Network Working Group P. Sood
Internet-Draft Google
Intended status: Standards Track P. Hoffman
Expires: October 26, 2020 ICANN
April 24, 2020
DNS Resolver Information Self-publication
draft-pp-add-resinfo-00
Abstract
This document describes methods for DNS resolvers to self-publish
information about themselves. The information is returned as a JSON
object. The names in this object are defined in an IANA registry
that allows for light-weight registration. Applications and
operating systems can use the methods defined here to get the
information from resolvers in order to make choices about how to send
future queries to those resolvers.
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-
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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 October 26, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Retrieving Resolver Information by DNS . . . . . . . . . . . 3
3. Retrieving Resolver Information by Well-Known URI . . . . . . 4
4. Contents of the Returned I-JSON Object . . . . . . . . . . . 4
4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. RESINFO RRtype . . . . . . . . . . . . . . . . . . . . . 5
5.2. Registry for DNS Resolver Information . . . . . . . . . . 5
5.3. resinfo Well-known URI . . . . . . . . . . . . . . . . . 6
5.4. resolver-info.arpa Special-Use Domain Name . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Ideas From Earlier Work that was Abandoned . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Historically, DNS stub resolvers typically communicated with the
recursive resolvers in their configuration without needing to know
anything about the features of the recursive resolvers. More
recently, recursive resolvers have different features that may cause
stub resolvers to make choices about which configured resolver from
its configuration to use, and also how to communicate with the
recursive resolver (such as over different transports). Thus stub
resolvers need a way to get information from recursive resolvers
about features that might affect the communication.
This document specifies methods for stub resolvers to ask recursive
resolvers for such information. In short, a new RRtype is defined
for stub resolvers to query using the DNS, and a new well-known URI
is defined for stub resolvers to query using HTTP over TLS.
The response from either method is the same: a JSON object. The JSON
object MUST use the I-JSON message format defined in [RFC7493]. Note
that [RFC7493] was based on RFC 7159, but RFC 7159 was replaced by
[RFC8259]. Requiring the use of I-JSON instead of more general JSON
format greatly increases the likelihood of interoperability.
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The information that a resolver might want to give to a recursive
resolver is not defined in this document; instead other documents
will follow that will specify that information and the format that it
comes in.
1.1. Definitions
In the rest of this document, the term "resolver" without
qualification means "recursive resolver" as defined in [RFC8499].
Also, the term "stub" is used to mean "stub resolver".
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.
2. Retrieving Resolver Information by DNS
A stub that wants to use the DNS to get information about a resolver
can use the DNS query defined here. The query a stub resolver uses
is resolver-info.arpa/IN/RESINFO. The RRtype "RESINFO" is defined in
this document, and the IANA assignment is given in Section 5.1. The
contents of the Rdata in the response to this query is defined in
Section 4. If the resolver understands the RESINFO RRtype, the RRset
in the Answer section MUST have exactly one record.
The name resolver-info.arpa is defined in this document, and the IANA
assignment is given in Section 5.4. As described in Section 5.4, the
zone resolver-info.arpa is not actually delegated and never will be.
The resolver that receives this query acts as if it is delegated, and
responds with its own RESINFO data in the Answer section.
A resolver that receives a query with the RRtype of RESINFO with a
QNAME of resolver-info.arpa acts as if it is delegated, and responds
with its own RESINFO data in the Answer section. The resolver can
generate this reply with special code to capture queries for these
types of addresses; if the resolver can be configured to also be
authoritative for some zones, it can use that configuration to
actually be authoritative for the addresses on which it responds.
Any query for the RESINFO RRtype that is not to resolver-info.arpa/IN
is meaningless and MUST result in a NODATA or NXDOMAIN response.
Resolvers would not need any special code to meet this requirement;
they only need code to handle the RESINFO RRtype that is in resolver-
info.arpa/IN.
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3. Retrieving Resolver Information by Well-Known URI
A stub that wants to use HTTPS to get information about a resolver
can use the well-known URI defined here. Because this uses HTTPS,
the stub has the possibility of authenticating the TLS connection.
If the connection cannot be authenticated (such as if the stub only
knows the IP address of the resolver and the resolver's certificate
does not have the IP address, or the correct IP address), the stub
MAY still use the results with the same lack of assuredness as it
would have with using a DNS request described in Section 2.
The stub MUST use the HTTP GET method. The URI used to get the
resolver information is :
https://IPADDRESSOFRESOLVER/.well-known/resinfo/
https://DOMAINNAMEOFRESOLVER/.well-known/resinfo/
This uses the ".well-known" URI mechanism defined in [RFC8615]. The
contents of the response to this query is defined in Section 4.
A resolver that uses this method to publish its information SHOULD,
if possible, have a TLS certificate whose subject identifiers contain
any of the IP addresses that stubs might be using for the resolver.
At the time that this document is published, getting IP addresses in
TLS certificates is possible, but there are only a few widely-trusted
CAs that issue such certificates. [RFC8738] describes a protocol
that may cause IP address certificates to become more common.
