Internet-Draft Proxying IP in HTTP January 2023
Pauly, et al. Expires 24 July 2023 [Page]
Workgroup:
MASQUE
Internet-Draft:
draft-ietf-masque-connect-ip-latest
Updates:
9298 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
T. Pauly, Ed.
Apple Inc.
D. Schinazi
Google LLC
A. Chernyakhovsky
Google LLC
M. Kuehlewind
Ericsson
M. Westerlund
Ericsson

Proxying IP in HTTP

Abstract

This document describes how to proxy IP packets in HTTP. This protocol is similar to UDP proxying in HTTP, but allows transmitting arbitrary IP packets. More specifically, this document defines a protocol that allows an HTTP client to create an IP tunnel through an HTTP server that acts as a proxy. This document updates RFC 9298.

About This Document

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

The latest revision of this draft can be found at https://ietf-wg-masque.github.io/draft-ietf-masque-connect-ip/draft-ietf-masque-connect-ip.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-masque-connect-ip/.

Discussion of this document takes place on the MASQUE Working Group mailing list (mailto:masque@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/masque/. Subscribe at https://www.ietf.org/mailman/listinfo/masque/.

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

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 24 July 2023.

Table of Contents

1. Introduction

HTTP provides the CONNECT method (see Section 9.3.6 of [HTTP]) for creating a TCP [TCP] tunnel to a destination and a similar mechanism for UDP [CONNECT-UDP]. However, these mechanisms cannot tunnel other protocols nor convey fields of the IP header.

This document describes a protocol for tunnelling IP to an HTTP server acting as an IP-specific proxy over HTTP. This can be used for various use cases such as point-to-network VPN, secure point-to-point communication, or general-purpose packet tunnelling.

IP proxying operates similarly to UDP proxying [CONNECT-UDP], whereby the proxy itself is identified with an absolute URL, optionally containing the traffic's destination. Clients generate these URLs using a URI Template [TEMPLATE], as described in Section 3.

This protocol supports all existing versions of HTTP by using HTTP Datagrams [HTTP-DGRAM]. When using HTTP/2 [HTTP/2] or HTTP/3 [HTTP/3], it uses HTTP Extended CONNECT as described in [EXT-CONNECT2] and [EXT-CONNECT3]. When using HTTP/1.x [HTTP/1.1], it uses HTTP Upgrade as defined in Section 7.8 of [HTTP].

2. 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 "IP proxy" to refer to the HTTP server that responds to the IP proxying request. If there are HTTP intermediaries (as defined in Section 3.7 of [HTTP]) between the client and the proxy, those are referred to as "intermediaries" in this document.

Note that, when the HTTP version in use does not support multiplexing streams (such as HTTP/1.1), any reference to "stream" in this document represents the entire connection.

3. Configuration of Clients

Clients are configured to use IP proxying over HTTP via an URI Template [TEMPLATE]. The URI template MAY contain two variables: "target" and "ipproto" (Section 4.5). The optionality of the variables needs to be considered when defining the template so that either the variable is self-identifying or it is possible to exclude it in the syntax.

Examples are shown below:

https://example.org/.well-known/masque/ip/{target}/{ipproto}/
https://proxy.example.org:4443/masque/ip?t={target}&i={ipproto}
https://proxy.example.org:4443/masque/ip{?target,ipproto}
https://masque.example.org/?user=bob
Figure 1: URI Template Examples

The following requirements apply to the URI Template:

Clients SHOULD validate the requirements above; however, clients MAY use a general-purpose URI Template implementation that lacks this specific validation. If a client detects that any of the requirements above are not met by a URI Template, the client MUST reject its configuration and abort the request without sending it to the IP proxy.

As with UDP proxying, some client configurations for IP proxies will only allow the user to configure the proxy host and proxy port. Clients with such limitations MAY attempt to access IP proxying capabilities using the default template, which is defined as: "https://$PROXY_HOST:$PROXY_PORT/.well-known/masque/ip/{target}/{ipproto}/", where $PROXY_HOST and $PROXY_PORT are the configured host and port of the IP proxy, respectively. IP proxy deployments SHOULD offer service at this location if they need to interoperate with such clients.

4. Tunnelling IP over HTTP

To allow negotiation of a tunnel for IP over HTTP, this document defines the "connect-ip" HTTP Upgrade Token. The resulting IP tunnels use the Capsule Protocol (see Section 3.2 of [HTTP-DGRAM]) with HTTP Datagrams in the format defined in Section 6.

To initiate an IP tunnel associated with a single HTTP stream, a client issues a request containing the "connect-ip" upgrade token. The target of the tunnel is indicated by the client to the IP proxy via the "target_host" and "target_port" variables of the URI Template; see Section 3.

When sending its IP proxying request, the client SHALL perform URI template expansion to determine the path and query of its request, see Section 3.

