Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Standards Track                               A. Mankin
Expires: September 6, 2020                                    Salesforce
                                                            S. Dickinson
                                                              Sinodun IT
                                                          March 05, 2020

          Specification of DNS over Dedicated QUIC Connections


   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
   performance 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

   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 September 6, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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.  Design Considerations . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Scope is Limited to the Stub to Resolver Scenario . . . .   4
     3.2.  Provide DNS Privacy . . . . . . . . . . . . . . . . . . .   5
     3.3.  Design for Minimum Latency  . . . . . . . . . . . . . . .   5
     3.4.  No Specific Middlebox Bypass Mechanism  . . . . . . . . .   6
   4.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Connection Establishment  . . . . . . . . . . . . . . . .   6
       4.1.1.  Draft Version Identification  . . . . . . . . . . . .   6
       4.1.2.  Port Selection  . . . . . . . . . . . . . . . . . . .   7
     4.2.  Stream Mapping and Usage  . . . . . . . . . . . . . . . .   7
       4.2.1.  Server Initiated Transactions . . . . . . . . . . . .   8
       4.2.2.  Stream Reset  . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Connection Management . . . . . . . . . . . . . . . . . .   8
     4.4.  Connection Resume and 0-RTT . . . . . . . . . . . . . . .   9
   5.  Implementation Requirements . . . . . . . . . . . . . . . . .   9
     5.1.  Authentication  . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Fall Back to Other Protocols on Connection Failure  . . .  10
     5.3.  Address Validation  . . . . . . . . . . . . . . . . . . .  10
     5.4.  Response Sizes  . . . . . . . . . . . . . . . . . . . . .  10
     5.5.  DNS Message IDs . . . . . . . . . . . . . . . . . . . . .  11
     5.6.  Padding . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.7.  Connection Handling . . . . . . . . . . . . . . . . . . .  11
       5.7.1.  Connection Reuse  . . . . . . . . . . . . . . . . . .  11
       5.7.2.  Connection Close  . . . . . . . . . . . . . . . . . .  12
       5.7.3.  Idle Timeouts . . . . . . . . . . . . . . . . . . . .  12
     5.8.  Flow Control Mechanisms . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  13
     7.1.  Privacy Issues With Zero RTT data . . . . . . . . . . . .  13
     7.2.  Privacy Issues With Session Resume  . . . . . . . . . . .  14
     7.3.  Traffic Analysis  . . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Registration of DoQ Identification String . . . . . . . .  15
     8.2.  Reservation of Dedicated Port . . . . . . . . . . . . . .  15
       8.2.1.  Port number 784 for experimentations  . . . . . . . .  15
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16

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     10.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Domain Name System (DNS) concepts are specified in [RFC1034].  This
   document presents a mapping of the DNS protocol [RFC1035] over QUIC
   transport [I-D.ietf-quic-transport] [I-D.ietf-quic-tls].  DNS over
   QUIC is refered here as DoQ, in line with the terminology presented
   in [I-D.ietf-dnsop-terminology-ter].  The goals of the DoQ mapping

   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

   2.  Provide an improved level of source address validation for DNS
       servers compared to classic DNS over UDP [RFC1035].

   3.  Provide a transport that is not constrained by path MTU
       limitations on the size of DNS responses it can send.

   4.  Explore the potential performance gains of using QUIC as a DNS
       transport, versus other solutions like DNS over UDP (DNS/UDP)
       [RFC1035] or DoT [RFC7858].

   In order to achieve these goals, the focus of this document is
   limited to the "stub to recursive resolver" scenario also addressed
   by [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 zone transfers [RFC5936], as these
       are not relevant to the stub to recursive resolver scenario.

   2.  No attempt is made to evade potential blocking of DNS/QUIC
       traffic by middleboxes.

   Users interested in zone transfers should continue using TCP based
   solutions and will also want to take note of work in progress to
   encrypt zone transfers using DoT [I-D.ietf-dprive-xfr-over-tls].
   Users interested in evading middleboxes should consider using
   solutions like DNS/HTTPS [RFC8484].

   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

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   HTTP in [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 3 presents the reasoning that guided the
   proposed design.  Section 4 specifies the actual mapping of DoQ.
   Section 5 presents guidelines on the implementation, usage and
   deployment of DoQ.

