Network Working Group V. Bertola
Internet-Draft Open-Xchange
Intended status: Informational September 10, 2019
Expires: March 13, 2020
Recommendations for DNS Privacy Client Applications
draft-bertola-bcp-doh-clients-01
Abstract
This document presents operational, policy and security
considerations for the authors and publishers of client applications
that choose to implement DNS resolution through any of the protocols
that provide private, encrypted connections between the application
itself and the DNS resolver. As these protocols, depending on
implementation choices and deployment models, may impact the Internet
significantly at the architectural, legal and policy levels, the
document records the current consensus on how these protocols should
be used by applications, especially user-facing applications meant
for mass usage by non-technical consumers.
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
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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 March 13, 2020.
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
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Notation and Conventions . . . . . . . . . . . . 3
3. Architectures for Name Resolution Services . . . . . . . . . 3
4. Issues and Recommendations . . . . . . . . . . . . . . . . . 5
4.1. Trust Model and User Choice . . . . . . . . . . . . . . . 5
4.2. Consolidation . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Competition and Network Neutrality . . . . . . . . . . . 9
4.4. Namespace Fragmentation . . . . . . . . . . . . . . . . . 10
4.5. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.6. Content Access Control . . . . . . . . . . . . . . . . . 12
4.7. Security and Network Management . . . . . . . . . . . . . 13
4.8. Jurisdiction . . . . . . . . . . . . . . . . . . . . . . 15
4.9. Disaster Recovery . . . . . . . . . . . . . . . . . . . . 17
4.10. User Support . . . . . . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
7. Human Rights Considerations . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
As a reaction to growing concerns about widespread "pervasive
monitoring" activities, the IETF declared these practices to be an
attack [RFC7258] and started work to promote the encryption of the
transport of information across the Internet.
The Domain Name System [RFC1034] is a fundamental element of the
Internet, as almost any online activity starts with one or more DNS
queries, which can be used to track the services and the content that
the user is accessing, and even to redirect or disallow such access;
DNS traffic deriving from the activity of human beings constitutes
sensitive and valuable personal information. Section 2.4.1 of
[I-D.bortzmeyer-dprive-rfc7626-bis] describes the risks created by
the unencrypted transmission of such information.
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To mitigate these risks, two new standards have been developed to
encrypt the transport of DNS queries and replies between the user's
machine and the recursive resolver: DNS-over-TLS [RFC7858] and DNS-
over-HTTPS [RFC8484]. The adoption of these protocols is still
limited, but early deployments, especially of the latter, have raised
a number of issues that pertain to consolidation and centralization,
other privacy risks, various cases of content control, network
security and management, applicable jurisdiction and more.
These issues, if not addressed, could outweigh the benefits deriving
from the encryption of DNS transport. Some of them can be addressed
at the server side of the connection; they are the subject of
[I-D.ietf-dprive-bcp-op]. However, some of these issues derive from
the behaviour of client applications that implement the protocols and
use them to query the DNS as necessary for their activities.
This document presents the best practices that address these issues
at the client side of the connection and that, as far as possible,
could allow an uncontroversial and positive deployment of encrypted
DNS transport protocols.
2. Requirements Notation and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Throughout this document, values are quoted to indicate that they are
to be taken literally. When using these values in protocol messages,
the quotes MUST NOT be used as part of the value.
3. Architectures for Name Resolution Services
It is possible for a device to perform full DNS name resolution on
its own, without relying on any recursive DNS resolver - indeed, this
was often the case in the early usage of the DNS.
However, since when the Internet became a mass affair, the DNS name
resolution service in consumer Internet access services has been
generally provided by a recursive DNS resolver on the local network
("local resolver"), supplied by the same ISP that is providing the
user with Internet access, often through automated configuration
mechanisms such as DHCP [RFC2131].
More recently, public DNS resolvers ("remote resolvers"), provided on
an Internet scale by a few big operators, have been gaining ground;
users have been able to set them as the resolver for all their
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applications at once, by changing a configuration item in their
devices.