A successful response indicates that the IP proxy is willing to open an IP forwarding tunnel between it and the client. Any response other than a successful response indicates that the tunnel has not been formed.

The lifetime of the IP forwarding tunnel is tied to the IP proxying request stream. Closing that stream (in HTTP/3 via the FIN bit on a QUIC STREAM frame, or a QUIC RESET_STREAM frame) closes the associated IP tunnel.

Along with a successful response, the IP proxy can send capsules to assign addresses and advertise routes to the client (Section 4.6). The client can also assign addresses and advertise routes to the IP proxy for network-to-network routing.

By virtue of the definition of the Capsule Protocol (see Section 3.2 of [HTTP-DGRAM]), IP proxying requests do not carry any message content. Similarly, successful IP proxying responses also do not carry any message content.

4.1. HTTP/1.1 Request

When using HTTP/1.1 [HTTP/1.1], an IP proxying request will meet the following requirements:

  • the method SHALL be "GET".
  • the request SHALL include a single Host header field containing the origin of the IP proxy.
  • the request SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per Section 7.6.1 of [HTTP]).
  • the request SHALL include an Upgrade header field with value "connect-ip".

An IP proxying request that does not conform to these restrictions is malformed. The recipient of such a malformed request MUST respond with an error and SHOULD use the 400 (Bad Request) status code.

4.2. HTTP/1.1 Response

The IP 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 response SHALL include a Connection header field with value "Upgrade" (note that this requirement is case-insensitive as per Section 7.6.1 of [HTTP]).
  • the response SHALL include a single Upgrade header field with value "connect-ip".
  • the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].

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

4.3. HTTP/2 and HTTP/3 Requests

When using HTTP/2 [HTTP/2] or HTTP/3 [HTTP/3], IP proxying requests use HTTP Extended CONNECT. This requires that servers send an HTTP Setting as specified in [EXT-CONNECT2] and [EXT-CONNECT3] and that requests use HTTP pseudo-header fields with the following requirements:

  • The :method pseudo-header field SHALL be "CONNECT".
  • The :protocol pseudo-header field SHALL be "connect-ip".
  • The :authority pseudo-header field SHALL contain the authority of the IP proxy.
  • The :path and :scheme pseudo-header fields SHALL NOT be empty. Their values SHALL contain the scheme and path from the URI Template after the URI Template expansion process has been completed; see Section 3. Variables in the URI template can determine the scope of the request, such as requesting full-tunnel IP packet forwarding, or a specific proxied flow; see Section 4.5.

An IP proxying request that does not conform to these restrictions is malformed (see Section 8.1.1 of [HTTP/2] and Section 4.1.2 of [HTTP/3]).

4.4. HTTP/2 and HTTP/3 Responses

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

  • the HTTP status code on the response SHALL be in the 2xx (Successful) range.
  • the response SHALL meet the requirements of HTTP responses that start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].

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

4.5. Limiting Request Scope

Unlike UDP proxying requests, which require specifying a target host, IP proxying requests can allow endpoints to send arbitrary IP packets to any host. The client can choose to restrict a given request to a specific IP prefix or IP protocol by adding parameters to its request. When the IP proxy knows that a request is scoped to a target prefix or protocol, it can leverage this information to optimize its resource allocation; for example, the IP proxy can assign the same public IP address to two IP proxying requests that are scoped to different prefixes and/or different protocols.

The scope of the request is indicated by the client to the IP proxy via the "target" and "ipproto" variables of the URI Template; see Section 3. Both the "target" and "ipproto" variables are optional; if they are not included, they are considered to carry the wildcard value "*".

target:

The variable "target" contains a hostname or IP prefix of a specific host to which the client wants to proxy packets. If the "target" variable is not specified or its value is "*", the client is requesting to communicate with any allowable host. "target" supports using DNS names, IPv6 prefixes and IPv4 prefixes. Note that IPv6 scoped addressing zone identifiers are not supported. If the target is an IP prefix (IP address optionally followed by a percent-encoded slash followed by the prefix length in bits), the request will only support a single IP version. If the target is a hostname, the IP proxy is expected to perform DNS resolution to determine which route(s) to advertise to the client. The IP proxy SHOULD send a ROUTE_ADVERTISEMENT capsule that includes routes for all addresses that were resolved for the requested hostname, that are accessible to the IP proxy, and belong to an address family for which the IP proxy also sends an Assigned Address.

ipproto:

The variable "ipproto" contains an IP protocol number, as defined in the "Assigned Internet Protocol Numbers" IANA registry maintained at <https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml>. If present, it specifies that a client only wants to proxy a specific IP protocol for this request. If the value is "*", or the variable is not included, the client is requesting to use any IP protocol.

