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draft-ietf-dprive-dnsoquic-02.txt
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Network Working Group C. Huitema
Internet-Draft Private Octopus Inc.
Intended status: Standards Track A. Mankin
Expires: August 26, 2021 Salesforce
S. Dickinson
Sinodun IT
February 22, 2021
Specification of DNS over Dedicated QUIC Connections
draft-ietf-dprive-dnsoquic-02
Abstract
This document describes the use of QUIC to provide transport privacy
for DNS. The encryption provided by QUIC has similar properties to
that provided by TLS, while QUIC transport eliminates the head-of-
line blocking issues inherent with TCP and provides more efficient
error corrections than UDP. DNS over QUIC (DoQ) has privacy
properties similar to DNS over TLS (DoT) specified in RFC7858, and
latency characteristics similar to classic DNS over UDP.
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 http://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 August 26, 2021.
Copyright Notice
Copyright (c) 2021 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
(http://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
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Document work via GitHub . . . . . . . . . . . . . . . . . . 4
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 4
4.1. Scope is Limited to the Stub to Resolver Scenario . . . . 5
4.2. Provide DNS Privacy . . . . . . . . . . . . . . . . . . . 5
4.3. Design for Minimum Latency . . . . . . . . . . . . . . . 6
4.4. No Specific Middlebox Bypass Mechanism . . . . . . . . . 6
4.5. No Server Initiated Transactions . . . . . . . . . . . . 7
5. Specifications . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Connection Establishment . . . . . . . . . . . . . . . . 7
5.1.1. Draft Version Identification . . . . . . . . . . . . 7
5.1.2. Port Selection . . . . . . . . . . . . . . . . . . . 7
5.2. Stream Mapping and Usage . . . . . . . . . . . . . . . . 8
5.2.1. Transaction Errors . . . . . . . . . . . . . . . . . 8
5.3. DoQ Error Codes . . . . . . . . . . . . . . . . . . . . . 8
5.4. Connection Management . . . . . . . . . . . . . . . . . . 9
5.5. Connection Resume and 0-RTT . . . . . . . . . . . . . . . 10
5.6. Message Sizes . . . . . . . . . . . . . . . . . . . . . . 10
6. Implementation Requirements . . . . . . . . . . . . . . . . . 11
6.1. Authentication . . . . . . . . . . . . . . . . . . . . . 11
6.2. Fall Back to Other Protocols on Connection Failure . . . 11
6.3. Address Validation . . . . . . . . . . . . . . . . . . . 11
6.4. DNS Message IDs . . . . . . . . . . . . . . . . . . . . . 12
6.5. Padding . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.6. Connection Handling . . . . . . . . . . . . . . . . . . . 12
6.6.1. Connection Reuse . . . . . . . . . . . . . . . . . . 12
6.6.2. Resource Management and Idle Timeout Values . . . . . 12
6.7. Processing Queries in Parallel . . . . . . . . . . . . . 13
6.8. Flow Control Mechanisms . . . . . . . . . . . . . . . . . 13
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 14
7.1. Performance Measurements . . . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15
9.1. Privacy Issues With 0-RTT data . . . . . . . . . . . . . 15
9.2. Privacy Issues With Session Resume . . . . . . . . . . . 16
9.3. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. Registration of DoQ Identification String . . . . . . . 17
10.2. Reservation of Dedicated Port . . . . . . . . . . . . . 17
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10.2.1. Port number 8853 for experimentations . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 19
12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Supporting AXFR . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Domain Name System (DNS) concepts are specified in "Domain names -
concepts and facilities" [RFC1034]. The transmission of DNS queries
and responses over UDP and TCP is specified in "Domain names -
implementation and specification" [RFC1035]. This document presents
a mapping of the DNS protocol over the QUIC transport
[I-D.ietf-quic-transport] [I-D.ietf-quic-tls]. DNS over QUIC is
referred here as DoQ, in line with the "Terminology for DNS
Transports and Location" [I-D.ietf-dnsop-terminology-ter]. The goals
of the DoQ mapping are:
1. Provide the same DNS privacy protection as DNS over TLS (DoT)
[RFC7858]. This includes an option for the client to
authenticate the server by means of an authentication domain name
as specified in "Usage Profiles for DNS over TLS and DNS over
DTLS" [RFC8310].
