MASQUE                                                     M. Kuehlewind
Internet-Draft                                             M. Westerlund
Intended status: Standards Track                                M. Ihlar
Expires: 13 January 2022                                       Z. Sarker
                                                            12 July 2021

           The CONNECT-IP HTTP method for proxying IP traffic


   This draft specifies a new HTTP method CONNECT-IP to proxy IP
   traffic.  CONNECT-IP uses HTTP/3 Datagrams to use QUIC Datagrams for
   efficient transport of proxied IP packets, with the possibility to
   fallback to HTTP/3 over reliable QUIC streams, or even HTTP 1.x and

   CONNECT-IP supports two modes: a tunneling mode where IP packets are
   forwarded without modifications and flow forwarding mode which
   supports optimization for individual IP flows forwarded to the
   targeted peer.  To request tunneling or flow forwarding, a client
   connects to a proxy server by initiating a HTTP/3 connection and
   sends a CONNECT-IP request which either indicates the address of the
   proxy or the target peer.  The proxy then forwards payload received
   on that stream or in an HTTP datagram with a certain stream ID.

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 (, 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

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   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 2022.

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   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Tunnel mode
     1.2.  Flow Forwarding mode
       1.2.1.  Motivation of IP flow model for flow forwarding
     1.3.  Definitions
   2.  The CONNECT-IP method
     2.1.  Data encapsulation
     2.2.  Datagram Formats
       2.2.1.  Tunnel Mode IPv4 Format
       2.2.2.  Tunnel Mode IPv6 Format
       2.2.3.  Flow Forwarding Format
       2.2.4.  ICMP Message Format
   3.  HTTP Headers
     3.1.  IP-Protocol Header for CONNECT-IP
     3.2.  IP-Version header for CONNECT-IP
     3.3.  IP-Address header for CONNECT-IP
     3.4.  IP-Address-Handling Header for CONNECT-IP
     3.5.  Conn-ID Header for CONNECT-IP
   4.  Client Connect-IP Request
     4.1.  Requesting flow forwarding
     4.2.  Requesting tunnel mode
   5.  MASQUE server behavior
     5.1.  Error handling
     5.2.  IP address selection in flow forwarding mode
     5.3.  Constructing the IP header in flow forwarding mode
     5.4.  Decapsulation of tunnel mode IP Packets
     5.5.  Receiving an IP packet
   6.  Additional signalling
     6.1.  ECN
     6.2.  ICMP handling
     6.3.  MTU considerations
   7.  Examples
   8.  Security considerations
   9.  IANA considerations
     9.1.  HTTP Method
     9.2.  HTTP Header
     Normative References
     Informative References
   Authors' Addresses

1.  Introduction

   This document specifies the CONNECT-IP method for IPv4 [RFC0791] and
   IPv6 [RFC8200] tunneling and flow forwarding over HTTP/3.

   CONNECT-IP supports two modes: a tunneling mode where IP packets are
   forwarded without modifications and flow forwarding mode which
   supports optimization for individual IP flows forwarded to the
   targeted peer.

1.1.  Tunnel mode

   In tunnel mode the client requests to tunnel IP packets to and from
   one or more servers via the proxy.  The Connect-IP request to the
   proxy establishes such a tunnel and optionally indicates the IP
   address or IP address range that will be allowed to be used by and
   forwarded to the client.

   The tunnel mode is indicated by the ":authority" pseudo-header field
   of the CONNECT-IP request contain the host and listing port of the
   proxy itself.  In this mode the proxy just blindly forwards all
   payload on its external interface without any modification and also
   forwards all incoming traffic to registered clients as payload within
   the respective tunnel association.  That means all incoming traffic,
   where the destination address matches an by the client indicated IP
   address or range of IP addresses, is forwarded to the client over the
   tunnel association, except a more specific flow forwarding
   association exists where both destination and source IP address as
   well as any additionally used identifier match (see section
   Section 5.5).

   However, a proxy MUST offer this service only for known clients and
   clients MUST be authenticated during connection establishment.  The
   proxy SHOULD inspect the source IP address of the IP packet in the
   tunnel payload and only forward if the IP address matches the set of
   client IP addresses.  Optionally, a proxy also MAY offer this service
   only for a limited set of target addresses.  In such a case the proxy
   SHOULD also inspect the destination IP address of the tunnel payload
   as well as the source address of incoming packets from target servers
   and reject packets with unknown addresses with an error.

