Internet Engineering Task Force (IETF)                        M. Thomson
Request for Comments: 9287                                       Mozilla
Category: Standards Track                                    August 2022
ISSN: 2070-1721


                        Greasing the QUIC Bit

Abstract

  This document describes a method for negotiating the ability to send
  an arbitrary value for the second-most significant bit in QUIC
  packets.

Status of This Memo

  This is an Internet Standards Track document.

  This document is a product of the Internet Engineering Task Force
  (IETF).  It represents the consensus of the IETF community.  It has
  received public review and has been approved for publication by the
  Internet Engineering Steering Group (IESG).  Further information on
  Internet Standards is available in Section 2 of RFC 7841.

  Information about the current status of this document, any errata,
  and how to provide feedback on it may be obtained at
  https://www.rfc-editor.org/info/rfc9287.

Copyright Notice

  Copyright (c) 2022 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
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  to this document.  Code Components extracted from this document must
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  Trust Legal Provisions and are provided without warranty as described
  in the Revised BSD License.

Table of Contents

  1.  Introduction
  2.  Conventions and Definitions
  3.  The Grease QUIC Bit Transport Parameter
    3.1.  Clearing the QUIC Bit
    3.2.  Using the QUIC Bit
  4.  Security Considerations
  5.  IANA Considerations
  6.  References
    6.1.  Normative References
    6.2.  Informative References
  Author's Address

1.  Introduction

  The version-independent definition of QUIC [QUIC-INVARIANTS]
  intentionally describes a very narrow set of fields that are visible
  to entities other than endpoints.  Beyond those characteristics that
  are invariant, very little about the "wire image" [RFC8546] of QUIC
  is visible.

  The second-most significant bit of the first byte in every QUIC
  packet is defined as having a fixed value in QUIC version 1 [QUIC].
  The purpose of having a fixed value is to allow endpoints to
  efficiently distinguish QUIC from other protocols; see [DEMUX] for a
  description of a system that might use this property.  As this bit
  can identify a packet as QUIC, it is sometimes referred to as the
  "QUIC Bit".

  Where endpoints and the intermediaries that support them do not
  depend on the QUIC Bit having a fixed value, sending the same value
  in every packet is more of a liability than an asset.  If systems
  come to depend on a fixed value, then it might become infeasible to
  define a version of QUIC that attributes semantics to this bit.

  In order to safeguard future use of this bit, this document defines a
  QUIC transport parameter that indicates that an endpoint is willing
  to receive QUIC packets containing any value for this bit.  By
  sending different values for this bit, the hope is that the value
  will remain available for future use [USE-IT].

2.  Conventions and Definitions

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
  "OPTIONAL" in this document are to be interpreted as described in
  BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
  capitals, as shown here.

  This document uses terms and notational conventions from [QUIC].

3.  The Grease QUIC Bit Transport Parameter

  The grease_quic_bit transport parameter (0x2ab2) is defined for QUIC
  version 1 [QUIC].  This transport parameter can be sent by both
  client and server.  The transport parameter is sent with an empty
  value; an endpoint that understands this transport parameter MUST
  treat receipt of a non-empty value of the transport parameter as a
  connection error of type TRANSPORT_PARAMETER_ERROR.

  An endpoint that advertises the grease_quic_bit transport parameter
  MUST accept packets with the QUIC Bit set to a value of 0.  The QUIC
  Bit is defined as the second-most significant bit of the first byte
  of QUIC packets (that is, the value 0x40).

3.1.  Clearing the QUIC Bit

  Endpoints that receive the grease_quic_bit transport parameter from a
  peer SHOULD set the QUIC Bit to an unpredictable value unless another
  extension assigns specific meaning to the value of the bit.

  Endpoints can set the QUIC Bit to 0 on all packets that are sent
  after receiving and processing transport parameters.  This could
  include Initial, Handshake, and Retry packets.

  A client MAY also set the QUIC Bit to 0 in Initial, Handshake, or
  0-RTT packets that are sent prior to receiving transport parameters
  from the server.  However, a client MUST NOT set the QUIC Bit to 0
  unless the Initial packets it sends include a token provided by the
  server in a NEW_TOKEN frame (Section 19.7 of [QUIC]), received less
  than 604800 seconds (7 days) prior on a connection where the server
  also included the grease_quic_bit transport parameter.

     |  This 7-day limit allows for changes in server configuration.
     |  If server configuration changes and a client does not set the
     |  QUIC Bit, then it is possible that a server will drop packets,
     |  resulting in connection failures.

