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DNS IPv6 Transport Operational Guidelines
draft-momoka-dnsop-3901bis-03

Document Type Active Internet-Draft (individual)
Authors Momoka Yamamoto , Tobias Fiebig
Last updated 2023-10-23
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draft-momoka-dnsop-3901bis-03
dnsop                                                          Momoka. Y
Internet-Draft                      The University of Tokyo/WIDE Project
Obsoletes: 3901 (if approved)                                  T. Fiebig
Intended status: Informational                                   MPI-INF
Expires: 22 April 2024                                   20 October 2023

               DNS IPv6 Transport Operational Guidelines
                     draft-momoka-dnsop-3901bis-03

Abstract

   This memo provides guidelines and documents Best Current Practice for
   operating authoritative and recursive DNS servers given that queries
   and responses are carried in a mixed environment of IPv4 and IPv6
   networks.  It expands beyond [RFC3901] in so far that it now
   considers the reality of progressing IPv4 exhaustion, which will make
   IPv6-only resolvers necessary in the long-term.

   This document obsoletes RFC 3901. (if approved)

Discussion Venues

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

   Source for this draft and an issue tracker can be found at
   https://github.com/momoka0122y/draft-dnsop-3901bis.

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 https://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 22 April 2024.

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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
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Name Space Fragmentation  . . . . . . . . . . . . . . . . . .   4
     3.1.  Misconfigurations Causing IP Version Related Name Space
           Fragmentation . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Reasons for Intentional IP Version Related Name Space
           Fragmentation . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Policy Based Avoidance of Name Space Fragmentation  . . . . .   5
     4.1.  Guidelines for DNS Zone Configuration . . . . . . . . . .   6
     4.2.  Guidelines for DNS Resolvers  . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     Normative References  . . . . . . . . . . . . . . . . . . . . .   7
     Informative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Despite IPv6 being first discussed in the mid 1990s [RFC1883],
   consistent deployment throughout the whole Internet has not yet been
   accomplished [RFC9386].  Hence, today, the Internet is a mixture of
   IPv4, dual-stack (networks connected via both IP versions), and IPv6
   networks.

   This creates a complex landscape where authoritative name servers
   might be accessible only via specific network protocols
   [V6DNSRDY-23].  At the same time, DNS resolvers may only be able to
   access the Internet via either IPv4 or IPv6.  This poses a challenge
   for such resolvers because they may encounter names for which queries

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   must be directed to authoritative name servers with which they do not
   share an IP version during the name resolution process
   [draft-momoka-v6ops-ipv6-only-resolver-02].

   In this document, we discuss:

   *  IP version related namespace fragmentation and best-practices for
      avoiding it.

   *  Guidelines for configuring authoritative name servers for zones.

   *  Guidelines for operating recursive DNS resolvers.

   While transitional technologies and dual-stack setups may mitigate
   some of the issues of DNS resolution in a mixed protocol-version
   Internet, making DNS data accessible over both IPv4 and IPv6 is the
   most robust and flexible approach, as it allows resolvers to reach
   the information they need without requiring intermediary translation
   or forwarding services which may introduce additional failure cases.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   This document uses DNS terminology as described in [RFC8499].
   Furthermore, the following terms are used with a defined meaning:

   IPv4 name server:
      This refers to a name server providing DNS services reachable via
      IPv4.  It does not imply anything about what DNS data is served,
      but requires DNS queries to be received and answered over IPv4.

   IPv6 name server:
      This refers to a name server providing DNS services reachable via
      IPv6.  It does not imply anything about what DNS data is served,
      but requires DNS queries to be received and answered over IPv6.

   Dual-stack name server:
      A name server that is both an "IPv4 name server" and also an "IPv6
      name server".

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3.  Name Space Fragmentation

   A resolver that tries to look up a name starts out at the root, and
   follows referrals until it is referred to a name server that is
   authoritative for the name.  If somewhere down the chain of referrals
   it is referred to a name server that is, based on the referral, only
   accessible over a transport which the resolver cannot use, the
   resolver is unable to continue DNS resolution.

   If this occurs, the DNS has, effectively, fragmented based on the
   resolver's and authoritative's mismatching IP version support.

