Internet DRAFT - draft-fhllr-dnsop-dohoperator
draft-fhllr-dnsop-dohoperator
dnsop A. Fidler
Internet-Draft BT plc
Intended status: Informational B. Hubert
Expires: May 6, 2021 OpenXchange
J. Livingood
Comcast
J. Reid
RTFM llp
N. Leymann
Deutsche Telekom AG
November 2, 2020
DNS over HTTPS (DoH) Considerations for Operator Networks
draft-fhllr-dnsop-dohoperator-00
Abstract
The introduction of DNS over HTTPS (DoH), defined in RFC8484,
presents a number of challenges to network operators. These are
described in this document. The objective is to document the problem
space and make suggestions that could help inform network operators
on how to take account of DoH deployment. This document also
identifies topics that may require further analysis.
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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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 May 6, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Contrasting DoH and Conventional DNS . . . . . . . . . . . . 3
4. Regulatory and Policy Considerations . . . . . . . . . . . . 4
4.1. Local Policy Constraints . . . . . . . . . . . . . . . . 5
4.2. Regulatory and Legal Impacts . . . . . . . . . . . . . . 5
4.3. Regulatory Constraints . . . . . . . . . . . . . . . . . 6
5. Network Operations . . . . . . . . . . . . . . . . . . . . . 6
5.1. Impact on DNS query logging . . . . . . . . . . . . . . . 6
5.2. CDN endpoint selection . . . . . . . . . . . . . . . . . 6
5.3. Redirection for captive portals . . . . . . . . . . . . . 7
5.4. Managed network services . . . . . . . . . . . . . . . . 7
5.5. Resolver capacity management . . . . . . . . . . . . . . 7
5.6. Discovery considerations . . . . . . . . . . . . . . . . 8
5.7. Failure recovery . . . . . . . . . . . . . . . . . . . . 8
5.8. Impact on Network Address Translation . . . . . . . . . . 9
5.9. Load balancing and failover . . . . . . . . . . . . . . . 9
6. User Support . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Provisioning . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Privacy Concerns . . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Human Rights Considerations . . . . . . . . . . . . . . . . . 15
11. Open Issues for Further Study . . . . . . . . . . . . . . . . 15
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. Normative References . . . . . . . . . . . . . . . . . . 16
14.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
Traditional DNS traffic between stub resolvers, recursive servers and
authoritative servers is not encrypted. This can pose a privacy
challenge for Internet users, because their access to named network
resources can potentially be tracked through their DNS queries. In
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principle, any network element along the path between the user and
resolving or authoritative servers could observe this unencrypted
traffic. DoT (DNS over TLS) [RFC7858] is one proposal for providing
privacy of DNS queries and DNS over HTTPS (DoH) [RFC8484] is another.
Both DoH and DoT encrypt the communications between the end client
(user) and recursive resolver. Plaintext DNS traffic between
recursive and authoritative servers is generally less of a privacy
concern because it usually does not contain information such as the
source address of the initial query that could identify the end
client.
2. Terminology
DoH Server: A server supporting the DNS over HTTPS is called a "DoH
server" to differentiate it from a "DNS server" (one that only
provides DNS service over one or more of the other transport
protocols standardised for DNS). Similarly, a client that supports
the DNS over HTTPS is called a "DoH client".
Do53: DNS over port 53 - conventional plaintext DNS. Do53 server and
Do53 client are the respective terms for a server or client that uses
conventional port 53 DNS.
Operator: A large Internet service provider, typically a cable
company or fixed/mobile telco with a national or international
network.
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 RFC 2119 [RFC2119].
3. Contrasting DoH and Conventional DNS
With conventional DNS (Do53), using UDP or TCP port 53, most users
are assigned the IP addresses of several recursive resolvers via DHCP
or similar network bootstrapping mechanism. These are usually the IP
addresses of recursive resolvers that are administered by the network
operator. Although there is currently no equivalent to this for DoH,
the ADD Working Group is developing solutions for DoH server
discovery.
Users sometimes also change to third-party recursive resolvers. In
some cases, they may even operate their own local resolver. It is
not yet clear how or if DoH will be applied in these scenarios more
generally. Current DoH behaviour of the most widely used web
browsers is documented and reasonably well understood. The same
cannot yet be said for operating system software: stub resolver
libraries and web toolkits for instance.