2. Provide an improved level of source address validation for DNS
servers compared to classic DNS over UDP.
3. Provide a transport that is not constrained by path MTU
limitations on the size of DNS responses it can send.
4. Explore the characteristics of using QUIC as a DNS transport,
versus other solutions like DNS over UDP [RFC1035], DoT
[RFC7858], or DNS over HTTPS (DoH) [RFC8484].
In order to achieve these goals, the focus of this document is
limited to the "stub to recursive resolver" scenario also addressed
by DoT [RFC7858]. That is, the protocol described here works for
queries and responses between stub clients and recursive servers.
The specific non-goals of this document are:
1. No attempt is made to support AXFR "DNS Zone Transfer Protocol
(AXFR)" [RFC5936] or IXFR "Incremental Zone Transfer in DNS"
[RFC1885], as these mechanisms are not relevant to the stub to
recursive resolver scenario. (This may change in future versions
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of this draft. See Appendix A for a discussion of changes
required for AXFR support.)
2. No attempt is made to evade potential blocking of DNS over QUIC
traffic by middleboxes.
3. No attempt to support server initiated transactions, are these
are not relevant for the "stub to recursive resolver" scenario,
see Section 4.5.
Users interested in zone transfers should continue using TCP based
solutions and will also want to take note of work in progress to
support "DNS Zone Transfer-over-TLS" [I-D.ietf-dprive-xfr-over-tls].
Specifying the transmission of an application over QUIC requires
specifying how the application's messages are mapped to QUIC streams,
and generally how the application will use QUIC. This is done for
HTTP in "Hypertext Transfer Protocol Version 3
(HTTP/3)"[I-D.ietf-quic-http]. The purpose of this document is to
define the way DNS messages can be transmitted over QUIC.
In this document, Section 4 presents the reasoning that guided the
proposed design. Section 5 specifies the actual mapping of DoQ.
Section 6 presents guidelines on the implementation, usage and
deployment of DoQ.
2. Key Words
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 BCP 14 [RFC8174].
3. Document work via GitHub
(THIS SECTION TO BE REMOVED BEFORE PUBLICATION) The Github repository
for this document is at https://github.com/huitema/dnsoquic.
Proposed text and editorial changes are very much welcomed there, but
any functional changes should always first be discussed on the IETF
DPRIVE WG (dns-privacy) mailing list.
4. Design Considerations
This section and its subsection present the design guidelines that
were used for DoQ. This section is informative in nature.
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4.1. Scope is Limited to the Stub to Resolver Scenario
Usage scenarios for the DNS protocol can be broadly classified in
three groups: stub to recursive resolver, recursive resolver to
authoritative server, and server to server. This design focuses only
on the "stub to recursive resolver" scenario following the approach
taken in DoT [RFC7858] and "Usage Profiles for DNS over TLS and DNS
over DTLS" [RFC8310].
QUESTION: Should this document specify any aspects of configuration
of discoverability differently to DoT?
No attempt is made to address the recursive to authoritative
scenarios. Authoritative resolvers are discovered dynamically
through NS records. It is noted that at the time of writing work is
ongoing in the DPRIVE working group to attempt to address the
analogous problem for DoT [I-D.ietf-dprive-phase2-requirements]. In
the absence of an agreed way for authoritative to signal support for
QUIC transport, recursive resolvers would have to resort to some
trial and error process. At this stage of QUIC deployment, this
would be mostly errors, and does not seem attractive. This could
change in the future.
