Internet-Draft CONNECT-UDP ECN Extension January 2021
Schinazi Expires 9 July 2021 [Page]
Network Working Group
Intended Status:
Standards Track
D. Schinazi
Google LLC

An ECN Extension to CONNECT-UDP


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

Discussion of this work is encouraged to happen on the MASQUE IETF mailing list ( or on the GitHub repository which contains the draft:

Discussion Venues

This note is to be removed before publishing as an RFC.

Source for this draft and an issue tracker can be found at

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 9 July 2021.

Table of Contents

1. Introduction

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

Discussion of this work is encouraged to happen on the MASQUE IETF mailing list ( or on the GitHub repository which contains the draft:

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.

3. Datagram Encoding of Proxied UDP Packets

If a client supports this extension and HTTP/3 datagrams [H3DGRAM], it can attempt to use datagrams for ECN information. This is done by allocating four datagram flow identifiers (as opposed to one in traditional CONNECT-UDP) and communicating them to the proxy using named elements on the "Datagram-Flow-Id" header. These names are "ecn-ect0", "ecn-ect1", and "ecn-ce". For example:

  Datagram-Flow-Id = 42, 44; ecn-ect0, 46; ecn-ect1, 48; ecn-ce

If the proxy wishes to support datagram encoding of this extension, it echoes those named elements in its CONNECT-UDP response. The unnamed element now represents Not-ECT, whereas the one in "ecn-ect0" represents ECT(0), "ecn-ect1" represents ECT(1) and "ecn-ce" represents CE; see Section 5 of [ECN] for the definition of these IP header fields.

When the proxy receives a datagram from the given flow identifier, it sets the IP packet's ECN bits accordingly on the UDP packet it sends to the target. Similarly, in the other direction the flow identifier represents which ECN bits were seen on the UDP packets received from the target.

4. Stream Encoding of Proxied UDP Packets

If HTTP/3 datagrams are not supported, the stream is used to convey UDP payloads, and the CONNECT-UDP Stream Chunk Type is used to indicate the values of the ECN bits, as defined below:

  | Value |      Type       | ECN Field |
  | 0x00  | UDP_PACKET      |  Not-ECT  |
  | 0x31  | UDP_PACKET_ECT0 |  ECT(0)   |
  | 0x32  | UDP_PACKET_ECT1 |  ECT(1)   |
  | 0x33  | UDP_PACKET_CE   |  CE       |

The proxy then uses the the CONNECT-UDP Stream Chunk Type on received UDP payloads to set the ECN bits on the IP packets it sends to the target, and in the reverse direction to indicate which ECN bits received from the target.

5. HTTP Intermediaries

HTTP/3 DATAGRAM flow identifiers are specific to a given HTTP/3 connection. However, in some cases, an HTTP request may travel across multiple HTTP connections if there are HTTP intermediaries involved; see Section 2.3 of [RFC7230].

Intermediaries that support this extension and HTTP/3 datagrams MUST negotiate all four flow identifiers separately on the client-facing and server-facing connections. This is accomplished by having the intermediary parse the unnamed element and the "ecn-ect0", "ecn-ect1", and "ecn-ce" named elements in the "Datagram-Flow-Id" header on all CONNECT-UDP requests it receives, and sending the same four flow identifiers in the "Datagram-Flow-Id" header on the response.

Intermediaries MUST NOT send the "ECN" header with a value of 1 to the client on its response unless it has received that same value in the response it received from the server.

6. Security Considerations

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

7. IANA Considerations

7.1. HTTP Header

This document will request IANA to register the "ECN" header in the "Permanent Message Header Field Names" registry maintained at <>.

  | Header Field Name | Protocol | Status |   Reference   |
  |        ECN        |   http   |  std   | This document |

7.2. Flow Identifier Parameters

This document will request IANA to register the "ecn-ect0", "ecn-ect1", and "ecn-ce" flow identifier parameters in the "HTTP Datagram Flow Identifier Parameters" registry (see [H3DGRAM]):

  |   Key    |       Description       | Is Name |   Reference   |
  | ecn-ect0 | UDP payload with ECT(0) |   Yes   | This document |
  | ecn-ect1 | UDP payload with ECT(1) |   Yes   | This document |
  | ecn-ce   | UDP payload with CE     |   Yes   | This document |

7.3. Stream Chunk Type Registration

This document will request IANA to register the following entry in the "CONNECT-UDP Stream Chunk Type" registry [CONNECT-UDP]:

  | Value |      Type       |       Description       |   Reference   |
  | 0x31  | UDP_PACKET_ECT0 | UDP payload with ECT(0) | This document |
  | 0x32  | UDP_PACKET_ECT1 | UDP payload with ECT(1) | This document |
  | 0x33  | UDP_PACKET_CE   | UDP payload with CE     | This document |

8. Normative References

Schinazi, D., "The CONNECT-UDP HTTP Method", Work in Progress, Internet-Draft, draft-ietf-masque-connect-udp-02, , <>.
Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, , <>.
Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in Progress, Internet-Draft, draft-schinazi-quic-h3-datagram-05, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Nottingham, M. and P. Kamp, "Structured Field Values for HTTP", Work in Progress, Internet-Draft, draft-ietf-httpbis-header-structure-19, , <>.


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