2.  Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC8174].

3.  Design Considerations

   This section and its subsection present the design guidelines that
   were used for DoQ.  This section is informative in nature.

3.1.  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 [RFC7858] and [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 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

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   currently well served by using DNS over TCP.  There is no attempt to
   support them in this proposed mapping of DNS to QUIC.

3.2.  Provide DNS Privacy

   DNS privacy considerations are described in [RFC7626].  [RFC7858]
   defines how to mitigate some of these issues by transmitting DNS
   messages over TLS and TCP and [RFC8310] specifies 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 [I-D.ietf-quic-tls], enabling encryption
   of the QUIC transport.  Transmitting DNS messages over QUIC will
   provide essentially the same privacy protections as [RFC7858] and
   [RFC8310].  Further discussion on this is provided in Section 7.

3.3.  Design for Minimum Latency

   QUIC is specifically designed to reduce the delay between HTTP
   queries and HTTP responses.  This is achieved through three main

   1.  Support for 0-RTT data during session resumption.

   2.  Support for advanced error recovery procedures as specified in

   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.

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   These considerations will be reflected in the mapping of DNS traffic
   to QUIC streams in Section 4.2.

3.4.  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
   HTTP over QUIC.  This difference can be noted by firewalls and
   middleboxes.  There may be environments in which HTTP/QUIC will be
   allowed, but DoQ will be disallowed and blocked by these middle

   It is recognized that this might be a problem, but there is currently
   no indication on how widespread that problem might be.  The problem
   might be acute enough that the only realistic solution would be to
   communicate with independent recursive resolvers using DNS/HTTPS, or
   maybe DNS/HTTP/QUIC.  Or the problem might be rare enough and the
   performance gains significant enough that the appropriate solution
   would be to use DoQ most of the time, and fall back to DNS/HTTPS some
   of the time.  Measurements and experimentation will inform that

   It may indeed turn out that the complexity and overhead concerns are
   negligible compared to the potential advantages of DNS/HTTPS, such as
   integration with web services or firewall traversal, and that DoQ
   does not provide sufficient performance gains to justify a new
   protocol.  We will evaluate that once implementations are available
   and can be compared.

4.  Specifications

4.1.  Connection Establishment

   DoQ connections are established as described in
   [I-D.ietf-quic-transport].  During connection establishment, DoQ
   support is indicated by selecting the ALPN token "dq" in the crypto

4.1.1.  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.

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   Implementations of draft versions of the protocol MUST add the string
   "-" and the corresponding draft number to the identifier.  For
   example, draft-huitema-dprive-dnsoquic-00 is identified using the
   string "doq-h00".

4.1.2.  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 8, 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
   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 DNS/UDP as specified in [RFC1035].
   Similarly, using port 853 would cause confusion between DoQ and DNS/
   DTLS as specified in [RFC8094].

4.2.  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 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 [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.

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4.2.1.  Server Initiated Transactions

   There are planned traffic patterns in which a server sends
   unsolicited queries to a client, such as for example PUSH messages
   defined in [I-D.ietf-dnssd-push].  These occur when a client
   subscribes to changes for a particular DNS RRset or resource record
   type.  When a PUSH server wishes to send such updates it MUST select
   the next available server initiated bidirectional stream, in
   conformance with [I-D.ietf-quic-transport].

   The server 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 client 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 server initiated DNS transaction consumes a single
   stream.  This means that the servers's first query occurs on QUIC
   stream 1, the second on 5, and so on.

4.2.2.  Stream Reset

   Stream transmission may be abandoned by either party, using the
   stream "reset" facility.  A stream reset indicates that one party is
   unwilling to continue processing the transaction associated with the
   stream.  The corresponding transaction MUST be abandoned.  A Server
   Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the initiator of
   the transaction.

4.3.  Connection Management

   Section 10 of the QUIC transport specifications
   [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.  This document
   does not recommend a specific value of the idle timer.

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   Clients SHOULD monitor the idle time incurred on their connection to
   the server, defined by the time spend 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 aServer Failure (SERVFAIL, [RFC1035]) SHOULD be notified to the
   initiator of the transaction.

4.4.  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 7.2.

