MASQUE                                                       D. Schinazi
Internet-Draft                                                Google LLC
Intended status: Standards Track                            12 July                          7 October 2021
Expires: 13 January 10 April 2022

                      The CONNECT-UDP

                     UDP Proxying Support for HTTP Method
                    draft-ietf-masque-connect-udp-04
                    draft-ietf-masque-connect-udp-05

Abstract

   This document describes the CONNECT-UDP HTTP method.  CONNECT-UDP is
   similar how to proxy UDP over HTTP.  Similar to how
   the HTTP CONNECT method, but it uses UDP instead of TCP. method allows proxying TCP over HTTP, this document
   defines a new mechanism to proxy UDP.  It is built using HTTP
   Extended CONNECT.

Discussion Venues

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

   Discussion of this document takes place on the MASQUE WG mailing list
   (masque@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/masque/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-masque/draft-ietf-masque-connect-udp.

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 https://datatracker.ietf.org/drafts/current/.

   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 13 January 10 April 2022.

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   document authors.  All rights reserved.

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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Definitions . . . . . . . . . . . . . . .   2   3
   2.  Supported HTTP Versions .  Configuration of Clients  . . . . . . . . . . . . . . . . . .   3
   3.  The CONNECT-UDP Method  HTTP Exchanges  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Encoding of Proxied UDP Packets
     3.1.  Proxy Handling  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Proxy Handling
     3.2.  HTTP Request over HTTP/1.1  . . . . . . . . . . . . . . .   5
     3.3.  HTTP Response over HTTP/1.1 . . . . . . . . . . . . . . .   5
   6.
     3.4.  HTTP Request over HTTP/2 and HTTP/3 . . . . . . . . . . .   6
     3.5.  HTTP Response over HTTP/2 and HTTP/3  . . . . . . . . . .   7
     3.6.  Note About Draft Versions . . . . . . . . . . . . . . . .   7
   4.  Encoding of Proxied UDP Packets . . . . . . . . . . . . . . .   7
   5.  Performance Considerations  . . . . . . . . . . . . . . . . .   5
     6.1.   8
     5.1.  MTU Considerations  . . . . . . . . . . . . . . . . . . .   9
     5.2.  Tunneling of ECN Marks  . . . . . . . . . . . . . . . . .   6
   7.   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  10
     7.1.  HTTP Method . . . Upgrade Token  . . . . . . . . . . . . . . . . . . .  10
     7.2.  Datagram Format Type  .   6
     8.2.  URI Scheme Registration . . . . . . . . . . . . . . . . .   7
   9.  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8  13

1.  Introduction

   This document describes the CONNECT-UDP HTTP method.  CONNECT-UDP is
   similar how to proxy UDP over HTTP.  Similar to how
   the HTTP CONNECT method (see section 4.3.6 of [RFC7231]),
   but it uses UDP [UDP] instead Section 9.3.6 of [SEMANTICS]) allows proxying
   TCP [TCP].

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 [TCP] over HTTP, this document are defines a new mechanism to be interpreted as described proxy
   UDP [UDP].

   UDP Proxying supports all versions of HTTP and uses HTTP Datagrams
   [HTTP-DGRAM].  When using HTTP/2 or HTTP/3, UDP proxying uses HTTP
   Extended CONNECT as described in [EXT-CONNECT2] and [EXT-CONNECT3].
   When using HTTP/1.x, UDP proxying uses HTTP Upgrade as defined in
   Section 7.8 of [SEMANTICS].

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.

   In this document, we use the term "proxy" to refer to the HTTP server
   that opens the UDP socket and responds to the CONNECT-UDP UDP proxying request.
   If there are HTTP intermediaries (as defined in Section 2.3 3.7 of
   [RFC7230])
   [SEMANTICS]) between the client and the proxy, those are referred to
   as "intermediaries" in this document.

2.  Supported HTTP Versions

   The CONNECT-UDP method is defined for all versions of HTTP.  UDP
   payloads are sent using HTTP Datagrams [HTTP-DGRAM].

   Note that, 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 represents the entire connection.