Thus, the current architecture for mainstream DNS resolution services
relies on the following assumptions:
1. All the applications on the same device use the same resolver,
through a library provided by the operating system;
2. By default, the device will automatically discover and use the
resolver provided by the local network;
3. The user is in charge of deciding which resolver will be used,
either by silently accepting the default, or by setting a
specific resolver in the device configuration.
Early deployments of DNS-over-TLS have generally followed the same
model; in the first mobile operating system that has implemented
support for the protocol, the system will try to discover whether the
resolver configured in the operating system supports DNS-over-TLS
connections, and if so, it will automatically upgrade the connection
to the new protocol while continuing to use the same resolver;
otherwise, it will keep using the unencrypted connection.
Early deployments of DNS-over-HTTPS have followed a different model.
The first major Web browser releasing support for DNS-over-HTTPS has
announced the intention to follow a service architecture based on
different assumptions:
1. Each application will use its own resolver, bypassing the library
provided by the operating system;
2. No automatic discovery of resolvers on the local network is
performed;
3. The application is in charge of determining which resolver will
be used, which could be different than the one configured in the
operating system, and can direct this choice by selecting and
providing one as the default for all users globally, or even by
limiting the user's choice to a list of resolvers vetted by the
application maker.
In the rest of the document, we will refer to this new architecture
as "application-level name resolution", and to the traditional one as
"network-level name resolution". More specifically, we will refer to
point 3 of the above list as "application-level resolver selection".
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While the document will also address the issues that derive simply
from the switch to an encrypted connection, most of the issues that
have been noticed during the early deployment efforts for DNS-over-
HTTPS do not derive from the protocol in itself, but rather from the
switch to application-level name resolution under the assumptions
above, and most frequently from the adoption of application-level
resolver selection.
Other possible architectures have also been identified: for example,
applications could use different resolvers for each of the different
servers that they have to connect to, or the servers could push DNS
records to the client even before they are actually queried. As
these models are still speculative, the issues that they would
generate are not currently addressed by this document.
4. Issues and Recommendations
This section classifies the issues that are created by the deployment
of encrypted DNS protocols and/or by the change of resolution
architectures on the client side, and presents recommendations to
address them.
4.1. Trust Model and User Choice
With network-level name resolution, users are in charge of the choice
of the resolver used by all their applications. Advanced and
educated users make full use of that opportunity, and choose to send
their DNS queries to an operator they trust, either by configuring a
specific resolver in the operating system or on the router that
manages their home network, or as part of a broader traffic
encryption and redirection service (e.g. VPNs). Other users will
just rely on the local network's server; for home users, this will be
provided by their Internet access provider, which they also picked,
thus giving them at least some degree of trust. A different, less
trusted relationship exists when users that did not configure a
specific server connect to a local network which is not their own,
for example in Internet cafes or hotels; in that case, they may be
led to use a resolver which they do not trust.
Also, in the absence of encryption, the local network operator could
still be able to track or even alter the DNS queries and replies that
the user has directed to a non-local resolver. Unless this has been
agreed with the user or is mandated by applicable legislation, this
would be a breach of the user's trust and is a good reason to promote
the adoption of encrypted DNS protocols.
With application-level name resolution, and especially with
application-level resolver selection, users lose at least part of
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their control. Some applications may actually not give the user any
choice, and just use their own resolver all the times; some others
may provide configuration options, but still direct the queries to
their own resolver as a default, requiring specific action for users
to keep their DNS traffic going to the resolver that they already
configured in the operating system.
Such a change of default behaviour would break the expectations of
many users; unless appropriate communication is given and consent is
acquired, both the users that explicitly configured a resolver in the
operating system, and the users that want their device to use the
local network's resolver, will be surprised by the application
sending DNS queries to another server instead. On the other hand,
for less technical users that trust the application maker to make a
better choice of resolvers on their behalf, the new behaviour could
be in line with their expectations.