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RFC 8484 defines the protocol for DNS over HTTPS (DoH). When DoH is
used, client and server DNS traffic is encrypted using a TLS RFC 8446
[RFC8446] channel, typically to port 443. DoH clients will have
little need for conventional DNS apart from an initial bootstrap
query to find the IP addresses of a suitable DoH server. In some
cases, this will mean the bulk of the client's DNS resolver traffic
bypasses an operator's DNS resolver infrastructure because that
traffic uses the resolver service provided by a third-party DoH
server.
When DoH is used, the traditional DNS client-server model of clients
making queries and waiting for a reply from a server might well
change. It can be expected that DoH servers will sometimes use DoH
opportunistically. For instance a web server could include
application/dns-message elements in the returned HTML data,
anticipating the domain names that the web browser might need to
resolve before rendering some web page. In this scenario, the
browser would not need to lookup those names with DoH or conventional
DNS because the relevant DNS data have already been supplied.
DoH is already widely implemented and deployed by browser vendors.
All the major web browsers support DoH. Sometimes, DoH is enabled by
default. In others, configuration changes are needed to get the
browser to use DoH instead of conventional DNS.
Since DoH is not yet natively supported by the most widely-used DNS
implementations, DoH servers may need some sort of proxy or "shim"
module to convert between application/dns-message elements in HTML
and conventional DNS queries and responses. A number of
organisations are already offering public DoH resolution service,
typically using anycast technology. Some operators have either
deployed or are planning to deploy DoH resolver service in their
networks.
DoH changes the current, well established business model where an end
user (customer) pays for Internet connectivity and recursive DNS
service is part of that offering from the ISP. When DoH is used, the
customer may be dependent on DoH servers operated by third parties
and have no contractual or business relationship with those
providers. It also cannot be assumed that these DoH servers will be
operating under the same policy and regulatory conditions that are
applied by the end user's ISP.
4. Regulatory and Policy Considerations
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4.1. Local Policy Constraints
Operator networks often have local policy constraints which require
some form of DNS blocking or rewriting - for example to offer
customers parental controls, to restrict access to illegal content or
to mimimise end user exposure to malware, phishing attacks and so on.
These tend to be implemented by using data from threat intelligence
providers, usually some sort of RPZ feed that is incorporated into
the configuration of the operator's DNS resolver infrastructure.
It is not yet clear how or if this functionality can be made
available by DoH servers. These protective measures will be less
effective once DoH is used because end user DNS traffic will largely
bypass the operator's DNS infrastructure, rendering such content and
security protections useless. Some of these measures may be offered
by some DoH servers, but as yet there is no defined mechanism to
ensure that all local policy is implemented.
4.2. Regulatory and Legal Impacts
Operators can also be required to perform DNS blocking and filtering
or rewriting for legal reasons: handling takedown notices or
complying with court orders. This may also be necessary for
operational and/or security reasons such as dealing with botnets and
DDoS attacks. [CSRIC]
As before, it is not yet clear how or if DoH servers will provide
this functionality. Some of these measures may be offered by some
DoH servers, but there is no defined mechanism to ensure that all
local policy is implemented, particularly those required in certain
jurisdictions today. Current protective measures may be less
effective once DoH is used because customer DNS traffic will be able
to bypass the operator's DNS infrastructure.
Conventional recursive DNS services are generally located in the
country where an operator is based. Since third-party DoH service
providers are likely to be based and/or operated from outside those
local countries, different protections and regulatory considerations
may apply to the protection, storage and processing of user data
processed on those servers. Typical regulations that could apply
include General Data Protection Regulation (EU) 2016/679 [GDPR] and
the EU-US Privacy Shield Framework [USPS]. These can sometimes have
global scope - GDPR for instance. Overseas regulations may have
lower, higher or even no commitments governing such services compared
to those that would apply to a local operator. The potential impact
of these regulatory obligations with respect to DoH services is
unclear, including whether or not they apply or even could be applied
at all.
