Internet DRAFT - draft-tjw-dnsop-3901bis
draft-tjw-dnsop-3901bis
DNSOP T. Wicinski. (ed)
Internet-Draft 23 October 2023
Obsoletes: 3901 (if approved)
Intended status: Best Current Practice
Expires: 25 April 2024
DNS IPv6 Transport Operational Guidelines
draft-tjw-dnsop-3901bis-01
Abstract
This memo provides guidelines and Best Current Practice for operating
DNS in a world where queries and responses are carried in a mixed
environment of IPv4 and IPv6 networks.
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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This Internet-Draft will expire on 25 April 2024.
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
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Name Space Fragmentation: following the referral chain . . . 2
4. Policy Based Avoidance of Name Space Fragmentation . . . . . 3
5. Common Causes of Name Resolution Failure in IPv6 . . . . . . 3
6. DNS IPv6 Transport recommended Guidelines . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
10. Informative References . . . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Internet is well on its way to a mixture of IPv4 and IPv6
networks. The concern is that a resolver using only a particular
version of IP and querying information about another node using the
same version of IP can not do it because somewhere in the chain of
servers accessed during the resolution process, one or more of them
will only be accessible with the other version of IP.
2. Terminology
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. DNS terminology is as described in
[RFC8499].
The phrase "IPv4 name server" indicates a name server available over
IPv4 transport. It does not imply anything about what DNS [RFC1034]
[RFC1035] data is served. Likewise, "IPv6 name server" [RFC3596]
indicates a name server available over IPv6 transport. The phrase
"dual-stack name server" indicates a name server that is configured
to run both IPv4 and IPv6.
3. Name Space Fragmentation: following the referral chain
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 only accessible over a
transport which the resolver cannot use, the resolver is unable to
finish the task.
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With all DNS data only available over IPv4 transport everything is
simple. IPv4 resolvers can use the intended mechanism of following
referrals from the root and down while IPv6 resolvers have to work
through a "translator", i.e., they have to use a recursive name
server on a so-called "dual stack" host as a "forwarder" since they
cannot access the DNS data directly.
With all DNS data only available over IPv6 transport everything would
be equally simple, with the exception of IPv4 recursive name servers
having to switch to a forwarding configuration.
The transition from IPv4 only to a mixture of IPv4 and IPv6, with
three categories of DNS data depending on whether the information is
available only over IPv4 transport, only over IPv6 or both.
Having DNS data available on both transports is the optimal
situation.
4. Policy Based Avoidance of Name Space Fragmentation
Today there are only a small number of DNS zones that are available
over IPv6-only.
The recommended approach to maintain name space continuity is to use
administrative policies, as described in the next section.
5. Common Causes of Name Resolution Failure in IPv6
Successful name resolution under IPv6 demands careful attention to
certain configuration prerequisites. Configuration mistakes can be
summarised to the following.
* Parent zone not IPv6-resolvable: For a zone to be resolvable via
IPv6, the parent zones up to the root zone must be
IPv6-resolvable. Any non-IPv6-resolvable zone breaks the
delegation chain for all its children.
* No AAAA records for NS names: If none of the NS records for a zone
in their parent zone have associated AAAA records, resolution via
IPv6 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 IPv6 GLUE record, i.e., a parent must serve
the corresponding AAAA record(s) as ADDITIONAL data when returning
the NS record in the ANSWER section.
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* No 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 AAAA
record(s) in its zone, IPv6-only resolution will fail even if the
parent provides GLUE, when the recursive server validates the
delegation path. One such example is Unbound with the setting
harden-glue: yes–the default.
* Zone of out-of-bailiwick NS not resolving: If an NS record of a
zone is out-of-bailiwick, the corresponding zone must be
IPv6-resolvable as well. It is insufficient if the name pointed
to by the NS record has an associated AAAA record.
Recognizing and addressing these configuration requirements is
fundamental to the seamless operation of DNS in an environment that
blends IPv4 and IPv6. [https://link.springer.com/
chapter/10.1007/978-3-031-28486-1_22 (https://link.springer.com/
chapter/10.1007/978-3-031-28486-1_22)]
6. DNS IPv6 Transport recommended Guidelines
In order to preserve name space continuity, the following
administrative policies are recommended:
* every recursive name server SHOULD support the local network
configuration. If the local network supports both IPv4 and IPv5,
the resolver SHOULD be dual stack.
* If the service is offering IPv4 as a Service (IPv4aaS), the
recursive name server SHOULD accept IPv6, and support dual stack
recursive methods.
* every authorative DNS zone SHOULD be dual stack IPv4/IPv6.
A DNS zone can be served by at least one IPv4-reachable authoritative
name server.
This rules out DNS zones served only by IPv6-only authoritative name
servers.
Note: zone validation processes SHOULD ensure that there is at least
one IPv4 address record available for the name servers of any child
delegations within the zone.
7. IANA Considerations
None
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8. Security Considerations
None
9. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.
10. Informative References
[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>.
Acknowledgements
Mark Andrews. No, really.
Author's Address
Tim Wicinski
Elkins, WV 26241
United States of America
Email: tjw.ietf@gmail.com
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