1.2.  Flow Forwarding mode

   In flow forwarding mode 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 for a particular upper layer
   protocol.  This mode also enables 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.  However,
   it does not support flow establishment by an external peer.  This
   specification supports forwarding of incoming traffic to one of the
   clients only if an active mapping has previously been created based
   on an IP-CONNECT request.  Clients that need to support reception of
   flows established by external peer need to use tunnel mode.

   This mode covers the point-to-point use case
   [I-D.ietf-masque-ip-proxy-reqs] and allows for flow-based
   optimizations and a larger effective maximum packet size through the
   tunnel.  The target IP address is provided by the client as part of
   the CONNECT-IP request.  The sources address is either independently
   selected by the proxy or can be requested to be either the same as
   used in a previous and currently active CONNECT-IP request or
   different from currently requests by the same client.  The client
   also indicates the upper layer protocol, thus defining the three
   tuple used as primary selector for the flow.

   In this mode the payload between the client and proxy does not
   contain the IP header in order to reduce overhead.  Any additional
   information (other than the source and destination IP addresses and
   ports as well as the upper layer protocol identifier) that is needed
   to construct the IP header or to inform the client about information
   from received IP packets can be signalled as part of the CONNECT-IP
   request or using HTTP/3 Datagram [I-D.ietf-masque-h3-datagram] later.

   In flow forwarding mode, usually one upper-layer end-to-end
   connection is associated to one CONNECT-IP forwarding association.
   While it would be possible for a client to use the same forwarding
   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.  As such, this is not recommended for
   connection-oriented transmissions.  In order to enable multiple flow
   forwarding associations to the same server, the flow forwarding mode
   supports a way to specify some additional upper layer protocol
   selectors, e.g.  TCP source and destination port, to enable multiple
   CONNECT-IP request for the same three tuple, see CONN-ID header
   Section 3.5.

   The default model for address handling in this specification is that
   the proxy (Masque Server) will have a pool of one or more IP
   addresses that it can lend to the MASQUE client and routable over its
   external interface.  Other potential use cases and address handling
   are possible, potentially requiring further extensions.

   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 most crucial
   information identified that requires client interaction is ECN
   [RFC3168] and ICMP [RFC0792] [RFC4443] handling.

   This document defines the following IP header field treatment.

   Required to be determined in Connect-IP request and response:

   *  IP version

   *  IP Source Address

   *  IP Destination Address (target address)

   *  Upper Layer Protocol (IPv4 Protocol field / IPv6 Next Header

   Can be chosen by Proxy on transmission:

   *  IPv6 Flow label (per Connect-IP flow mode request)

   *  IPv4 Time to live / IPv6 Hop Limit (proxy configured)

   *  Diffserv Codepoint, default is set to 0 (Best Effort)

   May optionally be provided on a per packet basis

   *  Explicit Congestion Notification in both directions.

   The consequence of this is certain limitations that future extension
   can address.  For packets that are sent from the target server to the
   client, the client will not get any information on the actual value
   of TTL/Hop Count, DSCP, or flow label when received by the proxy.
   Instead these field are set and consumed by the proxy only.

   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

1.2.1.  Motivation of IP flow model for flow forwarding

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

   *  Minimized per packet overhead: The per packet overhead is reduced
      to basic framing of the IP payload for each IP packet and flow
      identifiers.  This enables a larger effective Maximum Transmission
      Unit (MTU) than tunnel mode.

   *  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.

   Disadvantages of this model are the following:

   *  Client to server focused solution: Accepting non-solicited peer-
      initiated traffic is not supported.

1.3.  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

   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.

2.  The CONNECT-IP method

   This document defines a new HTTP [I-D.ietf-httpbis-semantics] method
   CONNECT-IP to convert streams into tunnels or initialize HTTP
   datagram flows [I-D.ietf-masque-h3-datagram] to a forwarding proxy.
   Each stream can be used separately to establish forwarding to
   potentially different remote hosts.  Unlike the HTTP CONNECT method,
   CONNECT-IP does not request the proxy to establish a TCP connection
   to the remote target host.  Instead the tunnel payload will be
   forwarded as individual IP packets (tunnel mode) or right on top of
   the IP layer (flow forwarding), meaning the proxy has to identify
   messages boundaries to each message before forwarding (see section
   Section 5).

