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IPv6 only capable resolver utilising NAT64
draft-momoka-v6ops-ipv6-only-resolver-01

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Momoka Yamamoto , Yasunobu Toyota
Last updated 2023-07-05 (Latest revision 2023-03-09)
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draft-momoka-v6ops-ipv6-only-resolver-01
v6ops                                            山本 桃歌 (M. Yamamoto)
Internet-Draft                      The University of Tokyo/WIDE Project
Intended status: Informational                     豊田 安信 (Y. Toyota)
Expires: 10 September 2023                  Keio University/WIDE Project
                                                            9 March 2023

               IPv6 only capable resolver utilising NAT64
                draft-momoka-v6ops-ipv6-only-resolver-01

Abstract

   By performing IPv4 to IPv6 translation, IPv6-only iterative resolvers
   can operate in an IPv6-only environment.  When a specific DNS zone is
   only served by an IPv4-only authoritative server, the iterative
   resolver will translate the IPv4 address to IPv6 to access the
   authoritative server's IPv4 address via stateful NAT64.  This
   mechanism allows IPv6-only iterative resolvers to initiate
   communications to IPv4-only authoritative servers.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the IPv6 Operations
   Working Group mailing list (v6ops@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/v6ops/.

   Source for this draft and an issue tracker can be found at
   https://github.com/momoka0122y/draft-momoka-ipv6-only-resolver.

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-
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 10 September 2023.

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Copyright Notice

   Copyright (c) 2023 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 (https://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
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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation and Problem Solved . . . . . . . . . . . . . . . .   3
     3.1.  Deployment Scenarios and Examples . . . . . . . . . . . .   4
   4.  Solution with existing protocols  . . . . . . . . . . . . . .   5
     4.1.  Finding an Authoritative server with only IPv4
           addresses . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Generation of the IPv6 Representations of IPv4
           Addresses . . . . . . . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Obtaining the Pref64::/n of the stateful NAT64  . . .   6
       4.2.2.  Performing the Synthesis  . . . . . . . . . . . . . .   6
     4.3.  Use of the iterative resolver as DNS64  . . . . . . . . .   6
   5.  Deployment Notes  . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document describes how an IPv6-only iterative resolver can use
   stateful NAT64 [NAT64] to connect to an IPv4-only authoritative
   server by performing IPv4 to IPv6 translation [RFC6052] when sending
   a query.  When a specific DNS zone is only served by an IPv4-only
   authoritative server (which has only an A record), an IPv6-only
   iterative resolver cannot resolve that zone due to having no access
   to an IPv4 network.  However, by performing IPv4 to IPv6 translation
   and utilizing the stateful NAT64, accessing an IPv4-only

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   authoritative server will be possible.

2.  Terminology

   *  Iterative resolver: A DNS server that repeatedly makes non-
      recursive queries and follows referrals and/or aliases.  The
      iterative resolution algorithm is described in Section 5.3.3 of
      [RFC1034]

   *  IPv6-only iterative resolvers: Iterative resolvers that only have
      IPv6 connectivity.

   *  IPv6/IPv4 translator: A device that translates IPv6 packets to
      IPv4 packets and vice versa.  It is only required that the
      communication initiated from the IPv6 side be supported.

   *  IPv4-only authoritative server: An authoritative server with only
      IPv4 connectivity, or an authoritative server with only an A
      record registered so it can only be accessed by IPv4.

3.  Motivation and Problem Solved

   An iterative resolver is one of the applications that require IPv4
   connectivity.  As stated in BCP91 [RFC3901], “every recursive name
   server SHOULD be either IPv4-only or dual stack.” This is because
   some authoritative servers do not support IPv6.  As of 2023, even
   some of the most frequently queried authoritative servers cannot be
   accessed via IPv6.  Without the utilization of NAT64, IPv6-only
   resolvers need to forward queries to a dual-stack recursive name
   server performing the iterative queries.

   The current situation where an iterative resolver cannot operate
   without IPv4 reachability may hinder the operation of a network's own
   iterative resolver in an IPv6-only network.  Therefore, this document
   describes how iterative resolvers can be used without issues in
   IPv6-only networks by utilizing NAT64.

   The NAT64/DNS64 mechanism enables IPv6-only clients in a network to
   communicate with remote IPv4-only nodes.  However, using literal IPv4
   addresses instead of DNS names will fail (unless 464XLAT [RFC6877] is
   used).  An iterative resolver cannot use the DNS64 because it is a
   service that uses literal IP addresses.  This problem can be solved
   by the iterative resolver converting IPv4 addresses to IPv6 by adding
   the Pref64::/n prefix, and thus the IPv6 packet conveying the query
   is directed to a stateful NAT64 gateway that converts the IPv6 packet
   to an IPv4 packet.  With this implementation, an iterative resolver
   can be operated even inside an IPv6-only network.