   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.  Implementation Requirements

5.1.  Authentication

   For the stub to recursive resolver scenario, the authentication
   requirements are the same as described in [RFC7858] and [RFC8310].
   There is no need to authenticate the client's identity in either

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5.2.  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 [RFC7858] and [RFC8310], depending on their privacy

   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.

5.3.  Address Validation

   The QUIC transport specification defines Address Validation
   procedures to avoid servers being used in address amplification
   attacks (see section 8 of [I-D.ietf-quic-transport]).  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 [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 defined in [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
   [I-D.ietf-quic-transport]).  This define 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.

5.4.  Response Sizes

   DoQ does not suffer from the same limitations on the size of queries
   and responses that as DNS/UDP [RFC1035] does.  Queries and Responses
   are sent on QUIC streams, which in theory can carry up to 2^62 bytes.
   However, clients or servers MAY impose a limit on the maximum size of
   data that they can accept over a given stream.  This is controlled in
   QUIC by the 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.

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   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.

   Clients and servers SHOULD treat these parameters as the practical
   maximum of queries and responses.  If the EDNS parameters of a Query
   indicate a lower message size, servers MUST comply with that

5.5.  DNS Message IDs

   When sending queries over a QUIC connection, the DNS Message ID MUST
   be set to zero.

5.6.  Padding

   There are mechanisms specified for both padding individual DNS
   messages [RFC7830], [RFC8467] and padding within QUIC packets (see
   Section 8.6 of [I-D.ietf-quic-transport]), which may contain multiple

   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 [RFC8467].

5.7.  Connection Handling

   [RFC7766] provides updated guidance on DNS/TCP much of which is
   applicable to DoQ.  This section attempts to specify how those
   considerations apply to DoQ.

5.7.1.  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.

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5.7.2.  Connection Close

   In order to amortize QUIC and TLS connection setup costs, clients and
   servers SHOULD NOT immediately close a QUIC connection after each
   response.  Instead, clients and servers SHOULD reuse existing QUIC
   connections for subsequent queries as long as they have sufficient
   resources.  In some cases, this means that clients and servers may
   need to keep idle connections open for some amount of time.

   Under normal operation DNS clients typically initiate connection
   closing on idle connections; however, DNS servers can close the
   connection if the idle timeout set by local policy is exceeded.
   Also, connections can be closed by either end under unusual
   conditions such as defending against an attack or system failure/

   Clients and servers that keep idle connections open MUST be robust to
   termination of idle connection by either party.  As with current DNS
   over TCP, DNS servers MAY close the connection at any time (perhaps
   due to resource constraints).  As with current DNS/TCP, clients MUST
   handle abrupt closes and be prepared to reestablish connections and/
   or retry queries.

5.7.3.  Idle Timeouts

   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 for DNS/TCP, as described in [RFC7766].
   Failure to do so may lead to resource exhaustion and denial of

   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.  Current work in this area may also
   assist DoT clients and servers in selecting useful timeout values
   [RFC7828] [RFC8490] [TDNS].

   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, but SHOULD NOT pick value lower than 20 seconds.

   Per section 10.2 of QUIC transport specification, the effective value
   of the idle timeout is computed as the minimum of the values
   advertised by the two endpoints.

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5.8.  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

6.  Security Considerations

   The security considerations of DoQ should be comparable to those of
   DoT [RFC7858].

7.  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 from 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 [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 "Zero-RTT" data.  This can provide
   interesting latency gains, but it raises two concerns:

   1.  Adversaries could replay the zero-RTT data and infer its content
       from the behavior of the receiving server.

   2.  The zero-RTT mechanism relies on TLS resume, which can provide
       linkability between successive client sessions.

   These issues are developed in Section 7.1 and Section 7.2.

7.1.  Privacy Issues With Zero RTT data

   The zero-RTT data can be replayed by adversaries.  That data may
   triggers a query by a recursive resolver to an 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 [RFC7626].  The
   attack is partially mitigated by reducing the observability of this

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   traffic.  However, the risk is amplified for 0-RTT data, because the
   attacker might replay it at chosen times, several times.

   The recommendation in [RFC8446] is that the capability to use 0-RTT
   data should be turned off by default, on 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)?

