ADD WG T. Reddy
Internet-Draft McAfee
Intended status: Standards Track M. Boucadair
Expires: September 30, 2021 Orange
March 29, 2021
DNS Resolver Information
draft-reddy-add-resolver-info-01
Abstract
This document specifies a method for DNS resolvers to publish
information about themselves. Clients can use the resolver
information to identify the capabilities of DNS resolvers.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Retrieving Resolver Information . . . . . . . . . . . . . . . 3
4. Format of the Resolver Information . . . . . . . . . . . . . 3
5. Resolver Information . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. RESINFO RRtype . . . . . . . . . . . . . . . . . . . . . 5
7.2. DNS Resolver Information Registration . . . . . . . . . . 5
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
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 the delivered DNS
service, means to help stub resolvers to identify the capabilities of
the resolver 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 means to
retrieve information from the discovered recursive resolvers about
their capabilities.
This document fills that void by specifying a method for stub
resolvers to retrieve such information. To that aim, a new RRtype is
defined for stub resolvers to query the recursive resolvers. The
information that a resolver might want to give is defined in
Section 5.
Retrieved information can be used to feed the server selection
procedure.
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.
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This document makes use of the terms defined in [RFC8499].
'Encrypted DNS' refers to a DNS protocol that provides an encrypted
channel between a DNS client and server (e.g., DoT, DoH, or DoQ).
3. Retrieving Resolver Information
A stub resolver that wants to retrieve the resolver information may
use the RRtype "RESINFO" defined in this document (see Section 7.1).
The content of the RDATA in a response to RRtype query is defined in
Section 5. If the resolver understands the RESINFO RRtype, the RRset
in the Answer section MUST have exactly one record.
The client can retrieve the resolver information using the RESINFO
RRtype 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
first retrieve a CNAME that aliases `_dns.resolver.arpa` to
`_dns.$HOSTNAME` and then retrieve the resolver information using the
RESINFO RRtype and QNAME of the `$HOSTNAME`.
4. Format of the Resolver Information
The resolver information is returned as a JSON object. Precisely,
the JSON object MUST use the I-JSON message format [RFC7493].
Note that [RFC7493] was based on [RFC7159], but [RFC7159] was
replaced by [RFC8259]. Requiring the use of I-JSON instead of
more general JSON format greatly increases the likelihood of
interoperability.
The JSON object returned by a DNS query may contain any name/value
pairs. All names MUST consist only of lower-case ASCII characters,
digits, and hyphens (that is, Unicode characters U+0061 through 007A,
U+0030 through U+0039, and U+002D). These names MUST be 63
characters or shorter.
All names in the returned object MUST either be defined in the IANA
registry Section 7.2 or begin with the substring "temp-" for names
defined for local use only.
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5. Resolver Information
The resolver information includes the following attributes:
qnameminimization: If the DNS server supports QNAME minimisation
[RFC7816] to improve DNS privacy, the parameter value is set to
true. This is a mandatory attribute.
extendeddnserror: If the DNS server supports extended DNS error
(EDE) [RFC8914] to return additional information about the cause
of DNS errors, the parameter lists the possible extended DNS error
codes that can be returned by the DNS server. This is an optional
attribute.
Note that the extended error code "Blocked" defined in
Section 4.16 of [RFC8914] identifies access to domains is
blocked due to an policy by the operator of the DNS server,
extended error code "Censored" defined in Section 4.17 of
[RFC8914] identifies access to domains is blocked based on a
requirement from an external entity and the extended error code
"Filtered" defined in Section 4.18 of [RFC8914] identifies
access to domains is blocked based on the request from the
client to blacklist domains.
clientauth: If the DNS server requires client authentication, the
parameter value is set to true. For example, when not on the
enterprise network (e.g., coffee shop) yet needing to access the
enterprise Encrypted DNS server, roaming users can use client
authentication to access the Enterprise-provided Encrypted DNS
server. This is an optional attribute.
resinfourl: 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. This is an optional attribute.
identityurl: An URL that points to a human-friendly description of
the resolver identity to display to the end-user.
New attributes can be defined as per the procedure defined in
Section 7.2.
As specified in [RFC7493], the I-JSON object is encoded as UTF8.
[RFC7493] explicitly allows the returned objects to be in any order.
Figure 1 shows an example of resolver information.
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{
"qnameminimization": true,
"extendeddnserror": [
15,
16,
17
],
"clientauth": false,
"resinfourl": "https://resolver.example.com/guide",
"identityurl": "https://resolver.example.com/user-friendly-name"
}
Figure 1: An Example of Resolver Information
6. Security Considerations
Unless a DNS request to retrieve the resolver information is
encrypted (e.g., sent over DNS-over-TLS (DoT) [RFC7858] or DNS-over-
HTTPS (DoH)) [RFC8484], the response is susceptible to forgery. The
DNS resolver information can be retrieved after the encrypted
connection is established to the DNS server. If the client wishes to
retrieve the resolver information before the encryption connection is
established to the DNS resolver, the client MUST use local DNSSEC
validation.
7. IANA Considerations
Note to the RFC Editor: Please update [RFCXXXX] with the RFC
number to be assigned to this document.
7.1. RESINFO RRtype
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 an I-JSON
Reference: [RFCXXXX]
7.2. DNS Resolver Information Registration
This document requests IANA to create a new registry entitled "DNS
Resolver Information". This registry contains definitions of the
names 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 name to be used in the JSON object. The name MUST conform
to the definition of "string" in I-JSON message format. 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 data to be used in the JSON object.
Description: Provides a description of the attribute
Specification: The reference specification for the registered
element.
The initial content of this registry is provided in Table 1.
+-------------------+---------+---------------------+---------------+
| Name | Value | Specification | Specification |
| | Type | | |
+-------------------+---------+---------------------+---------------+
| qnameminimization | boolean | Indicates whether | [RFCXXXX] |
| | | qnameminimization | |
| | | is enabled or not | |
| extendeddnserror | number | Lists the set of | [RFCXXXX] |
| | | extended DNS errors | |
| clientauth | boolean | Indicates whether | [RFCXXXX] |
| | | client | |
| | | authentication is | |
| | | required or not | |
| resinfourl | string | Provides an | [RFCXXXX] |
| | | unstructured | |
| | | resolver | |
| | | information that is | |
| | | used for | |
| | | troubleshooting | |
| identityurl | string | Points to a human- | [RFCXXXX] |
| | | friendly | |
| | | description of the | |
| | | resolver identity | |
| | | to display to the | |
| | | end-user | |
+-------------------+---------+---------------------+---------------+
Table 1: Initial RESINFO Registry
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8. 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, and Shashank Jain for the discussion and comments.
9. References
9.1. Normative References
[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>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
[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/info/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/info/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/info/rfc8914>.
9.2. Informative References
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[I-D.pp-add-resinfo]
Sood, P. and P. Hoffman, "DNS Resolver Information Self-
publication", draft-pp-add-resinfo-02 (work in progress),
June 2020.
[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/info/rfc7858>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/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/info/rfc8499>.
[RRTYPE] IANA, "Resource Record (RR) TYPEs",
<http://www.iana.org/assignments/dns-parameters/dns-
parameters.xhtml#dns-parameters-4>.
Authors' Addresses
Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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