However, also given the high sensitivity of the personal information
embedded in DNS queries, it is important to ensure that it is
ultimately the user, rather than any third party, that determines
where their DNS queries should go, and explicitly consents to any
choice of resolver that cannot be expected, or to delegating the
choice to another party.
This leads to the following recommendations:
1. Users MUST have the final word on which resolver is used by each
application.
2. Applications MUST NOT use a different resolver operator than the
one that would be used by the operating system, unless the user
has actively told the application to use a different resolver
operator and has given explicit and informed consent to the
change.
3. Applications MUST provide users with a configuration mechanism
that allows them to tell the application to use any resolver the
user wants.
4. Applications SHOULD provide users with adequate information on
the location, ownership, data management policies and operational
practices of each resolver, at least for the resolvers that they
provide as hard-coded configuration options.
5. Applications SHOULD support, if available, easy ways for the user
to direct all applications on the device to use a specific
resolver and a specific protocol, without the need to configure
them one by one.
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For recommendation #2, it may happen that the resolver configured in
the operating system does not support encrypted DNS protocols. In
this case, the application SHOULD first of all try to determine
whether the operator of the non-encrypted resolver that would be used
by the operating system also provides any encrypted DNS resolver,
through standardized discovery mechanisms such as
[I-D.ietf-doh-resolver-associated-doh]; in that case, it SHOULD use
that operator's encrypted resolver instead of the unencrypted one.
For recommendation #4, the guidelines in [I-D.ietf-dprive-bcp-op]
SHOULD be followed; applications could explore ways to make them more
understandable to average Internet users, for example through the use
of standardized visual aids. At the same time, due to the complexity
and changing nature of this information, applications could simply
provide links to where the operator makes it available; a
standardized and automated way for resolvers to make this information
available to applications would be desirable.
For recommendation #5, in most operating systems and devices it is
yet to be discussed how to achieve the objective of letting the user
set the preferred resolver and protocol in all the applications at
once; the principle, however, deserves to be stated as a recommended
direction for future development.
4.2. Consolidation
Currently, with network-level name resolution, DNS resolution
activities are globally spread across a huge number of resolvers,
possibly in the range of the hundreds of thousands or even millions;
while some consolidation is happening, mostly into some big remote
resolver platforms, still it takes the thousand biggest resolvers to
aggreagate 90% of global DNS traffic. Users that keep the default of
using the local network's resolver see their personal DNS queries
spread across multiple servers as they move; users that configure a
specific public resolver have their queries concentrated on a single
resolver system, but they can pick one that they trust.
However, in many cases, the global market for user applications is
much more consolidated than the global market for Internet access and
for DNS resolution services. More specifically, estimates for the
global browser market currently show one maker having around 60% of
the market, and the first four together having over 90% of it. While
these market shares may change in the future, the presence of one or
a few dominant browsers has almost always been the case since the
advent of mass usage of the World Wide Web.
As application-level name resolution turns the application maker into
a potential gatekeeper in the choice of the resolver, there is a
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concern that each application maker could lead its users to the
adoption of one specific resolver operator, or limit their choice to
a few options that the maker has picked for its own reasons.
While it is understandable that an application maker may want to help
its users make a good choice of resolver by using its technical
expertise to evaluate and select a narrow set of recommended
resolvers, this practice would open opportunities for misuse, as
applications could recommend resolvers not because of a fair
evaluation, but because of an existing business partnership in the
mutual economic interest, or even because the resolver is run
directly by the application maker.
In the end, this could lead to a dramatic consolidation of global
name resolution operators, with a few server systems managing the
broad majority of global resolutions. This, in turn, would have
several negative consequences, which will be discussed in the
following sections of the document.
However, consolidation is an architectural problem in itself; the
Internet was designed to be as decentralized as possible, to increase
its resilience and ultimately the freedom of its users. The concern
over the centralizing effect of encrypted DNS protocols has been
recorded for example in [I-D.arkko-iab-internet-consolidation],
section 2.5, and has to be addressed by preventing the use of a
strong position in the market for a specific type of client
application, especially a ubiquitous one such as browsers, to
centralize DNS resolutions and establish a strong position in DNS
name resolution services.