Using the terms IPv6address, IPv4address, and reg-name from [URI], the "target" and "ipproto" variables MUST adhere to the format in Figure 2, using notation from [ABNF]. Additionally:

  • if "target" contains an IPv6 literal or prefix, the colons (":") MUST be percent-encoded. For example, if the target host is "2001:db8::42", it will be encoded in the URI as "2001%3Adb8%3A%3A42".
  • If present, the IP prefix length in "target" SHALL be preceded by a percent-encoded slash ("/"): "%2F". The IP prefix length MUST represent an integer between 0 and the length of the IP address in bits, inclusive.
  • "ipproto" MUST represent an integer between 0 and 255 inclusive, or the wildcard value "*".
target = IPv6prefix / IPv4prefix / reg-name / "*"
IPv6prefix = IPv6address ["%2F" 1*3DIGIT]
IPv4prefix = IPv4address ["%2F" 1*2DIGIT]
ipproto = 1*3DIGIT / "*"
Figure 2: URI Template Variable Format

4.6. Capsules

This document defines multiple new capsule types that allow endpoints to exchange IP configuration information. Both endpoints MAY send any number of these new capsules.

4.6.1. ADDRESS_ASSIGN Capsule

The ADDRESS_ASSIGN capsule (see Section 11.4 for the value of the capsule type) allows an endpoint to inform its peer of the list of IP addresses or prefixes it has assigned to it. Every capsule contains the full list of IP prefixes currently assigned to the receiver. Any of these addresses can be used as the source address on IP packets originated by the receiver of this capsule.

ADDRESS_ASSIGN Capsule {
  Type (i) = ADDRESS_ASSIGN,
  Length (i),
  Assigned Address (..) ...,
}
Figure 3: ADDRESS_ASSIGN Capsule Format

The ADDRESS_ASSIGN capsule contains a sequence of zero or more Assigned Addresses.

Assigned Address {
  Request ID (i),
  IP Version (8),
  IP Address (32..128),
  IP Prefix Length (8),
}
Figure 4: Assigned Address Format
Request ID:

Request identifier, encoded as a variable-length integer. If this address assignment is in response to an Address Request (see Section 4.6.2), then this field SHALL contain the value of the corresponding field in the request. Otherwise, this field SHALL be zero.

IP Version:

IP Version of this address assignment, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

IP Address:

Assigned IP address. If the IP Version field has value 4, the IP Address field SHALL have a length of 32 bits. If the IP Version field has value 6, the IP Address field SHALL have a length of 128 bits.

IP Prefix Length:

The number of bits in the IP Address that are used to define the prefix that is being assigned, encoded as an unsigned 8-bit integer. This MUST be less than or equal to the length of the IP Address field, in bits. If the prefix length is equal to the length of the IP Address, the receiver of this capsule is only allowed to send packets from a single source address. If the prefix length is less than the length of the IP address, the receiver of this capsule is allowed to send packets from any source address that falls within the prefix.

If an ADDRESS_ASSIGN capsule does not contain an address that was previously transmitted in another ADDRESS_ASSIGN capsule, that indicates that the address has been removed. An ADDRESS_ASSIGN capsule can also be empty, indicating that all addresses have been removed.

In some deployments of IP proxying in HTTP, an endpoint needs to be assigned an address by its peer before it knows what source address to set on its own packets. For example, in the Remote Access case (Section 8.1) the client cannot send IP packets until it knows what address to use. In these deployments, the endpoint that is expecting an address assignment MUST send an ADDRESS_REQUEST capsule. This isn't required if the endpoint does not need any address assignment, for example when it is configured out-of-band with static addresses.

While ADDRESS_ASSIGN capsules are commonly sent in response to ADDRESS_REQUEST capsules, endpoints MAY send ADDRESS_ASSIGN capsules unprompted.

4.6.2. ADDRESS_REQUEST Capsule

The ADDRESS_REQUEST capsule (see Section 11.4 for the value of the capsule type) allows an endpoint to request assignment of IP addresses from its peer. The capsule allows the endpoint to optionally indicate a preference for which address it would get assigned.

ADDRESS_REQUEST Capsule {
  Type (i) = ADDRESS_REQUEST,
  Length (i),
  Requested Address (..) ...,
}
Figure 5: ADDRESS_REQUEST Capsule Format

The ADDRESS_REQUEST capsule contains a sequence of one or more Requested Addresses.

Requested Address {
  Request ID (i),
  IP Version (8),
  IP Address (32..128),
  IP Prefix Length (8),
}
Figure 6: Requested Address Format
Request ID:

Request identifier, encoded as a variable-length integer. This is the identifier of this specific address request. Each request from a given endpoint carries a different identifier. Request IDs MUST NOT be reused by an endpoint, and MUST NOT be zero.

IP Version:

IP Version of this address request, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

IP Address:

Requested IP address. If the IP Version field has value 4, the IP Address field SHALL have a length of 32 bits. If the IP Version field has value 6, the IP Address field SHALL have a length of 128 bits.

