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MASQUE                                                     M. Kuehlewind
Internet-Draft                                             M. Westerlund
Intended status: Standards Track                                M. Ihlar
Expires: 6 May 2021                                            Z. Sarker
                                                         2 November 2020

             The CONNECT-IP method for proxying IP traffic


   This draft specifies a new HTTP/3 method CONNECT-IP to proxy IP
   traffic.  CONNECT-IP can be used to convert a QUIC stream into a
   tunnel or initialise an HTTP datagram flow to a forwarding proxy.
   Each stream or HTTP datagram flow can be used separately to establish
   forwarding of an IP flow to potentially different remote hosts.  To
   request forwarding, a client connects to a proxy server by initiating
   a HTTP/3 connection and sends a CONNECT-IP indicating the address of
   the target server.  The proxy server then forwards payload received
   on that stream or in an HTTP datagram with a certain flow ID to the
   target server after adding an IP header to each of the frames

Discussion Venues

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

   Discussion of this document takes place on the MASQUE Working Group
   mailing list (masque@ietf.org), which is archived at

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

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   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 6 May 2021.

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 (https://trustee.ietf.org/
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Motivation of IP flow model . . . . . . . . . . . . . . .   5
   2.  The CONNECT-IP method . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Stream-based mode . . . . . . . . . . . . . . . . . . . .   7
     2.2.  Datagram-based mode . . . . . . . . . . . . . . . . . . .   7
     2.3.  IP-Protocol Header for CONNECT-IP . . . . . . . . . . . .   8
     2.4.  Conn-ID Header for CONNECT-IP . . . . . . . . . . . . . .   8
   3.  Client behavior . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  MASQUE server behavior  . . . . . . . . . . . . . . . . . . .   9
     4.1.  Error handling  . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  IP address selection and NAT  . . . . . . . . . . . . . .  10
     4.3.  Constructing the IP header  . . . . . . . . . . . . . . .  10
     4.4.  Receiving an IP packet  . . . . . . . . . . . . . . . . .  11
   5.  MASQUE signalling . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Config file . . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  ECN . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.3.  ICMP handling . . . . . . . . . . . . . . . . . . . . . .  12
     5.4.  MTU considerations  . . . . . . . . . . . . . . . . . . .  12
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  Security considerations . . . . . . . . . . . . . . . . . . .  12
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  HTTP Method . . . . . . . . . . . . . . . . . . . . . . .  13
     8.2.  HTTP Header . . . . . . . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  13

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   References  . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     Normative References  . . . . . . . . . . . . . . . . . . . . .  13
     Informative References  . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   This document specifies the CONNECT-IP method for IPv4 [RFC0791] and
   IPv6 [RFC8200] flows when they are proxied according to the MASQUE
   proposal over HTTP/3.

   The approach taken in this paper does not send the IP header as part
   of the payload between the client and proxy in order to reduce
   overhead.  The target IP address and other IP flow related
   information is provided by the client as part of the CONNECT-IP
   request.  The sources address is selected by the proxy as further
   discussed below.  Other information that might be needed to construct
   the IP header or to inform the client about information from received
   IP packets can be signalled separately.

   This proposal is based on the analysis provided in
   [I-D.westerlund-masque-transport-issues] indicating that most
   information in the IP header is either IP flow related or can or even
   should be provided by the proxy as the IP communication endpoint
   without the need for input from the client.  The only information
   identified that requires client interaction is ECN [RFC3168] and ICMP
   [RFC0792] [RFC4443] handling.  This document proposes an event-based
   handling for both, which may not provide unambiguous mapping to one
   specific IP packet that triggered the event but trades this off for
   lower overhead.

   This document uses an IP flow definition that is tighter than just
   source and destination address of the IP packet.  To reduce the
   overhead a number of IP header field values that are static in the
   context of an upper layer protocol connection, e.g. when UDP or TCP
   are used, are associated with an MASQUE IP flow at creation.  These
   fields include the Protocol (IPv4) / Next Header (IPv6), IPv6 flow
   label, Diffserv Code Point (DSCP), TTL / Hop Limit, where a default
   value or locally generated value based on the CONNECT-IP context is
   sufficient.  Signalling of other dedicated values may be desired in
   certain deployments, e.g for DCSP [RFC2474].  However, DSCP is in any
   case a challenge due to local domain dependency of the used DSCP
   values and the forwarding behavior and traffic treatment they
   represent.  Future use cases for DSCP, as well as new IPv6 extension
   headers or destination header options[RFC8200] may require additional
   signaling.  Therefore, it is important that the signaling is

