Internet DRAFT - draft-ietf-add-resolver-info
draft-ietf-add-resolver-info
ADD T. Reddy
Internet-Draft Nokia
Intended status: Standards Track M. Boucadair
Expires: 1 September 2024 Orange
29 February 2024
DNS Resolver Information
draft-ietf-add-resolver-info-11
Abstract
This document specifies a method for DNS resolvers to publish
information about themselves. DNS clients can use the resolver
information to identify the capabilities of DNS resolvers. How such
an information is then used by DNS clients is out of the scope of
this document.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Adaptive DNS Discovery
Working Group mailing list (add@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/add/.
Source for this draft and an issue tracker can be found at
https://github.com/boucadair/add-resolver-information.
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 1 September 2024.
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Copyright Notice
Copyright (c) 2024 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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Retrieving Resolver Information . . . . . . . . . . . . . . . 3
4. Format of the Resolver Information . . . . . . . . . . . . . 4
5. Resolver Information Keys/Values . . . . . . . . . . . . . . 4
6. An Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. RESINFO RR Type . . . . . . . . . . . . . . . . . . . . . 6
8.2. DNS Resolver Information Key Registration . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Historically, DNS clients communicated with recursive resolvers
without needing to know anything about the features supported by
these resolvers. However, recent developments (e.g., Extended Error
Reporting [RFC8914] or encrypted DNS) imply that earlier assumption
no longer generally applies. Typically, DNS clients can discover and
authenticate encrypted DNS resolvers provided by a local network
(e.g., using the Discovery of Network-designated Resolvers (DNR)
[RFC9463] and the Discovery of Designated Resolvers (DDR) [RFC9462]),
however, these DNS clients can't retrieve information from the
discovered recursive resolvers about their capabilities. Instead of
depending on opportunistic approaches, DNS clients need a more
reliable mechanism to discover the features that are supported by
resolvers.
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This document fills that void by specifying a method for stub
resolvers to retrieve such information. To that aim, a new resource
record (RR) type is defined for DNS clients to query the recursive
resolvers. The information that a resolver might want to expose is
defined in Section 5.
Retrieved information can be used to feed the server selection
procedure. However, that selection procedure is out of the scope of
this document.
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.
This document makes use of the terms defined in [RFC8499]. The
following additional terms are used:
Encrypted DNS: Refers to a DNS scheme where DNS exchanges are
transported over an encrypted channel between a DNS client and
server (e.g., DNS over HTTPS (DoH) [RFC8484], DNS over TLS (DoT)
[RFC7858], or DNS over QUIC (DoQ) [RFC9250]).
Encrypted DNS resolver: Refers to a DNS resolver that supports any
encrypted DNS scheme.
Reputation: "The estimation in which an identifiable actor is held,
especially by the community or the Internet public generally"
(Section 1 of [RFC7070].
3. Retrieving Resolver Information
A DNS client that wants to retrieve the resolver information may use
the RR type "RESINFO" defined in this document.
The content of the RDATA in a response to a query for RESINFO RR
QTYPE is defined in Section 5. If the resolver understands the
RESINFO RR type, the RRSet in the Authority section MUST have exactly
one record. RESINFO is a property of the resolver and is not subject
to recursive resolution.
A DNS client can retrieve the resolver information using the RESINFO
RR type and the QNAME of the domain name that is used to authenticate
the DNS resolver (referred to as the Authentication Domain Name (ADN)
in DNR [RFC9463]).
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If the Special-Use Domain Name "resolver.arpa", defined in [RFC9462],
is used to discover an encrypted DNS resolver, the client can
retrieve the resolver information using the RESINFO RR type and QNAME
of "resolver.arpa". In this case, a client has to contend with the
risk that a resolver does not support RESINFO. The resolver might
pass the query upstream, and then the client can receive a positive
RESINFO response either from a legitimate DNS resolver or an
attacker. The DNS client MUST set the Recursion Desired (RD) bit of
the query to 0 to ensure that the response is provided by the
resolver. If the resolver does not support RESINFO, it will return
an authoritative name error.
