Internet DRAFT - draft-mglt-add-rdp
draft-mglt-add-rdp
add D. Migault
Internet-Draft Ericsson
Intended status: Informational July 28, 2020
Expires: January 29, 2021
DNS Resolving service Discovery Protocol (DRDP)
draft-mglt-add-rdp-03
Abstract
This document describes the DNS Resolver Discovery Protocol (DRDP)
that enables a DNS client to discover various available local and
global resolving service. The discovery is primarily initiated by a
DNS client, but a resolving service may also inform the DNS client
other resolving services are available and eventually preferred.
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 January 29, 2021.
Copyright Notice
Copyright (c) 2020 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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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Pointer to a list of Resolving Domains . . . . . . . . . . . 5
6. Discovery of Resolving Services . . . . . . . . . . . . . . . 6
7. TTL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. SvcParamKey . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Resolver advertising other service sub type . . . . . . . . . 8
10. Migration to service sub types . . . . . . . . . . . . . . . 8
11. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11.1. Use of protected channel is RECOMMENDED . . . . . . . . 8
11.2. DNSSEC is RECOMMENDED . . . . . . . . . . . . . . . . . 9
11.3. TLSA is RECOMMENDED . . . . . . . . . . . . . . . . . . 10
12. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
15. Appendices . . . . . . . . . . . . . . . . . . . . . . . . . 12
15.1. DRDP Requirements . . . . . . . . . . . . . . . . . . . 12
15.2. Discovery of specific service instance . . . . . . . . . 13
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
16.1. Normative References . . . . . . . . . . . . . . . . . . 14
16.2. Informative References . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Requirements Notation
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. Introduction
A DNS client can proceed to DNS resolution using various resolving
services. These services can be local or global and can use a wide
range of DNS transport protocols such as, for example, standard DNS
[RFC1035], DNS over TLS [RFC7858] or DNS over HTTPS [RFC8484]. The
local scope of these services may take various forms. For example,
it could be associated to a network perspective ( restricted to the
network the DNS client is connected to ) or to an application
perspective ( restricted to some domain names ).
The purpose of the DNS Resolving service Discovery Protocol (DRDP) is
to discover resolving services available to the DNS client. These
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available resolving services to a given DNS client may highly depend
on its location or browsing activity. The number of resolving
services available to the DNS client is expected to remain quite
consequent and evolve over time. Similarly, characteristics
associated to these resolving services may also evolve over time. As
a result, the DNS client is unlikely willing to synchronize such a
huge data base of resolving services. DRDP proposes an alternative
that consists in adaptively discovering the available resolving
services based on the DNS client context.
DRDP adopts a hierarchical approach where the DNS client (or DRDP
client) discovers the resolving services from resolving domains (RD)
or a pointer to a list of resolving domains (Pointer).
The document does not describe how the DNS client is provisioned with
RD or RD_list. The DNS client may obtain the contextual resolving
domains via various way, including a configuration, via DHCP Options
[I-D.btw-add-home] or derived from specific procedures [I-D.mglt-add-
drdp-isp]. The DNS client is expected to discover resolving services
from all RD or RD_list before proceeding to a selection process. The
selection process of the resolving service is out of scope of this
document.
3. Terminology
DNS client the client that sends DNS queries fro resolution. In
this document the DNS client designates also the end entity that
is collecting information about the available Resolving Services
and then proceed to the selection of a subset them. The selection
is processed according to the DNS client's policy.
Resolving Service designates a service that receives DNS queries
from a DNS client and resolves them. A Resolving Service is
implemented by one or multiple resolvers.
Resolver: A resolver designates the software or hardware handling the
DNS exchange. See [RFC7719] for more details.
DNS transport designates the necessary parameters a DNS client needs
to establish a session with a Resolving Service.
Resolving Domain a DNS domain that hosts one or multiple resolving
services.
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4. Overview
DRDP is a DNS based protocol that addresses the requirements listed
in Section 15.1. The figure below represents provides a high level
description of DRDP.