   This document specifies CONNECT-IP for HTTP 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

   *  The ":authority" pseudo-header field contains either the host
      address to connect to (equivalent to the authority-form of the
      request-target of CONNECT-UDP [I-D.ietf-masque-connect-udp] or
      CONNECT requests; see Section 3.2.3 of
      [I-D.ietf-httpbis-messaging]) or the host and port of the proxy if
      tunnel mode is requested

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

   Unlike the CONNECT method, CONNECT-IP does not sequentially 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, unless in tunnel mode and requesting
   assignment of an external IP address.  However, the client,
   especially on tunnel mode, SHOULD limit the amount of traffic sent to
   the proxy before a 2xx (Successful) response is received.

   The forwarding stays active as long as the respective stream is open.
   A Forwarded IP packet can be either an encapsulated HTTP datagram on
   the same HTTP stream as the CONNECT-IP request, or as a HTTP datagram
   sent over QUIC datagram.

2.1.  Data encapsulation

   Once the CONNECT-IP method has completed, only CAPSULE
   [I-D.ietf-masque-h3-datagram] 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 of type

   Each HTTP Datagram frame contains one of the below specified data
   formats (Section 2.2) depending on request forwarding mode and given
   headers and parameters.

   Stream based forwarding provides in-order and reliable delivery but
   may introduce Head of Line (HoL) Blocking if independent messages are
   send over the same CONNECT-IP association.  On streams payload data
   is encapsulated in the CAPSULE Frame using the DATAGRAM capsule
   (type=0x02) [I-D.ietf-masque-h3-datagram].

   The client can, in addition to stream-based forwarding, request use
   of HTTP/3 datagrams [I-D.ietf-masque-h3-datagram].

   To request datagram support the client sends H3_DATAGRAM SETTINGS
   parameter with a value of 1 [I-D.ietf-masque-h3-datagram].  Datagram
   support MUST only be requested when the QUIC datagram extension
   [I-D.ietf-quic-datagram] was successfully negotiated during the QUIC

   Datagrams provide un-ordered and unreliable delivery.  In theory
   both, stream- as well as datagram-based forwarding, can be used in
   parallel, however, for most transmissions it is expected to only use

   While IP packets sent over streams only have to respect the end-to-
   end MTU between the client and the target server, packets sent in
   datagrams are further restricted by the QUIC packet size of the QUIC
   tunnel and any overhead within the QUIC tunnel packet.  Ideally, the
   proxy can provide MTU and overhead information to the client.  The
   client MUST take the estimated overhead into account when indicating
   the MTU to the application (see section Section 6.3).

2.2.  Datagram Formats

   This section defines the different datagram formats used by Connect-
   IP.  Even if only one format is currently used it is expected that
   for some usages future extension may require the flexibility to use
   multiple different formats for a given CONNECT-IP request.

2.2.1.  Tunnel Mode IPv4 Format

   The Datagram contains one full IPv4 Packet per [RFC0791].  Used in
   tunnel mode and when the IP Version is 4 per the IP-Version header or
   explicit given target address.

2.2.2.  Tunnel Mode IPv6 Format

   The Datagram contains one full IPv6 Packet per [RFC8200].  Used in
   tunnel mode and when the IP Version is 6 per the IP-Version header or
   explicit given target address.

2.2.3.  Flow Forwarding Format

   The Datagram contains only the IP payload.  This is defined as the
   payload following the IPv4 header and any options for IPv4, and for
   IPv6 as the payload following the IPv6 header and any extension
   header.  Used for Flow Forwarding mode.

2.2.4.  ICMP Message Format

   This datagram contains a summary message of the ICMP message received
   and validated for the respective IP flow.  The message format carries
   the ICMP packet for ICMPv4 [RFC0792] or ICMPv6 [RFC4443].  This
   format is chosen for forward compatibility.  From an implementation
   perspective the client don't need to verify the checksum or validate
   the header fields because that is done by the server.  However, some
   type codes, like IMCPv4 type 2, (Packet Too Big) carries an MTU field
   that the implementation want to read beyond understanding the meaning
   of the type and code combination.

3.  HTTP Headers

   Note: This section should be improved by clarifying if headers are in
   request, response or both.

3.1.  IP-Protocol Header for CONNECT-IP

   In order to construct the IP header the the proxy 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
   proxy, this information has to be provided by the client for each
   CONNECT-IP request for flow forwarding.