3.  The CONNECT-UDP Method

2.  Configuration of Clients

   Clients are configured to use UDP Proxying over HTTP via an URI
   Template [TEMPLATE].  The CONNECT-UDP URI template MUST contain exactly two
   variables: "target_host" and "target_port".  Examples are shown
   below:

   https://masque.example.org/{target_host}/{target_port}/
   https://proxy.example.org:4443/masque?h={target_host}&p={target_port}
   https://proxy.example.org:4443/masque{?target_host,target_port}

                      Figure 1: URI Template Examples

   Since the original HTTP CONNECT method allowed conveying the target
   host and port but not the scheme, proxy authority, path, nor query,
   there exist proxy configuration interfaces that only allow the user
   to configure the proxy host and the proxy port.  Client
   implementations of this specification that are constrained by such
   limitations MUST use the default template which is defined as:
   "https://$PROXY_HOST:$PROXY_PORT/{target_host}/{target_port}/" where
   $PROXY_HOST and $PROXY_PORT are the configured host and port of the
   proxy respectively.  Proxy deployments SHOULD use the default
   template to facilitate interoperability with such clients.

3.  HTTP Exchanges

   This document defines the "connect-udp" HTTP Upgrade Token. "connect-
   udp" uses the Capsule Protocol as defined in [HTTP-DGRAM].

   A "connect-udp" request requests that the recipient establish a
   tunnel over a single HTTP stream to the destination origin target server
   identified by the request-target and, if "target_host" and "target_port" variables of the
   URI template (see Section 2).  If the request is successful, thereafter restrict its
   behavior the
   proxy commits to blind forwarding of packets, in both directions, converting received HTTP Datagrams into UDP packets
   and vice versa until the tunnel is closed.  Tunnels are commonly used
   to create an end-to-
   end end-to-end virtual connection, which can then be secured
   using QUIC [QUIC] or another protocol running over UDP.

   The request-target of a CONNECT-UDP request is a

   When sending its UDP proxying request, the client SHALL perform URI [RFC3986] which
   uses
   template expansion to determine the "masque" scheme and an immutable path and query of "/".  For example:

        CONNECT-UDP masque://target.example.com:443/ HTTP/1.1
        Host: target.example.com:443

   When its request.
   target_host supports using HTTP/2 [H2] or later, CONNECT-UDP requests use HTTP
   pseudo-headers with DNS names, IPv6 literals and IPv4
   literals.  Note that this URI template expansion requires using pct-
   encoding, so for example if the following target_host is "2001:db8::42", it
   will be encoded in the URI as "2001%3Adb8%3A%3A42".

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

   Responses to UDP proxying requests are not cacheable.

3.1.  Proxy Handling

   Upon receiving a UDP proxying request, the recipient proxy extracts
   the "target_host" and "target_port" variables from the URI it has
   reconstructed from the request headers, and establishes a tunnel by
   directly opening a UDP socket to the requested target.

   Unlike TCP, UDP is connection-less.  The proxy that opens the UDP
   socket has no way of knowing whether the destination is reachable.
   Therefore it needs to respond to the request without waiting for a
   packet from the target.  However, if the target_host is a DNS name,
   the proxy MUST perform DNS resolution before replying to the HTTP
   request.  If DNS resolution fails, the proxy MUST fail the request
   and SHOULD send details using the Proxy-Status header [PROXY-STATUS].

   Proxies can use connected UDP sockets if their operating system
   supports them, as that allows the proxy to rely on the kernel to only
   send it UDP packets that match the correct 5-tuple.  If the proxy
   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 request.  Packets that do not match MUST be discarded by the
   proxy.

   The lifetime of the socket is tied to the request stream.  The proxy
   MUST keep the socket open while the request stream is open.  If a
   proxy is notified by its operating system that its socket is no
   longer usable, it MUST close the request stream.  Proxies MAY choose
   to close sockets due to a period of inactivity, but they MUST close
   the request stream before closing the socket.  Proxies that close
   sockets after a period of inactivity SHOULD NOT use a period lower
   than two minutes, see Section 4.3 of [BEHAVE].