   In a mixed IP Internet, fragmentation can occur for different
   reasons.  One reason is that DNS zones are consistently configured to
   support only either IPv4 or IPv6.  Another reason is due to
   misconfigurations that make a zone unresolvable by either IPv4 or
   IPv6-only resolvers.  The latter cases are often hard to identify, as
   the impact of misconfigurations for only one IP version (IPv4 or
   IPv6) may be hidden in a dual-stack setting.  In the worst case, a
   specific name may only be resolvable via dual-stack enabled
   resolvers.

3.1.  Misconfigurations Causing IP Version Related Name Space
      Fragmentation

   Even when an administrator thinks they have enabled support for a
   specific IP version on their authoritative name server, various
   misconfigurations may break the DNS delegation chain of a zone for
   that protocol and prevent any of its records from resolving for
   clients only supporting that IP version.  These misconfigurations can
   be kept hidden if most clients can successfully fall back to the
   other IP version.  As such, these issues are more common for IPv6
   resolution related name space fragmentation.

   The following name related misconfigurations can cause broken
   delegation for one IP version:

   No A/AAAA records for NS names:
      If none of the NS records for a zone in their parent zone have
      associated A or AAAA records, while holding the inverse record,
      resolution via the concerned IP version is not possible.

   Missing GLUE:
      If the name from an NS record for a zone is in-bailiwick, i.e.,
      the name is within the zone or below, a parent zone must contain
      an IPv4 and IPv6 GLUE record, i.e., a parent must serve the
      corresponding A or AAAA record(s) as ADDITIONAL data when
      returning the NS record in the ANSWER section.

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   No A/AAAA record for in-bailiwick NS:
      If an NS record of a zone points to a name that is in-bailiwick
      but the name lacks corresponding A or AAAA record(s) in its zone,
      resolution via the concerned IP version will fail even if the
      parent provides GLUE, when the recursive server validates the
      delegation path.

   Zone of out-of-bailiwick NSes not resolving:
      If an NS record of a zone is out-of-bailiwick, the corresponding
      zone must be resolvable via the IP version in question as well.
      It is insufficient if the name pointed to by the NS record has an
      associated A or AAAA record correspondingly.

   Parent zone not resolvable via one IP version:
      For a zone to be resolvable via an IP version the parent zones up
      to the root zone must be resolvable via that IP version as well.
      Any zone not resolvable via the concerned IP version breaks the
      delegation chain for all its children.

   The above misconfigurations are not mutually exclusive.

   Furthermore, any of the misconfigurations above may also materialize
   not via a missing Resource Record (RR) but via an RR providing the IP
   address of a nameserver that is not configured to answer queries via
   that IP version [V6DNSRDY-23].

3.2.  Reasons for Intentional IP Version Related Name Space
      Fragmentation

   Intentional IP related name space fragmentation occurs if an operator
   consciously decides to not deploy IPv4 or IPv6 for a part of the
   resolution chain.  Most commonly, this is realized by consciously not
   listing A/AAAA records for NS names in and out of bailiwick,
   including missing GLUE.  At the time of writing, the share of zones
   not resolvable via IPv4 is negligible, while a little less than 40%
   of zones are not resolvable via IPv6 [V6DNSRDY-23].  However, as IPv4
   exhaustion becomes more critical, this will change in the future

4.  Policy Based Avoidance of Name Space Fragmentation

   With the final exhaustion of IPv4 pools in RIRs, e.g., [RIPEV4], and
   the progressing deployment of IPv6, there no longer is a "preferred"
   IP version.  Yet, while we now observe the first zones becoming
   exclusively IPv6 resolvable, we also still see a major portion of
   zones solely relying on legacy IP [V6DNSRDY-23].  Hence, at the
   moment, dual stack connectivity is instrumental to be able to resolve
   zones and avoid name space fragmentation.

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   Having zones served only by name servers reachable via one IP version
   would fragment the DNS.  Hence, we need to find a way to avoid this
   fragmentation.

   The recommended approach to maintain name space continuity is to use
   administrative policies, as described in this section.

4.1.  Guidelines for DNS Zone Configuration

   It is usually recommended that DNS zones contain at least two name
   servers, which are geographically diverse and operate under different
   routing policies [IANANS].  To reduce the chance of DNS name space
   fragmentation, it is RECOMMENDED that at least two NS for a zone are
   dual stack name servers.  Specifically, this means that the following
   minimal requirements SHOULD be implemented for a zone:

   IPv4 adoption:
      Every authoritative DNS zone SHOULD be served by at least one
      IPv4-reachable authoritative name server to maintain name space
      continuity.  The delegation configuration (Resolution of the
      parent, resolution of out-of-bailiwick names, GLUE) MUST not rely
      on IPv6 connectivity being available.  As we acknowledge IPv4
      scarcity, operators MAY opt to not provide DNS services via IPv4,
      if they can ensure that all clients expected to resolve this zone
      do support DNS resolution via IPv6.