1. The DRDP client considers the source of resolving domains (RD).
This document defines two ways to collect RDs: RD are directly
provisioned - in our case rd.org) , or RD are retrieved from a
Pointer - in our case rd_pointer.org. In the later case RD are
collected from a DNS request of type PTR. In the case of Pointer
being rd_pointer.org, the QNAME of the PTR request would be
b._dns.rd_pointer.org.
2. The DRDP client collects the resolving services and associated
parameters under the umbrella of each RD. The resolving services
offered by the RD are collected via a DNS request of type SVCB
and the associated parameters are provided through SvcParameters.
In the case of the RD being rd.org, the QNAME of the SVCB request
would be _dns.rd.org.
+---------------------------------------------+
+---------------->| source of Resolving Domains |
| +---------------------------------------------+
1. collect | * resolving domains (rd.org) |
Resolving Domains | * list of resolving domains (rd_pointer.net)|
| | * other means: configuration, DHCP, |
| | Website co-hosting, derived |
| +---------------------------------------------+
|
+-------------+ +---------------------------------------------+
| DRDP client |----->| Resolving Domain |
+-------------+ +---------------------------------------------+
2. collect | rd.1.com, ..., rd.i.com, ..., rd.n.com |
Resolving Services +---------------------|------------------|----+
and associated | | |
parameters +---------------------|------------------|----+
| Resolving Services | | |
+---------------------v------------------v----+
| +-------------------+ +--------------+ |
3. Proceed | | doh.resolver.net | | doh.isp.com | |
Selection | +-------------------+ ... +--------------+ |
| | dot.resolver.net | | do53.isp.com | |
| +-------------------+ +--------------+ |
| | do53.resolver.net | |
| +-------------------+ |
+---------------------------------------------+
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5. Pointer to a list of Resolving Domains
A Pointer is a FQDN that points to a list of FQDN that designates RD.
If Pointer is represented by rd_pointer.net, the associated RDs are
retrieved by the DNS query of type PTR for b._dns.rd_pointer.org.
The zone file below is inspired from DNS-SD where b indicates a
browsing domain, _dns indicates the DNS resolving service,
rd_pointer.org the Pointer and rd.1.com, ... rd.i.com the associated
RDs. Note that they do not necessarily need to share a TLD. The
order of the resolving domains is irrelevant, and the zone
administrator SHOULD regularly reorder them. The RRsets MUST be
signed with DNSSEC.
b._dns.rd_pointer.net PTR rd.1.com
[...]
b._dns.rd_pointer.net PTR rd.n.com
Using the DNS provides the advantage to retrieve the resolving domain
without requiring other libraries than DNS as well as benefit from
the DNS caching infrastructure including the use of the TTL.
An EDNS buffer size of 1232 bytes will avoid fragmentation on nearly
all current networks. This is based on an MTU of 1280, which is
required by the IPv6 specification, minus 48 bytes for the IPv6 and
UDP headers. This document RECOMMENDS that the number of RDs
associated to a Pointer do not generate fragmentation of the DNS UDP
packet. It is believed to address most common needs or expectation
from a vast majority of stub DNS client.
When the number of RD exceeds this limit, the DNS client may carry
this over TCP which is likely to be supported by DNS client wiling to
upgrade to DoH or DoT resolving services. However, the transfer of
large number of RDs is considered as an application specificity that
would benefit benefit from the compression of the transferred data
provided by ftp or http. In such case, these application may define
there own specific mechanism to provision the RDs.
As of July 27 2020, 1232 bytes correspond to the 94 first most
popular FQDN listed by [moz.com]. The current size of such lists
[curl][dnsprivacy.org] have less than 50 resolving domains. Other
lists such as [public-dns.info] have as much as 11.000 entries, but
such lists seems to contain open resolvers which is out side of the
scope of a selection process.
Web browser (Google Chrome) also have lists over 10.000 entries, but
in case a significant number of entries seems to be IP addresses that
have a very limited network scope ( e.g. limited to the ISP ). The
length of the list in scope to the DNS client is in fact significant
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smaller in term of IP addresses and even smaller if resolving domain
are able to represent multiple IP addresses. Overall, the size of
such lists are currently due to the absence of discovery protocols.