This would already be addressed by the recommendations in section
4.1, but it also leads to the following additional recommendations:
1. Applications MUST NOT prioritize any specific resolver over
others unless told so by the user, or design their user
interaction to lead users towards choosing a specific resolver or
one of a few specific resolvers.
2. If possible, and if desired by the user, applications SHOULD
provide ways to spread their DNS resolution traffic across the
highest possible number of recursive resolvers. [NOTE: this
recommendation is actually a placeholder, as there are drawbacks
to this idea and other, better methods could be devised - this is
TBD]
3. If applications would like to ensure that their users can pick a
resolver that has been vetted under a set of criteria, the
definition, verification and enforcement of these criteria SHOULD
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be deferred to an independent multi-stakeholder organization,
making these criteria public and objective and giving any
resolver operator from any part of the Internet a fair chance to
be admitted to the list of vetted services; in any case, users
MUST still be free to adopt servers outside of the vetted list if
they so desire.
4.3. Competition and Network Neutrality
The possible inception of a stricter relationship between application
makers and resolver operators also creates issues related to
competition, which can in turn have effects on the architecture and
performance of the network and on its capacity for permissionless
innovation, and compromise the neutrality of network transport, as
DNS resolution is a fundamental step in establishing any network
connection.
In addition to the consolidation effect described in the previous
section, any relationship between the application maker and a
resolver operator that could lead the application to direct users to
a specific resolver could be used to reduce the opportunities
available to other resolver operators, including innovative ones, and
even to other application makers, for example by virtue of exclusive
service agreements. This can be a likely case when the application
maker and the resolver operator are the same entity, but it could
happen also when the application maker and the resolver operator are
two different entities that have established a business partnership
in the mutual interest.
Another case of anti-competitive effect could happen when the
resolver operator also operates another service that depends for its
effectiveness on the results of the DNS resolution process - for
example, content delivery networks. Resolver operators that also
operate CDNs could provide slower or less effective DNS resolution
for access to content distributed by their competitors.
While this matter will also be under the purview of national and
international market regulations, there are some recommendations - in
addition to those in the previous section, that also address this
issue - that can be made in terms of best practices, to neutralize as
far as possible any direct relationship between the application maker
and the resolver operator:
[ to be discussed ]
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4.4. Namespace Fragmentation
If each application could pick a different resolver, there is a
chance that different applications would receive different replies to
the same DNS queries, leading to confusing user experiences,
potential attack surfaces and network management and debugging
problems, and in the end to the fragmentation of the Internet into
non fully interoperable chunks.
The only way to prevent any occurrence of this case would be to
require all applications on the same device to use the same resolver,
as in the current network-level resolution model; however, such
requirement would be considered too restrictive. Recommendations #2
and #3 in section 4.1 are however meant to make this case a special
exception, rather than the norm, and thus mitigate this problem.
However, when allowing different applications to use different
resolvers, there is a situation that would significantly endanger the
stability of the Internet. Currently, as the application and the
resolver are generally provided by two independent entities, and as
the application cannot know in advance which resolver will be used,
applications cannot rely on predetermined non-standard behaviour by a
specific resolver. With application-level resolver selection,
applications that enjoy a significant market share could direct users
to resolvers that employ alternate DNS namespaces that they control,
or start to create and remove top level domains outside of the
collectively agreed policy frameworks.
The global uniqueness of the DNS namespace and its collective policy-
making procedures should be preserved, and this leads to the
following additional recommendation:
1. Applications SHOULD NOT adopt alternate DNS namespaces or promote
the use of resolvers that do not rely on the global DNS root
server system.
2. Applications SHOULD NOT deviate from the DNS namespace management
policies, technical standards and operational practices that are
defined in the relevant Internet governance venues.
Regarding recommendation #1, there may be specific use cases in which
a user may want to use an alternate namespace and root server set,
and applications, if they want, should be free to support them;
however, these cases must be exceptions and not for mainstream usage.