   A successful response (as defined in Section 3.3 and Section 3.5)
   indicates that the proxy has opened a socket to the requested target
   and is willing to proxy UDP payloads.  Any response other than a
   successful response indicates that the request has failed, and the
   client MUST therefore abort the request.

3.2.  HTTP Request over HTTP/1.1

   When using HTTP/1.1, a UDP proxying request will meet the following
   requirements:

   *  the method SHALL be "CONNECT".

   *  the request-target SHALL use absolute-form (see Section 3.2.2 of
      [MESSAGING]).

   *  the request SHALL include a single Host header containing the
      origin of the proxy.

   *  the request SHALL include a single "Connection" header with value
      "Upgrade".

   *  the request SHALL include a single "Upgrade" header with value
      "connect-udp".

   For example, if the client is configured with URI template
   "https://proxy.example.org/{target_host}/{target_port}/" and wishes
   to open a UDP proxying tunnel to target 192.0.2.42:443, it could send
   the following request:

   CONNECT https://proxy.example.org/192.0.2.42/443/ HTTP/1.1
   Host: proxy.example.org
   Connection: upgrade
   Upgrade: connect-udp

                Figure 2: Example HTTP Request over HTTP/1.1

3.3.  HTTP Response over HTTP/1.1

   The proxy SHALL indicate a successful response by replying with the
   following requirements:

   *  the HTTP status code on the response SHALL be 101 (Switching
      Protocols).

   *  the reponse SHALL include a single "Connection" header with value
      "Upgrade".

   *  the response SHALL include a single "Upgrade" header with value
      "connect-udp".

   *  the response SHALL NOT include any Transfer-Encoding or Content-
      Length header fields.

   If any of these requirements are not met, the client MUST treat this
   proxying attempt as failed and abort the connection.

   For example, the proxy could respond with:

   HTTP/1.1 101 Switching Protocols
   Connection: upgrade
   Upgrade: connect-udp

               Figure 3: Example HTTP Response over HTTP/1.1

3.4.  HTTP Request over HTTP/2 and HTTP/3

   When using HTTP/2 [H2] or HTTP/3 [H3], UDP proxying requests use HTTP
   pseudo-headers with the following requirements:

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

   *  The ":scheme" ":protocol" pseudo-header field is set to "masque". SHALL be "connect-udp".

   *  The ":path" ":authority" pseudo-header field is set to "/". SHALL contain the authority
      of the proxy.

   *  The ":authority" ":path" and ":scheme" pseudo-header field contains fields SHALL NOT be empty.
      Their values SHALL contain the host scheme and port to
      connect to (similar to path from the authority-form of URI
      template after the request-target of
      CONNECT requests; see [RFC7230], Section 5.3). URI template expansion process has been
      completed.

   A CONNECT-UDP UDP proxying request that does not conform to these restrictions is
   malformed (see [H2], Section 8.1.2.6).

   The recipient proxy establishes a tunnel by directly opening a UDP
   socket to the request-target.  Any 2xx (Successful) response
   indicates that 8.1.2.6 of [H2]).

   For example, if the proxy has opened client is configured with URI template
   "https://proxy.example.org/{target_host}/{target_port}/" and wishes
   to open a socket UDP proxying tunnel to target 192.0.2.42:443, it could send
   the request-target following request:

   HEADERS
   :method = CONNECT
   :protocol = connect-udp
   :scheme = https
   :path = /192.0.2.42/443/
   :authority = proxy.example.org

                 Figure 4: Example HTTP Request over HTTP/2

3.5.  HTTP Response over HTTP/2 and is willing to HTTP/3

   The proxy UDP payloads.  Any response other than SHALL indicate a successful response indicates that the tunnel has not yet been
   formed.

   A proxy MUST NOT send by replying with any
   2xx (Successful) HTTP status code, without any Transfer-Encoding or
   Content-Length header
   fields in a 2xx (Successful) response to CONNECT-UDP.  A fields.

