Network Working Group K. Fujiwara
Internet-Draft JPRS
Updates: 2181 (if approved) W. Toorop
Intended status: Standards Track NLnet Labs
Expires: 4 September 2025 3 March 2025
Clarifications to the DNS Ranking Data
draft-fujiwara-dnsop-ranking-data-00
Abstract
This document obsoletes Section 5.4.1 (Ranking data) of RFC 2181, and
specifies directives whereby the source of the data determines for
what purposes it may be used.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
4. Directives . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Additional Considerations . . . . . . . . . . . . . . . . . . 3
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. Normative References . . . . . . . . . . . . . . . . . . . . 4
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The DNS server assumed in Section 5.4.1 (Ranking data) of [RFC2181]
is considered to be a model with a shared database described in
Section 2.2 (Common configurations) of [RFC1035] that has both
Authoritative server and Recursive Resolver functions. It is assumed
that information obtained from zone files, zone transfers, and name
resolution will be mixed together.
However, at the time of writing, this is no longer the practice of
name servers and resolvers. Zone transfers transfer the same data
from primaries to secondary servers without any modification. An
authoritative name server function does not mix and return
information obtained from name resolution.
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.
Many of the specialized terms used in this document are defined in
DNS Terminology [RFC9499].
3. Problem Statement
In the past, recursive resolvers would return data from referral
responses, such as delegation information or glue, in the answer
section of responses; however, modern recursive resolvers complete
name resolution with an authoritative response from an authoritative
server that has authority through delegation. However, there is no
clear documentation of this.
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"The Ranking Data" only indicates the priority among data, not its
validity. Attacks using responses that do not correspond to queries
and additional data that is not required have been considered and
reported, so unnecessary data should be discarded.
Currently, responses from authoritative servers are considered to
include authoritative name resolution results (NXDOMAIN, NODATA, the
RRSet requested), non-authoritative delegation information,
unnecessary data, and other types of errors, and each of these is
considered to affect how resolvers handle the data. Therefore,
directives on how to handle the data are needed.
4. Directives
1. Authoritative servers MUST NOT merge zone data. (zone data should
be retrieved from a source (zone file, internal database, zone
transfer)
2. Name resolution results (Answer section, or NXDOMAIN, NODATA)
MUST be authoritative responses from authoritative servers that
has authority through delegation.
3. Non-authoritative responses (referral/delegation responses) from
authoritative servers MUST only be used to query the delegated
authoritative server during the name resolution.
4. Names and IP addresses of the authoritative name servers for
zones (such as the root zone) that are built-in or loaded from
"hints" files, MUST only be used for priming a resolver for those
zones [RFC9609].
5. Additional Considerations
[ Further directives could be made, they may be DNS software
implementation guidelines, which would be large in scale, so it is
necessary to consider whether to proceed with them. ]
* If a DNS server plays different roles for different namespaces
(authoritative server, recursive resolver, forwarder), it MUST NOT
merge DNS data for each role.
For example, a recursive resolver that returns a fixed zone as a
split-horizon DNS can be interpreted as acting as an authoritative
server below a certain domain name, but as a recursive resolver
otherwise.
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* The Additional Section returned as the result of name resolution
MUST be exactly the same as the Additional Section that came from
the authoritative response from the authoritative server, or a
separate authoritative response resulting from name resolution.
* Full-service resolvers SHOULD only accept the following data from
authoritative servers:
- NS and DS RRSets (+RRSIG) in the Authority Section of the
delegation response and Glue A/AAAA in the Additional Section,
- SOA RRs (+RRSIG) in the Authority Section of authoritative
NXDOMAIN and NODATA responses in response to the query,
- the Answer Section (+RRSIG) of the authoritative response in
response to the query, and
- any additional sections allowed by type (delegated domain
name),
and SHOULD NOT accept any other information.
6. IANA Considerations
This document requests no IANA actions.
7. Security Considerations
8. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/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/rfc/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/rfc/rfc2181>.
[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/rfc/rfc8174>.
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[RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
RFC 9499, DOI 10.17487/RFC9499, March 2024,
<https://www.rfc-editor.org/rfc/rfc9499>.
[RFC9609] Koch, P., Larson, M., and P. Hoffman, "Initializing a DNS
Resolver with Priming Queries", BCP 209, RFC 9609,
DOI 10.17487/RFC9609, February 2025,
<https://www.rfc-editor.org/rfc/rfc9609>.
Authors' Addresses
Kazunori Fujiwara
Japan Registry Services Co., Ltd.
Japan
Email: fujiwara@jprs.co.jp
Willem Toorop
NLnet Labs
Science Park 400
1098 XH Amsterdam
Netherlands
Email: willem@nlnetlabs.nl
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