IP Prefix Length:

Length of the IP Prefix requested, in bits, encoded as an unsigned 8-bit integer. MUST be lesser or equal to the length of the IP Address field, in bits.

If the IP Address is all-zero (0.0.0.0 or ::), this indicates that the sender is requesting an address of that address family but does not have a preference for a specific address. In that scenario, the prefix length still indicates the sender's preference for the prefix length it is requesting.

Upon receiving the ADDRESS_REQUEST capsule, an endpoint SHOULD assign an IP address to its peer, and then respond with an ADDRESS_ASSIGN capsule to inform the peer of the assignment. Note that the receiver of the ADDRESS_REQUEST capsule is not required to assign the requested address, and that it can also assign some requested addresses but not others.

If an endpoint receives an ADDRESS_REQUEST capsule that contains zero Requested Addresses, it MUST abort the IP proxying request stream.

4.6.3. ROUTE_ADVERTISEMENT Capsule

The ROUTE_ADVERTISEMENT capsule (see Section 11.4 for the value of the capsule type) allows an endpoint to communicate to its peer that it is willing to route traffic to a set of IP address ranges. This indicates that the sender has an existing route to each address range, and notifies its peer that if the receiver of the ROUTE_ADVERTISEMENT capsule sends IP packets for one of these ranges in HTTP Datagrams, the sender of the capsule will forward them along its preexisting route. Any address which is in one of the address ranges can be used as the destination address on IP packets originated by the receiver of this capsule.

ROUTE_ADVERTISEMENT Capsule {
  Type (i) = ROUTE_ADVERTISEMENT,
  Length (i),
  IP Address Range (..) ...,
}
Figure 7: ROUTE_ADVERTISEMENT Capsule Format

The ROUTE_ADVERTISEMENT capsule contains a sequence of IP Address Ranges.

IP Address Range {
  IP Version (8),
  Start IP Address (32..128),
  End IP Address (32..128),
  IP Protocol (8),
}
Figure 8: IP Address Range Format
IP Version:

IP Version of this range, encoded as an unsigned 8-bit integer. MUST be either 4 or 6.

Start IP Address and End IP Address:

Inclusive start and end IP address of the advertised range. If the IP Version field has value 4, these fields SHALL have a length of 32 bits. If the IP Version field has value 6, these fields SHALL have a length of 128 bits. The Start IP Address MUST be lesser or equal to the End IP Address.

IP Protocol:

The Internet Protocol Number for traffic that can be sent to this range, encoded as an unsigned 8-bit integer. If the value is 0, all protocols are allowed. ICMP traffic is always allowed, regardless of the value of this field.

Upon receiving the ROUTE_ADVERTISEMENT capsule, an endpoint MAY start routing IP packets in these ranges to its peer.

Each ROUTE_ADVERTISEMENT contains the full list of address ranges. If multiple ROUTE_ADVERTISEMENT capsules are sent in one direction, each ROUTE_ADVERTISEMENT capsule supersedes prior ones. In other words, if a given address range was present in a prior capsule but the most recently received ROUTE_ADVERTISEMENT capsule does not contain it, the receiver will consider that range withdrawn.

If multiple ranges using the same IP protocol were to overlap, some routing table implementations might reject them. To prevent overlap, the ranges are ordered; this places the burden on the sender and makes verification by the receiver much simpler. If an IP Address Range A precedes an IP address range B in the same ROUTE_ADVERTISEMENT capsule, they MUST follow these requirements:

  • IP Version of A MUST be lesser or equal than IP Version of B
  • If the IP Version of A and B are equal, the IP Protocol of A MUST be lesser or equal than IP Protocol of B.
  • If the IP Version and IP Protocol of A and B are both equal, the End IP Address of A MUST be strictly less than the Start IP Address of B.

If an endpoint receives a ROUTE_ADVERTISEMENT capsule that does not meet these requirements, it MUST abort the IP proxying request stream.

5. Context Identifiers

The mechanism for proxying IP in HTTP defined in this document allows future extensions to exchange HTTP Datagrams that carry different semantics from IP payloads. Some of these extensions can augment IP payloads with additional data or compress IP header fields, while others can exchange data that is completely separate from IP payloads. In order to accomplish this, all HTTP Datagrams associated with IP proxying request streams start with a Context ID field; see Section 6.

Context IDs are 62-bit integers (0 to 262-1). Context IDs are encoded as variable-length integers; see Section 16 of [QUIC]. The Context ID value of 0 is reserved for IP payloads, while non-zero values are dynamically allocated. Non-zero even-numbered Context IDs are client-allocated, and odd-numbered Context IDs are proxy-allocated. The Context ID namespace is tied to a given HTTP request; it is possible for a Context ID with the same numeric value to be simultaneously allocated in distinct requests, potentially with different semantics. Context IDs MUST NOT be re-allocated within a given HTTP namespace but MAY be allocated in any order. The Context ID allocation restrictions to the use of even-numbered and odd-numbered Context IDs exist in order to avoid the need for synchronization between endpoints. However, once a Context ID has been allocated, those restrictions do not apply to the use of the Context ID; it can be used by any client or IP proxy, independent of which endpoint initially allocated it.

