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Document Type Replaced Internet-Draft (masque WG)
Author David Schinazi
Last updated 2020-08-15 (Latest revision 2020-04-16)
Replaced by draft-ietf-masque-connect-udp, draft-ietf-masque-connect-udp, draft-ietf-masque-connect-udp, RFC 9298
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Network Working Group                                        D. Schinazi
Internet-Draft                                                Google LLC
Intended status: Experimental                              16 April 2020
Expires: 18 October 2020

                      The CONNECT-UDP HTTP Method


   This document describes the CONNECT-UDP HTTP method.  CONNECT-UDP is
   similar to the HTTP CONNECT method, but it uses UDP instead of TCP.

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

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 18 October 2020.

Copyright Notice

   Copyright (c) 2020 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
   Provisions Relating to IETF Documents (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Definitions . . . . . . . . . . . . . . .   2
   2.  Supported HTTP Versions . . . . . . . . . . . . . . . . . . .   2
   3.  The CONNECT-UDP Method  . . . . . . . . . . . . . . . . . . .   3
   4.  Encoding of Proxied UDP Packets . . . . . . . . . . . . . . .   4
   5.  Datagram-Flow-Id Header Definition  . . . . . . . . . . . . .   5
   6.  Server Handling . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .   5
     8.2.  HTTP Header . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document describes the CONNECT-UDP HTTP method.  CONNECT-UDP is
   similar to the HTTP CONNECT method (see section 4.3.6 of [RFC7231]),
   but it uses UDP [UDP] instead of TCP [TCP].

   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",
   "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.  Supported HTTP Versions

   The CONNECT-UDP method is defined for all versions of HTTP.  When the
   HTTP version used runs over QUIC [QUIC], UDP payloads can be sent
   over QUIC DATAGRAM frames [DGRAM].  Otherwise they are sent on the
   stream where the CONNECT-UDP request was made.  Note that when
   multiple proxies are involved in a CONNECT-UDP request, all the HTTP
   connections along the path need to be using HTTP/3 [H3] or later in
   order for UDP payloads to be sent over QUIC DATAGRAM frames.
   Additionally, when the HTTP version in use does not support
   multiplexing streams (such as HTTP/1.1), then any reference to
   "stream" in this document is meant to represent the entire

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3.  The CONNECT-UDP Method

   The CONNECT-UDP method requests that the recipient establish a tunnel
   over a single HTTP stream to the destination origin server identified
   by the request-target and, if successful, thereafter restrict its
   behavior to blind forwarding of packets, in both directions, until
   the tunnel is closed.  Tunnels are commonly used to create an end-to-
   end virtual connection, through one or more proxies, which can then
   be secured using QUIC or another protocol running over UDP.

   A client sending a CONNECT-UDP request MUST send the authority form
   of request-target (Section 5.3 of [RFC7230]); i.e., the request-
   target consists of only the host name and port number of the tunnel
   destination, separated by a colon.  For example,

        CONNECT-UDP HTTP/1.1

   When using HTTP/2 [H2] or later, CONNECT-UDP requests use HTTP
   pseudo-headers with the following requirements:

   *  The ":method" pseudo-header field is set to "CONNECT-UDP".

   *  The ":scheme" and ":path" pseudo-header fields MUST be omitted.

   *  The ":authority" pseudo-header field contains the host and port to
      connect to (equivalent to the authority-form of the request-target
      of CONNECT-UDP requests (see [RFC7230], Section 5.3)).

   A CONNECT-UDP request that does not conform to these restrictions is
   malformed (see [H2], Section

   The recipient proxy can establish a tunnel either by directly opening
   a UDP socket to the request-target or, if configured to use another
   proxy, by forwarding the CONNECT-UDP request to the next inbound
   proxy.  Any 2xx (Successful) response indicates that the sender (and
   all inbound proxies) will switch to tunnel mode immediately after the
   blank line that concludes the successful response's header section;
   data received after that blank line is from the server identified by
   the request-target.  Any response other than a successful response
   indicates that the tunnel has not yet been formed and that the
   connection remains governed by HTTP.

   A tunnel is closed when a tunnel intermediary detects that either
   side has closed its connection: the intermediary MUST attempt to send
   any outstanding data that came from the closed side to the other
   side, close both connections, and then discard any remaining data
   left undelivered.

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   A server MUST NOT send any Transfer-Encoding or Content-Length header
   fields in a 2xx (Successful) response to CONNECT.  A client MUST
   treat a response to CONNECT-UDP containing any Content-Length or
   Transfer-Encoding header fields as malformed.