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   The CONNECT-IP method establishes an outgoing IP flow, from the
   MASQUE server's external address to the target server's address
   specified by the client.  The method also enable reception and
   relaying of the reverse IP flow from the target address to the MASQUE
   server to ensure that return traffic can be received by the client.
   This specification supports forwarding of incoming traffic to one of
   the clients that have a QUIC tunnel connection with the proxy only if
   an active mapping has previously been created based on an IP-CONNECT

   Following the points above, this document assumes that usually one
   upper-layer end-to-end connection is associated to one CONNECT-IP
   request/one tunnelling association.  While it would be possible for a
   client to use the same tunnelling association for multiple end-to-end
   connections to the same target server, as long as they all require
   the same Protocol (IPv4) / Next Header (IPv6) value, this would lead
   to the use of the same flow ID for all connections and complicate the
   use of ECN as feedback cannot be associated with a single packet/
   connection.  As such this is not recommended for connection-oriented
   transmissions.  Alternatively, the proposed approach in this document
   could be extended to support per-packet signalling in HTTP datagrams
   and DATA frames on streams to address this restriction, however, this
   would increase per-packet overhead and design decisions in this
   document where taken in order minimise byte overhead.

1.1.  Definitions

   *  Proxy: This document uses proxy as synonym for the MASQUE Server
      or an HTTP proxy, depending on context.

   *  Client: The endpoint initiating a MASQUE tunnel and IP relaying
      with the proxy.

   *  Target host: A remote endpoint the client wishes to establish bi-
      directional communication with via tunnelling over the proxy.

   *  IP proxying: A proxy forwarding IP payloads to a target for an IP
      flow.  Data is decapsulate at the proxy and amended by a IP header
      before forwarding to the target.  Packet boundaries need to be
      preserved or signalled between the client and proxy.

   *  IP flow: A flow of IP packets between two hosts as identified by
      their IP addresses, and where all the packets share some
      properties.  These properties include source/destination address,
      protocol / next header field, flow label (IPv6 only), and DSCP per

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   Address = IP address

                        Target Address --+
   +--------+           +--------+         \ +--------+
   |        |  Path #1  |        | Path #2  V|        |
   | Client |<--------->|  Proxy |<--------->| Target |
   |        |          ^|        |^          |        |
   +--------+         / +--------+ \         +--------+
                     /              \
                    /                +-- Proxy's external address
                  +-- Proxy's service address

                  Figure 1: The nodes and their addresses

   Figure 1 provides an overview figure of the involved nodes, i.e.
   client, proxy, and target host.  There are also two network paths.
   Path #1 is the client to proxy path, where IP proxying is provided
   over an HTTP/3 session, usually over QUIC, to tunnel IP flow(s).
   Path #2 is the path between the proxy and the target.

   The client will use the proxy's service address to establish a
   transport connection on which to request IP proxying using HTTP/3
   CONNECT-IP.  The proxy will then relay the client's IP flows to the
   target host.  The IP header from the proxy to the target carries the
   proxy's external address as source address and the target's address
   as destination address.

   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.

1.2.  Motivation of IP flow model

   The chose IP flow model is selected due to several advantages:

   *  Shared functionality with CONNECT-UDP: The UDP flow proxying
      functionality of CONNECT-UDP will need to establish, store and
      process the same IP header related fields and state.  So this can
      be accomplished by simply removing the UDP specific processing of

   *  CONNECT-IP can establish a new IP flow in 0-RTT: No network
      related latencies in establishing new flow.

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   *  Minimized per packet overhead: The per packet overhead is reduced
      to basic framing of the IP payload for each IP packet and flow

   Disadvantages of this model are the following:

   *  Client server focused solution: Accepting non-solicited server-
      initiated traffic is challenging and require MASQUE server to
      client signalling when incoming packets are receiived at the

   Discussion: This IP flow model appears less suitable if one targets
   network proxying or running server functionality on the client side.
   However, the functionality specified in this documnet is anyway
   required for CONNECT-UDP and should therefore be utiilized to also
   reduce overhead for IP proxying.  A potential solution to also
   support network proxying is to add another modes for CONNECT-IP which
   would tunnel the complete IP header over the MASQUE forwarding
   connection.  However, this puts addition requirements on the MASQUE
   server related to IP router functionality, source address validation,
   and possibly network address translation and therefore requires
   further discussion.