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4.3. Regulatory Constraints
Logs containing individual DNS queries and the IP addresses or other
data correlating those queries to specific users or homes may in some
legal jurisdictions be considered as Personal Data or PII, Personally
Identifying Information. In such jurisdictions detailed DNS query
logs may be subject to data protection and retention regulations, or
other legal and/or compliance requirements.
Operators can also be subject to regulation or other legal
instruments that require DNS query logs to be retained for a certain
period of time and made available for law enforcement purposes as
needed, such as under a court order or other legal process.
Since DoH potentially bypasses conventional DNS resolvers on which
these privacy, regulatory, and legal requirements are imposed, it
will reduce or eliminate the potential social value of these rules,
and may even be viewed by some countries as a potential breach of
regulatory compliance (whether by ISPs, DoH server operators, or
others).
5. Network Operations
5.1. Impact on DNS query logging
Analysis of resolver query data is an important task in most operator
networks. This can help with traffic management, load balancing and
capacity planning as well as network and user security. Widespread
uptake of DoH will mean an operator has reduced visibility of the DNS
traffic in their network. Query traffic logged by traditional
resolving servers will be less representative (or even completely
unrepresentative) of the overall DNS activity in an operator's
network.
5.2. CDN endpoint selection
End user queries made with DoH could mean that lookups return answers
that are sub-optimal. i.e. directing clients to a distant CDN node
that is outside the operator's network instead of to the localised
CDN node(s) installed inside that network or directly interconnected
with that network. Those DNS responses would be keyed on the source
IP address of a resolving DoH server, possibly operated by a third
party, rather than an address of one of the operator's resolving DNS
servers or end client IP address information that those resolving
servers might choose to provide through the Client Subnet EDNS0
option RFC 7871 [RFC7871].
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The impact to an operator of directing clients to a distant CDN node
that is outside the operator's network is not only slower access to
resources provided by the CDN. It also incurs higher costs for the
operator because traffic is routed over the operator's backbone and
peering links rather than remaining within a part of the network that
is geographically or topologically close to the end-user.
Additionally, operators have powerful technical, operational and
business incentives to provide optimal user experience for their
customers, particularly in terms of latency and speed of Internet
services. This involves working with multiple CDN and content
providers to ensure best performance when delivering those services,
for example by providing Client Subnet EDNS0 option information. One
risk is that DoH services could be provided by operators or
distributors of web content who have different motivations. For
instance a provider of DoH service may choose to offer fast access to
the content that they host or distribute, but may decide not to offer
the geographic information of the end-user (for privacy, policy or
business reasons) to competing content providers/distributors.
5.3. Redirection for captive portals
Network operators also often use captive portal DNS to provide
customer self-service activation and related customer account
provisioning, billing and support activities. For example, captive
portal DNS is used extensively to support functions such as self-
service provisioning of customer owned and managed Customer Premises
Equipment (CPE), service support, mobile pay as you go top up and
access to national/regional WiFi hot spots. DoH traffic may bypass
these operator-supplied functions that are essential for managing the
network. This would significantly disrupt the manner in which
networks are operated and managed.
5.4. Managed network services
The provision of managed network services, for instance to corporate
or other enterprise clients will be affected by DoH. It could
negatively affect bring-your-own-device policies which might
introduce devices into these networks that are configured to use
third party DoH servers. For instance there is a risk that internal
domain names used extensively in such networks could leak to external
DoH servers, presenting obvious privacy and security issues.
5.5. Resolver capacity management
Large operator networks are likely to operate their own DoH servers
because of local policy or business considerations. This could mean
an increase in TCP-based DNS traffic to port 443 as DoH displaces
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conventional UDP-based queries to port 53. Transitioning from a
primarily UDP-based service to TCP-based DoH would likely require
substantial network capacity enhancements to an operator's DNS
infrastructure. This might also require changes to existing load
balancing and failover architectures. Establishing a DoH service in
these environments would absolutely impact operational management and
support.
It is unclear how much end-user DNS traffic will migrate to DoH and
how quickly that happens since this will depend on the uptake of DoH-
capable applications. There is also uncertainty about the default
behaviour of these applications, for instance try DoH first then fall
back to conventional DNS, use DoH only, try DoH and DNS in parallel
and accept whichever answers first, etc. These unknowns have a
further obvious impact on capacity planning and network operations.