The DNS protocol is also used for zone transfers. In the AXFR zone
transfer scenario [RFC5936], the client emits a single AXFR query,
and the server responds with a series of AXFR responses. This
creates a unique profile, in which a query results in several
responses. Supporting that profile would complicate the mapping of
DNS queries over QUIC streams. Zone transfers are not used in the
stub to recursive scenario that is the focus here, and seem to be
currently well served by using DNS over TCP. There is no attempt to
support either AXFR or IXFR in this proposed mapping of DNS to QUIC.
4.2. Provide DNS Privacy
DoT [RFC7858] defines how to mitigate some of the issues described in
"DNS Privacy Considerations" [RFC7626] by specifying how to transmit
DNS messages over TLS. The "Usage Profiles for DNS over TLS and DNS
over DTLS" [RFC8310] specify Strict and Opportunistic Usage Profiles
for DoT including how stub resolvers can authenticate recursive
resolvers.
QUIC connection setup includes the negotiation of security parameters
using TLS, as specified in "Using TLS to Secure QUIC"
[I-D.ietf-quic-tls], enabling encryption of the QUIC transport.
Transmitting DNS messages over QUIC will provide essentially the same
privacy protections as DoT [RFC7858] including Strict and
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Opportunistic Usage Profiles [RFC8310]. Further discussion on this
is provided in Section 9.
4.3. Design for Minimum Latency
QUIC is specifically designed to reduce the delay between HTTP
queries and HTTP responses. This is achieved through three main
components:
1. Support for 0-RTT data during session resumption.
2. Support for advanced error recovery procedures as specified in
"QUIC Loss Detection and Congestion Control"
[I-D.ietf-quic-recovery].
3. Mitigation of head-of-line blocking by allowing parallel delivery
of data on multiple streams.
This mapping of DNS to QUIC will take advantage of these features in
three ways:
1. Optional support for sending 0-RTT data during session resumption
(the security and privacy implications of this are discussed in
later sections).
2. Long-lived QUIC connections over which multiple DNS transactions
are performed, generating the sustained traffic required to
benefit from advanced recovery features.
3. Fast resumption of QUIC connections to manage the disconnect-on-
idle feature of QUIC without incurring retransmission time-outs.
4. Mapping of each DNS Query/Response transaction to a separate
stream, to mitigate head-of-line blocking. This enables servers
to respond to queries "out of order". It also enables clients to
process responses as soon as they arrive, without having to wait
for in order delivery of responses previously posted by the
server.
These considerations will be reflected in the mapping of DNS traffic
to QUIC streams in Section 5.2.
4.4. No Specific Middlebox Bypass Mechanism
The mapping of DNS over QUIC is defined for minimal overhead and
maximum performance. This means a different traffic profile than
HTTP3 over QUIC. This difference can be noted by firewalls and
middleboxes. There may be environments in which HTTP3 over QUIC will
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be able to pass through, but DoQ will be blocked by these middle
boxes.
4.5. No Server Initiated Transactions
As stated in Section 1, this document does not specify support for
server initiated transactions because these are not relevant for the
"stub to recursive resolver" scenario. Note that "DNS Stateful
Operations" (DSO) [RFC8490] are only applicable for DNS over TCP and
DNS over TLS. DSO is not applicable to DNS over HTTP since HTTP has
its own mechanism for managing sessions, and this is incompatible
with the DSO; the same is true for DNS over QUIC.
5. Specifications
5.1. Connection Establishment
DoQ connections are established as described in the QUIC transport
specification [I-D.ietf-quic-transport]. During connection
establishment, DoQ support is indicated by selecting the ALPN token
"doq" in the crypto handshake.
5.1.1. Draft Version Identification
*RFC Editor's Note:* Please remove this section prior to publication
of a final version of this document.
Only implementations of the final, published RFC can identify
themselves as "doq". Until such an RFC exists, implementations MUST
NOT identify themselves using this string.