Registration is the action by which an endpoint informs its peer of the semantics and format of a given Context ID. This document does not define how registration occurs. Future extensions MAY use HTTP header fields or capsules to register Context IDs. Depending on the method being used, it is possible for datagrams to be received with Context IDs that have not yet been registered. For instance, this can be due to reordering of the packet containing the datagram and the packet containing the registration message during transmission.

6. HTTP Datagram Payload Format

When associated with IP proxying request streams, the HTTP Datagram Payload field of HTTP Datagrams (see [HTTP-DGRAM]) has the format defined in Figure 9. Note that when HTTP Datagrams are encoded using QUIC DATAGRAM frames, the Context ID field defined below directly follows the Quarter Stream ID field which is at the start of the QUIC DATAGRAM frame payload:

IP Proxying HTTP Datagram Payload {
  Context ID (i),
  Payload (..),
}
Figure 9: IP Proxying HTTP Datagram Format
Context ID:

A variable-length integer that contains the value of the Context ID. If an HTTP/3 datagram which carries an unknown Context ID is received, the receiver SHALL either drop that datagram silently or buffer it temporarily (on the order of a round trip) while awaiting the registration of the corresponding Context ID.

Payload:

The payload of the datagram, whose semantics depend on value of the previous field. Note that this field can be empty.

IP packets are encoded using HTTP Datagrams with the Context ID set to zero. When the Context ID is set to zero, the Payload field contains a full IP packet (from the IP Version field until the last byte of the IP Payload).

Clients MAY optimistically start sending proxied IP packets before receiving the response to its IP proxying request, noting however that those may not be processed by the IP proxy if it responds to the request with a failure, or if the datagrams are received by the IP proxy before the request. Since receiving addresses and routes is required in order to know that a packet can be sent through the tunnel, such optimistic packets might be dropped by the IP proxy if it chooses to provide different addressing or routing information than what the client assumed.

When an endpoint receives an HTTP Datagram containing an IP packet, it will parse the packet's IP header, perform any local policy checks (e.g., source address validation), check their routing table to pick an outbound interface, and then send the IP packet on that interface or pass it to a local application.

In the other direction, when an endpoint receives an IP packet, it checks to see if the packet matches the routes mapped for an IP tunnel, and performs the same forwarding checks as above before transmitting the packet over HTTP Datagrams.

Note that endpoints will decrement the IP Hop Count (or TTL) upon encapsulation but not decapsulation. In other words, the Hop Count is decremented right before an IP packet is transmitted in an HTTP Datagram. This prevents infinite loops in the presence of routing loops, and matches the choices in IPsec [IPSEC].

IPv6 requires that every link have an MTU of at least 1280 bytes [IPv6]. Since IP proxying in HTTP conveys IP packets in HTTP Datagrams and those can in turn be sent in QUIC DATAGRAM frames which cannot be fragmented [DGRAM], the MTU of an IP tunnel can be limited by the MTU of the QUIC connection that IP proxying is operating over. This can lead to situations where the IPv6 minimum link MTU is violated. IP proxying endpoints that support IPv6 MUST ensure that the IP tunnel link MTU is at least 1280 (i.e., that they can send HTTP Datagrams with payloads of at least 1280 bytes). This can be accomplished using various techniques:

If an endpoint is using QUIC DATAGRAM frames to convey IPv6 packets, and it detects that the QUIC MTU is too low to allow sending 1280 bytes, it MUST abort the IP proxying request stream.

Endpoints MAY implement additional filtering policies on the IP packets they forward.

7. Error Signalling

Since IP proxying endpoints often forward IP packets onwards to other network interfaces, they need to handle errors in the forwarding process. For example, forwarding can fail if the endpoint does not have a route for the destination address, or if it is configured to reject a destination prefix by policy, or if the MTU of the outgoing link is lower than the size of the packet to be forwarded. In such scenarios, IP proxying endpoints SHOULD use ICMP [ICMP] [ICMPv6] to signal the forwarding error to its peer.

Endpoints are free to select the most appropriate ICMP errors to send. Some examples that are relevant for IP proxying include:

In order to receive these errors, endpoints need to be prepared to receive ICMP packets. If an endpoint sends ROUTE_ADVERTISEMENT capsules, its routes SHOULD include an allowance for receiving ICMP messages. If an endpoint does not send ROUTE_ADVERTISEMENT capsules, such as a client opening an IP flow through an IP proxy, it SHOULD process proxied ICMP packets from its peer in order to receive these errors. Note that ICMP messages can originate from a source address different from that of the IP proxying peer.