   If any of these requirements are not met, the client MUST treat a response to CONNECT-UDP containing any Content-Length or
   Transfer-Encoding header fields this
   proxying attempt as malformed.

   A payload within a CONNECT-UDP request message has no defined
   semantics; failed and abort the request.

   For example, the proxy could respond with:

   HEADERS
   :status = 200

                Figure 5: Example HTTP Response over HTTP/2

3.6.  Note About Draft Versions

   [[RFC editor: please remove this section before publication.]]

   In order to allow implementations to support multiple draft versions
   of this specification during its development, we introduce the
   "connect-udp-version" header.  When sent by the client, it contains a CONNECT-UDP request with
   list of draft numbers supported by the client (e.g., "connect-udp-
   version: 0, 2").  When sent by the proxy, it contains a non-empty payload is
   malformed.

   Responses to single draft
   number selected by the CONNECT-UDP method are proxy from the list provided by the client
   (e.g., "connect-udp-version: 2").  Sending this header is RECOMMENDED
   but not cacheable. required.

4.  Encoding of Proxied UDP Packets

   UDP packets are encoded using HTTP Datagrams [HTTP-DGRAM].  The [HTTP-DGRAM] with the
   UDP_PAYLOAD HTTP Datagram Format Type (see value in Section 7.2).
   When using the UDP_PAYLOAD HTTP Datagram Format Type, the payload of
   a UDP packet (referred to as "data octets" in [UDP]) is sent
   unmodified in the "HTTP Datagram Payload" field of an HTTP Datagram.

   In order to use HTTP Datagrams, the CONNECT-UDP client will first decide whether
   or not to use HTTP Datagram Contexts and then register its context ID
   (or lack thereof) using the corresponding registration capsule, see
   [HTTP-DGRAM].

   Since HTTP Datagrams require prior negotiation (for example, in
   HTTP/3 it is necessary

   When sending a REGISTER_DATAGRAM_CONTEXT or
   REGISTER_DATAGRAM_NO_CONTEXT capsule using the "Datagram Format Type"
   set to both send and receive UDP_PAYLOAD, the H3_DATAGRAM
   SETTINGS Parameter), clients "Datagram Format Additional Data" field SHALL
   be empty.  Servers MUST NOT send any HTTP Datagrams until
   they have established support on a given connection.  If negotiation
   of HTTP Datagrams fails (for example if an HTTP/3 SETTINGS frame was
   received without the H3_DATAGRAM SETTINGS Parameter), register contexts using the client UDP_PAYLOAD
   HTTP Datagram Format Type.  Clients MUST
   consider its CONNECT-UDP request as failed.

   The proxy that is creating the UDP socket to NOT register more than one
   context using the destination responds
   to UDP_PAYLOAD HTTP Datagram Format Type.  Endpoints
   MUST NOT close contexts using the CONNECT-UDP request with a 2xx (Successful) response, and
   indicates it supports UDP_PAYLOAD HTTP Datagrams by sending Datagram Format
   Type.  If an endpoint detects a violation of any of these
   requirements, it MUST abort the corresponding
   registration capsule. stream.

   Clients MAY optimistically start sending proxied UDP packets before
   receiving the response to its CONNECT-UDP UDP proxying 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 the datagrams arrive are received by the proxy
   before the CONNECT-UDP request.

   Extensions to CONNECT-UDP this mechanism MAY leverage the "Context Extensions" field
   of registration capsules define new HTTP Datagram Format
   Types in order to negotiate use different semantics or
   encoding encodings for UDP
   payloads.

5.  Proxy Handling

   Unlike TCP, UDP is connection-less.  The proxy 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.

   Proxies can use connected UDP sockets if their operating system
   supports them, as that allows the proxy to rely on the kernel to only
   send it UDP packets that match the correct 5-tuple.  If the proxy
   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 proxy.

   The lifetime of the socket is tied to the CONNECT-UDP stream.  The
   proxy MUST keep the socket open while the CONNECT-UDP stream is open.
   Proxies MAY choose to close sockets due to a period of inactivity,
   but they MUST close the CONNECT-UDP stream before closing the socket.