2.  The CONNECT-IP method

   This document defines a new HTTP/3 [I-D.ietf-quic-http] method
   CONNECT-IP to convert streams into tunnels or initialise HTTP
   datagram flows [I-D.schinazi-quic-h3-datagram] to a forwarding proxy.
   Each stream can be used separately to establish forwarding of one
   connection to potentially different remote hosts.  Unlike the HTTP
   CONNECT method, CONNECT-IP does not request the forwarding proxy to
   establish a TCP connection to the remote target host.  Instead the
   tunnel payload will be forwarded right on top of the IP layer,
   meaning the forwarding proxy has to identify messages boundaries and
   then adds an IP header to each message before forwarding (see section
   Section 4).

   This document specifies CONNECT-IP only for HTTP/3 following the same
   semantics as the CONNECT method.  As such a CONNECT-IP request MUST
   be constructed as follows:

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

   *  The ":scheme" and ":path" pseudo-header fields are omitted

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   *  The ":authority" pseudo-header field contains the host and port to
      connect to (equivalent to the authority-form of the request-target
      of CONNECT requests; see Section 3.2.3 of

   A CONNECT request that does not conform to these restrictions is
   malformed; see Section 4.1.3 of [I-D.ietf-quic-http].

   The forwarding stays active as long as the respective stream is open.
   Forwarding can be either be realised by sending data on that stream
   together with an indication of message length (see Section 2.1) or
   use of HTTP/3 datagrams [I-D.schinazi-quic-h3-datagram] where the
   payload of one frame is mapped to one IP packet (see Section 2.2).

2.1.  Stream-based mode

   Once the CONNECT-IP method has completed, only DATA frames are
   permitted to be sent on that stream.  Extension frames MAY be used if
   specifically permitted by the definition of the extension.  Receipt
   of any other known frame type MUST be treated as a connection error

   Each HTTP DATA frame MUST to contain the payload of one IP packet.

   Stream based mode provides in-order and reliable delivery but may
   introduce Head of Line (HoL) Blocking if independent messages are
   send in the IP payload.

2.2.  Datagram-based mode

   The client can, in addition to stream mode, request support of
   datagram mode using HTTP/3 datagrams [I-D.schinazi-quic-h3-datagram]
   to forward IP payload.

   To request datagram support the client adds an Datagram-Flow-Id
   Header to the CONNECT-IP request as specified for CONNECT-UDP in
   [I-D.schinazi-masque-connect-udp].  Datagram mode MUST only be
   requested when the QUIC datagram extension [I-D.ietf-quic-datagram]
   was successfully negotiated during the QUIC handshake.

   Datagram mode provides un-order and unreliable delivery.  In theory
   both, stream as well as datagram mode, can be used in parallel,
   however, for most transmissions it is expected to only use one.

   While IP packets sent in stream-based mode only have to respect the
   end-to-end MTU between the client and the target server, packets sent
   in datagram mode are further restricted by the QUIC packet size of
   the QUIC tunnel and any overhead within the QUIC tunnel packet.  The

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   proxy should provide MTU and overhead information to the client.  The
   client MUST take this overhead into account when indicating the MTU
   to the application.

2.3.  IP-Protocol Header for CONNECT-IP

   In order to construct the IP header the MASQUE server needs to fill
   the "Protocol" field in the IPv4 header or "Next header" field in the
   IPv6 header.  As the IP payload is otherwise mostly opaque to the
   MASQUE forwarding server, this information has to be provided by the
   client for each CONNECT-IP request.  Therefore this document define a
   new header field that is mandatory to use with CONNECT-IP called "IP-

   IP-Protocol is a Item Structured Header
   [I-D.ietf-httpbis-header-structure].  Its value MUST be an Integer.
   Its ABNF is:

     IP-Protocol = sf-integer

2.4.  Conn-ID Header for CONNECT-IP

   This document further defines a new header field to be used with
   CONNECT-IP "Conn-ID".  The Conn-ID HTTP header field indicates the
   value, offset, and length of a field in the IP payload that can be
   used by the MASQUE as a connection identifier in addition to the IP
   address tuple when multiple connections are proxied to the same
   target server.

   Conn-ID is a Item Structured Header
   [I-D.ietf-httpbis-header-structure].  Its value MUST be a Byte
   Sequence.  Its ABNF is:

     Conn-ID = sf-binary

   The following parameters are defined:

   *  A parameter whose name is "offset", and whose value is an Integer
      indicating the offset of the identifier field starting from the
      beginning of a datagram or HTTP frame on the forwarding stream.

   *  A parameter whose name is "length", and whose value is an Integer
      indicating the length of the identifier field starting from the

   Both parameters MUST be present and the header MUST be ignored if
   these parameter are not present.

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   This function can be used to e.g. indicate the source port field in
   the IP payload when containing a TCP packet.