4. Format of the Resolver Information
The resolver information record uses the same format as DNS TXT
records. As a reminder, the format rules for TXT records are defined
in the base DNS specification (Section 3.3.14 of [RFC1035]) and
further elaborated in the DNS-based Service Discovery (DNS-SD)
specification (Section 6.1 of [RFC6763]). The recommendations to
limit the TXT record size are discussed in Section 6.1 of [RFC6763].
Similar to DNS-SD, the RESINFO RR type uses "key/value" pairs to
convey the resolver information. Each "key/value" pair is encoded
using the format rules defined in Section 6.3 of [RFC6763]. Using
standardized "key/value" syntax within the RESINFO RR type makes it
easier for future keys to be defined. If a DNS client sees unknown
keys in a RESINFO RR type, it MUST silently ignore them. The same
rules for the keys as those defined in Section 6.4 of [RFC6763] MUST
be followed for RESINFO.
Keys MUST either be defined in the IANA registry (Section 8.2) or
begin with the substring "temp-" for names defined for local use
only.
5. Resolver Information Keys/Values
The following resolver information keys are defined:
qnamemin: If the DNS resolver supports QNAME minimisation [RFC9156]
to improve DNS privacy, the key is present. Note that, as per the
rules for the keys defined in Section 6.4 of [RFC6763], if there
is no '=' in a key, then it is a boolean attribute, simply
identified as being present, with no value.
This is an optional attribute.
exterr: If the DNS resolver supports extended DNS errors (EDE)
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option [RFC8914] to return additional information about the cause
of DNS errors, the value of this key lists the possible extended
DNS error codes that can be returned by this DNS resolver. When
multiple values are present, these values MUST be comma-separated.
This is an optional attribute.
infourl: An URL that points to the generic unstructured resolver
information (e.g., DoH APIs supported, possible HTTP status codes
returned by the DoH server, or how to report a problem) for
troubleshooting purposes. The server that exposes such
information is called "resolver information server".
The resolver information server MUST support the content-type
'text/html'. The DNS client MUST reject the URL if the scheme is
not "https". The URL SHOULD be treated only as diagnostic
information for IT staff. It is not intended for end user
consumption as the URL can possibly provide misleading
information. A DNS client MAY choose to display the URL to the
end user, if and only if the encrypted resolver has sufficient
reputation, according to some local policy (e.g., user
configuration, administrative configuration, or a built-in list of
respectable resolvers).
This is an optional attribute.
New keys can be defined as per the procedure defined in Section 8.2.
6. An Example
Figure 1 shows an example of a published resolver information record.
resolver.example.net. 7200 IN RESINFO qnamemin exterr=15,16,17
infourl=https://resolver.example.com/guide
Figure 1: An Example of Resolver Information Record
As mentioned in Section 3, a DNS client that discovers the ADN
"resolver.example.net" of its resolver using DNR will issue a query
for RESINFO RR QTYPE for that ADN and will learn that the resolver
supports:
* QNAME minimisation,
* Blocked (15), Censored (16), and Filtered (17) EDEs, and
* that more information can be retrieved from
https://resolver.example.com/guide.
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7. Security Considerations
DNS clients communicating with discovered DNS resolvers MUST use one
of the following measures to prevent DNS response forgery attacks:
1. Establish an authenticated secure connection to the DNS resolver.
2. Implement local DNSSEC validation (Section 10 of [RFC8499]) to
verify the authenticity of the resolver information.
It is important to note that, of these two measures, only the first
one can apply to queries for 'resolver.arpa'.
An encrypted resolver may return incorrect information in RESINFO.
If the client cannot validate the attributes received from the
resolver, that will be used for resolver selection or displayed to
the end-user, the client should process those attributes only if the
encrypted resolver has sufficient reputation according to local
policy (e.g., user configuration, administrative configuration, or a
built-in list of reputable resolvers). This approach limits the
ability of a malicious encrypted resolver to cause harm with false
claims.
8. IANA Considerations
Note to the RFC Editor: Please update "RFCXXXX" occurrences with
the RFC number to be assigned to this document.
