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Network Working Group                                         C. Huitema
Internet-Draft                                      Private Octopus Inc.
Intended status: Standards Track                               A. Mankin
Expires: October 29, 2020                                     Salesforce
                                                            S. Dickinson
                                                              Sinodun IT
                                                          April 27, 2020


          Specification of DNS over Dedicated QUIC Connections
                     draft-ietf-dprive-dnsoquic-00

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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 29, 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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
     3.5.  No Server Initiated Transactions  . . . . . . . . . . . .   6
   4.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Connection Establishment  . . . . . . . . . . . . . . . .   7
       4.1.1.  Draft Version Identification  . . . . . . . . . . . .   7
       4.1.2.  Port Selection  . . . . . . . . . . . . . . . . . . .   7
     4.2.  Stream Mapping and Usage  . . . . . . . . . . . . . . . .   7
       4.2.1.  Transaction Errors  . . . . . . . . . . . . . . . . .   8
     4.3.  DoQ Error Codes . . . . . . . . . . . . . . . . . . . . .   8
     4.4.  Connection Management . . . . . . . . . . . . . . . . . .   9
     4.5.  Connection Resume and 0-RTT . . . . . . . . . . . . . . .   9
     4.6.  Message Sizes . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Implementation Requirements . . . . . . . . . . . . . . . . .  10
     5.1.  Authentication  . . . . . . . . . . . . . . . . . . . . .  10
     5.2.  Fall Back to Other Protocols on Connection Failure  . . .  11
     5.3.  Address Validation  . . . . . . . . . . . . . . . . . . .  11
     5.4.  DNS Message IDs . . . . . . . . . . . . . . . . . . . . .  11
     5.5.  Padding . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.6.  Connection Handling . . . . . . . . . . . . . . . . . . .  12
       5.6.1.  Connection Reuse  . . . . . . . . . . . . . . . . . .  12
       5.6.2.  Resource Management and Idle Timeout Values . . . . .  12
     5.7.  Processing Queries in Parallel  . . . . . . . . . . . . .  13
     5.8.  Flow Control Mechanisms . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  13
     7.1.  Privacy Issues With 0-RTT data  . . . . . . . . . . . . .  14
     7.2.  Privacy Issues With Session Resume  . . . . . . . . . . .  14
     7.3.  Traffic Analysis  . . . . . . . . . . . . . . . . . . . .  15
   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  . . . . . . . .  16
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16



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     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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.

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






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   3.  No attempt to support server initiated transactions, are these
       are not relevant for the "stub to recursive resolver" scenario,
       see Section 3.5.

   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 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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14 [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 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



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   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.

3.2.  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
   Opportunistic Usage Profiles [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
   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.




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   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 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
   HTTP3 over QUIC.  This difference can be noted by firewalls and
   middleboxes.  There may be environments in which HTTP3 over QUIC will
   be able to pass through, but DoQ will be blocked by these middle
   boxes.

3.5.  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.

4.  Specifications







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4.1.  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.

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.

   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".

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 the use of DNS over UDP [RFC1035].
   Similarly, using port 853 would cause confusion between DoQ and DNS
   over DTLS [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 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



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   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.

4.2.1.  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.

4.3.  DoQ Error Codes

   The following error codes are defined for use when abruptly
   terminating streams, aborting reading of streams, or immediately
   closing connections:

   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.

   DOQ_TRANSPORT_PARAMETER_ERROR (0x02):  One or some of the transport
      parameters proposed by the peer are not acceptable.








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4.4.  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 5.6.2.

   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.

4.5.  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




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   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.

4.6.  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 maximum size of messages 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.

   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 MUST set these two parameters to the value 65535.
   If they receive a different value, they SHOULD close the QUIC
   connection with an application error "Invalid Parameter".

   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.

5.  Implementation Requirements

5.1.  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.




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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 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.

5.3.  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.

5.4.  DNS Message IDs

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

5.5.  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]).



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   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].

5.6.  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.

5.6.1.  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.

5.6.2.  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)

   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



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   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.

5.7.  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.

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
   send on a single DoQ connection.

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 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.




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   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 7.1 and Section 7.2.

7.1.  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.

   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)?

7.2.  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.





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   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 5.5 to
   mitigate this attack.

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 [RFC7301].

   The "doq" string identifies DoQ:

   Protocol: DoQ

   Identification Sequence: 0x64 0x6F 0x71 ("doq")

   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



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   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 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.

10.  References

10.1.  Normative References

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

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

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



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   [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,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [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, <https://www.rfc-editor.org/info/rfc7301>.

   [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,
              <https://www.rfc-editor.org/info/rfc7766>.

   [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>.

   [RFC7873]  Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
              Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
              <https://www.rfc-editor.org/info/rfc7873>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.







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10.2.  Informative References

   [DNS0RTT]  Kahn Gillmor, D., "DNS + 0-RTT", Message to DNS-Privacy WG
              mailing list, April 2016, <https://www.ietf.org/mail-
              archive/web/dns-privacy/current/msg01276.html>.

   [I-D.ietf-dprive-phase2-requirements]
              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.

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

   [I-D.ietf-dprive-xfr-over-tls]
              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.

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

   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-27 (work in
              progress), March 2020.

   [RFC1885]  Conta, A. and S. Deering, "Internet Control Message
              Protocol (ICMPv6) for the Internet Protocol Version 6
              (IPv6)", RFC 1885, DOI 10.17487/RFC1885, December 1995,
              <https://www.rfc-editor.org/info/rfc1885>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.

   [RFC7626]  Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
              DOI 10.17487/RFC7626, August 2015,
              <https://www.rfc-editor.org/info/rfc7626>.







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   [RFC7828]  Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
              edns-tcp-keepalive EDNS0 Option", RFC 7828,
              DOI 10.17487/RFC7828, April 2016,
              <https://www.rfc-editor.org/info/rfc7828>.

   [RFC7830]  Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
              DOI 10.17487/RFC7830, May 2016,
              <https://www.rfc-editor.org/info/rfc7830>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

   [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>.

   [RFC8467]  Mayrhofer, A., "Padding Policies for Extension Mechanisms
              for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
              October 2018, <https://www.rfc-editor.org/info/rfc8467>.

   [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,
              <https://www.rfc-editor.org/info/rfc8490>.

Authors' Addresses

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

   Email: huitema@huitema.net


   Allison Mankin
   Salesforce

   Email: amankin@salesforce.com









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   Sara Dickinson
   Sinodun IT
   Oxford Science Park
   Oxford  OX4 4GA
   U.K.

   Email: sara@sinodun.com












































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