In the future, DHCP and/or DCHPv6 and/or RA may have options that
allow the configuration to contain the domain name of a resolver. If
so, this can be used for matching the domain name in the TLS
certificate. Until that time, the second form of the URI is probably
not useful.
4. Contents of the Returned I-JSON Object
The JSON object returned by a DNS query or an HTTPS query MAY contain
any name/value pairs.
All names in the returned object MUST either be defined in the IANA
registry or, if for local use only, begin with the substring "temp-".
The IANA registry (Section 5.2) will never register names that begin
with "temp-".
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), and MUST be 63 characters or shorter.
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As defined in Section 5.2, the IANA registry will not register names
that begin with "temp-", so these names can be used freely by any
implementer.
Note that the message returned by the resolver MUST be in I-JSON
format. I-JSON requires that the message MUST be encoded in UTF8.
4.1. Example
The I-JSON object that a resolver returns might look like the
following:
{
"temp-field2": 42
}
As specified in [RFC7493], the I-JSON object is encoded as UTF8.
[RFC7493] explicitly allows the returned objects to be in any order.
5. IANA Considerations
5.1. RESINFO RRtype
This document defines a new DNS RR type, RESINFO, whose value TBD
will be allocated by IANA from the "Resource Record (RR) TYPEs" sub-
registry of the "Domain Name System (DNS) Parameters" registry:
Type: RESINFO
Value: TBD
Meaning: Information self-published by a resolver as an I-JSON (RFC
7493) object
Reference: This document
5.2. Registry for DNS Resolver Information
IANA will create a new registry titled "DNS Resolver Information"
that will contain definitions of the names that can be used with the
protocols defined in this document. The registration procedure is by
Expert Review and Specification Required, as defined in [RFC8126].
The specification that is required for registration can be either an
Internet-Draft or an RFC. The reviewer for this registry is
instructed to generally be liberal in what they accept into the
registry: as long as the specification that comes with the
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registration request is reasonably understandable, the registration
should be accepted.
The registry has the following fields for each element:
Name: The name to be used in the JSON object. This name MUST NOT
begin with "temp-". This name MUST conform to the definition of
"string" in I-JSON [RFC7493] message format.
Value type: The type of data to be used in the JSON object.
Specification: The name of the specification for the registered
element.
5.3. resinfo Well-known URI
Before this draft is complete, mail will be sent to wellknown-uri-
review@ietf.org in order to be registered in the "Well-Known URIs"
registry at IANA. The mail will contain the following:
URI suffix: resinfo
Change controller: IETF
Specification document(s): This document
Status: permanent
5.4. resolver-info.arpa Special-Use Domain Name
IANA will record the domain name "resolver-info.arpa" in the
"Special-Use Domain Names" registry [SUDN]. IANA MUST NOT delegate
resolver-info.arpa in the .arpa zone.
6. Security Considerations
Unless a DNS request for resolver-info.arpa/IN/RESINFO as described
in Section 2 is sent over DNS-over-TLS (DoT) [RFC7858] or DNS-over-
HTTPS (DoH) [RFC8484], the response is susceptible to forgery. Given
that one of the first expected uses for the protocol in this document
is expected to be to find out whether DoT or DoH is available for the
resolver, it is thus expected that most if not all such DNS requests
will be sent without any chance of authentication. Stubs and
resolvers SHOULD use normal DNS methods for avoiding forgery such as
query ID randomization and source port randomization.
An application that is using an operating system API to send queries
for resolver-info.arpa/IN/RESINFO or a subdomain will only know if
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query went over authenticated DoT or DoH if the API supports
returning that authentication information. Currently, no common APIs
support that type of response.
A stub resolver will know if it is using DoT or DoH, but it would
only know if the communication is authenticated if there is an API or
system call for the stub resolver to know that.
7. References
7.1. 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>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<https://www.rfc-editor.org/info/rfc7493>.
[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>.
[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>.
[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>.
[SUDN] "Special-Use Domain Names", n.d.,
<https://www.iana.org/assignments/
special-use-domain-names/>.
7.2. Informative References
[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>.
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[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>.
[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>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC8738] Shoemaker, R., "Automated Certificate Management
Environment (ACME) IP Identifier Validation Extension",
RFC 8738, DOI 10.17487/RFC8738, February 2020,
<https://www.rfc-editor.org/info/rfc8738>.
Appendix A. Ideas From Earlier Work that was Abandoned
This document is based on work done earlier in the DNSOP working
group, and personal drafts before that.
In that earlier work, "<reverse-ip>.{in-addr,ip6}.arpa" was proposed
as the domain name to allow for the possibility of DNSSEC-signed
responses. However, it was pointed out that people often do not
control their reverse IP names and thus their ISP (or their ISP's
ISP) could spoof responses and make them look legitimate by signing
with DNSSEC.
Acknowledgments
The idea of various types of servers publishing information about
themselves has been around for decades. However this idea has not
been used in the DNS. This document aims to fix this omission.
Roy Arends contributed many ideas to an earlier version of this draft
before it was moved to the ADD working group.
Authors' Addresses
Puneet Sood
Google
Email: puneets@google.com
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Paul Hoffman
ICANN
Email: paul.hoffman@icann.org
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