   IP-Protocol is a Item Structured Header [RFC8941].  Its value MUST be
   an Integer.  Its ABNF is:

     IP-Protocol = sf-integer

3.2.  IP-Version header for CONNECT-IP

   IP-Version is a Item Structured Header [RFC8941].  Its value MUST be
   an Integer and either 4 or 6.  This information is used by the proxy
   to check if the requested IP version is supported by the network that
   the proxy is connected to, as well as to check the destination or
   source IP address for compliance.

     IP-Version = sf-integer

3.3.  IP-Address header for CONNECT-IP

   IP-Address is an Item Structured Header [RFC8941].  Its value MUST be
   an String contain an IP address or IP address range of the same IP
   version as indicated in the IP-Version header.  The address must be
   specified in the format specified by TBD.

   This header is used to request the use of a certain IP address or IP
   address range by the client to be used as source IP address in tunnel
   mode.  If the IP-Address header is not presented, the proxy is
   implicitly requested to assign an IP address or IP address range and
   provide this information to the client with the HTTP response.

   If the the client does not provide an IP address or IP address range
   is has to wait for the proxy response before any payload data can be
   sent in tunnel mode.  If the request is denied by the proxy, any sent
   payload data will be discarded and a new CONNECT-IP request has to be

   The header is also used as a response header from the proxy to the
   client to indicate the actual IP address or IP address range that
   should be used by the client in tunnel mode or will be used by the
   proxy in flow forwarding mode.

     IP-Address = sf-string

3.4.  IP-Address-Handling Header for CONNECT-IP

   This header can be used to request the use of a stable address for
   multiple active flow forwarding associations.  The first association
   will be established with an IP selected by the proxy unless also the
   IP-Address header (Section 3.3) is provided and accepted by proxy.
   However, additional forwarding association can be requested by the
   client to use the same IP address as a previous request by specifying
   the stream ID as value in this header.  This header can also be used
   to ensure that a "new", not yet for this client used address is
   selected by setting a value that is larger than the maximum stream

   IP-Address-Handling is a Item Structured Header [RFC8941].  Its value
   MUST be an Integer and indicates the stream ID of the corresponding
   active flow forwarding association.  Its ABNF is:

     IP-Address-Handling = sf-integer

3.5.  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 proxy as a connection identifier in addition to the IP
   address and protocol tuple when multiple connections are proxied to
   the same target server for incoming traffic on the service address.

   Conn-ID is a Item Structured Header [RFC8941].  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.

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

4.  Client Connect-IP Request

4.1.  Requesting flow forwarding

   To request flow forwarding, 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.  Further the CONNECT-IP
   request MUST contain the IP-Protocol header (Section 3.1) and MAY
   contain the IP-Address-Handling (Section 3.4) or the Conn-ID
   (Section 3.5) header.

4.2.  Requesting tunnel mode

   In tunnel mode, the CONNECT-IP request MUST contain the IP-Version
   header to indicate if IPv4 or IPv6 is used for the IP packet in the
   tunnel payload.  Further, the request MAY contain an IP-Address
   header to request use of an IP address or IP address range.

5.  MASQUE server behavior

   Upon the establishment of a HTTP Connection with the proxy on its
   service addresses.  HTTP level capabilities will be exchanged in the
   HTTP SETTINGS frame.  This will determine if support of datagrams is
   indicated.  If indicated by the client, the MASQUE server SHALL send
   a H3_DATAGRAM SETTINGS parameter with a value of 1 to indicates is

   A MASQUE server that receives an IP-CONNECT request examines the
   target URL to determine if this request is for tunnel or flow
   forwarding mode.  Based on the mode it determines if the required
   headers are present and which of the optional headers that are

   The proxy maintains a database with mappings between the HTTP
   connections and stream IDs and the IP level selectors and Conn-ID
   information.  Using this database and the pool of available addresses
   and the requests IP-Address-Handling, Conn-ID, IP-Version, IP-Address
   headers (if included) to select a source IP address.  This selection
   for flow forwarding mode is further discussed below in Section 5.2.
   For Tunnel Mode, the proxy determine if the proposed IP address per
   IP-Version and IP-Address headers is possible to use if included,
   else selects a otherwise unused address from its pool.  For tunnel
   mode the IP selector for incoming traffic for this HTTP Connection
   and Stream ID is simply the IP destination address.

   Once the mapping is successfully established, the proxy sends a
   HEADERS frame containing a 2xx series status code to the client.  The
   response MUST contain an IP-Address header indicating the outgoing
   source IP address or IP address range selected by the proxy.