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3.1.  Deployment Scenarios and Examples

   The deployment of IPv6-only networks is in progress, as demonstrated
   by [draft-xie-v6ops-framework-md-ipv6only-underlay].  By operating an
   IPv6-only network and limiting IPv4 reachability to NAT64 devices,
   operators can reduce IPv4 usage and concentrate on IPv6 operations,
   which is generally believed to lower operational costs and optimize
   operations compared to a dual-stack environment.

   In examples of past RFCs, name resolvers have always had an IPv4
   address.  For example, all three use cases for DNS64 in RFC 6147 are
   dual-stack name servers.

               +---------------------+         +---------------+
               |IPv6 network         |         |    IPv4       |
               |              +-------------+  |  Internet     |
               |           |--| Name server |--|               |
               |           |  | with DNS64  |  |  +----+       |
               |  +----+   |  +-------------+  |  | H2 |       |
               |  | H1 |---|         |         |  +----+       |
               |  +----+   |   +------------+  |  192.0.2.1    |
               |           |---| IPv6/IPv4  |--|               |
               |           |   | Translator |  |               |
               |           |   +------------+  |               |
               |           |         |         |               |
               +---------------------+         +---------------+

      Figure 1: Example network setup of the use of DNS64 described in
                             RFC6147 Section7.1

               +---------------------+         +---------------+
               |IPv6 network         |         |    IPv4       |
               |                 +--------+    |  Internet     |
               |           |-----| Name   |----|               |
               | +-----+   |     | server |    |  +----+       |
               | | H1  |   |     +--------+    |  | H2 |       |
               | |with |---|         |         |  +----+       |
               | |DNS64|   |   +------------+  |  192.0.2.1    |
               | +----+    |---| IPv6/IPv4  |--|               |
               |           |   | Translator |  |               |
               |           |   +------------+  |               |
               |           |         |         |               |
               +---------------------+         +---------------+

      Figure 2: Example network setup of the use of DNS64 described in
                             RFC6147 Section7.2

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   However, it is necessary to consider the existence of an IPv6 single-
   stack full-service resolver.  In this document we consider an
   IPv6-only network where the iterative resolver is inside the
   IPv6-only network and does not have an IPv4 address.  This is to
   restrict IPv4 management to the NAT64 device.

         +--------------------------+         +----------------------+
         | IPv6 network             |         |    IPv4              |
         |                          |         |  Internet            |
         |                |         |         |                      |
         | +----------+   |         |         |  +--------------+    |
         | |IPv6-only |   |         |         |  |Authoritative |    |
         | |Iterative |   |         |         |  |server        |    |
         | |resolver  |---|   +------------+  |  +--------------+    |
         | +----------+   |---| IPv6/IPv4  |--|  192.0.2.1           |
         |                |   | Translator |  |                      |
         |                    +------------+  |                      |
         |                          |         |                      |
         +--------------------------+         +----------------------+

       Figure 3: Network example referenced in this document with an
                        IPv6-only iterative resolver

4.  Solution with existing protocols

   This section provides the mechanism of an IPv6-only capable resolver
   utilizing stateful NAT64.  We will assume we have one or more IPv6/
   IPv4 translator boxes [NAT64] connecting an IPv6 network to an IPv4
   network.  The stateful NAT64 device provides translation service and
   bridges the two networks, allowing communication between IPv6-only
   hosts and IPv4-only hosts.  The IPv6-only capable resolver proposed
   in this document performs the IPv4 to IPv6 synthesis for the resolver
   to communicate with IPv4 servers via stateful NAT64.  By using
   stateful NAT64, this IPv6-only iterative resolver can be considered
   dual stack in the sense of BCP91 [RFC3901].

4.1.  Finding an Authoritative server with only IPv4 addresses

   Before the iterative resolver sends queries to start a resolution, it
   may sort the SLIST data structure described in [RFC1034] to use the
   authoritative servers with IPv6 addresses first, and use servers with
   only an IPv4 address later.  If the resolver finds only an A record
   for an authoritative server, the resolver should perform address
   synthesis to the IPv4 address of the authoritative server, converting
   IPv4 addresses to IPv6 by adding the prefix Pref64::/n, so that the
   IPv6 packet carrying the query is routed to a stateful NAT64 gateway,
   which converts the IPv6 packet to an IPv4 packet.  It is not
   recommended to synthesise an IPv4 address of an authoritative server

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   if it also has an IPv6 address.

