Internet-Draft CONNECT-UDP ECN Extension March 2022
Schinazi Expires 29 September 2022 [Page]
Intended Status:
Standards Track
D. Schinazi
Google LLC

An ECN Extension to CONNECT-UDP


CONNECT-UDP allows proxying UDP packets over HTTP. This document describes an extension to CONNECT-UDP that allows conveying ECN information on proxied UDP packets.

Discussion Venues

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This Internet-Draft will expire on 29 September 2022.

Table of Contents

1. Introduction

CONNECT-UDP [CONNECT-UDP] allows proxying UDP packets over HTTP. This document describes an extension to CONNECT-UDP that allows conveying ECN [ECN] information on proxied UDP packets.

1.1. 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.

2. Context Identifiers

The "Context Identifiers" section of [CONNECT-UDP] defines the concept of context IDs and how they can be used to extend CONNECT-UDP. When a client wishes to use ECN with CONNECT-UDP, it generates an unique client-allocated context ID. In this document, we'll refer to that context ID as the "chosen context ID". Note that, by definition of client-allocated context IDs, the chosen context ID will always be a non-zero even number. We also add the restriction that the chosen context ID MUST be strictly less than 1015. If the client has run out of available context ID values that match this requirement for this CONNECT-UDP request, it MUST NOT use the ECN extension with this CONNECT-UDP request.

4. Encoding of ECN bits

When an HTTP Datagram [HTTP-DGRAM] associated with a CONNECT-UDP stream uses the chosen context ID as its context ID, its "Payload" field contains the following format (using the notation from the "Notational Conventions" section of [QUIC]):

CONNECT-UDP Payload with ECN {
  Must be Zero (6),
  ECN Bits (2),
  UDP Payload (..),
Figure 3: CONNECT-UDP Payload with ECN
Must be Zero:

6 bits that MUST be sent as zero. Receivers MUST validate that these bits are zero and MUST silently drop the HTTP Datagram if they have any other value. Extensions to this mechanism MAY relax this requirement.

ECN Bits:

The ECN bits, sent in the same order as they appear in the IP header.

UDP Payload:

The UDP Payload, as defined in the "HTTP Datagram Payload Format" section of [CONNECT-UDP].

When the proxy receives a datagram with the chosen context ID, it sets the IP packet's ECN bits accordingly on the UDP packet it sends to the target. Similarly, in the other direction the ECN Bits field represents which ECN bits were seen on the UDP packets received from the target.

5. A Note about Future Extensions

This CONNECT-UDP extension uses an HTTP field to register its chosen context ID. Future extensions to CONNECT-UDP can use the same strategy to register their chosen context ID(s) via another HTTP field. This strategy is best for CONNECT-UDP extensions that only need to register context IDs during the HTTP request and response.

Some extensions may need to register context IDs after the request and response have been exchanged, for example an extension that wishes to compress QUIC connection IDs [QUIC] is not aware of all connection IDs at request time. In such cases, extensions can use new Capsule Types (see [HTTP-DGRAM]) to perform context ID registration.

6. Security Considerations

This document does not have additional security considerations beyond those defined in [CONNECT-UDP].

7. IANA Considerations

This document will request IANA to register the following entry in the "HTTP Field Name" registry:

Field Name:





provisional (permanent if this document is approved)


This document



8. Normative References

Schinazi, D., "UDP Proxying Support for HTTP", Work in Progress, Internet-Draft, draft-ietf-masque-connect-udp-08, , <>.
Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, , <>.
Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", Work in Progress, Internet-Draft, draft-ietf-masque-h3-datagram-08, , <>.
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Nottingham, M. and P-H. Kamp, "Structured Field Values for HTTP", RFC 8941, DOI 10.17487/RFC8941, , <>.


This proposal was inspired directly or indirectly by prior work from many people. The author would like to thank contributors the MASQUE working group.

Author's Address

David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America