Network Working Group                                      M. Kuehlewind
Internet-Draft                                               B. Trammell
Intended status: Informational                                ETH Zurich
Expires: September 9, 2017                                March 08, 2017

              Applicability of the QUIC Transport Protocol


   This document discusses the applicability of the QUIC transport
   protocol, focusing on caveats impacting application protocol
   development and deployment over QUIC.  Its intended audience is
   designers of application protocol mappings to QUIC, and implementors
   of these application protocols.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   2
   2.  The Necessity of Fallback . . . . . . . . . . . . . . . . . .   3
   3.  Zero RTT: Here There Be Dragons . . . . . . . . . . . . . . .   3
   4.  Stream versus Flow Multiplexing . . . . . . . . . . . . . . .   4
   5.  Prioritization  . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Graceful connection closure . . . . . . . . . . . . . . . . .   5
   7.  Information exposure and the Connection ID  . . . . . . . . .   5
   8.  Use of Versions and Cryptographic Handshake . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   5
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     12.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   QUIC [I-D.ietf-quic-transport] is a new transport protocol currently
   under development in the IETF quic working group, focusing on support
   of semantics as needed for HTTP/2 [I-D.ietf-quic-http] such as
   stream-multiplexing to avoid head-of-line blocking.  Based on current
   deployment practices, QUIC is encapsulated in UDP and encrypted by
   default.  This means the version of QUIC that is currently under
   development will integrate TLS 1.3 [I-D.ietf-quic-tls] to encrypt all
   payload data and most header information.

   This document provides guidance for application developers that want
   to use the QUIC protocol without implementing it on their own.  This
   includes general guidance for application use of HTTP/2 over QUIC as
   well as the use of other application layer protocols over QUIC.  For
   specific guidance on how to integrate HTTP/2 with QUIC, see

   In the following sections we discuss specific caveats to QUIC's
   applicability, and issues that application developers must consider
   when using QUIC as a transport for their application.

1.1.  Notational Conventions

   The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when these words are capitalized, they
   have a special meaning as defined in [RFC2119].

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2.  The Necessity of Fallback

   QUIC uses UDP as a substrate for userspace implementation and port
   numbers for NAT and middlebox traversal.  While there is no evidence
   of widespread, systematic disadvantage of UDP traffic compared to TCP
   in the Internet [Edeline16], somewhere between three [Trammell16] and
   five [Swett16] percent of networks simply block UDP traffic.  All
   applications running on top of QUIC must therefore either be prepared
   to accept connectivity failure on such networks, or be engineered to
   fall back to some other transport protocol.  This fallback SHOULD
   provide TLS 1.3 or equivalent cryptographic protection, if available,
   in order to keep fallback from being exploited as a downgrade attack.
   In the case of HTTP, this fallback is TLS 1.3 over TCP.

   These applications must operate, perhaps with impaired functionality,
   in the absence of features provided by QUIC not present in the
   fallback protocol.  For fallback to TLS over TCP, the most obvious
   difference is that TCP does not provide stream multiplexing and
   therefore stream multiplexing would need to be implemented in the
   application layer if needed.  Further, TCP by default does not
   support 0-RTT session resumption.  TCP Fast Open could be used, but
   might no be supported by the far end or could be blocked on the
   network path.  Note that there is some evidence of middleboxes
   blocking SYN data even if TFO was successfully negotiated (see
   [PaaschNanog]).  Moreover, while encryption (in this case TLS) is
   inseparable integrated with QUIC, TLS negotiation over TCP can be
   blocked.  In case it is RECOMMENDED to abort the connection, allowing
   the application to present a suitable prompt to the user that secure
   communication is unavailable.

   We hope that the deployment of a proposed standard version of the
   QUIC protocol will provide an incentive for these networks to permit
   QUIC traffic.  Indeed, the ability to treat QUIC traffic statefully
   as discussed in section 3.1 of [draft-kuehlewind-quic-manageability]
   would remove one network management incentive to block this traffic.

3.  Zero RTT: Here There Be Dragons

   QUIC provides for 0-RTT connection establishment (see section 3.2 of
   [I-D.ietf-quic-transport]).  However, data in the frames contained in
   the first packet of a such a connection must be treated specially by
   the application layer.  Since a retransmission of these frames
   resulting from a lost acknowledgment may cause the data to appear
   twice, either the application-layer protocol has to be designed such
   that all such data is treated as idempotent, or there must be some
   application-layer mechanism for recognizing spuriously retransmitted
   frames and dropping them.

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   Applications that cannot treat data that may appear in a 0-RTT
   connection establishment as idempotent MUST NOT use 0-RTT
   establishment.  For this reason the QUIC transport SHOULD provide an
   interface for the application to indicate if 0-RTT support is in
   general desired or a way to indicate if data is idempotent.