7.2.  Privacy Issues With Session Resume

   The QUIC session resume mechanism reduces the cost of reestablishing
   sessions and enables zero-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 privacy benefits.  This evaluation will
   obviously depend on the level of trust between stub and recursive.

7.3.  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 5.6 to
   mitigate this attack.

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8.  IANA Considerations

8.1.  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 established in [RFC7301].

   The "doq" string identifies DoQ:

   Protocol: DoQ

   Identification Sequence: 0x64 0x71 ("dq")

   Specification: This document

8.2.  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
   TBD for 'DNS query-response
   protocol run over QUIC'.

      Service Name           domain-s
      Transport Protocol(s)  TCP/UDP
      Assignee               IESG
      Contact                IETF Chair
      Description            DNS query-response protocol run over QUIC
      Reference              This document

8.2.1.  Port number 784 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 784.  This port is marked in the IANA
   registry as unassigned.

9.  Acknowledgements

   This document liberally borrows text from [I-D.ietf-quic-http] edited
   by Mike Bishop, and from [RFC7858] authored by Zi Hu, Liang Zhu, John
   Heidemann, Allison Mankin, Duane Wessels, and Paul Hoffman.

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   The privacy issue with 0-RTT data and session resume were analyzed by
   Daniel Kahn Gillmor (DKG) in a message to the IETF "DPRIV" working
   group [DNS0RTT].

   Thanks to our wide cast of supporters.

10.  References

10.1.  Normative References

              Hoffman, P., "Terminology for DNS Transports and
              Location", draft-ietf-dnsop-terminology-ter-01 (work in
              progress), February 2020.

              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-27 (work in progress), February 2020.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-27 (work
              in progress), February 2020.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <>.

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <>.

   [RFC7873]  Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
              Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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   [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,

10.2.  Informative References

   [DNS0RTT]  Kahn Gillmor, D., "DNS + 0-RTT", Message to DNS-Privacy WG
              mailing list, April 2016, <

              Pusateri, T. and S. Cheshire, "DNS Push Notifications",
              draft-ietf-dnssd-push-25 (work in progress), October 2019.

              Livingood, J., Mayrhofer, A., and B. Overeinder, "DNS
              Privacy Requirements for Exchanges between Recursive
              Resolvers and Authoritative Servers", draft-ietf-dprive-
              phase2-requirements-00 (work in progress), December 2019.

              Bortzmeyer, S. and S. Dickinson, "DNS Privacy
              Considerations", draft-ietf-dprive-rfc7626-bis-04 (work in
              progress), January 2020.

              Zhang, H., Aras, P., Toorop, W., Dickinson, S., and A.
              Mankin, "DNS Zone Transfer-over-TLS", draft-ietf-dprive-
              xfr-over-tls-00 (work in progress), November 2019.

              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", draft-ietf-quic-http-27 (work in progress),
              February 2020.

              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-26 (work in
              progress), February 2020.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,

   [RFC7626]  Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
              DOI 10.17487/RFC7626, August 2015,

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   [RFC7766]  Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
              D. Wessels, "DNS Transport over TCP - Implementation
              Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,

   [RFC7828]  Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
              edns-tcp-keepalive EDNS0 Option", RFC 7828,
              DOI 10.17487/RFC7828, April 2016,

   [RFC7830]  Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
              DOI 10.17487/RFC7830, May 2016,

   [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, <>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

   [RFC8467]  Mayrhofer, A., "Padding Policies for Extension Mechanisms
              for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
              October 2018, <>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,

   [RFC8490]  Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
              Lemon, T., and T. Pusateri, "DNS Stateful Operations",
              RFC 8490, DOI 10.17487/RFC8490, March 2019,

   [TDNS]     Zhu, L., Hu, Z., Heidemann, J., Wessels, D., Mankin, A.,
              and N. Somaiya, "Connection-Oriented DNS to Improve
              Privacy and Security", 2015 IEEE Symposium on Security and
              Privacy (SP), DOI 10.1109/SP.2015.18, May 2015,

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Authors' Addresses

   Christian Huitema
   Private Octopus Inc.
   427 Golfcourse Rd
   Friday Harbor  WA 98250


   Allison Mankin


   Sara Dickinson
   Sinodun IT
   Oxford Science Park
   Oxford  OX4 4GA


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