8.1. RESINFO RR Type
This document requests IANA to update this entry from the "Resource
Record (RR) TYPEs" registry of the "Domain Name System (DNS)
Parameters" registry group available at [RRTYPE]:
Type: RESINFO
Value: 261
Meaning: Resolver Information as Key/Value Pairs
Reference: RFCXXXX
8.2. DNS Resolver Information Key Registration
This document requests IANA to create a new registry entitled "DNS
Resolver Information Keys" under the "Domain Name System (DNS)
Parameters" registry group ([IANA-DNS]). This new registry contains
definitions of the keys that can be used to provide the resolver
information.
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The registration procedure is Specification Required (Section 4.6 of
[RFC8126]).
The structure of the registry is as follows:
Name: The key name. The name MUST conform to the definition in
Section 4 of this document. The IANA registry MUST NOT register
names that begin with "temp-", so these names can be used freely
by any implementer.
Description: A description of the registered key.
Specification: The reference specification for the registered
element.
The initial content of this registry is provided in Table 1.
+==========+=====================================+===============+
| Name | Description | Specification |
+==========+=====================================+===============+
| qnamemin | The presence of the key name | RFCXXXX |
| | indicates that QNAME minimization | |
| | is enabled | |
+----------+-------------------------------------+---------------+
| exterr | Lists the set of supported extended | RFCXXXX |
| | DNS errors. It must be an INFO- | |
| | CODE decimal value in the "Extended | |
| | DNS Error Codes" registry. | |
+----------+-------------------------------------+---------------+
| infourl | Provides an URL that points to an | RFCXXXX |
| | unstructured resolver information | |
| | that is used for troubleshooting | |
+----------+-------------------------------------+---------------+
Table 1: Initial RESINFO Registry
9. References
9.1. 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>.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/rfc/rfc6763>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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>.
[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/rfc/rfc8914>.
[RFC9156] Bortzmeyer, S., Dolmans, R., and P. Hoffman, "DNS Query
Name Minimisation to Improve Privacy", RFC 9156,
DOI 10.17487/RFC9156, November 2021,
<https://www.rfc-editor.org/rfc/rfc9156>.
[RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", RFC 9462,
DOI 10.17487/RFC9462, November 2023,
<https://www.rfc-editor.org/rfc/rfc9462>.
[RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N.,
and T. Jensen, "DHCP and Router Advertisement Options for
the Discovery of Network-designated Resolvers (DNR)",
RFC 9463, DOI 10.17487/RFC9463, November 2023,
<https://www.rfc-editor.org/rfc/rfc9463>.
9.2. Informative References
[I-D.pp-add-resinfo]
Sood, P. and P. E. Hoffman, "DNS Resolver Information
Self-publication", Work in Progress, Internet-Draft,
draft-pp-add-resinfo-02, 30 June 2020,
<https://datatracker.ietf.org/doc/html/draft-pp-add-
resinfo-02>.
[IANA-DNS] IANA, "Domain Name System (DNS) Parameters",
<http://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml#dns-parameters-4>.
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[RFC7070] Borenstein, N. and M. Kucherawy, "An Architecture for
Reputation Reporting", RFC 7070, DOI 10.17487/RFC7070,
November 2013, <https://www.rfc-editor.org/rfc/rfc7070>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>.
[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/rfc/rfc8499>.
[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/rfc/rfc9250>.
[RRTYPE] IANA, "Resource Record (RR) TYPEs",
<https://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml>.
Acknowledgments
This specification leverages the work that has been documented in
[I-D.pp-add-resinfo].
Thanks to Tommy Jensen, Vittorio Bertola, Vinny Parla, Chris Box, Ben
Schwartz, Tony Finch, Daniel Kahn Gillmor, Eric Rescorla, Shashank
Jain, Florian Obser, Richard Baldry, and Martin Thomson for the
discussion and comments.
Thanks to Mark Andrews, Joe Abley, Paul Wouters, and Tim Wicinski for
the discussion on the RR formatting rules.
Special thanks to Tommy Jensen for the careful and thoughtful
Shepherd review.
Thanks to Johan Stenstam and Jim Reid for the dns-dir reviews, Ray
Bellis for the RRTYPE allocation review, and Arnt Gulbrandsen for the
ART review.
Thanks to Eric Vyncke for the AD review.
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Authors' Addresses
Tirumaleswar Reddy
Nokia
India
Email: kondtir@gmail.com
Mohamed Boucadair
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
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