6.  Performance Considerations

   Proxies SHOULD strive to avoid increasing burstiness of UDP traffic:
   they SHOULD NOT queue packets in order to increase batching.

   When the protocol running over UDP that is being proxied uses
   congestion control (e.g., [QUIC]), the proxied traffic will incur at
   least two nested congestion controllers.  This can reduce performance
   but the underlying HTTP connection MUST NOT disable congestion
   control unless it has an out-of-band way of knowing with absolute
   certainty that the inner traffic is congestion-controlled.

   If a client or proxy with a connection containing a CONNECT-UDP UDP proxying
   request stream disables congestion control, it MUST NOT signal ECN
   support on that connection.  That is, it MUST mark all IP headers
   with the Not-
   ECT Not-ECT codepoint.  It MAY continue to report ECN feedback
   via ACK_ECN frames, as the peer may not have disabled congestion
   control.

   When the protocol running over UDP that is being proxied uses loss
   recovery (e.g., [QUIC]), and the underlying HTTP connection runs over
   TCP, the proxied traffic will incur at least two nested loss recovery
   mechanisms.  This can reduce performance as both can sometimes
   independently retransmit both can sometimes
   independently retransmit the same data.  To avoid this, HTTP/3
   datagrams SHOULD be used.

5.1.  MTU Considerations

   When using HTTP/3 with the QUIC Datagram extension [DGRAM], UDP
   payloads are transmitted in QUIC DATAGRAM frames.  Since those cannot
   be fragmented, they can only carry payloads up to a given length
   determined by the QUIC connection configuration and the path MTU.  If
   a proxy is using QUIC DATAGRAM frames and it receives a UDP payload
   from the target that will not fit inside a QUIC DATAGRAM frame, the
   proxy SHOULD NOT send the UDP payload in a DATAGRAM capsule, as that
   defeats the end-to-end unreliability characteristic that methods such
   as Datagram Packetization Layer Path MTU Discovery (DPLPMTUD) depend
   on [RFC8899].  In this scenario, the same data.  To avoid this, HTTP/3
   datagrams proxy SHOULD be used.

6.1. drop the UDP
   payload and send an ICMP "Packet Too Big" message to the target
   [RFC4443].

5.2.  Tunneling of ECN Marks

   CONNECT-UDP

   UDP proxying does not create an IP-in-IP tunnel, so the guidance in
   [RFC6040] about transferring ECN marks between inner and outer IP
   headers does not apply.  There is no inner IP header in CONNECT-UDP UDP proxying
   tunnels.

   Note that CONNECT-UDP UDP proxying clients do not have the ability in this
   specification to control the ECN codepoints on UDP packets the proxy
   sends to the server, nor can proxies communicate the markings of each
   UDP packet from server to proxy.

   A CONNECT-UDP UDP proxy MUST ignore ECN bits in the IP header of UDP packets
   received from the server, and MUST set the ECN bits to Not-
   ECT Not-ECT on UDP
   packets it sends to the server.  These do not relate to the ECN
   markings of packets sent between client and proxy in any way.

7.

6.  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 UDP proxying SHOULD restrict its use to authenticated
   users.

   Because the CONNECT method creates a TCP connection to the target,
   the target has to indicate its willingness to accept TCP connections
   by responding with a TCP SYN-ACK before the proxy can send it
   application data.  UDP doesn't have this property, so a CONNECT-UDP UDP proxy
   could send more data to an unwilling target than a CONNECT proxy.
   However, in practice denial of service attacks target open TCP ports
   so the TCP SYN-ACK does not offer much protection in real scenarios.
   Proxies MUST NOT introspect the contents of UDP payloads as that
   would lead to ossification of UDP-based protocols by proxies.

8.

7.  IANA Considerations

8.1.

7.1.  HTTP Method Upgrade Token

   This document will request IANA to register "CONNECT-UDP" "connect-udp" in the HTTP
   Method
   Upgrade Token Registry (IETF review) maintained at
   <https://www.iana.org/assignments/http-methods>.