3.  Client behavior

   To request IP proxying, the client sends a CONNECT-IP request to the
   forwarding proxy indicating the target host and port in the
   ":authority" pseudo-header field.  The host portion is either an IP
   literal encapsulated within square brackets, an IPv4 address in
   dotted-decimal form, or a registered name.  Different to the TCP-
   based CONNECT, CONNECT-IP does not trigger a connection establishment
   process from the proxy to the target host.  Therefore, the client
   does not need to wait for an HTTP response in order to send
   forwarding data.

   Forwarding data can either directly on the same HTTP stream as the
   CONNECT-IP request (see Section Section 2.1), or an HTTP datagram
   encapsulated in a QUIC datagram can be sent (see
   Section Section 2.2), even in the same QUIC packet.  To request use
   of the datagram mode, the CONNECT-IP request MUST indicate the
   datagram flow ID in the Datagram-Flow-Id Header.

   QUESTION: datagram flow IDs are allocated by a flow id allocation
   service at the server in [I-D.schinazi-quic-h3-datagram].  However,
   with CONNECT-IP you can always send your first message directly on
   the same stream right after the CONNECT-IP request and sever could
   provide you a flow ID together with a "2xx" response to the CONNECT-
   IP request.  Wouldn't that be easier and faster?

4.  MASQUE server behavior

   A MASQUE server that receives an IP-CONNECT request, opens a raw
   socket and creates state to map a connection identifier, which might
   be a tuple, to a target IP address.  Once this is successfully
   established, the proxy sends a HEADERS frame containing a 2xx series
   status code to the client.  To indicate support of datagram mode, if
   requested by the client, the MASQUE server reflects the Datagram-
   Flow-Id Header from the client's request on the HTTP response.

   All DATA frames received on that stream as well as all HTTP/3
   datagrams with the specified Datagram-flow-ID are forwarded to the
   target server by adding an IP header (see section Section 4.3 below)
   and sending the packet on the respective raw socket.

   IP packets received from the target server are mapped to an active
   forwarding connection and its payload is then respectively forwarded
   in an DATA frame or HTTP/3 datagram to the client (see section
   Section 4.4 below).

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4.1.  Error handling

   TBD (e.g. out of IP address, conn-id collision)

4.2.  IP address selection and NAT

   Since a MASQUE server adds the IP header when sending the IP payload
   towards the target server, it also select an source IP address from
   its pool of IP address that are routed to the MASQUE server.

   If no additional information about a payload field that can be used
   as an identifier based on Conn-ID header is provided by the client,
   the masque server uses the source/destination address 2-tuple in
   order to map an incoming IP packet to an active forwarding
   connection.  As such the MASQUE proxy MUST select a source IP address
   that leads to a unique tuple.  The same IP address can be used for
   different clients when those client connect to different target
   servers, however, this also means that potentially multiple IP
   address are used for the same client when multiple connection to one
   target server are needed.  This can be problematic if the source
   address is used by the target server as an identifier.

   If the Conn-ID header is provided, the MASQUE server should use that
   field as an connection identifier together with source and
   destination address, as a 3-tuple.  In this case it is recommended to
   use a stable IP address for each client, while the same IP address
   might still be used for multiple clients, if not indicated
   differently by the client in the configuration file.  Note that if
   the same IP address is used for multiple clients, this can still lead
   to an identifier collision and the IP-CONNECT request MUST be reject
   if such a collision is detect.

4.3.  Constructing the IP header

   To retrieve the source and destination address the proxy looks up the
   mapping for the datagram flow ID or stream identifier.  The IP
   version, flow label, DiffServ codepoint (DSCP), and hop limit/TTL is
   selected by the proxy.  The IPv4 Protocol or IPv6 Next Header field
   is set based on the information provided by the IP-Protocol header in
   the CONNECT-IP request.

   MASQUE server MUST set the Don't Fragment (DF) flag in the IPv4
   header.  Payload that does not fit into one IP packet MUST be
   dropped.  A dropping indication should be provided to the client.
   Further the MASQUE server should provide MTU information.

   The ECN field is by default set to non-ECN capable transport (non-
   ECT).  Further ECN handling is described in Section Section 5.2.

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4.4.  Receiving an IP packet

   When the MASQUE proxy receives an incoming IP packet, it checks if
   the source and destination IP address maps to an active forwarding
   connection.  If one or more mappings exists, it further checks if
   this mapping contains additional identifier information as provided
   by the Conn-ID Header of the CONNECT-IP request.  If this field maps
   as well, the IP payload is forwarded to the client.  If no active
   mapping is found, the IP packet is discarded.

   The masque server should use the same forwarding mode as used by the
   client.  If both modes, datagram and stream based, are used, it is
   recommended to use the same mode as most recently used by the client
   or datagram mode as default.  Alternatively, the client might
   indicate a preference in the configuration file.