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4.5. Privacy
Protecting the user's privacy is the primary aim of transitioning the
DNS to encrypted communications. However, risks to privacy deriving
from DNS communications are not limited to the eavesdropping of
unencrypted DNS communications; [I-D.bortzmeyer-dprive-rfc7626-bis]
lists, in section 2.4.2, several privacy risks that still exist even
when DNS communications are encrypted; and, in section 2.5.1, it
describes the risks that derive from the behaviour of the resolver in
use, independently from whether the connection is encrypted or not.
To address the former category of privacy risks, some have suggested
that, through the use of DNS-over-HTTPS, the user's requests could be
hidden within unrelated HTTPS traffic, locating DNS-over-HTTPS
servers at the same IP address and port of widely used web servers.
However, this method creates security and legal issues that are
documented in the following sections of this document, and so it is
not recommended unless the privacy gain must prevail upon any other
consideration, for example because of the extreme sensitivity of the
online activity or because of a hostile environment that could lead
to significant personal risks.
In all other cases, users that feel the need for further obfuscation
of their encrypted DNS communication should rather be directed to
spreading their communications across a great number of encrypted
resolvers, as per recommendation #2 of section 4.2, making it harder
to track the entirety of their DNS exchanges. Moreover, if privacy
is so important, users should consider that they also need to encrypt
the rest of the communications, and not just the resolution of domain
names; thus, using a VPN for all their traffic might just be easier
and better.
To address the latter category of privacy risks, the first and
foremost mitigation measure is to allow each user to pick a resolver
that is managed by an organization that they trust, under appropriate
regulatory conditions, privacy policies and operational practices.
While "privacy-friendly" applications might (and, indeed, should)
help users in making this choice, there is not a unique, globally
applicable agreement on what constitutes a "privacy-friendly"
resolver, and it is hard to ensure that all application makers will
always make disinterested choices in the pure interest of the user;
so it must be the user, in the end, to decide who to entrust with
their personal information. The recommendations in sections 4.1 and
4.2 thus also contribute to mitigate this type of risks.
In addition, specific technical recommendations can be made to
prevent applications from adopting practices that would make it
easier for the resolver operator to track and fingerprint the user,
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mirroring the ones that have been developed in
[I-D.ietf-dprive-bcp-op] section 5:
1. Applications MUST authenticate the resolver they connect to, if
they have securely discovered the information required to do so.
2. In the case of DNS-over-HTTPS, applications SHOULD NOT attach or
receive HTTP cookies on the connections used for the DNS message
exchange, unless there is a specific use case for cookies that
has been explicitly requested by the user.
3. [to be continued]
For recommendation #1, and for DNS-over-TLS, a discussion of resolver
authentication methods and possibilities can be found in [RFC8310].
For recommendation #2, additional considerations on privacy when
using HTTPS as a transport mechanism for other protocols can be found
in section 6.1 of [I-D.ietf-httpbis-bcp56bis].
4.6. Content Access Control
DNS name resolution services are commonly chosen as a platform to
control user access to content; while there are other mechanisms in
use, checking and blocking destinations at the DNS level is an
effective and relatively inexpensive one. As a consequence, the
choice of the resolver also determines whether the user will be able
to access certain destinations on not, depending on the policies
applied by the individual resolver.
Sometimes, on unencrypted DNS connections, content control policies
will also be applied to DNS connections directed to other resolvers
having a different policy than the local network's one, though this
is made impossible by the switch to encrypted DNS connections.
The motivations, the procedures, and the types of content subject to
blocking are very variable. Some of the filtering activities are
meant to increase the security and health of the network; they can be
aimed at non-human clients, such as bots, trying to prevent them from
connecting to their command and control servers; or they can try to
prevent unaware users from connecting to phishing and malware
websites.
Other filtering activities are meant to make some content
inaccessible because it violates the law in the user's and/or the
resolver's jurisdiction, or because of court rulings that mandate the
block. In authoritarian countries, content may be blocked to prevent
criticism of the ruling entity, while in democratic countries it can
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be blocked to defend the safety and rights of some parties and
prevent violence and attacks on democracy. Destinations may also be
made inaccessible, independently from their content, for lack of
compliance with any applicable regulation, such as requirements for
licenses or the payment of taxes in the user's country.