Implementations of draft versions of the protocol MUST add the string
"-" and the corresponding draft number to the identifier. For
example, draft-ietf-dprive-dnsoquic-00 is identified using the string
"doq-i00".
5.1.2. Port Selection
By default, a DNS server that supports DoQ MUST listen for and accept
QUIC connections on the dedicated UDP port TBD (number to be defined
in Section 10), unless it has mutual agreement with its clients to
use a port other than TBD for DoQ. In order to use a port other than
TBD, both clients and servers would need a configuration option in
their software.
By default, a DNS client desiring to use DoQ with a particular server
MUST establish a QUIC connection to UDP port TBD on the server,
unless it has mutual agreement with its server to use a port other
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than port TBD for DoQ. Such another port MUST NOT be port 53 or port
853. This recommendation against use of port 53 for DoQ is to avoid
confusion between DoQ and the use of DNS over UDP [RFC1035].
Similarly, using port 853 would cause confusion between DoQ and DNS
over DTLS [RFC8094].
5.2. Stream Mapping and Usage
The mapping of DNS traffic over QUIC streams takes advantage of the
QUIC stream features detailed in Section 2 of the QUIC transport
specification [I-D.ietf-quic-transport].
The stub to resolver DNS traffic follows a simple pattern in which
the client sends a query, and the server provides a response. This
design specifies that for each subsequent query on a QUIC connection
the client MUST select the next available client-initiated
bidirectional stream, in conformance with the QUIC transport
specification [I-D.ietf-quic-transport].
The client MUST send the DNS query over the selected stream, and MUST
indicate through the STREAM FIN mechanism that no further data will
be sent on that stream.
The server MUST send the response on the same stream, and MUST
indicate through the STREAM FIN mechanism that no further data will
be sent on that stream.
Therefore, a single client initiated DNS transaction consumes a
single stream. This means that the client's first query occurs on
QUIC stream 0, the second on 4, and so on.
5.2.1. Transaction Errors
Peers normally complete transactions by sending a DNS response on the
transaction's stream, including cases where the DNS response
indicates a DNS error. For example, a Server Failure (SERVFAIL,
[RFC1035]) SHOULD be notified to the initiator of the transaction by
sending back a response with the Response Code set to SERVFAIL.
If a peer is incapable of sending a DNS response due to an internal
error, it may issue a QUIC Stream Reset with error code
DOQ_INTERNAL_ERROR. The corresponding transaction MUST be abandoned.
5.3. DoQ Error Codes
The following error codes are defined for use when abruptly
terminating streams, aborting reading of streams, or immediately
closing connections:
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DOQ_NO_ERROR (0x00): No error. This is used when the connection or
stream needs to be closed, but there is no error to signal.
DOQ_INTERNAL_ERROR (0x01): The DoQ implementation encountered an
internal error and is incapable of pursuing the transaction or the
connection
5.4. Connection Management
Section 10 of the QUIC transport specification
[I-D.ietf-quic-transport] specifies that connections can be closed in
three ways:
o idle timeout
o immediate close
o stateless reset
Clients and servers implementing DNS over QUIC SHOULD negotiate use
of the idle timeout. Closing on idle timeout is done without any
packet exchange, which minimizes protocol overhead. Per section 10.2
of the QUIC transport specification, the effective value of the idle
timeout is computed as the minimum of the values advertised by the
two endpoints. Practical considerations on setting the idle timeout
are discussed in Section 6.6.2.
Clients SHOULD monitor the idle time incurred on their connection to
the server, defined by the time spent since the last packet from the
server has been received. When a client prepares to send a new DNS
query to the server, it will check whether the idle time is
sufficient lower than the idle timer. If it is, the client will send
the DNS query over the existing connection. If not, the client will
establish a new connection and send the query over that connection.
Clients MAY discard their connection to the server before the idle
timeout expires. If they do that, they SHOULD close the connection
explicitly, using QUIC's CONNECTION_CLOSE mechanisms, and indicating
the Application reason "No Error".