8. Examples

IP proxying in HTTP enables many different use cases that can benefit from IP packet proxying and tunnelling. These examples are provided to help illustrate some of the ways in which IP proxying in HTTP can be used.

8.1. Remote Access VPN

The following example shows a point-to-network VPN setup, where a client receives a set of local addresses, and can send to any remote host through the IP proxy. Such VPN setups can be either full-tunnel or split-tunnel.

IP A IP B IP D IP IP C Client IP Subnet C ? Proxy IP E IP ...
Figure 10: VPN Tunnel Setup

In this case, the client does not specify any scope in its request. The IP proxy assigns the client an IPv4 address (192.0.2.11) and a full-tunnel route of all IPv4 addresses (0.0.0.0/0). The client can then send to any IPv4 host using a source address in its assigned prefix.

[[ From Client ]]             [[ From IP Proxy ]]

SETTINGS
  H3_DATAGRAM = 1

                              SETTINGS
                                ENABLE_CONNECT_PROTOCOL = 1
                                H3_DATAGRAM = 1

STREAM(44): HEADERS
:method = CONNECT
:protocol = connect-ip
:scheme = https
:path = /vpn
:authority = proxy.example.com
capsule-protocol = ?1

                              STREAM(44): HEADERS
                              :status = 200
                              capsule-protocol = ?1

                              STREAM(44): CAPSULE
                              Capsule Type = ADDRESS_ASSIGN
                              (Request ID = 0
                               IP Version = 4
                               IP Address = 192.0.2.11
                               IP Prefix Length = 32)

                              STREAM(44): CAPSULE
                              Capsule Type = ROUTE_ADVERTISEMENT
                              (IP Version = 4
                               Start IP Address = 0.0.0.0
                               End IP Address = 255.255.255.255
                               IP Protocol = 0) // Any

DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated IP Packet

                              DATAGRAM
                              Quarter Stream ID = 11
                              Context ID = 0
                              Payload = Encapsulated IP Packet
Figure 11: VPN Full-Tunnel Example

A setup for a split-tunnel VPN (the case where the client can only access a specific set of private subnets) is quite similar. In this case, the advertised route is restricted to 192.0.2.0/24, rather than 0.0.0.0/0.

[[ From Client ]]             [[ From IP Proxy ]]

                              STREAM(44): CAPSULE
                              Capsule Type = ADDRESS_ASSIGN
                              (Request ID = 0
                               IP Version = 4
                               IP Address = 192.0.2.42
                               IP Prefix Length = 32)

                              STREAM(44): CAPSULE
                              Capsule Type = ROUTE_ADVERTISEMENT
                              (IP Version = 4
                               Start IP Address = 192.0.2.0
                               End IP Address = 192.0.2.255
                               IP Protocol = 0) // Any
Figure 12: VPN Split-Tunnel Capsule Example

8.2. IP Flow Forwarding

The following example shows an IP flow forwarding setup, where a client requests to establish a forwarding tunnel to target.example.com using SCTP (IP protocol 132), and receives a single local address and remote address it can use for transmitting packets. A similar approach could be used for any other IP protocol that isn't easily proxied with existing HTTP methods, such as ICMP, ESP, etc.

IP A IP B IP IP C Client IP C D Proxy IP D
Figure 13: Proxied Flow Setup

In this case, the client specfies both a target hostname and an IP protocol number in the scope of its request, indicating that it only needs to communicate with a single host. The IP proxy is able to perform DNS resolution on behalf of the client and allocate a specific outbound socket for the client instead of allocating an entire IP address to the client. In this regard, the request is similar to a traditional CONNECT proxy request.

The IP proxy assigns a single IPv6 address to the client (2001:db8:1234::a) and a route to a single IPv6 host (2001:db8:3456::b), scoped to SCTP. The client can send and receive SCTP IP packets to the remote host.

[[ From Client ]]             [[ From IP Proxy ]]

SETTINGS
  H3_DATAGRAM = 1

                              SETTINGS
                                ENABLE_CONNECT_PROTOCOL = 1
                                H3_DATAGRAM = 1

STREAM(44): HEADERS
:method = CONNECT
:protocol = connect-ip
:scheme = https
:path = /proxy?target=target.example.com&ipproto=132
:authority = proxy.example.com
capsule-protocol = ?1

                              STREAM(44): HEADERS
                              :status = 200
                              capsule-protocol = ?1

                              STREAM(44): CAPSULE
                              Capsule Type = ADDRESS_ASSIGN
                              (Request ID = 0
                               IP Version = 6
                               IP Address = 2001:db8:1234::a
                               IP Prefix Length = 128)

                              STREAM(44): CAPSULE
                              Capsule Type = ROUTE_ADVERTISEMENT
                              (IP Version = 6
                               Start IP Address = 2001:db8:3456::b
                               End IP Address = 2001:db8:3456::b
                               IP Protocol = 132)

DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated SCTP/IP Packet

                              DATAGRAM
                              Quarter Stream ID = 11
                              Context ID = 0
                              Payload = Encapsulated SCTP/IP Packet
Figure 14: Proxied SCTP Flow Example

8.3. Proxied Connection Racing

The following example shows a setup where a client is proxying UDP packets through an IP proxy in order to control connection establishment racing through an IP proxy, as defined in Happy Eyeballs [HEv2]. This example is a variant of the proxied flow, but highlights how IP-level proxying can enable new capabilities even for TCP and UDP.