The opinions on the appropriateness of these practices are highly
influenced by local culture, history and socio-political
environments, as well as by each individual's set of values, and it
is thus impossible to make blanket recommendations on whether and
when they should be forbidden, allowed, or actively supported; the
only possible recommendation is to follow the applicable regulations.
In some cases, however, users actually demand DNS-based content
control services to shape their own Internet access: for example,
families that want to make sure that their children using the
Internet from home cannot access inappropriate websites; businesses
that want to restrict the way their employees can use the Internet in
the office during working hours.
This leads to the following recommendations:
1. Applications MUST NOT prevent users from using any DNS-based
content control service that they freely choose to adopt.
2. Applications SHOULD comply with any legislation and legal ruling
on content control that applies to them in the jurisdiction where
they are being used.
Further considerations on the relationship between applications and
applicable legislation will be made in section 4.7.
4.7. Security and Network Management
Network management and network security practices often rely on
checks and policies implemented at the DNS level, through the
monitoring and mangling of the DNS queries that the users of the
local network send to the local resolver. For example, these
practices include checking for any unusual patterns in DNS traffic to
detect devices that have been infected with malware; blocking queries
for known botnet command-and-control servers to make it impossible
for bots to communicate with them and take orders; implementing a
content control list of web destinations that the network
administrator considers dangerous; associating certain names to
different IP addresses, some of which may be private, depending on
the client and on its topological location; creating names in special
use or non-standard top level domains and making them resolvable only
from the inside of the local network.
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Especially the use of local names and "split horizon" configurations
is a widely used security practice in corporate network environments;
using a resolver located outside of the network would break this
mechanism and at the same time leak information that would be very
valuable to an attacker.
These practices rely on forcing all the users of the local network to
use the local resolver, rather than a remote public resolver; this
requirement is generally enforced through one or more of the
following practices:
a. Making sure that all devices that are connected to the local
network are configured to use the local resolver, disallowing the
users from modifying this configuration entry;
b. Blocking access to remote resolvers at the edge of the local
network, for example through firewalls and blocks by destination
IP address and/or port;
c. Examining, and if necessary amending, all DNS queries and replies
in transit towards remote resolvers.
The switch to encrypted DNS connections makes practice c) generally
impossible; the switch to application-level resolver selection also
makes a) impossible, unless the network administrator can prevent the
installation of any application on all the devices connected to the
network, which is not easily feasible in most cases. Finally, the
implementation of "mixed mode" DNS-over-HTTPS, obfuscating the
traffic within ordinary HTTPS connections to widely used web hosts,
would make also practice b) impossible.
So, the deployment of encrypted DNS over dedicated connections
disables c), but still leaves a) and b) as options to network
administrators; however, the deployment of DNS-over-HTTPS in mixed
mode disables all three practices and leaves the network
administrators powerless; additionally, it even provides an
undetectable data exfiltration vector for malicious applications that
are trying to steal confidential information from the local network
and forward it to the outside.
While disabling control by the local network administrator might
actually be a positive intent in very specific cases, disabling all
these security practices at once is dangerous and inappropriate in
most cases. It is especially problematic on private networks that
host sensitive or commercially valuable information, as they need to
be able to provide some degree of connectivity to the Internet while
scrutinizing and limiting its usage to guarantee security.
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Noting that even [RFC7258], in section 2, stresses that "Making
networks unmanageable to mitigate pervasive monitoring is not an
acceptable outcome", and calls for "an appropriate balance" between
encryption and network management needs, the following
recommendations, in addition to those in section 4.1., represent such
balance:
1. Applications SHOULD NOT adopt the practice of hiding their
encrypted DNS traffic in ways that prevent the local network
administrator from isolating it, monitoring it (without breaking
the encryption) and, if desired, blocking it; exceptions to this
principle MUST be motivated by a clear and compelling use case
which cannot be addressed otherwise, and their use MUST be
limited to such use case. [Note: of course I am sure that many
people will want to discuss this - the idea is to not stop this
from happening when it is really useful, but also restrict its
usage to when it is really useful, leaving network admins with
the possibility to block external encrypted resolvers if they
want, without starting a technical "arms race".]