Clients and servers MAY close the connection for a variety of other
reasons, indicated using QUIC's CONNECTION_CLOSE. Client and servers
that send packets over a connection discarded by their peer MAY
receive a stateless reset indication. If a connection fails, all
queries in progress over the connection MUST be considered failed,
and a Server Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the
initiator of the transaction.
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5.5. Connection Resume and 0-RTT
A stub resolver MAY take advantage of the connection resume
mechanisms supported by QUIC transport [I-D.ietf-quic-transport] and
QUIC TLS [I-D.ietf-quic-tls]. Stub resolvers SHOULD consider
potential privacy issues associated with session resume before
deciding to use this mechanism. These privacy issues are detailed in
Section 9.2.
When resuming a session, a stub resolver MAY take advantage of the
0-RTT mechanism supported by QUIC. The 0-RTT mechanism MUST NOT be
used to send data that is not "replayable" transactions. For
example, a stub resolver MAY transmit a Query as 0-RTT, but MUST NOT
transmit an Update.
5.6. Message Sizes
DoQ Queries and Responses are sent on QUIC streams, which in theory
can carry up to 2^62 bytes. However, DNS messages are restricted in
practice to a maximum size of 65535 bytes. This maximum size is
enforced by the use of a two-octet message length field in DNS over
TCP [RFC1035] and DNS over TLS [RFC7858], and by the definition of
the "application/dns-message" for DNS over HTTP [RFC8484]. DoQ
enforces the same restriction.
The flow control mechanism of QUIC control how much data can be sent
by QUIC nodes at a given time. The initial values of per stream flow
control parameters is defined by two transport parameters:
o initial_max_stream_data_bidi_local: when set by the client,
specifies the amount of data that servers can send on a "response"
stream without waiting for a MAX_STREAM_DATA frame.
o initial_max_stream_data_bidi_remote: when set by the server,
specifies the amount of data that clients can send on a "query"
stream without waiting for a MAX_STREAM_DATA frame.
For better performance, it is RECOMMENDED that clients and servers
set each of these two parameters to a value of 65535 or greater.
The Extension Mechanisms for DNS (EDNS) [RFC6891] allow peers to
specify the UDP message size. This parameter is ignored by DoQ. DoQ
implementations always assume that the maximum message size is 65535
bytes.
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6. Implementation Requirements
6.1. Authentication
For the stub to recursive resolver scenario, the authentication
requirements are the same as described in DoT [RFC7858] and "Usage
Profiles for DNS over TLS and DNS over DTLS" [RFC8310]. There is no
need to authenticate the client's identity in either scenario.
6.2. Fall Back to Other Protocols on Connection Failure
If the establishment of the DoQ connection fails, clients SHOULD
attempt to fall back to DoT and then potentially clear text, as
specified in DoT [RFC7858] and "Usage Profiles for DNS over TLS and
DNS over DTLS" [RFC8310], depending on their privacy profile.
DNS clients SHOULD remember server IP addresses that don't support
DoQ, including timeouts, connection refusals, and QUIC handshake
failures, and not request DoQ from them for a reasonable period (such
as one hour per server). DNS clients following an out-of-band key-
pinned privacy profile ([RFC7858]) MAY be more aggressive about
retrying DoQ connection failures.
6.3. Address Validation
Section 8 of the QUIC transport specification
[I-D.ietf-quic-transport] defines Address Validation procedures to
avoid servers being used in address amplification attacks. DoQ
implementations MUST conform to this specification, which limits the
worst case amplification to a factor 3.
DoQ implementations SHOULD consider configuring servers to use the
Address Validation using Retry Packets procedure defined in section
8.1.2 of the QUIC transport specification [I-D.ietf-quic-transport]).
This procedure imposes a 1-RTT delay for verifying the return
routability of the source address of a client, similar to the DNS
Cookies mechanism [RFC7873].
