Internet DRAFT - draft-sah-resolver-information
draft-sah-resolver-information
Network Working Group P. Sood
Internet-Draft Google
Intended status: Standards Track R. Arends
Expires: December 29, 2019 P. Hoffman
ICANN
June 27, 2019
DNS Resolver Information Self-publication
draft-sah-resolver-information-02
Abstract
This document describes methods for DNS resolvers to self-publish
information about themselves, such as whether they perform DNSSEC
validation or are available over transports other than what is
defined in RFC 1035. 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-
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 December 29, 2019.
Copyright Notice
Copyright (c) 2019 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
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publication of this document. Please review these documents
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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 . . . . . . . . . . . 5
4.1. The "inventory" name . . . . . . . . . . . . . . . . . . 6
4.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. RESINFO RRtype . . . . . . . . . . . . . . . . . . . . . 6
5.2. Registry for DNS Resolver Information . . . . . . . . . . 6
5.3. resolver-info Well-known URI . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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
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[RFC8259]. Requiring the use of I-JSON instead of more general JSON
format greatly increases the likelihood of interoperability.
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.
It is important to note that the protocol defined here is only for
recursive resolvers, not for authoritative servers. Authoritative
servers MUST NOT answer queries that are defined in this protocol.
(It is likely that a later protocol will allow authoritative servers
to give information in a method similar to the one described in this
document.)
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 <reverse-ip>.{in-addr,ip6}.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.
In this section, "<reverse-ip>.{in-addr,ip6}.arpa" is the domain name
associated with the reverse lookup of an IP address of the resolver
(resolvers can have multiple addresses). For example, if the
resolver is at 192.0.2.1, the query would be 1.2.0.192.in-
addr.arpa/IN/RESINFO.
A resolver that receives a query with the RRtype of RESINFO with a
QNAME of <reverse-ip>.{in-addr,ip6}.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
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also be authoritative for some zones, it can use that configuration
to actually be authoritative for the addresses on which it responds.
A stub that knows a specific type of information it wants MAY ask for
that information by prepending a label with the name of the
information in its query. For example, if the stub knows that it
wants information whose name is "temp-field2", it would send the
query temp-field2.<reverse-ip>.{in-addr,ip6}.arpa/IN/RESINFO. As
described in Section 4, the JSON object in the response is likely to
have name/value pairs in addition to the one requested.
Any query for the RESINFO RRtype that is not in <reverse-ip>.{in-
addr,ip6}.arpa/IN or a subdomain of <reverse-ip>.{in-addr,ip6}.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 not in
<reverse-ip>.{in-addr,ip6}.arpa/IN or a subdomain of <reverse-
ip>.{in-addr,ip6}.arpa/IN .
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 one of:
https://IPADDRESSOFRESOLVER/.well-known/resolver-info/
https://DOMAINNAMEOFRESOLVER/.well-known/resolver-info/
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 protocol to publish its information SHOULD,
if possible, have a TLS certificate whose subject identifiers are any
IP address that the resolver is available on, as well as any domain
names that the resolver operator uses 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. [I-D.ietf-acme-ip] describes a new
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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.
4. Contents of the Returned I-JSON Object
The JSON object returned by a DNS query or an HTTPS query MUST
contain at least one name/value pair: "inventory", described later in
this section. The returned object MAY contain any other name/value
pairs.
The requirement for the inclusion of the "inventory" name/value pair
is so that systems retrieving the information over DNS can create
specific queries. Using specific queries can reduce the number of
round trips in the case where the answers to queries become large.
The "inventory" name/value pair MUST be included in the response even
if the query was for a single name.
If the request was over DNS using a subdomain under <reverse-ip>.{in-
addr,ip6}.arpa, the resolver SHOULD return an object that contains a
name/value pair with that name if the resolver has that information.
If the resolver does not have information for that name, it MUST NOT
return the name in the object.
If the request was over HTTPS, the resolver SHOULD return an object
with all known name/value pairs for which it has information.
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.
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.
This document only defines one element that can returned:
"inventory". All other elements will be defined in other documents.
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4.1. The "inventory" name
The "inventory" name lists all of the types of information for which
the resolver has data. The value is an array of strings.
4.2. Example
The I-JSON object that a resolver returns might look like the
following:
{
"temp-field2": 42,
"temp-field1": [ "There is", "no \u000B!" ],
"inventory": [ "inventory", "temp-field1", "temp-field2" ]
}
As specified in [RFC7493], the I-JSON object is encoded as UTF8.
This example has no un-escaped non-ASCII characters only because they
are not currently allowed in Internet Drafts. For example, the
exclamation mark in the second name/value pair could instead be the
double exclamation mark character, U+203C.
[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].
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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
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. resolver-info 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: resolver-info
Change controller: IETF
Specification document(s): This document
Status: permanent
6. Security Considerations
Unless a DNS request for <reverse-ip>.{in-addr,ip6}.arpa/IN/RESINFO,
or a subdomain, as described in Section 2 is sent over DNS-over-TLS
(DoT) [RFC7858] or DNS-over-HTTPS (DoH) [RFC8484], or unless the
<reverse-ip>.{in-addr,ip6}.arpa zone is signed with DNSSEC, the
response is susceptible to forgery. Stubs and resolvers SHOULD use
normal DNS methods for avoiding forgery such as query ID
randomization and source port randomization. A stub resolver will
know if it is using DoT or DoH, and if it is using DoT it will know
if the communication is authenticated (DoH is always authenticated).
An application that is using an operating system API to send queries
for <reverse-ip>.{in-addr,ip6}.arpa/IN/RESINFO or a subdomain will
only know if query went over authenticated DoT or DoH if the API
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supports returning that authentication information. Currently, no
common APIs support that type of response.
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>.
7.2. Informative References
[I-D.ietf-acme-ip]
Shoemaker, R., "ACME IP Identifier Validation Extension",
draft-ietf-acme-ip-06 (work in progress), May 2019.
[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>.
[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>.
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[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
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.
Erik Kline suggested using "<reverse-ip>.{in-addr,ip6}.arpa" as the
domain name to allow for the possibility of DNSSEC-signed responses.
Authors' Addresses
Puneet Sood
Google
Email: puneets@google.com
Roy Arends
ICANN
Email: roy.arends@icann.org
Paul Hoffman
ICANN
Email: paul.hoffman@icann.org
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