2. [to be continued]
Further reasons supporting recommendation #1 can be found in sections
4.5 and 4.8.
4.8. Jurisdiction
The current prevailing practice of using local resolvers, located
topologically near to the user, generally ensures that the resolver
and the user fall under the same jurisdiction. This allows the
country managing such jurisdiction to apply rules and policies to the
user's Internet access by acting upon the resolver, recommending or
mandating actions to the ISP that runs the resolver.
The use of remote resolvers, in most cases located in a different
country and under a different jurisdiction than the user, has already
provided a way for users to bypass their local laws. Many countries
have tolerated this loss of sovereignty because it only affected a
minority of users, possibly smarter technical users that could have
anyway found other ways to bypass national rules applied at the
resolver level, such as running their own recursive resolver. Other
countries have instead engaged in enforcing their Internet access
rules at other levels, such as by requiring firewalls at each
connection between any national network and the broader Internet and
filtering out destinations by IP address, or requiring the ISPs to
apply similar blocks on each user's Internet connectivity.
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In [RFC7754], the IETF has recommended the use of filtering at the
endpoints, rather than inside the network, to address issues that
require access control to Internet destinations; but filtering at the
edges is much harder to set up and to enforce for countries, and the
same RFC agrees that "a hybrid approach that combines endpoint-based
filtering with network filtering may prove least damaging". In this
regard, making resolver-level law-mandated filtering policies
impossible is anyway likely to push more countries to mandate
heavier, more damaging filtering practices at the IP address level.
From the user's viewpoint, a change in jurisdiction may be beneficial
or damaging, depending on which issues are most important for the
user and on the applicable legislation in the user's and, if
different, in the resolver's country. Users located in jurisdictions
that restrict their rights may actively seek to use a resolver in a
different jurisdiction to bypass the restrictions. Users that enjoy
a high degree of rights in their country, such as extended
protections for privacy and network neutrality, may reject the use of
a resolver in another jurisdiction not to lose such protections.
It is out of scope for the IETF to decide whether the policies and
laws of any country should be supported or opposed. By leaving as
much control as possible to the user, as recommended in section 4.1,
each user is allowed to decide whether to seek the use of a resolver
in a different jurisdiction or stay within their own, bearing the
responsibility for any legal consequence that might derive from that
decision; and it is important that such a decision is not taken
lightly and especially is not taken by the application without
telling the user, as the user could otherwise unwillingly end up in
legal troubles.
At the same time, while individual users and individual application
makers may have different views and follow other practices, it is
inappropriate for the IETF as a whole to promote the deployment of
technologies in a way that is explicitly designed to undermine any
country's sovereignty and jurisdiction. This is another reason to
support recommendation #1 in section 4.7 and recommendation #2 in
section 4.6. More generally, the following recommendations can be
devised:
1. Applications SHOULD clearly inform the user whenever the resolver
that it is going to be employed lies under a jurisdiction
different than the one of the user.
2. Applications SHOULD NOT adopt a resolver located under a
jurisdiction different than the user's one, unless the user has
explicitly consented to such change of jurisdiction, and unless
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the user's jurisdiction allows the use of resolvers located in a
different country.
4.9. Disaster Recovery
Remote resolvers rely on global Internet connectivity to be able to
serve users from every part of the world. However, there may be
cases in which long distance Internet connectivity is so poor to make
the use of remote resolvers ineffective, or has been greatly reduced
or even completely severed by the effects of natural disasters,
upstream legal and contractual issues or any other special situation.
In these cases, it is important that applications can continue
working if connectivity to a local resolver can be established, as
the resolver, even with global connectivity issues, can still provide
access to much needed local resources.