5.  MASQUE signalling

   One stream of the underlying QUIC connection can be used as a
   signalling channel between the client and proxy.  Both the client and
   the masque server can send or request an JSON [RFC7159] configuration
   file by sending an HTTP POST or GET to "/.well-known/masque/config".
   Further the masque server can PUSH status updates about certain
   forwarding streams or datagram flows, e.g. contain ECN [RFC3168]
   counters or the outside facing IP address used for this connection,
   to "/.well-known/masque/<id>".

   Note: Alternative approach would be to use HTTP headers with IP-
   CONNECT for initial negotiation and new HTTP frame format(s) to
   provide per-packet information (e.g ECN) or event-based information
   (e.g.  ICMP).

5.1.  Config file

   TBD (indicate IP address handling, forwarding mode preference,

5.2.  ECN

   ECN requires coordination with the end-to-end communication points as
   it should only be used if the endpoints are also capable and willing
   to signal congestion notifications to the other end and react
   accordingly if a congestion notification is received.

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   Therefore, if ECN is used, the proxy needs to inform the client of a
   congestion notification (IP CE codepoint) was observed in any IP
   header of a received packet from the target server.  This can be
   realised by maintaining an CE counter in the proxy and send an
   updated JSON stream file if the counter changes.

   Further, clients must indicate to the proxy for each forwarding flow/
   stream if the ECT(0) or ECT(1) codepoint should be set.  The client
   can update this during the lifetime of a forwarding connection,
   however, there is no guarantee which packet will be forwarded with
   the updated information or the old information as QUIC datagrams may
   be delivered out of order.  If the IP payload is e.g. carrying TCP,
   today, ECN is only used after the handshake.  But if not all data
   packets after the handshake are immediately ECT marked, this should
   not have a huge impact.

   It may be desirable for the endpoint to validate ECN usage on the
   path.  In this case validation can either be done by the proxy
   independently or the proxy has to provide not only the number or
   received observed CE markings but also the number of sent and other
   received markings.  This need further discussion.

5.3.  ICMP handling


5.4.  MTU considerations


6.  Examples


7.  Security considerations

   This document does currently not discuss risks that are generic to
   the MASQUE approach.

   Any CONNECT-IP specific risks need further consideration in future,
   especially when the handling of IP functions is defined in more

8.  IANA considerations

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8.1.  HTTP Method

   This document (if published as RFC) registers "CONNECT-IP" in the
   HTTP Method Registry maintained at <https://www.iana.org/assignments/

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

8.2.  HTTP Header

   This document (if published as RFC) registers the "Conn-Id" and "IP-
   Protocol" header in the "Permanent Message Header Field Names"
   registry maintained at <https://www.iana.org/assignments/message-

     | Header Field Name | Protocol | Status |   Reference   |
     | Conn-Id           |   http   |  exp   | This document |
     | IP-Protocol       |   http   |  exp   | This document |



Normative References

              Nottingham, M. and P. Kamp, "Structured Field Values for
              HTTP", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-header-structure-19, 3 June 2020,

              Fielding, R., Nottingham, M., and J. Reschke, "HTTP/1.1
              Messaging", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-messaging-12, 2 October 2020,

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              Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
              Datagram Extension to QUIC", Work in Progress, Internet-
              Draft, draft-ietf-quic-datagram-01, 24 August 2020,

              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-32, 20 October 2020, <http://www.ietf.org/

              Schinazi, D., "The CONNECT-UDP HTTP Method", Work in
              Progress, Internet-Draft, draft-schinazi-masque-connect-
              udp-00, 16 April 2020, <http://www.ietf.org/internet-

              Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in
              Progress, Internet-Draft, draft-schinazi-quic-h3-datagram-
              05, 12 October 2020, <http://www.ietf.org/internet-drafts/

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,

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

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [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/info/rfc8174>.

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   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

Informative References

              Westerlund, M., Ihlar, M., Sarker, Z., and M. Kuehlewind,
              "Transport Considerations for IP and UDP Proxying in
              MASQUE", Work in Progress, Internet-Draft, draft-
              westerlund-masque-transport-issues-00, 10 July 2020,

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,

   [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,

Authors' Addresses

   Mirja Kuehlewind

   Email: mirja.kuehlewind@ericsson.com

   Magnus Westerlund

   Email: magnus.westerlund@ericsson.com

   Marcus Ihlar

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   Email: marcus.ihlar@ericsson.com

   Zaheduzzaman Sarker

   Email: zaheduzzaman.sarker@ericsson.com

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