5.6. Discovery considerations
Some networks offer DNS resolution services on locally scoped
addresses that are not globally meaningful - for instance RFC1918 or
link-local addresses. This arrangement is commonly found in operator
and enterprise networks. Discovery of DoH servers (or other forms of
encrypted DNS transport) in these environments is likely to rely on
bootstrapping from a locally-addressed Do53 resolver to the chosen
DoH server. That DoH server could either be offering resolution
service at the same local address as the Do53 resolver, or at a
different, possibly global, address. Both options need to be
considered. In both cases the DoH server would offer a TLS
certificate proving ownership of a name. This name should be
meaningful to the end client, conveying the identity of the resolver
operator. However given the lack of network authentication it does
not currently seem possible to mandate a requirement that the name
has to match anything that could be present in the client's
configuration.
Many network operators use stub resolvers or proxies in CPE to handle
end-user DNS requests. Depending on how the network is organised,
these stub resolvers and proxies can either present public or private
IP addresses to client devices. When these CPE devices use private
IP addresses, it will complicate encrypted DNS discovery.
5.7. Failure recovery
It is not clear how DoH services will affect customers' approach to
disaster recovery and fault reporting or influence their business
continuity planning. For instance, if a client loses connectivity or
access to their chosen DoH provider(s), they may lose Internet
service even though they remain connected to the operator's network
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and could otherwise use conventional DNS resolution services. It is
assumed, but cannot be guaranteed, that DoH-capable applications will
fall back to conventional DNS whenever DoH service fails.
Applications might however be configured to only use DoH apart from
an initial bootstrapping query that uses conventional DNS.
5.8. Impact on Network Address Translation
Techniques such as DNS64 [RFC6147] and NAT64 [RFC6146] are widely
used for devices with IPv6-only transport, particularly in mobile
networks to ensure continued access to parts of the Internet that are
IPv4-only. These generally require the operator's DNS resolver
server to carry out some form of IP address mapping. It is not known
what impact DoH will have in these environments. It is unlikely that
this will work with third party DoH providers because they will not
have information about the operator's network that would allow them
to map these IPv6 addresses.
In networks where the translator prefix is not the well-known prefix
defined by RFC6146, the client's use of a DoH resolver outside the
operator's network will prevent access to IPv4-only content, because
the resolver will not know the correct prefix to use in its response.
Even when the well-known prefix is used, the DoH resolver may not be
configured to correctly use it in its response.
5.9. Load balancing and failover
Operator networks make extensive use of DNS-based solutions for load
balancing and service failover. These might not work as expected
with DoH clients which bypass the operator's DNS resolver
infrastructure. Further operational problems may arise if stale DNS
data are held in a DoH client's cache.
6. User Support
o Adoption of DoH is likely to decouple DNS from the provision of
Internet connectivity. For most users, DNS resolution is
currently part of the service provided by their ISP. With DoH,
users can be expected to rely on DoH service providers and are
likely to have no business or contractual relationship with those
providers.
o Getting meaningful consent from users - how?
o The role of user consent and whether it is a necessary factor in
the processing of user data is contextual. It depends on the
nature of relationships between the involved parties - largely the
ISP, the DoH provider(s) and the end user - and how those
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relationships were established. Prevailing legislation and
regulation such as GDPR can also be an important consideration,
albeit one that is obviously out of scope for an IETF document.
It is not clear whether reconfiguration of a device or moving it
from one network to another would constitute implied consent in a
legal sense.
o In any case, only a fraction of Internet users understand the
mechanics of DNS resolution, which makes obtaining informed and
meaningful consent difficult. Service providers should seek to
explain data use in a way that's understandable to most people.
Sustained and collective efforts by service providers to educate
users (policymakers, legal scholars, teachers, etc.) about the
Internet infrastructure to foster common understanding of these
issues would be helpful.
o How will users be able to opt in/out of DoH services?
o Users may want to give meaningful consent to use DNS filters.