IP A IP B IP C IP E Client IP C E IP D F Proxy IP F IP D
Figure 15: Proxied Connection Racing Setup

As with proxied flows, the client specfies both a target hostname and an IP protocol number in the scope of its request. When the IP proxy performs DNS resolution on behalf of the client, it can send the various remote address options to the client as separate routes. It can also ensure that the client has both IPv4 and IPv6 addresses assigned.

The IP proxy assigns the client both an IPv4 address (192.0.2.3) and an IPv6 address (2001:db8:1234::a) to the client, as well as an IPv4 route (198.51.100.2) and an IPv6 route (2001:db8:3456::b), which represent the resolved addresses of the target hostname, scoped to UDP. The client can send and recieve UDP IP packets to the either of the IP proxy addresses to enable Happy Eyeballs through the IP proxy.

[[ From Client ]]             [[ From IP Proxy ]]

SETTINGS
  H3_DATAGRAM = 1

                              SETTINGS
                                ENABLE_CONNECT_PROTOCOL = 1
                                H3_DATAGRAM = 1

STREAM(44): HEADERS
:method = CONNECT
:protocol = connect-ip
:scheme = https
:path = /proxy?ipproto=17
:authority = proxy.example.com
capsule-protocol = ?1

                              STREAM(44): HEADERS
                              :status = 200
                              capsule-protocol = ?1

                              STREAM(44): CAPSULE
                              Capsule Type = ADDRESS_ASSIGN
                              (Request ID = 0
                               IP Version = 4
                               IP Address = 192.0.2.3
                               IP Prefix Length = 32),
                              (Request ID = 0
                               IP Version = 6
                               IP Address = 2001:db8::1234:1234
                               IP Prefix Length = 128)

                              STREAM(44): CAPSULE
                              Capsule Type = ROUTE_ADVERTISEMENT
                              (IP Version = 4
                               Start IP Address = 198.51.100.2
                               End IP Address = 198.51.100.2
                               IP Protocol = 17),
                              (IP Version = 6
                               Start IP Address = 2001:db8:3456::b
                               End IP Address = 2001:db8:3456::b
                               IP Protocol = 17)
...

DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated IPv6 Packet

DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated IPv4 Packet

Figure 16: Proxied Connection Racing Example

9. Extensibility Considerations

Extensions to IP proxying in HTTP can define behavior changes to this mechanism. Such extensions SHOULD define new capsule types to exchange configuration information if needed. It is RECOMMENDED for extensions that modify addressing to specify that their extension capsules be sent before the ADDRESS_ASSIGN capsule and that they do not take effect until the ADDRESS_ASSIGN capsule is parsed. This allows modifications to address assignement to operate atomically. Similarly, extensions that modify routing SHOULD behave similarly with regards to the ROUTE_ADVERTISEMENT capsule.

10. Security Considerations

There are significant risks in allowing arbitrary clients to establish a tunnel that permits sending to arbitrary hosts, as that could allow bad actors to send traffic and have it attributed to the IP proxy. IP proxies SHOULD restrict its use to authenticated users. The HTTP Authorization header [HTTP] MAY be used to authenticate clients. More complex authentication schemes are out of scope for this document but can be implemented using extensions.

Falsifying IP source addresses in sent traffic has been common for denial of service attacks. Implementations of this mechanism need to ensure that they do not facilitate such attacks. In particular, there are scenarios where an endpoint knows that its peer is only allowed to send IP packets from a given prefix. For example, that can happen through out of band configuration information, or when allowed prefixes are shared via ADDRESS_ASSIGN capsules. In such scenarios, endpoints MUST follow the recommendations from [BCP38] to prevent source address spoofing.

11. IANA Considerations

11.1. HTTP Upgrade Token

This document will request IANA to register "connect-ip" in the HTTP Upgrade Token Registry maintained at <https://www.iana.org/assignments/http-upgrade-tokens>.