6. Discovery of Resolving Services
The discovery of resolving services is performed by the RDP client
with all the available RDs. Given a RD rd.org, a DRDP client sends a
DNS request of type SVCB for _dns.rd.org.
The example below presents the use of an AliasForm followed by a
ServiceForm which allows an indirection. The Alias form is not
madatory and instead only ServiceForm associated to _dns.rd.org could
have been used instead.
The SvcFieldPriority indicates the preference of the RD. It
typically enables an operator to indicate that an encrypted DNS is
preferred.
The SvcParamKey alpn MUST be present when TLS is used as its presence
and value indicates the DNS transport. The absence of the alpn
SvcParamKey indicates Do53, alpn set to dot indicates DoT is served
while h* indicates DoH is served. Note that the port value (53, 853,
443) is not used to determine the DNS transport as non standard port
MAY be used. The example below uses an non standard port 5353 for
illustrative purpose.
Other SvcParam are detailed in Section 8 and are optional. A
SvcParam not understood by the DNS client MUST be ignored.
The RRsets MUST be protected with DNSSEC and when alpn is provided a
TLSA RRset SHOULD be present. These RRsets have been omitted for
clarity.
## Discovery of all service instances
_dns.rd.org. 7200 IN SVCB 0 svc.example.com.
svc.example.com. 7200 IN SVCB 12 ( svc0.example.net.
port="5353" user-display="Legacy Resolver" )
svc.example.com. 7200 IN SVCB 1 ( svc1.example.net. alpn="dot"
port="5353" esniconfig="..."
user-display="Preferred Example's Choice" )
svc.example.com. 7200 IN SVCB 3 ( svc2.example.net. alpn="h2"
port="5353" esniconfig="..." user-display= )
svc.example.com. 7200 IN SVCB 2 ( svc3.example.net. alpn="h3"
port="5353" esniconfig="..." user-display= )
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Note that Section 15.2 provides another variant to perform RDP. Such
variant is left for further discussion and address the need to be
able to narrow down the discovery to a subset of resolving services
such as DoH-only or DoT-only services.
Some notes:
1. _domain uses SVCB but does not have TLS. While SVCB has been
created essentially for TLS based service, this does not appear
to be mandatory.
2. Should we have some constraints regarding the SvcDomainName and
QNAME ?
3. do we need the service subsets
7. TTL
The DNS client SHOULD perform DRDP at regular intervals as indicated
by its policy.
The selection process MAY remove resolving services with short TTL
lower than a day as it indicates some source of instalbility. Given
a subset of selected resolving services, the DNS client may perform
DRDP 1 hour before an SVB RRset expires.
8. SvcParamKey
This section defines a set of SvcParamKey that MAY be use to carry
the necessary informations for the selection process.
alpn :
esniconfig :
port :
user-display indicates a strings in UTF-8 that is expected to be
representative to a potential end user. Though there is no
restriction in the scope of that string. The string is likely to
represent the service within the resolving domain.
uri_template designates the URI template for DoH. This key MUST NOT
be present on non DoH services and MUST be ignored by the DNS
client on non DoH resolving Services.
auth_domain indicates the list of authoritative domain name the
resolving service has strong relation with. It is expected that a
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resolving service may prefer to perform DNS resolution over these
domains to that specific resolving service as to preserve its
privacy. This information MUST be verified and validated.
scope_domain indicates the limitation of resolved domains. When
present DNS request sent to the resolution service MUST belong to
that domain.
filtering indicates the presence of a filtering service
ip_subnet indicates a subnetwork restriction. This is mostly useful
for resolving services that are not globally.
dnssec indicates whether dnssec is enabled or not.
9. Resolver advertising other service sub type
A resolving service receiving a DNS request over a service sub type
MAY be willing to advertise the DNS client that other sub service
type are available. This is especially useful, when, for example, a
resolver wants that the DNS resolver switches to other service sub
types that are more secure.
In order to do so the resolver MAY provide in the additional data
field the _dns SRVCB of ServiceForm.