   IPv6 adoption:
      Every authoritative DNS zone SHOULD be served by at least one
      IPv6-reachable authoritative name server to maintain name space
      continuity.  The delegation configuration (Resolution of the
      parent, resolution of out-of-bailiwick names, GLUE) MUST not rely
      on IPv4 connectivity being available.

   Consistency:
      Both IPv4 and IPv6 transports should serve identical DNS data to
      ensure a consistent resolution experience across different network
      types.

   Note: zone validation processes SHOULD ensure that there is at least
   one IPv4 address record and one IPv6 address record available for the
   name servers of any child delegations within the zone.

4.2.  Guidelines for DNS Resolvers

   Every iterative name server SHOULD be dual stack.

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   While the zones that IPv6-only iterative resolvers can resolve are
   growing but do not yet cover all zones, they cannot fully resolve all
   zones.  Hence, a recursive resolver MAY be IPv6-only, if it uses a
   transition mechanism for IPv4 reachability
   [draft-momoka-v6ops-ipv6-only-resolver-02] or use a configuration
   where such resolvers forward queries failing IPv6 only DNS resolution
   to a set of dual-stack recursive name servers that perform the actual
   recursive queries.

   Similarly, a recursive resolver MAY be IPv4-only, if it use a
   configuration where such resolvers forward queries failing IPv4 only
   DNS resolution to a set of dual-stack recursive name servers that
   perform the actual recursive queries.

5.  Security Considerations

   TODO: This requires some input as, e.g., dual-stack services have
   implications for ratelimiting etc.

   The guidelines described in this memo introduce no new security
   considerations into the DNS protocol or associated operational
   scenarios.

6.  IANA Considerations

   This document asks IANA to update its technical requirements for
   authoritative name servers to require an IPv4 and an IPv6 address for
   each authoritative server [IANANS].

Acknowledgments

   TODO: acknowledge people.

   Thank you for reading this draft.

References

Normative References

   [RFC1883]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 1883, DOI 10.17487/RFC1883,
              December 1995, <https://www.rfc-editor.org/info/rfc1883>.

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

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   [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/info/rfc3901>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

Informative References

   [draft-momoka-v6ops-ipv6-only-resolver-02]
              山本 桃歌 (Yamamoto, M.) and 豊田 安信 (Y. Toyota), "IPv6-only
              Capable Resolvers Utilising NAT64", Work in Progress,
              Internet-Draft, draft-momoka-v6ops-ipv6-only-resolver-02,
              8 September 2023, <https://datatracker.ietf.org/doc/draft-
              momoka-v6ops-ipv6-only-resolver/02/>.

   [IANANS]   IANA, "Technical requirements for authoritative name
              servers",
              <https://www.iana.org/help/nameserver-requirements>.

   [RFC9386]  Fioccola, G., Volpato, P., Palet Martinez, J., Mishra, G.,
              and C. Xie, "IPv6 Deployment Status", RFC 9386,
              DOI 10.17487/RFC9386, April 2023,
              <https://www.rfc-editor.org/info/rfc9386>.

   [RIPEV4]   RIPE NCC, "The RIPE NCC has run out of IPv4 Addresses",
              November 2019, <https://www.ripe.net/publications/news/
              about-ripe-ncc-and-ripe/the-ripe-ncc-has-run-out-of-
              ipv4-addresses>.

   [V6DNSRDY-23]
              Streibelt, F., Sattler, P., Lichtblau, F., Hernandez-
              Gañán, C., Gasser, O., and T. Fiebig, "How Ready is DNS
              for an IPv6-Only World?", March 2023,
              <https://link.springer.com/
              chapter/10.1007/978-3-031-28486-1_22>.

Authors' Addresses

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

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   Additional contact information:

      山本 桃歌
      The University of Tokyo/WIDE Project

   Tobias Fiebig
   Max-Planck-Institut fuer Informatik
   Campus E14
   66123 Saarbruecken
   Germany
   Phone: +49 681 9325 3527
   Email: tfiebig@mpi-inf.mpg.de

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