DoQ implementations that configure Address Validation using Retry
Packets SHOULD implement the Address Validation for Future
Connections procedure defined in section 8.1.3 of the QUIC transport
specification [I-D.ietf-quic-transport]). This defines how servers
can send NEW TOKEN frames to clients after the client address is
validated, in order to avoid the 1-RTT penalty during subsequent
connections by the client from the same address.
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6.4. DNS Message IDs
When sending queries over a QUIC connection, the DNS Message ID MUST
be set to zero.
6.5. Padding
There are mechanisms specified for padding individual DNS messages in
"The EDNS(0) Padding Option" [RFC7830] and for padding within QUIC
packets (see Section 8.6 of the QUIC transport specification
[I-D.ietf-quic-transport]).
Implementations SHOULD NOT use DNS options for padding individual DNS
messages, because QUIC transport MAY transmit multiple STREAM frames
containing separate DNS messages in a single QUIC packet. Instead,
implementations SHOULD use QUIC PADDING frames to align the packet
length to a small set of fixed sizes, aligned with the
recommendations of the "Padding Policies for Extension Mechanisms for
DNS (EDNS(0))" [RFC8467].
6.6. Connection Handling
"DNS Transport over TCP - Implementation Requirements" [RFC7766]
provides updated guidance on DNS over TCP, some of which is
applicable to DoQ. This section attempts to specify which and how
those considerations apply to DoQ.
6.6.1. Connection Reuse
Historic implementations of DNS stub resolvers are known to open and
close TCP connections for each DNS query. To avoid excess QUIC
connections, each with a single query, clients SHOULD reuse a single
QUIC connection to the recursive resolver.
In order to achieve performance on par with UDP, DNS clients SHOULD
send their queries concurrently over the QUIC streams on a QUIC
connection. That is, when a DNS client sends multiple queries to a
server over a QUIC connection, it SHOULD NOT wait for an outstanding
reply before sending the next query.
6.6.2. Resource Management and Idle Timeout Values
Proper management of established and idle connections is important to
the healthy operation of a DNS server. An implementation of DoQ
SHOULD follow best practices similar to those specified for DNS over
TCP [RFC7766], in particular with regard to:
o Concurrent Connections (Section 6.2.2)
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o Security Considerations (Section 10)
Failure to do so may lead to resource exhaustion and denial of
service.
Clients that want to maintain long duration DoQ connections SHOULD
use the idle timeout mechanisms defined in Section 10.2 of the QUIC
transport specification [I-D.ietf-quic-transport]. Clients and
servers MUST NOT send the edns-tcp-keepalive EDNS(0) Option [RFC7828]
in any messages sent on a DoQ connection (because it is specific to
the use of TCP/TLS as a transport). If any message sent on a DoQ
connection contains an edns-tcp-keepalive EDNS(0) Option, this is a
fatal error and the recipient of the defective message MUST forcibly
abort the connection immediately.
This document does not make specific recommendations for timeout
values on idle connections. Clients and servers should reuse and/or
close connections depending on the level of available resources.
Timeouts may be longer during periods of low activity and shorter
during periods of high activity.
Clients that are willing to use QUIC's 0-RTT mechanism can
reestablish connections and send transactions on the new connection
with minimal delay overhead. These clients MAY chose low values of
the idle timer.
6.7. Processing Queries in Parallel
As specified in Section 7 of "DNS Transport over TCP - Implementation
Requirements" [RFC7766], resolvers are RECOMMENDED to support the
preparing of responses in parallel and sending them out of order. In
DoQ, they do that by sending responses on their specific stream as
soon as possible, without waiting for availability of responses for
previously opened streams.
6.8. Flow Control Mechanisms
Servers and Clients manage flow control as specified in QUIC.
Servers MAY use the "maximum stream ID" option of the QUIC transport
to limit the number of streams opened by the client. This mechanism
will effectively limit the number of DNS queries that a client can
send on a single DoQ connection.