  A server MUST set the QUIC Bit to 0 only after processing transport
  parameters from a client.  A server MUST NOT remember that a client
  negotiated the extension in a previous connection and set the QUIC
  Bit to 0 based on that information.

  An endpoint MUST NOT set the QUIC Bit to 0 without knowing whether
  the peer supports the extension.  As Stateless Reset packets
  (Section 10.3 of [QUIC]) are only used after a loss of connection
  state, endpoints are unlikely to be able to set the QUIC Bit to 0 on
  Stateless Reset packets.

3.2.  Using the QUIC Bit

  The purpose of this extension is to allow for the use of the QUIC Bit
  by later extensions.

  Extensions to QUIC that define semantics for the QUIC Bit can be
  negotiated at the same time as the grease_quic_bit transport
  parameter.  In this case, a recipient needs to be able to distinguish
  a randomized value from a value carrying information according to the
  extension.  Extensions that use the QUIC Bit MUST negotiate their use
  prior to acting on any semantic.

  For example, an extension might define a transport parameter that is
  sent in addition to the grease_quic_bit transport parameter.  Though
  the value of the QUIC Bit in packets received by a peer might be set
  according to rules defined by the extension, they might also be
  randomized as specified in this document.

  The receipt of a transport parameter for an extension that uses the
  QUIC Bit could be used to confirm that a peer supports the semantic
  defined in the extension.  To avoid acting on a randomized signal,
  the extension can require that endpoints set the QUIC Bit according
  to the rules of the extension but defer acting on the information
  conveyed until the transport parameter for the extension is received.

  Extensions that define semantics for the QUIC Bit can be negotiated
  without using the grease_quic_bit transport parameter.  However,
  including both extensions allows for the QUIC Bit to be greased even
  if the alternative use is not supported.

4.  Security Considerations

  This document introduces no new security considerations for endpoints
  or entities that can rely on endpoint cooperation.  However, this
  change makes the task of identifying QUIC more difficult without
  cooperation of endpoints.  This sometimes works counter to the
  security goals of network operators who rely on network
  classification to identify threats; see Section 3.1 of
  [MANAGEABILITY] for a more comprehensive treatment of this topic.

5.  IANA Considerations

  This document registers the grease_quic_bit transport parameter in
  the "QUIC Transport Parameters" registry established in Section 22.3
  of [QUIC].  The following fields are registered:

  Value:  0x2ab2

  Parameter Name:  grease_quic_bit

  Status:  Permanent

  Specification:  RFC 9287

  Date:  2022-07-13

  Change Controller:  IETF ([email protected])

  Contact:  QUIC Working Group ([email protected])

  Notes:  (none)

6.  References

6.1.  Normative References

  [QUIC]     Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
             Multiplexed and Secure Transport", RFC 9000,
             DOI 10.17487/RFC9000, May 2021,
             <https://www.rfc-editor.org/info/rfc9000>.

  [QUIC-INVARIANTS]
             Thomson, M., "Version-Independent Properties of QUIC",
             RFC 8999, DOI 10.17487/RFC8999, May 2021,
             <https://www.rfc-editor.org/info/rfc8999>.

  [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119,
             DOI 10.17487/RFC2119, March 1997,
             <https://www.rfc-editor.org/info/rfc2119>.

  [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>.

6.2.  Informative References

  [DEMUX]    Aboba, B., Salgueiro, G., and C. Perkins, "Multiplexing
             Scheme Updates for QUIC", Work in Progress, Internet-
             Draft, draft-ietf-avtcore-rfc7983bis-06, 5 August 2022,
             <https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-
             rfc7983bis-06>.

  [MANAGEABILITY]
             Kuehlewind, M. and B. Trammell, "Manageability of the QUIC
             Transport Protocol", Work in Progress, Internet-Draft,
             draft-ietf-quic-manageability-18, 15 July 2022,
             <https://datatracker.ietf.org/doc/html/draft-ietf-quic-
             manageability-18>.

  [RFC8546]  Trammell, B. and M. Kuehlewind, "The Wire Image of a
             Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
             2019, <https://www.rfc-editor.org/info/rfc8546>.

  [USE-IT]   Thomson, M. and T. Pauly, "Long-Term Viability of Protocol
             Extension Mechanisms", RFC 9170, DOI 10.17487/RFC9170,
             December 2021, <https://www.rfc-editor.org/info/rfc9170>.

Author's Address

  Martin Thomson
  Mozilla
  Email: [email protected]

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