Therefore, there should be an option for users to enable and
disable DoH with neither behaviour assumed. Such permissions
should also apply to DoH queries made by web-based apps using an
API, not just the queries directly entered by the user. When
users do provide consent for DoH-related data processing, the
architecture must also support the ability for them to withdraw
this consent at any time.
o How do users select their "trusted" DoH Provider? i.e. How is a
user or application supplied with a list of DoH providers? How
does it choose between them and what are the selection criteria?
Presumably these could/should be considerations for the ADD
Working Group.
o Clarification is needed on trusted certificate approach, e.g. is
it enforced at application rather than the kernel/operating system
layer?
o Can/should discrete apps be able to choose their own DoH server?
Suppose a banking app is configured to use the bank's DoH
provider. Can that default be over-ridden? Should it?
o How does a user get told about (and approve) a change of DoH
service for a phone/tablet when they're roaming between mobile
telcos or using whatever DoH service is offered in $coffeeshop?
o How is an operator expected to support the customer or
troubleshoot problems caused by accidental or intentional change
of DoH server? If the DoH provider deletes all their historic DoH
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traffic, how do they support the ISP customer regarding
troubleshooting?
o How will DoH provisioning take account of existing customer
parental control/malware protection settings and flag the
consequences of selecting a new provider on these?
o How will browsers/applications explain DoH/DNS options to
customers so that they can make an informed decision, as many will
not appreciate what DNS is. If they select a third party DoH
provider, that may bypass their existing network operator's
content and malware protection controls. The end user will
presumably need to set these up again with their new DoH provider.
o How to explain to customers that they may need to check/contact
both their DoH provider(s) and network provider to resolver
performance and outage issues.
7. Provisioning
o If some list or registry of "trusted" DoH servers is needed, who/
what is going to maintain this and manage it? What criteria and
procedures are needed for adding or removing entries from that
list? How does a DoH provider become trusted or become untrusted?
o What are the requirements to become a DoH trusted recursive
resolver? Will browsers or applications only show global or
application-specific DoH provider options? How can regional
network operators offering DoH just to their customer base be
supported? How will browsers and applications know which regional
or local options exist and which of these should and should not be
honoured?
o An industry approach for DoH discovery, trust and selection that
operates in an open and transparent manner is needed. This should
give the customer meaningful consent options.
o How to configure CPE and other edge devices (e.g. smartphone) to
use the operator's chosen DoH provider.
o Can/should the operator's or application's choice of DoH server be
overridden by the customer?
o How do web applications get to specify the DoH server they want?
If web apps get to choose the DoH server, they could be pointing
to a malicious server (security issue) or allowing a DNS provider
other than that defined by the user to see the DNS queries
(privacy issue).
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o How will DoH provisioning and discovery take account of existing
customer parental control/malware protection settings and flag the
consequences of selecting a new provider on these?
o If a browser or other edge device can do DoH, what determines if
the DoH is the preferred the choice?, e.g. if CPE or set top box
devices also supports DNS over TLS, should DoH be an option? If
multiple options for DNS resolution are available, what decision
process is used to make the customer recommendation and how is
this trusted?
8. Privacy Concerns
Compared to traditional DNS, DoH offers more privacy protection
against passive surveillance because requests and replies are carried
over an encrypted channel. DoH offers an equivalent amount of
privacy protection against passive surveillance as DoT does because
both rely on TLS for their security properties.
Content Delivery Networks use techniques like EDNS-Client-Subnet
(ECS) to return DNS answers that direct a client to an optimal
location, for instance the CDN's node in the operator's network which
serves the end user. DoH has the potential to be more privacy
intrusive than ECS, largely because DoH is based on HTTP and can
leverage the rich per-user and per-device tracking that pervades the
web today. The implications of that are not yet well understood.
A DoH server will have a direct HTTPS connection to the client,
assuming there are no middleboxes in the path between them. That
could for example enable DoH servers operated by CDNs to carry out
much more fine-grained redirection and content delivery, perhaps even
on a per-user or per-user-session basis. They would be able to serve
content and advertisements based on the end user's choice of
operating system, their browser and that browser's configuration in
addition to the client's source IP address, web cookie data, or other
factors as is prevalent on the web today.