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7. Implementation Status
(THIS SECTION TO BE REMOVED BEFORE PUBLICATION) This section records
the status of known implementations of the protocol defined by this
specification at the time of posting of this Internet-Draft, and is
based on a proposal described in [RFC7942].
1. AdGuard launched a DoQ recursive resolver service in December
2020. They have released a suite of open source tools that
support DoQ:
1. AdGuard C++ DNS libraries [1] A DNS proxy library that
supports all existing DNS protocols including DNS-over-TLS,
DNS-over-HTTPS, DNSCrypt and DNS-over-QUIC (experimental).
2. DNS Proxy [2] A simple DNS proxy server that supports all
existing DNS protocols including DNS-over-TLS, DNS-over-
HTTPS, DNSCrypt, and DNS-over-QUIC. Moreover, it can work as
a DNS-over-HTTPS, DNS-over-TLS or DNS-over-QUIC server.
3. CoreDNS fork for AdGuard DNS [3] Includes DNS-over-QUIC
server-side support.
4. dnslookup [4] Simple command line utility to make DNS
lookups. Supports all known DNS protocols: plain DNS, DoH,
DoT, DoQ, DNSCrypt.
2. Quicdoq [5] Quicdoq is a simple open source implementation of DNS
over Quic. It is written in C, based on Picoquic [6].
3. Flamethrower [7] is an open source DNS performance and functional
testing utility written in C++ that has an experimental
implementation of DoQ.
4. aioquic [8] is an implementation of QUIC in Python. It includes
example client and server for DNS over QUIC.
7.1. Performance Measurements
To our knowledge, no benchmarking studies comparing DoT, DoH and DoQ
are published yet. However anecdotal evidence from the AdGuard DoQ
recursive resolver deployment [9] indicates that it performs well
compared to the other encrypted protocols, particularly in mobile
environments. Reasons given for this include that DoQ
o Uses less bandwidth due to a more efficient handshake (and due to
less per message overhead when compared to DoH).
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o Performs better in mobile environments due to the increased
resilience to packet loss
o Can maintain connections as users move between mobile networks via
its connection management
8. Security Considerations
The security considerations of DoQ should be comparable to those of
DoT [RFC7858].
9. Privacy Considerations
DoQ is specifically designed to protect the DNS traffic between stub
and resolver from observations by third parties, and thus protect the
privacy of queries sent by the stub. However, the recursive resolver
has full visibility of the stub's traffic, and could be used as an
observation point, as discussed in the revision of "DNS Privacy
Considerations" [I-D.ietf-dprive-rfc7626-bis]. These considerations
do not differ between DoT and DoQ and are not discussed further here.
QUIC incorporates the mechanisms of TLS 1.3 [RFC8446] and this
enables QUIC transmission of "0-RTT" data. This can provide
interesting latency gains, but it raises two concerns:
1. Adversaries could replay the 0-RTT data and infer its content
from the behavior of the receiving server.
2. The 0-RTT mechanism relies on TLS resume, which can provide
linkability between successive client sessions.
These issues are developed in Section 9.1 and Section 9.2.
9.1. Privacy Issues With 0-RTT data
The 0-RTT data can be replayed by adversaries. That data may trigger
queries by a recursive resolver to authoritative resolvers.
Adversaries may be able to pick a time at which the recursive
resolver outgoing traffic is observable, and thus find out what name
was queried for in the 0-RTT data.
This risk is in fact a subset of the general problem of observing the
behavior of the recursive resolver discussed in "DNS Privacy
Considerations" [RFC7626]. The attack is partially mitigated by
reducing the observability of this traffic. However, the risk is
amplified for 0-RTT data, because the attacker might replay it at
chosen times, several times.
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The recommendation for TLS 1.3 [RFC8446] is that the capability to
use 0-RTT data should be turned off by default, and only enabled if
the user clearly understands the associated risks.
QUESTION: Should 0-RTT only be used with Opportunistic profiles (i.e.
disabled by default for Strict only)?
