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: 26 August 2023 Orange
22 February 2023
DNS Resolver Information
draft-ietf-add-resolver-info-01
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 the
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 26 August 2023.
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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
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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. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. RESINFO RR Type . . . . . . . . . . . . . . . . . . . . . 5
7.2. DNS Resolver Information Key Registration . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Historically, DNS stub resolvers communicated with recursive
resolvers without needing to know anything about the features
supported by these recursive resolvers. As more and more recursive
resolvers expose different features that may impact delivered DNS
services, means to help stub resolvers to identify the capabilities
of resolvers are valuable. Typically, stub resolvers can discover
and authenticate encrypted DNS servers provided by a local network,
for example, using the techniques specified in [I-D.ietf-add-dnr] and
[I-D.ietf-add-ddr]. However, these stub resolvers need a mechanism
to retrieve information from the discovered recursive resolvers about
their capabilities.
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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 stub resolvers 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 scope.
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].
'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]).
3. Retrieving Resolver Information
A stub resolver 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 RR type query is defined in
Section 5. If the resolver understands the RESINFO RR type, the
RRSet in the Answer section MUST have exactly one record.
A DNS client can retrieve the resolver information using the RESINFO
RR type and QNAME of the domain name that is used to authenticate the
DNS server (referred to as ADN in [I-D.ietf-add-dnr]).
If the special use domain name "resolver.arpa" defined in
[I-D.ietf-add-ddr] is used to discover the encrypted DNS server, the
client can retrieve the resolver information using the RESINFO RR
type and QNAME of the designated resolver.
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4. Format of the Resolver Information
The resolver information uses the same format as DNS TXT records.
The intention of using the same format as TXT records is to convey a
small amount of useful information about a DNS resolver. As a
reminder, the format rules for TXT records are defined in
Section 3.3.14 of the DNS specification [RFC1035] and further
elaborated in Section 6.1 of the DNS-based Service Discovery (DNS-SD)
[RFC6763]. The recommendations to limit the TXT record size are
discussed in Section 6.2 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 7.2) 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)
[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, how to report a problem) for
troubleshooting purpose.
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The 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 possibily
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 a an optional attribute. For example, a DoT server may
not want to host an HTTPS server.
New keys can be defined as per the procedure defined in Section 7.2.
Figure 1 shows an example of a published resolver information record:
resolver.example.net. 7200 IN RESINFO qnamemin exterr=15,16,17
resinfourl=https://resolver.example.com/guide
Figure 1: An Example of Resolver Information Record
6. Security Considerations
Unless a DNS request to retrieve the resolver information is
encrypted (e.g., sent over DoT or DoH), the response is susceptible
to forgery. The DNS resolver information can be retrieved before or
after the encrypted connection is established to the DNS server by
using local DNSSEC validation.
7. IANA Considerations
Note to the RFC Editor: Please update "[RFCXXXX]" occurences with
the RFC number to be assigned to this document.
7.1. RESINFO RR Type
This document requests IANA to register a new value from the
"Resource Record (RR) TYPEs" subregistry of the "Domain Name System
(DNS) Parameters" registry available at [RRTYPE]:
Type: RESINFO
Value: TBD
Meaning: Resolver Information as Key/Value Pairs
Reference: [RFCXXXX]
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7.2. DNS Resolver Information Key Registration
This document requests IANA to create a new sub-registry entitled
"DNS Resolver Information Keys" under the "Domain Name System (DNS)
Parameters" registry ([IANA-DNS]). This new registry contains
definitions of the keys that can be used to provide the resolver
information.
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.
Value Type: The type of the value to be used in the key.
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 | Value | Description | Specification |
| | Type | | |
+==========+=========+=============================+===============+
| qnamemin | boolean | Indicates whether | [RFCXXXX] |
| | | 'qnameminimization' is | |
| | | enabled or not | |
+----------+---------+-----------------------------+---------------+
| exterr | number | Lists the set of extended | [RFCXXXX] |
| | | DNS errors | |
+----------+---------+-----------------------------+---------------+
| infourl | string | Provides an unstructured | [RFCXXXX] |
| | | resolver information that | |
| | | is used for troubleshooting | |
+----------+---------+-----------------------------+---------------+
Table 1: Initial RESINFO Registry
8. References
8.1. Normative References
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[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>.
[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>.
8.2. Informative References
[I-D.ietf-add-ddr]
Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", Work in
Progress, Internet-Draft, draft-ietf-add-ddr-10, 5 August
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
add-ddr-10>.
[I-D.ietf-add-dnr]
Boucadair, M., Reddy.K, T., Wing, D., Cook, N., and T.
Jensen, "DHCP and Router Advertisement Options for the
Discovery of Network-designated Resolvers (DNR)", Work in
Progress, Internet-Draft, draft-ietf-add-dnr-13, 13 August
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
add-dnr-13>.
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[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", n.d.,
<http://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml#dns-parameters-4>.
[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", n.d.,
<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, and Richard Baldry for the discussion and
comments.
Thanks to Mark Andrews, Joe Abley, Paul Wouters, Tim Wicinski, and
Steffen Nurpmeso for the discussion on the RR formatting rules.
Authors' Addresses
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Tirumaleswar Reddy
Nokia
India
Email: kondtir@gmail.com
Mohamed Boucadair
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
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