Global DoH providers will have access to significantly more DNS query
data, and therefore be able to perform richer big data analytics,
combining these insights with those obtained from other global
platforms (search engines, operating systems, browsers, ad trackers,
analytics services, web sites, mobile apps, payment systems,
e-commerce platforms, social networks, Bluetooth beacons, etc.),
potentially leading to a poor privacy outcome for consumers.
The DoH provider may adhere to different privacy policies than the
operator's DNS service, particularly where they are located in
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different jurisdictions. This may lead to better or worse privacy
outcomes for users.
Operators in some jurisdictions are required to perform DNS filtering
functions on traditional DNS queries and responses. If this
functionality has to be provided using DoH, the only available option
may be to fully proxy the HTTPS traffic. That represents more of a
privacy intrusion than filtering alone.
It is feasible that individual applications might have the ability to
select their own DoH server, bypassing the system- or operator-
defined DoH settings. That could lead to privacy violations because
DoH queries get sent to an arbitrary DoH server with unknown privacy
policies.
If users have no relationship with the DoH provider handling their
queries, they may have limited ability to exercise data protection
rights (erasure, objection, complaints, etc) or to pursue remedy for
breaches. This may be further complicated if the provider is unknown
to the end user, can't be easily contacted or is located in another
jurisdiction.
9. Security Considerations
DoH will give new opportunities for bad actors to propagate malware,
spam and botnets. Once they use DoH, as some botnets have already
started doing for command-and-control traffic, their DNS traffic will
be encrypted and anonymised, making it hard to deploy countermeasures
to protect against and mitigate these serious security threats. This
is likely to have an adverse impact on cybersecurity both at a
network/country level as well as for end users. Use of DoH could
make it slower to identify DNS-based DDoS attacks, more difficult to
attribute patient-zero for malware infections and harder to block
access to botnet command-and-control nodes. A proof of concept
exfiltration channel tool based on DoH [GODOH] already exists and it
is reasonable to expect others which are much less benign will emerge
in the future.
DoH queries and responses will be intermingled with other HTTPS port
443 traffic. This provides good traffic flow security for the
client, because it's not readily clear when a DoH request or reply is
taking place (unlike DoT). However network analytics may fail to
detect when a malware implant on the client is making DoH requests,
which would present a security risk.
Security of DoH relies on the TLS session for the HTTPS connection.
Therefore it inherits the security guarantees that TLS provides.
There may be interactions between DoH and TLS, for example issues
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arising from DoH servers handling large numbers of TLS connections to
DoH clients simultaneously, that have not yet been explored.
DNS query traffic is often made available to providers of threat
intelligence and reputation services. These providers typically
aggregate such data from many operators, process these datasets and
then generate whitelists and blocklists which operators can then
apply in their networks. DoH is likely to mean there will be a
reduced volume of query data readily available for this sort of
analysis. Overall DNS query traffic would be spread across a
combination of operator-run DNS resolver servers and a number of DoH
servers who might (or might not) make their query traffic available
to providers of threat intelligence and reputation services.
This will have two unwelcome results. First, threat intelligence and
reputation services will have fewer data to analyse and therefore
have a significantly less complete perspective of end users' DNS
behaviour. Second, the quality and effectiveness of the data
provided by threat intelligence and reputation services will be
materially diminished. This seems likely to reduce the security of
networks and users as a result.
Although DoH uses TLS to provides authentication and data integrity
of the channel between client and resolver, this does not guarantee
that the resolver is returning correct DNS data to the client. DoH
clients may need to perform DNSSEC validation to verify data received
from DoH servers.
There is a risk that internal domain names used extensively in
managed enterprise networks could leak to external DoH servers,
presenting obvious privacy and security issues.
DoH can be implemented within the browser, rather than the kernel or
an operating system library. It is not yet clear if that will make
endpoint-based malware detection more or less effective.
Browser APIs will allow web applications to make DoH queries. If
individual applications have the ability to select their own DoH
server, it is not clear if that change would only apply to DoH
lookups by that application or if they had broader scope. When these
changes over-ride system- or operator-defined DoH settings, they will
affect other processes running on the DoH client and effectively
hijack their DNS traffic by rerouting it to the application's DoH
provider.
