Mozilla

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tsv quic Header Path signal 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 .

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Table of Contents

• .  Introduction
• .  Conventions and Definitions
• .  The Grease QUIC Bit Transport Parameter
  • .  Clearing the QUIC Bit
  • .  Using the QUIC Bit
• .  Security Considerations
• .  IANA Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Author's Address

Introduction The version-independent definition of QUIC 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" 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 . The purpose of having a fixed value is to allow endpoints to efficiently distinguish QUIC from other protocols; see 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 .

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 when, and only when, they appear in all capitals, as shown here. This document uses terms and notational conventions from .

The Grease QUIC Bit Transport Parameter The grease_quic_bit transport parameter (0x2ab2) is defined for QUIC version 1 . 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).

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 (), received less than 604800 seconds (7 days) prior on a connection where the server also included the grease_quic_bit transport parameter. 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 () 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.

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.

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 for a more comprehensive treatment of this topic.

IANA Considerations This document registers the grease_quic_bit transport parameter in the "QUIC Transport Parameters" registry established in . 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)

References Normative References This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. This document defines the properties of the QUIC transport protocol that are common to all versions of the protocol. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Microsoft Corporation Cisco Systems University of Glasgow This document defines how QUIC, Datagram Transport Layer Security (DTLS), Real-time Transport Protocol (RTP), RTP Control Protocol (RTCP), Session Traversal Utilities for NAT (STUN), Traversal Using Relays around NAT (TURN), and ZRTP packets are multiplexed on a single receiving socket. This document updates RFC 7983 and RFC 5764. Work in Progress Ericsson Google Switzerland GmbH This document discusses manageability of the QUIC transport protocol, focusing on the implications of QUIC's design and wire image on network operations involving QUIC traffic. It is intended as a "user's manual" for the wire image, providing guidance for network operators and equipment vendors who rely on the use of transport- aware network functions. Work in Progress This document defines the wire image, an abstraction of the information available to an on-path non-participant in a networking protocol. This abstraction is intended to shed light on the implications that increased encryption has for network functions that use the wire image. The ability to change protocols depends on exercising the extension and version-negotiation mechanisms that support change. This document explores how regular use of new protocol features can ensure that it remains possible to deploy changes to a protocol. Examples are given where lack of use caused changes to be more difficult or costly.

Author's Address Mozilla

mt@lowentropy.net