10. Migration to service sub types
The principle of the discovery mechanism is that the resolver
indicates the available service sub types and let the DNS client
chose which sub type it prefers. On the other hand, the resolver MAY
also indicate a preference using the priority and weight fields.
Redirection MAY especially be needed when a DNS client is using the
Do53 and the resolver would like to upgrade the DNS client session to
a more secure session. This MAY require a specific ERROR code that
will request the DNS client to perform service discovery.
It is expected that DRDP MUST always be available via Do53. However,
this does not mean that a resolver is expected to implement the Do53
sub type service for a resolving service.
11. Security Considerations
11.1. Use of protected channel is RECOMMENDED
When available, it is recommended to chose a protected version of the
rdns service. More specifically, the use of end-to-end protection
ensures that the DNS client is connected to the expected platform and
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that its traffic cannot be intercepted on path. Typically, the
selection of resolver on the Internet (and not on your ISP network)
and the use of a non protected channel enables an attacker to monitor
your DNS traffic. The similar observation remains true if you are
connected to the resolver of your ISP. It is commonly believed that
trusting your ISP (that is your first hop) makes encryption
unecessary. Trusting your ISP is mandatory in any case, but the
associated level of trust with an protected channel is restricted to
the operation of the DNS platform. With non protected channel the
trust is extended to any segment between the DNS client and the
resolver, which is consequently larger. The use of a protected
channel is recommended as it will prevent anyone on path to monitor
your traffic.
11.2. DNSSEC is RECOMMENDED
The exchanges SHOULD be protected with DNSSEC to ensure integrity of
the information between the authoritative servers and the DNS client.
Without DNSSEC protection, DNS messages may be tampered typically
when they are transmitted over an unprotected channel either between
the DNS client and the resolver or between the resolver and the
authoritative servers. The messages may be tampered by an online
attacker intercepting the messages or by the intermediary devices.
It is important to realize that protection provided by TLS is limited
to the channel between the DNS client and the resolver. There are a
number of cases were the trust in the resolver is not sufficient
which justify the generalization of the use of DNSSEC. The following
examples are illustrative and are intended to be exhaustive.
First, the discovery exchanges may happen over an unprotected
channel, in which case, the messages exchanged may be tampered by
anyone on-path between the DNS client and the resolver as well as
between the resolver and the authoritative servers - including the
resolver. When TLS is used between the DNS client and the resolver,
this does not necessarily mean the DNS client trusts the resolver.
Typically, the TLS session may be established with a self-signed
certificate in which case the session is basically protected by a
proof-of-ownership. In other cases, the session may be established
based on Certificate Authorities (CA) that have been configured into
the TLS client, but that are not necessarily trusted by the DNS
client. In such cases, the connected resolver may be used to
discover resolvers from another domain. In this case, the resolver
is probably interacting with authoritative servers using untrusted
and unprotected channels. Integrity protection relies on DNSSEC.
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11.3. TLSA is RECOMMENDED
When TLS is used to protect the DNS exchanges, certificates or
fingerprint SHOULD be provided to implement trust into the
communication between the DNS client and the resolver. The TLS
session and the association of the private key to a specific identity
can be based on two different trust model. The Web PKI that will
rely on CA provisioned in the TLS library or the TA provided to the
DNS client. A DNS client SHOULD be able to validate the trust of a
TLS session based on the DNSSEC trust model using DANE.
When the DNS client is protecting its session to the resolver via
TLS, the DNS client may initiate an TLS session that is not validated
by a CA or a TLSA RRsets. The DNS client MUST proceed to the
discovery process and validate the certificate match the TLSA RRset.
In case of mismatch the DNS client MUST abort the session.
12. Privacy Considerations
When the discovery protocol is performed using a resolver that
belongs to one domain for another domain, or over an unprotected
channel, the DNS client must be conscious that its is revealing to
the resolver its intention to use another resolver. More
specifically, suppose an resolver is complying some legal
requirements that DNS traffic must be unencrypted. Using this
resolver to perform a resolver discovery reveals the intention of
potentially using alternative resolvers. Alternatively, narrowing
down the discovery over a specific sub type of resolver (DoT, or DoH)
may reveal to that resolver the type of communication. As result,
when performing a discovery over a domain that differs to the domain
the resolver belongs to, it is RECOMMENDED to request the SRV RRsets
associated to all different sub type of proposed services.