The interactions between infrastructure using Network Address
Translation (NAT) [RFC3022] and DoH is unclear. In situations where
a third party DoH server can return security threat data back to the
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operator of the originating network, its value is likely to be
diminished due to the IP address sharing inherent in using NAT.
10. Human Rights Considerations
Parental control systems relying on DNS filtering can be bypassed
using DoH. This may lead to increased ability of minors to access
restricted or otherwise inappropriate content on the Internet,
creating a conflict with the UN Convention on the Rights of the Child
[Insert Ref to actual treaty text.]
Using DoH to bypass local DNS filtering and provide anonymity for end
users is a mixed blessing. Using DoH to bypass country-based DNS
filtering may provide end users a way of bypassing censorship
mechanisms put in place by restrictive regimes. On the other hand,
DoH could also help criminals to evade detection by obscuring the
source of their attacks or botnet control nodes, while increasing the
commercial tracking of user activity and trade in that data.
In jurisdictions where DNS blocking schemes have been incorporated
into law, widespread deployment of DoH could encourage policy
approaches that are more restrictive of users' freedom of expression,
their ability to access information or limit the generation and
availability of online content.
11. Open Issues for Further Study
o DoH's reliance on TLS raises a number of concerns and unknowns.
These include OSCP stapling, certificate life-times, scalability
in managing session tickets, handling session resumption and the
duration of TLS sessions. The trade-offs between certificate
validation and session duration for possibly short-lived DoH
transactions are not yet well understood. These factors will need
careful analysis, particularly on DoH servers which get queries
from large numbers of DoH clients.
o The impact of DNS traffic migrating from UDP and port 53 to TCP
and port 443 needs to be modelled because of the extra packets and
round-trip times needed for TCP connection setup and the TLS
handshake: performance, capacity planning, network engineering and
so on.
o DoH can leverage the rich per-user and per-device tracking that
pervades the web today. Since the implications of that are not
yet well understood, further work in this area is needed.
o How DoH services will develop new functionality to overcome any
inherent performance impact from moving the service out of the
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operator network. For instance, optimisations to reduce latency
in 3/4/5G mobile networks.
o Clarification is needed around ECS blocking and options to avoid
impacting existing network operator on-net caching strategy.
o What DoH service metrics will be available for users to compare
DoH providers?
o DoH discovery in networks which use private IP addresses for CPE
and stub resolvers or proxies could be challenging. Presumably
this will be addressed in the add WG.
12. IANA Considerations
This memo includes no request to IANA.
13. Acknowledgements
Fill this in later
14. References
14.1. 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>.
14.2. Informative References
[CSRIC] FCC, "Cybersecurity Risk Management and Best Practices",
<https://transition.fcc.gov/to-be-confirmed>.
[GDPR] European Union, "General Data Protection Regulation (EU)
2016/679",
<https://eur-lex.europa.eu/eli/reg/2016/679/oj>.
[GODOH] Sensepost, "DNS exfiltration using DoH",
<https://sensepost.com/blog/2018/waiting-for-godoh/>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<https://www.rfc-editor.org/info/rfc3022>.
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[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[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>.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871,
DOI 10.17487/RFC7871, May 2016,
<https://www.rfc-editor.org/info/rfc7871>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[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>.
[USPS] US Secretary of Commerce, "EU-U.S. Privacy Shield
Framework",
<https://www.privacyshield.gov/EU-US-Framework>.
Authors' Addresses
Andy Fidler
BT plc
BT Adastral Park
Martlesham Heath, Ipswich IP5 3RE
UK
Email: andrew.fidler@bt.com
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Bert Hubert
OpenXchange
Rollnerstrasse 14
Nuremberg 90408
Germany
Email: bert.hubert@open-xchange.com
Jason Livingood
Comcast
1800 Arch Street
Philadelphia PA 19118
USA
Email: jason_livingood@comcast.com
Jim Reid
RTFM llp
St Andrews House
382 Hillington Road, Glasgow G51 4BL
Scotland
Email: jim@rfc1035.com
Nic Leymann
Deutsche Telekom AG
Friedrich-Ebert-Allee 140
Bonn 53113
Germany
Email: N.Leymann@telekom.de
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