     +-------------+------+------------+---------------+
     | Method Name | Safe | Idempotent |   Reference   |
     +-------------+------+------------+---------------+
     | CONNECT-UDP |  no  |     no     |
   <https://www.iana.org/assignments/http-upgrade-tokens>.

   Value:  connect-udp

   Description:  Proxying of UDP Payloads.

   Expected Version Tokens:  None.

   Reference:  This document |
     +-------------+------+------------+---------------+

8.2.  URI Scheme Registration document.

7.2.  Datagram Format Type

   This document will request IANA to register UDP_PAYLOAD in the URI scheme "masque".

   The syntax definition below uses Augmented Backus-Naur Form (ABNF)
   [RFC5234].  The definitions of "host" and "port" are adopted from
   [RFC3986].  The syntax of a MASQUE URI is:

   masque-URI = "masque:" "//" host ":" port "/"

   The "host" and "port" component MUST NOT be empty, and the "port"
   component MUST NOT be 0.

9. "HTTP
   Datagram Format Types" registry established by [HTTP-DGRAM].

                +=============+==========+===============+
                | Type        | Value    | Specification |
                +=============+==========+===============+
                | UDP_PAYLOAD | 0xff6f00 | This Document |
                +-------------+----------+---------------+

                 Table 1: Registered Datagram Format Type

8.  References

9.1.

8.1.  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-06, 5 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-quic-
              datagram-06>.

   [EXT-CONNECT2]
              McManus, P., "Bootstrapping WebSockets with HTTP/2",
              RFC 8441, DOI 10.17487/RFC8441, September 2018,
              <https://www.rfc-editor.org/rfc/rfc8441>.

   [EXT-CONNECT3]
              Hamilton, R., "Bootstrapping WebSockets with HTTP/3", Work
              in Progress, Internet-Draft, draft-ietf-httpbis-h3-
              websockets-00, 9 September 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              h3-websockets-00>.

   [H2]       Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7540>.

   [H3]       Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-34, 2 February 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-quic-
              http-34>.

   [HTTP-DGRAM]
              Schinazi, D. and L. Pardue, "Using Datagrams with HTTP",
              Work in Progress, Internet-Draft, draft-ietf-masque-h3-
              datagram-03, 12 July
              datagram-04, 6 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-masque-
              h3-datagram-03>.
              h3-datagram-04>.

   [MESSAGING]
              Fielding, R. T., Nottingham, M., and J. Reschke,
              "HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-messaging-19, 12 September 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              messaging-19>.

   [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/rfc/rfc9000>.

   [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/rfc/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5234>.

   [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,
              <https://www.rfc-editor.org/rfc/rfc7230>.

   [RFC7231]  "*** BROKEN REFERENCE ***".

   [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/rfc/rfc8174>.

   [SEMANTICS]
              Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
              Semantics", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-semantics-19, 12 September 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              semantics-19>.

   [TCP]      Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/rfc/rfc793>.

   [TEMPLATE] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/rfc/rfc6570>.

   [UDP]      Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/rfc/rfc768>.

9.2.

8.2.  Informative References

   [BEHAVE]   Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <https://www.rfc-editor.org/rfc/rfc4787>.

   [PROXY-STATUS]
              Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
              Response Header Field", Work in Progress, Internet-Draft,
              draft-ietf-httpbis-proxy-status-06, 16 August 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
              proxy-status-06>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/rfc/rfc4443>.

   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, DOI 10.17487/RFC6040, November
              2010, <https://www.rfc-editor.org/rfc/rfc6040>.

   [RFC8899]  Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
              Völker, "Packetization Layer Path MTU Discovery for
              Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
              September 2020, <https://www.rfc-editor.org/rfc/rfc8899>.

Acknowledgments

   This document is a product of the MASQUE Working Group, and the
   author thanks all MASQUE enthusiasts for their contibutions.  This
   proposal was inspired directly or indirectly by prior work from many
   people.  In particular, the author would like to thank Eric Rescorla
   for suggesting to use an HTTP method to proxy UDP.  Thanks to Lucas
   Pardue for their inputs on this document.

Author's Address

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

   Email: dschinazi.ietf@gmail.com