   All Datagram capsules received on that stream as well as all HTTP/3
   datagrams belonging to this CONNECT-IP association are processed for
   forwarding to the target server.  For flow forwarding mode the
   Datagram is processed as specified in Section 5.3 to produce IP
   packets that can be forwarded.  For tunnel-mode the complete IP
   packet are extracted from the Datagram and then forwarded as
   specified in Section 5.4.

   IP packets received from the target server are mapped to an active
   forwarding connection and are respectively forwarded in an CAPSULE
   DATAGRAM frame or HTTP/3 datagram to the client (see section
   Section 5.5 below).

5.1.  Error handling

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

5.2.  IP address selection in flow forwarding mode

   In flow forwarding mode the proxy constructs the IP header when
   sending the IP payload towards the target server and it selects an
   source IP address from its pool of IP addresses 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 proxy uses the source/destination address and protocol ID 3-tuple
   in order to map an incoming IP packet to an active forwarding
   connection.  The proxy MUST also consider if IP-Address-Handling
   header Section 3.4 is included and its value.  If the IP-Address-
   Handling header is not included and the there has been prior request
   the proxy SHOULD give the client the same source Address as the first
   flow forwarding request.  Given these constraints the MASQUE proxy
   MUST select a source IP address that leads to a unique tuple, and if
   that is not possible an error response is generated.  The same IP
   address MAY 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 as an
   identifier.  Therefore it is RECOMMENDED that clients are given
   unique addresses unless a large fraction of the pool has been

   If the Conn-ID header is provided, the proxy should use that field as
   an connection identifier together with protocol ID, source and
   destination address, as a 4-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.

   Note: Are we allowing multiple client's to share the same 3-tuple
   when using Conn-ID?  It might be good for privacy reasons however, it
   significantly increases the collision risk.

5.3.  Constructing the IP header in flow forwarding mode

   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.

   The proxy 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
   proxy 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 6.1.

5.4.  Decapsulation of tunnel mode IP Packets

   On receiving an HTTP Datagram containing any of the tunnel mode
   formats for IPv4 or IPv6 the proxy extracts the full IP packet.

   The proxy MUST verify that the extracted IP packet's source IP
   address matches any address associated with this CONNECTION-IP
   request, i.e. the assigned address or IP range.  This is to prevent
   source address spoofing in tunnel mode.

   Further the proxy should verify that the IP header length field
   correspond to the extracted packets length.

5.5.  Receiving an IP packet

   When the proxy receives an incoming IP packet on the external
   interface(s), it checks the packet selectors to find the mappings
   that match the given packet.

   If a client has a tunnel as well as multiple flow forwarding
   associations, the proxy need to check the mappings for the flow
   forwarding associations first, and only send it over the the tunnel
   association if no active flow forwarding is found.

   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 above is achieve by using the selector with the most number of
   fields that match the packet.

   If both datagram and stream based forwarding is supported, it is
   recommended for the proxy to use the same encapsulation as most
   recently used by the client or datagrams as default.  Further
   considerations might be needed here.

6.  Additional signalling

   Context ID as defined by [I-D.ietf-masque-h3-datagram] can be used to
   provide additional per association or per-payload signals.  As
   [I-D.ietf-masque-h3-datagram] is still work in progress, registration
   and use of Context IDs is left for future work at this point.

6.1.  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.

   The probing and verification in the upper layer protocol of end-to-
   end ECN requires per packet control over what value is set on IP
   packet transmission as well as which of all values are received by
   the proxy.  The QUIC specification is providing one such example in
   Section 13.4 of [RFC9000].  Thus in flow forwarding mode the proxy
   needs to be able to set and read the ECN values in sent and received
   IP packets respectively.  This may motivate that this functionality
   is optional to implement, even if supporting CONNECT-IP
   implementations in general will need to handle IP packets and their
   fields with fine grained control.  If optional some negotiation
   mechanism is needed.

   Possible realizations are:

   a) always have two bits before payload in flow forwarding model, e.g.
   by including the whole Type of Service (TOS) byte, which would also
   enable DSCP setting and reading.

   b) use 4 different context IDs depending on what ECN field value was
   received or should be set.

   This is work in process and will be further specified in a future
   version of this document.

6.2.  ICMP handling

   ICMP messages are directly forwarded in tunneling mode.  In flow
   forwarding mode a ICMP datagram format (Section 2.2.4) is used to
   send the information from some ICMP message to the client.