9.2. Privacy Issues With Session Resume
The QUIC session resume mechanism reduces the cost of re-establishing
sessions and enables 0-RTT data. There is a linkability issue
associated with session resume, if the same resume token is used
several times, but this risk is mitigated by the mechanisms
incorporated in QUIC and in TLS 1.3. With these mechanisms, clients
and servers can cooperate to avoid linkability by third parties.
However, the server will always be able to link the resumed session
to the initial session. This creates a virtual long duration
session. The series of queries in that session can be used by the
server to identify the client.
Enabling the server to link client sessions through session resume is
probably not a large additional risk if the client's connectivity did
not change between the sessions, since the two sessions can probably
be correlated by comparing the IP addresses. On the other hand, if
the addresses did change, the client SHOULD consider whether the
linkability risk exceeds the performance benefits. This evaluation
will obviously depend on the level of trust between stub and
recursive.
9.3. Traffic Analysis
Even though QUIC packets are encrypted, adversaries can gain
information from observing packet lengths, in both queries and
responses, as well as packet timing. Many DNS requests are emitted
by web browsers. Loading a specific web page may require resolving
dozen of DNS names. If an application adopts a simple mapping of one
query or response per packet, or "one QUIC STREAM frame per packet",
then the succession of packet lengths may provide enough information
to identify the requested site.
Implementations SHOULD use the mechanisms defined in Section 6.5 to
mitigate this attack.
10. IANA Considerations
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10.1. Registration of DoQ Identification String
This document creates a new registration for the identification of
DoQ in the "Application Layer Protocol Negotiation (ALPN) Protocol
IDs" registry [RFC7301].
The "doq" string identifies DoQ:
Protocol: DoQ
Identification Sequence: 0x64 0x6F 0x71 ("doq")
Specification: This document
10.2. Reservation of Dedicated Port
IANA is required to add the following value to the "Service Name and
Transport Protocol Port Number Registry" in the System Range. The
registry for that range requires IETF Review or IESG Approval
[RFC6335], and such a review was requested using the early allocation
process [RFC7120] for the well-known UDP port in this document.
Since port 853 is reserved for 'DNS query-response protocol run over
TLS' consideration is requested for reserving port 8853 for 'DNS
query-response
protocol run over QUIC'.
Service Name dns-over-quic
Port Number 8853
Transport Protocol(s) UDP
Assignee IESG
Contact IETF Chair
Description DNS query-response protocol run over QUIC
Reference This document
10.2.1. Port number 8853 for experimentations
*RFC Editor's Note:* Please remove this section prior to publication
of a final version of this document.
Early experiments MAY use port 8853. This port is marked in the IANA
registry as unassigned.
(Note that prior to version -02 of this draft, experiments were
directed to use port 784.)
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11. Acknowledgements
This document liberally borrows text from the HTTP-3 specification
[I-D.ietf-quic-http] edited by Mike Bishop, and from the DoT
specification [RFC7858] authored by Zi Hu, Liang Zhu, John Heidemann,
Allison Mankin, Duane Wessels, and Paul Hoffman.
The privacy issue with 0-RTT data and session resume were analyzed by
Daniel Kahn Gillmor (DKG) in a message to the IETF "DPRIVE" working
group [DNS0RTT].
Thanks to Tony Finch for an extensive review of the initial version
of this draft. Reviews by Paul Hoffman and interoperability tests
conducted by Stephane Bortzmeyer helped improve the definition of the
protocol.
12. References
12.1. Normative References
[I-D.ietf-dnsop-terminology-ter]
Hoffman, P., "Terminology for DNS Transports and
Location", draft-ietf-dnsop-terminology-ter-02 (work in
progress), August 2020.
[I-D.ietf-quic-tls]
Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
draft-ietf-quic-tls-34 (work in progress), January 2021.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-34 (work
in progress), January 2021.
[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>.
[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>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,