The absence of traffic that results from switching completely to a
newly discovered resolver right after the discovery process provides
an indication to the resolver the DNS client is switching to. It is
hard to make that switch unnoticed to the initial resolver and the
DNS resolver MUST assume this will be noticed. The information of
switching may be limited by sharing the traffic between different
resolvers, however, the traffic pattern associated to each resolver
may also reveal the switch. In addition, when the initial resolver
is provided by the ISP, the ISP is also able to monitor the IP
traffic and infer the switch. As a result, the DNS client SHOULD
assume the switch will be detected.
With DoT or DoH, the selection of port 443 will make the traffic
indistinguishable from HTTPS traffic. This means that an observer
will not be able to tell whether the traffic carries web traffic or
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DNS traffic. Note that it presents an interest if the server offers
both a web service as well as a resolution service. Note that many
resolvers have a dedicated IP address for the resolution service, in
which case, the information will be inferred from the IP address.
Note also that traffic analysis may infer this as well. Typically
suppose an IP address hosts one or multiple web sites that are not
popular as well as a resolving service. If this IP address is
associated frequent short size exchanges, it is likely that these
exchanges will be DNS exchanges rather than Web traffic. The size of
the packet may also be used as well as many other patterns. As a
result, the use port 443 to hide the DNS traffic over web traffic
should be considered as providing limited privacy.
13. IANA Considerations
This document requests the IANA the creation of the following
underscored node names in the Underscored and Globally Scoped DNS
Node Names registry https://www.iana.org/assignments/dns-parameters/
dns-parameters.xhtml#dns-parameters-14
RR Type | _NODE NAME | Reference
--------+------------+----------
SRVCB | _dns | RFC-TBD
SvcParamKey | NAME | Meaning | Reference
------------+--------------+-----------------------------+-----------
7 | user-display | User friendly string (UTF8) | RFC-TBD
| | to represent the resolver |
| uri_template | URI template |
| auth_domain | Domains the resolving |
| | service is authoritative |
| filetring | Filetring services provided |
| ip_subnet | ip ranges accepted. |
| dnssec | DNSSEC validation enabled |
14. Acknowledgments
We would like thank Mirja Kuehlewind as well as the GSMA IG for their
comments. We also thank Ted Hardie and Paul Hoffman for their feed
backs regarding the dns schemes for DoT and DoH.
We thank Ben Schwartz for the comments on the list size. We thank
Harald Alvestrand for its recommendation on having a model that
enable multiple third party providers to provide their own list of
resolving domains. We thank Stephan Bortzmeyer, Ralf Weber, Chris
Box for its clarifications.
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15. Appendices
15.1. DRDP Requirements
This section lists the DRDP requirements.
REQ 1: DRDP MUST enable a DNS client to discover the available
resolving services with their associated characteristics in order to
proceeds to a selection process. The selection process takes
resolving services identities and associated parameters and proceed
to the selection.
Any sort of resolving service selection is outside the scope of DRDP.
REQ 2: While the discovery process is triggered by the DNS client, a
third party MUST be able to provide necessary input information so a
resolving service discovery process can be triggered within a
specific context.
Provisioning protocols to provide this information is not as per say
in scope of DRDP. DRDP defines the format of the format for such
input as well as a set of such inputs.
REQ 3: Any information used in DRDP MUST be authenticated by its
owner. In particular, the characteristics associated to the
resolving service MUST be certified by the resolving service operator
/ owner and MUST be associated a validity period. In addition, a
third party providing a set of inputs MUST authenticate that set.
REQ 4: Information associated to the resolving services is intended
to enable the selection process that is assumed to match the end user
or application policy. The selection process is out of scope of
DRDP. Information may carry some characteristics of a resolving
service or hints that will help the selection. In particular an
operator of multiple resolving service MUST be able to associate a
preference to the proposed resolving services. To ease automation of
the selection as well as to make multiple applications benefit from
DRDP the information MUST be carried over a standardized format.