4.  Stream versus Flow Multiplexing

   QUIC's stream multiplexing feature allows applications to run
   multiple streams over a single connection, without head-of-line
   blocking between streams, associated at a point in time with a single
   five-tuple.  Streams are meaningful only to the application; since
   stream information is carried inside QUIC's encryption boundary, no
   information about the stream(s) whose frames are carried by a given
   packet is visible to the network.

   Stream multiplexing is not intended to be used for differentiating
   streams in terms of network treatment.  Application traffic requiring
   different network treatment SHOULD therefore be carried over
   different five-tuples (i.e.  multiple QUIC connections).  Given
   QUIC's ability to send application data on the first packet of a
   connection (if a previous connection to the same host has been
   successfully established to provide the respective credentials), the
   cost for establishing another connection are extremely low.

   [EDITOR'S NOTE: For discussion: If establishing a new connection does
   not seem to be sufficient, the protocol's rebinding functionality
   (see section 3.7 of [I-D.ietf-quic-transport]) could be extended to
   allow multiple five-tuples to share a connection ID simultaneously,
   instead of sequentially.]

5.  Prioritization

   Stream prioritization is not exposed to the network, nor to the
   receiver.  Prioritization can be realized by the sender and the QUIC
   transport should provide and interface for applications to prioritize
   streams [I-D.ietf-quic-transport].

   Priority handling of retransmissions may be implemented in the
   transport layer and [I-D.ietf-quic-transport] does not specify a
   specific way how this must be handled.  Currently QUIC only provides
   fully reliable stream transmission, and as such prioritization of
   retransmission is likely beneficial.  For not fully reliable streams
   priority scheduling of retransmissions over data of higher-priority
   streams might not be desired.  In this case QUIC could also provide
   an interface or derive the prioritization decision from the
   reliability level of the stream.

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6.  Graceful connection closure

   [EDITOR'S NOTE: give some guidance here about the steps an
   application should take; however this is still work in progress]

7.  Information exposure and the Connection ID

   QUIC exposed some information to the network in the unencrypted part
   of the header.  This is either because there is no encryption context
   established yet or because this information is intended to be
   consumed by the network.  Some of these information can be optionally
   exposed (still under discussion).  Given that exposing these
   information can have privacy implications, an application may
   indicate to not support exposure of certain information.

   In case of the connection ID this can be the case if the application
   has additional information that the client is not behind a NAT and
   the server is not behind a load balancer, and therefore it is
   unlikely that the addresses will be re-binded.

8.  Use of Versions and Cryptographic Handshake

   Versioning in QUIC may change the whole protocol behavior, beside
   some header fields that have been declared to be fixed.  As such a
   new or higher version of QUIC does not necessarily provide a better
   service but just a very different service, an application needs to be
   able to select which versions of QUIC it wants to use.

   The use of a different encryption scheme than TLS1.3 or higher needs
   a new version of QUIC.  [I-D.ietf-quic-transport] specifies
   requirements for the cryptographic handshake as currently realized by
   TLS1.3 and described in a separate specification [I-D.ietf-quic-tls].
   This split is performed to enable light-weight versioning with
   different cryptographic handshakes.

9.  IANA Considerations

   This document has no actions for IANA.

10.  Security Considerations

   See the security considerations in [I-D.ietf-quic-transport] and
   [I-D.ietf-quic-tls]; the security considerations for the underlying
   transport protocol are relevant for applications using QUIC, as well.

   Application developers should note that any fallback they use when
   QUIC cannot be used due to network blocking of UDP SHOULD guarantee
   the same security properties as QUIC; if this is not possible, the

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   connection SHOULD fail to allow the application to explicitly handle
   fallback to a less-secure alternative.  See Section 2.

11.  Acknowledgments

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

12.  References

12.1.  Normative References

              Thomson, M. and S. Turner, "Using Transport Layer Security
              (TLS) to Secure QUIC", draft-ietf-quic-tls-01 (work in
              progress), January 2017.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-01 (work
              in progress), January 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

12.2.  Informative References

              Kuehlewind, M. and B. Trammell, "Manageability of the QUIC
              Transport Protocol", March 2017.

              Edeline, K., Kuehlewind, M., Trammell, B., Aben, E., and
              B. Donnet, "Using UDP for Internet Transport Evolution
              (arXiv preprint 1612.07816)", December 2016.

              Bishop, M., "Hypertext Transfer Protocol (HTTP) over
              QUIC", draft-ietf-quic-http-01 (work in progress), January

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              Paasch, C., "Network Ssupport for TCP Fast Open (NANOG 67
              presentation)", June 2016.

   [Swett16]  Swett, I., "QUIC Deployment Experience at Google (IETF96
              QUIC BoF presentation)", July 2016.

              Trammell, B. and M. Kuehlewind, "Internet Path
              Transparency Measurements using RIPE Atlas (RIPE72 MAT
              presentation)", May 2016.

Authors' Addresses

   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


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