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Keywords: Header, Path signal

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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(https://trustee.ietf.org/license-info) in effect on the date of
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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 (iesg@ietf.org)
Contact: QUIC Working Group (quic@ietf.org)
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: mt@lowentropy.net