |     Dest IPv4 addr: 192.0.2.193                    |
        |     Dest IPv6 addr: 2001:db8:122::c000:2c1         |
        |--------------------------------------------------->|

                   Figure 4: Example of the process flow

6.  Security Considerations

   Considerations for security in this type of environment are primarily
   around the operation of the DHCPv6 protocol and the databases it
   uses.

   In the DHCPv6 server, should the database be compromised, it will
   deliver incorrect data to its DHCPv6 clients.  In the DHCPv6 client,



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   should its database be compromised by attack or polluted by an
   incorrect DHCPv6 server database, it will route data incorrectly.  In
   both cases, the security of the systems and their databases in an
   operational matter, not managed by protocol.

   However, the operation of the DHCPv6 protocol itself is also required
   to be correct - the server and its clients must recognize valid
   requests and reject invalid ones.  Therefore, DHCPv6 exchanges MUST
   be secured as described in [RFC3315].

7.  IANA Considerations

   We request that IANA allocate two DHCPv6 option codes for use by
   OPTION_V6_PLATPREFIX_LIST and OPTION_V6_PLATPREFIX from the "Option
   Codes" table.  Similarly, a request to IANA for assigning the
   NAT64-Type field codes.  The following initial values are assigned in
   this document (values are 16-bit unsigned intergers).

                         Name       |  Value  |   RFC
                   -----------------+---------+---------
                      Unspecified   |  0x00   | RFC6052
                         SIIT       |  0x01   | RFC7915
                     Stateful NAT64 |  0x02   | RFC6146
                       EAM-SIIT     |  0x03   | RFC7757

8.  Acknowledgements

   The authors will like to recognize the inputs from Tore Anderson in a
   previous version of this work.  Mohamed Boucadair provided very
   significant inputs.

9.  References

9.1.  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>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.







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   [RFC6877]  Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
              Combination of Stateful and Stateless Translation",
              RFC 6877, DOI 10.17487/RFC6877, April 2013,
              <http://www.rfc-editor.org/info/rfc6877>.

9.2.  Informative References

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [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>.

   [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>.

   [RFC7050]  Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
              the IPv6 Prefix Used for IPv6 Address Synthesis",
              RFC 7050, DOI 10.17487/RFC7050, November 2013,
              <http://www.rfc-editor.org/info/rfc7050>.

   [RFC7051]  Korhonen, J., Ed. and T. Savolainen, Ed., "Analysis of
              Solution Proposals for Hosts to Learn NAT64 Prefix",
              RFC 7051, DOI 10.17487/RFC7051, November 2013,
              <http://www.rfc-editor.org/info/rfc7051>.

   [RFC7757]  Anderson, T. and A. Leiva Popper, "Explicit Address
              Mappings for Stateless IP/ICMP Translation", RFC 7757,
              DOI 10.17487/RFC7757, February 2016,
              <http://www.rfc-editor.org/info/rfc7757>.





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   [RFC7915]  Bao, C., Li, X., Baker, F., Anderson, T., and F. Gont,
              "IP/ICMP Translation Algorithm", RFC 7915,
              DOI 10.17487/RFC7915, June 2016,
              <http://www.rfc-editor.org/info/rfc7915>.

Authors' Addresses

   Lishan Li
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-15201441862
   Email: lilishan9248@126.com


   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn


   Cong Liu
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6278-5822
   Email: gnocuil@gmail.com


   Jianping Wu
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6278-5983
   Email: jianping@cernet.edu.cn


   Fred Baker
   Goleta, CA  93117
   United States

   Email: fredbaker.ietf@gmail.com



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   Jordi Palet Martinez
   Consulintel, S.L.
   La Navata - Galapagar  28420
   Spain

   Email: jordi.palet@consulintel.es













































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