REQ 5: DRDP MUST be designed to be used indifferently by a DNS client
using any DNS transport protocol (Do53, DoT, DoH, ...). However,
DRDP SHOULD be able to restrict the information retrieved to a
certain type of resolving service, i.e. Do53, DoT, DoH.
REQ 6: DRDP deployment MUST NOT be disruptive for the legacy DNS
client or infrastructure and legacy client SHOULD be able to
incrementally include DRDP.
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15.2. Discovery of specific service instance
To reduce the size of the messages, the DNS client MAY also prefer to
query information of resolving services using a specific transport
(DNS, DoT, DoH) that are designated as sub sets. A DNS client MAY
list the different subsets of that resolving domain with a PTR query.
This document defines the following subsets _53._dns for DNS,
_853._dns for DoT and _443.__dns for DoH. Other subsets MAY be
defined in the future. A DNS client that does not understand a
subset SHOULD ignore it and maybe proceed to the discovery as defined
in Section 6.
All subsets MUST share the same resolving domain and be listed with a
PTR RRsets. The DNS client MAY NOT performed a DNS query of type
PTR, for example, if it has a previous knowledge of the existence of
the subset or if indicated by its policy. In this it MAY directly
proceed to the SRVCB resolution.
The same restrictions as defined in section Section 6 apply.
Note that while the SvcFieldPriority indicates the priority within a
subservice, this field MUST have a coherence across subservices. The
priority provided SHOULD be coherent with the case of a _dns SRVCB
query of section Section 6.
The figure below illustrates an example of zone file. RRSIG and TLSA
have been omitted for the purpose of clarity.
### Definition of the resolving service subsets
_dns.example.com PTR _53._dns.example.com
_dns.example.com PTR _853._dns.example.com
_dns.example.com PTR _443._dns.example.com
### services instances per service subset
_53._dns.example.com. 7200 IN SVCB 0 svc0.example.com.
svc0.example.com. 7200 IN SVCB 12 ( svc0.example.net.
port="5353" user-display="Legacy Resolver" )
_853._dns.example.com. 7200 IN SVCB 0 svc1.example.com.
svc1.example.com. 7200 IN SVCB 1 ( svc1.example.net. alpn="dot"
port="5353" esniconfig="..."
user-display="Preferred Example's Choice" )
_443_dns.example.com. 7200 IN SVCB 0 svc4.example.net.
svc4.example.com. 7200 IN SVCB 3 ( svc2.example.net. alpn="h2"
port="5353" esniconfig="..." user-display= )
svc4.example.com. 7200 IN SVCB 2 ( svc3.example.net. alpn="h3"
port="5353" esniconfig="..."
user-display="Testing QUIC")
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16. References
16.1. 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/info/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/info/rfc2119>.
[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>.
[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>.
[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>.
16.2. Informative References
[curl] "Publicly available servers", n.d.,
<https://github.com/curl/curl/wiki/DNS-over-
HTTPS#publicly-available-servers>.
[dnsprivacy.org]
"DNS Privacy Test Servers", n.d.,
<https://dnsprivacy.org/wiki/display/DP/
DNS+Privacy+Test+Servers#DNSPrivacyTestServers-
Publicresolvers>.
[I-D.btw-add-home]
Boucadair, M., Reddy.K, T., Wing, D., and N. Cook,
"Encrypted DNS Discovery and Deployment Considerations for
Home Networks", draft-btw-add-home-07 (work in progress),
July 2020.
[moz.com] "The Moz Top 500 Websites", n.d.,
<https://moz.com/top500>.
Migault Expires January 29, 2021 [Page 14]
Internet-Draft DRDP July 2020
[public-dns.info]
"Public DNS Server List", n.d.,
<https://public-dns.info/>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.
Author's Address
Daniel Migault
Ericsson
8275 Trans Canada Route
Saint Laurent, QC 4S 0B6
Canada
EMail: daniel.migault@ericsson.com
Migault Expires January 29, 2021 [Page 15]