Value:

connect-ip

Description:

Proxying of IP Payloads

Expected Version Tokens:

None

References:

This document

11.2. Creation of the MASQUE URI Suffixes Registry

This document requests that IANA create a new "MASQUE URI Suffixes" registry maintained at IANA_URL_TBD. This new registry governs the path segment that immediately follows "masque" in paths that start with "/.well-known/masque/", see <https://www.iana.org/assignments/well-known-uris> for the registration of "masque" in the "Well-Known URIs" registry. This new registry contains three columns:

Path Segment:

An ASCII string containing only characters allowed in tokens; see Section 5.6.2 of [HTTP]. Entries in this registry MUST all have distinct entries in this column.

Description:

A description of the entry.

Reference:

An optional reference defining the use of the entry.

The registration policy for this registry is Expert Review; see Section 4.5 of [IANA-POLICY].

There are initially two entries in this registry:

Table 1: New MASQUE URI Suffixes
Path Segment Description Reference
udp UDP Proxying RFC 9298
ip IP Proxying This Document

11.3. Updates to masque Well-Known URI

This document will request IANA to update the entry for the "masque" URI suffix in the "Well-Known URIs" registry maintained at <https://www.iana.org/assignments/well-known-uris>.

IANA is requested to update the "Reference" field to include this document in addition to previous values from that field.

IANA is requested to replace the "Related Information" field with "For sub-suffix allocations, see registry at IANA_URL_TBD." where IANA_URL_TBD is the URL of the new registry described in Section 11.2.

11.4. Capsule Type Registrations

This document will request IANA to add the following values to the "HTTP Capsule Types" registry maintained at <https://www.iana.org/assignments/http-capsule-protocol/http-capsule-protocol.xhtml>.

Table 2: New Capsules
Value Type Description Reference
0x1ECA6A00 ADDRESS_ASSIGN Address Assignment This Document
0x1ECA6A01 ADDRESS_REQUEST Address Request This Document
0x1ECA6A02 ROUTE_ADVERTISEMENT Route Advertisement This Document

12. References

12.1. Normative References

[ABNF]
Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234, , <https://www.rfc-editor.org/rfc/rfc2234>.
[BCP38]
Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827, , <https://www.rfc-editor.org/rfc/rfc2827>.
[DGRAM]
Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable Datagram Extension to QUIC", RFC 9221, DOI 10.17487/RFC9221, , <https://www.rfc-editor.org/rfc/rfc9221>.
[EXT-CONNECT2]
McManus, P., "Bootstrapping WebSockets with HTTP/2", RFC 8441, DOI 10.17487/RFC8441, , <https://www.rfc-editor.org/rfc/rfc8441>.
[EXT-CONNECT3]
Hamilton, R., "Bootstrapping WebSockets with HTTP/3", RFC 9220, DOI 10.17487/RFC9220, , <https://www.rfc-editor.org/rfc/rfc9220>.
[HTTP]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/rfc/rfc9110>.
[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, , <https://www.rfc-editor.org/rfc/rfc9297>.
[HTTP/1.1]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112, , <https://www.rfc-editor.org/rfc/rfc9112>.
[HTTP/2]
Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113, DOI 10.17487/RFC9113, , <https://www.rfc-editor.org/rfc/rfc9113>.
[HTTP/3]
Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114, , <https://www.rfc-editor.org/rfc/rfc9114>.
[IANA-POLICY]
Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, , <https://www.rfc-editor.org/rfc/rfc8126>.
[ICMP]
Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, , <https://www.rfc-editor.org/rfc/rfc792>.
[ICMPv6]
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, , <https://www.rfc-editor.org/rfc/rfc4443>.
[IPv6]
Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, , <https://www.rfc-editor.org/rfc/rfc8200>.
[QUIC]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, , <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, , <https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
[TCP]
Postel, J., "Transmission Control Protocol", RFC 793, DOI 10.17487/RFC0793, , <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, , <https://www.rfc-editor.org/rfc/rfc6570>.
[URI]
Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, , <https://www.rfc-editor.org/rfc/rfc3986>.

12.2. Informative References

[CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298, DOI 10.17487/RFC9298, , <https://www.rfc-editor.org/rfc/rfc9298>.
[HEv2]
Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: Better Connectivity Using Concurrency", RFC 8305, DOI 10.17487/RFC8305, , <https://www.rfc-editor.org/rfc/rfc8305>.
[IPSEC]
Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, , <https://www.rfc-editor.org/rfc/rfc4301>.
[PROXY-REQS]
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-03, , <https://datatracker.ietf.org/doc/html/draft-ietf-masque-ip-proxy-reqs-03>.

Acknowledgments

The design of this method was inspired by discussions in the MASQUE working group around [PROXY-REQS]. The authors would like to thank participants in those discussions for their feedback. Additionally, Alejandro Sedeño provided valuable feedback on the document.

Most of the text on client configuration is based on the corresponding text in [CONNECT-UDP].

Authors' Addresses

Tommy Pauly (editor)
Apple Inc.
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Alex Chernyakhovsky
Google LLC
Mirja Kuehlewind
Ericsson
Magnus Westerlund
Ericsson