   A payload within a CONNECT-UDP request message has no defined
   semantics; a CONNECT-UDP request with a non-empty payload is

   Responses to the CONNECT-UDP method are not cacheable.

4.  Encoding of Proxied UDP Packets

   When the HTTP connection between client and proxy supports HTTP/3
   datagrams [H3DGRAM], UDP packets can be encoded using QUIC DATAGRAM
   frames.  This support is ascertained by checking receipt of the
   H3_DATAGRAM SETTINGS Parameter.  Note that when there are multiple
   proxies involved, this support needs to be ascertained on all the
   HTTP connections that will carry proxied UDP packets.

   If the client supports HTTP/3 datagrams and has received the
   H3_DATAGRAM SETTINGS Parameter on this connection, it SHOULD attempt
   to use HTTP/3 datagrams.  This is accomplished by requesting a
   datagram flow identifier from the flow identifier allocation service
   [H3DGRAM].  That service generates an even flow identifier, and the
   client sends it to the server by using the "Datagram-Flow-Id" header
   (see Section 5).

   If there are multiple proxies involved, proxies along the chain MUST
   check whether their upstream connection supports HTTP/3 datagrams.
   If it does not, that proxy MUST remove the "Datagram-Flow-Id" header
   before forwarding the CONNECT-UDP request.

   The proxy that is creating the UDP socket to the destination responds
   to the CONNECT-UDP request with a 2xx (Successful) response, and MUST
   echo the "Datagram-Flow-Id" header.  Once the client has received the
   "Datagram-Flow-Id" header on the successful response, it knows that
   it can use the HTTP/3 datagram encoding to send proxied UDP packets
   for this particular destination.  It then encodes the payload of UDP
   datagrams into the payload of HTTP/3 datagrams.

   Clients MAY optimistically start sending proxied UDP packets before
   receiving the response to its CONNECT-UDP request, noting however
   that those may not be processed by the proxy if it responds to the
   CONNECT-UDP request with a failure, or if they arrive before the
   CONNECT-UDP request.

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   If HTTP/3 datagrams are not supported, the stream is used to convey
   UDP payloads, by prefixing them with a 16-bit length.

5.  Datagram-Flow-Id Header Definition

   "Datagram-Flow-Id" is a Item Structured Header [STRUCT-HDR].  Its
   value MUST be an Integer.  Its ABNF is:

     Datagram-Flow-Id = sh-integer

6.  Server Handling

   Unlike TCP, UDP is connection-less.  The HTTP server that opens the
   UDP socket has no way of knowing whether the destination is
   reachable.  Therefore it needs to respond to the CONNECT-UDP request
   without waiting for a TCP SYN-ACK.

   Servers can use connected UDP sockets if their operating system
   supports them, as that allows the HTTP server to rely on the kernel
   to only send it UDP packets that match the correct 5-tuple.  If the
   server uses a non-connected socket, it MUST validate the IP source
   address and UDP source port on received packets to ensure they match
   the client's CONNECT-UDP request.  Packets that do not match MUST be
   discarded by the server.

7.  Security Considerations

   There are significant risks in allowing arbitrary clients to
   establish a tunnel to arbitrary servers, as that could allow bad
   actors to send traffic and have it attributed to the proxy.  Proxies
   that support CONNECT-UDP SHOULD restrict its use to authenticated

8.  IANA Considerations

8.1.  HTTP Method

   This document will request IANA to register "CONNECT-UDP" in the HTTP
   Method Registry (IETF review) maintained at

     | Method Name | Safe | Idempotent |   Reference   |
     | CONNECT-UDP |  no  |     no     | This document |

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8.2.  HTTP Header

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

     | Header Field Name | Protocol | Status |   Reference   |
     | Datagram-Flow-Id  |   http   |  exp   | This document |

9.  Normative References

   [DGRAM]    Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
              Datagram Extension to QUIC", Work in Progress, Internet-
              Draft, draft-ietf-quic-datagram-00, 26 February 2020,

   [H2]       Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

   [H3]       Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-27, 21 February 2020, <

   [H3DGRAM]  Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in
              Progress, Internet-Draft, draft-schinazi-quic-h3-datagram-
              03, 12 March 2020, <

   [QUIC]     Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", Work in Progress, Internet-Draft,
              draft-ietf-quic-transport-27, 21 February 2020,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

              Nottingham, M. and P. Kamp, "Structured Field Values for
              HTTP", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-header-structure-17, 15 March 2020,

   [TCP]      Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,

   [UDP]      Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,


   This proposal was inspired directly or indirectly by prior work from
   many people.  The author would like to thank Eric Rescorla for
   suggesting to use an HTTP method to proxy UDP.

Author's Address

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


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