4.2.  Generation of the IPv6 Representations of IPv4 Addresses

4.2.1.  Obtaining the Pref64::/n of the stateful NAT64

   The iterative resolver can obtain the Pref64::/n used by the
   network's stateful NAT64 either by static configuration or by using
   discovery mechanisms.  Static configuration may be the most likely
   scenario, as the iterative resolver server may also serve as a DNS64
   server.

   The Port Control Protocol [RFC7225] or Router Advertisements
   [RFC8781] are two options available to the resolver if it wishes to
   use a discovery mechanism to find the Pref64::/n.  Using the
   mechanisms described in [RFC7050] or [draft-hunek-v6ops-nat64-srv]
   may not work because they require a resolver to work.

4.2.2.  Performing the Synthesis

   The address translation can be performed by following Section 2.3 of
   [RFC6052].  After the synthesis is done, the IPv6-only iterative
   resolver can send a query to the converted IPv6 address.

4.3.  Use of the iterative resolver as DNS64

   As the iterative resolver is used within an IPv6-only network, the
   server can also perform as DNS64 [DNS64] when an AAAA record is
   queried from a STUB resolver but the domain only has an A record.

5.  Deployment Notes

   TODO

6.  Security Considerations

   This algorithm does not change any part of the DNS message, just the
   packet type from IPv4 to IPv6 and the destination IP address from an
   IPv4 address to the synthesised IPv6 address, so there should be no
   problems with DNSSEC.

7.  IANA Considerations

   This document has no IANA actions.

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8.  Implementation Status

   BIND has a WIP branch.

   https://gitlab.isc.org/isc-projects/bind9/-/merge_requests/6334/
   commits

   Unbound has a PR from a contributor.

   https://github.com/NLnetLabs/unbound/issues/721

9.  References

9.1.  Normative References

   [DNS64]    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,
              <https://www.rfc-editor.org/rfc/rfc6147>.

   [NAT64]    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, <https://www.rfc-editor.org/rfc/rfc6146>.

   [RFC3901]  Durand, A. and J. Ihren, "DNS IPv6 Transport Operational
              Guidelines", BCP 91, RFC 3901, DOI 10.17487/RFC3901,
              September 2004, <https://www.rfc-editor.org/rfc/rfc3901>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc6052>.

9.2.  Informative References

   [draft-hunek-v6ops-nat64-srv]
              Huněk, M., "NAT64/DNS64 detection via SRV Records", Work
              in Progress, Internet-Draft, draft-hunek-v6ops-nat64-srv-
              04, 11 December 2022,
              <https://datatracker.ietf.org/doc/html/draft-hunek-v6ops-
              nat64-srv-04>.

   [draft-xie-v6ops-framework-md-ipv6only-underlay]
              Xie, C., Ma, C., Li, X., Mishra, G. S., Boucadair, M., and
              T. Graf, "Framework of Multi-domain IPv6-only Underlay
              Networks and IPv4 as a Service", Work in Progress,

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              Internet-Draft, draft-xie-v6ops-framework-md-ipv6only-
              underlay-05, 21 October 2022,
              <https://datatracker.ietf.org/doc/html/draft-xie-v6ops-
              framework-md-ipv6only-underlay-05>.

   [ietf-v6ops-ipv6-deployment]
              Fioccola, G., Volpato, P., Martinez, J. P., Mishra, G. S.,
              and C. Xie, "IPv6 Deployment Status", Work in Progress,
              Internet-Draft, draft-ietf-v6ops-ipv6-deployment-10, 1
              December 2022, <https://datatracker.ietf.org/doc/html/
              draft-ietf-v6ops-ipv6-deployment-10>.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/rfc/rfc1034>.

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

   [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,
              <https://www.rfc-editor.org/rfc/rfc7050>.

   [RFC7225]  Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
              Port Control Protocol (PCP)", RFC 7225,
              DOI 10.17487/RFC7225, May 2014,
              <https://www.rfc-editor.org/rfc/rfc7225>.

   [RFC8781]  Colitti, L. and J. Linkova, "Discovering PREF64 in Router
              Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
              2020, <https://www.rfc-editor.org/rfc/rfc8781>.

Acknowledgments

   TODO: acknowledge people.

   Thank you for reading this draft.

Authors' Addresses

   Momoka Yamamoto
   The University of Tokyo/WIDE Project
   Email: momoka.my6@gmail.com

   Additional contact information:

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      山本 桃歌
      The University of Tokyo/WIDE Project

   Yasunobu Toyota
   Keio University/WIDE Project
   Email: yas-nyan@sfc.wide.ad.jp

   Additional contact information:

      豊田 安信
      Keio University/WIDE Project

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