This leads to the following recommendation:
1. Applications, when using a remote resolver, SHOULD monitor the
availability of sufficient connectivity to it, and SHOULD prompt
the user to switch temporarily to a local resolver, if available,
when such connectivity is not available.
4.10. User Support
Functioning DNS resolution is a requirement to make Internet
connectivity work, and, when it does not, most users have a hard time
discerning the specific technical factor that prevents it from
working. As they generally acquire their Internet connectivity from
a local ISP, they will thus contact the ISP's support desk whenever
the connectivity does not work, regardless of the actual cause.
However, if the application is using a remote resolver, the ISP's
support desk will not be able to know whether such resolver is
experiencing operational issues or applying policies that make the
user's desired action fail.
It is thus important that application makers, remote resolver
operators and ISPs cooperate to allow users to get support on their
Internet access problems. For what regards applications, this leads
to the following recommendations:
1. Applications SHOULD make it easy for users to determine whether
any failure that they experience in the use of the application
can be attributed to a failure in DNS resolution.
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2. Applications SHOULD cooperate with remote resolver operators to
direct users that experience problems due to resolver failures to
the support service of the resolver operator.
3. Applications SHOULD provide easy ways for their users to retrieve
the information on the resolver currently in use, so that they
can pass on this information to whoever is helping them to
restore their connectivity.
5. Security Considerations
The use of encrypted DNS protocols is beneficial to security as it
prevents unauthorized third parties from altering the DNS queries and
replies, but it also creates new security risks by disrupting a
number of existing and commonly used practices for network security,
and by providing, under certain conditions, a mechanism for data
exfiltration from within a network through the submission of
appropriately designed DNS queries.
More detailed security considerations can be found in section 4.7 of
this document.
6. Privacy Considerations
The use of encrypted DNS protocols in itself is beneficial to privacy
as it prevents eavesdropping of the connection. However, the issues
created by the deployment model can lead to an overall loss of
privacy, for example because the user is led to adopt a resolver
operator that offers less privacy protection than the one they are
currently using, or that is located under a jurisdiction that offers
less privacy protection.
Issues specifically related to privacy, and recommendations to
address them, are discussed in section 4.5 of this document.
7. Human Rights Considerations
[ to be written ]
8. IANA Considerations
This document has no actions for IANA.
9. Acknowledgements
[ to be written ]
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10. References
10.1. 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>.
10.2. Informative References
[I-D.arkko-iab-internet-consolidation]
Arkko, J., Trammell, B., Nottingham, M., Huitema, C.,
Thomson, M., Tantsura, J., and N. Oever, "Considerations
on Internet Consolidation and the Internet Architecture",
draft-arkko-iab-internet-consolidation-02 (work in
progress), July 2019.
[I-D.bortzmeyer-dprive-rfc7626-bis]
Bortzmeyer, S. and S. Dickinson, "DNS Privacy
Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02
(work in progress), January 2019.
[I-D.ietf-doh-resolver-associated-doh]
Hoffman, P., "Associating a DoH Server with a Resolver",
draft-ietf-doh-resolver-associated-doh-03 (work in
progress), March 2019.
[I-D.ietf-dprive-bcp-op]
Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A.
Mankin, "Recommendations for DNS Privacy Service
Operators", draft-ietf-dprive-bcp-op-03 (work in
progress), July 2019.
[I-D.ietf-httpbis-bcp56bis]
Nottingham, M., "Building Protocols with HTTP", draft-
ietf-httpbis-bcp56bis-08 (work in progress), November
2018.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
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[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7754] Barnes, R., Cooper, A., Kolkman, O., Thaler, D., and E.
Nordmark, "Technical Considerations for Internet Service
Blocking and Filtering", RFC 7754, DOI 10.17487/RFC7754,
March 2016, <https://www.rfc-editor.org/info/rfc7754>.
[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>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[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>.
Author's Address
Vittorio Bertola
Open-Xchange
Via Treviso 12
Torino 10144
Italy
Email: vittorio.bertola@open-xchange.com
URI: https://www.open-xchange.com
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