   The proxy upon receiving an ICMP message with a destination of an IP
   address it performs flow forwarding on it needs to process the ICMP
   message.  First it should validate that the ICMP message and find if
   it matches any of its IP flow selectors (including Conn-ID).  In case
   there are multiple matching use the IP selector with the most number
   of field that matches fully.

   Some messages may be applicable both to the proxy and the client.
   For example an verified ICMPv6 Packet Too Big is applicable both to
   the proxy and the client.  Others like ICMPv6 Destination Unreachable
   (Type=1), Code=3 (Address unreachable) and Code=4 (Port unreachable)
   is only possible to act on by the client.

   QUESTION: Which ICMP messages should be suppressed by the proxy?

   If a matching IP selector was chosen, then lookup the mapping for the
   HTTP connection and Stream ID which this message should be sent to.
   Encapsulate the received ICMP message in the ICMP datagram format and
   send it to the client.

6.3.  MTU considerations

   The use of QUIC as a encapsulation between the client and proxy
   introduces additional overhead.  If datagrams are used to encapsulate
   packets between the proxy and client, the end-to-end packets must fit
   within one datagram but the size of the datagrams is limited by the
   tunneling encapsulation overhead.

   In forwarding mode the client is usually also the tunnel endpoint
   that knows about the tunnel overhead and can therefore restrict the
   size of the packets on the end-to-end connection accordingly.
   However, the target endpoint is usually not aware of the tunnel
   overhead.  Additional signalling on the end-to-end connection from
   the client to the target endpoint might be needed to restrict the
   packet size.  If QUIC is also used as end-to-end protocol, this could
   be realized by the transport parameter.  In additional, signal from
   the proxy to the client could be provided as an extension to indicate
   the tunnel overhand more accurately and flexibly over time.  Such
   signalling might the realized on the HTTP layer in order to take any
   additional limitations by HTTP intermediates into account.

   If the proxy receives an incoming packet from a target endpoint that
   is too big to fit within a datagram on the tunnel connection, the
   proxy MAY either forward the packet encapsulated in the CAPSULE
   frames on the respective stream or, if IPv4 with DF bit set or IPv6
   is used, the proxy MAY reject the packet and send an ICMPv4 Packet
   type 3 code 4, or ICMPv6 Too Big (PTB) message.

7.  Examples


8.  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

9.  IANA considerations

9.1.  HTTP Method

   This document (if published as RFC) registers "CONNECT-IP" in the
   HTTP Method Registry maintained at <

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

9.2.  HTTP Header

   This document (if published as RFC) registers the following header in
   the "Permanent Message Header Field Names" registry maintained at

     | Header Field Name   | Protocol | Status |   Reference   |
     | Conn-ID             |   http   |  exp   | This document |
     | IP-Protocol         |   http   |  exp   | This document |
     | IP-Address          |   http   |  exp   | This document |
     | IP-Address-Handling |   http   |  exp   | This document |
     | IP-Verison          |   http   |  exp   | This document |



Normative References

              Fielding, R. T., Nottingham, M., and J. Reschke,
              "HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-messaging-16, 27 May 2021,

              Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
              Semantics", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-semantics-16, 27 May 2021,

              Schinazi, D., "The CONNECT-UDP HTTP Method", Work in
              Progress, Internet-Draft, draft-ietf-masque-connect-udp-
              03, 5 January 2021,

              Schinazi, D. and L. Pardue, "Using QUIC Datagrams with
              HTTP/3", Work in Progress, Internet-Draft, draft-ietf-
              masque-h3-datagram-02, 26 May 2021,

              Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
              Datagram Extension to QUIC", Work in Progress, Internet-
              Draft, draft-ietf-quic-datagram-02, 16 February 2021,

              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-34, 2 February 2021,

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

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

   [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,

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

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

   [RFC8941]  Nottingham, M. and P-H. Kamp, "Structured Field Values for
              HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,

   [RFC9000]  Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", RFC 9000,
              DOI 10.17487/RFC9000, May 2021,

Informative References

              Chernyakhovsky, A., McCall, D., and D. Schinazi,
              "Requirements for a MASQUE Protocol to Proxy IP Traffic",
              Work in Progress, Internet-Draft, draft-ietf-masque-ip-
              proxy-reqs-02, 30 April 2021,

              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-02, 12 July 2021,

   [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,

Authors' Addresses

   Mirja Kuehlewind


   Magnus Westerlund


   Marcus Ihlar


   Zaheduzzaman Sarker