Internet DRAFT - draft-momoka-dnsop-3901bis
draft-momoka-dnsop-3901bis
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
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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
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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/
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Please review these documents carefully, as they describe your rights
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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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