| Internet-Draft | CONNECT-IP | April 2021 |
| Chernyakhovsky, et al. | Expires 14 October 2021 | [Page] |
This document describes the CONNECT-IP HTTP method. CONNECT-IP is similar to CONNECT-UDP, but allows transmitting IP packets, without being limited to just TCP like CONNECT or UDP like CONNECT-UDP.¶
This note is to be removed before publishing as an RFC.¶
Discussion of this document takes place on the Multiplexed Application Substrate over QUIC Encryption Working Group mailing list (masque@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/masque/.¶
Source for this draft and an issue tracker can be found at https://github.com/DavidSchinazi/draft-cms-masque-connect-ip.¶
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This document describes the CONNECT-IP HTTP method. CONNECT-IP is similar to CONNECT-UDP, but allows transmitting IP packets, without being limited to just TCP like CONNECT or UDP like CONNECT-UDP.¶
CONNECT-IP allows endpoints to set up an IP tunnel between one another. This can be used to implement a consumer VPN, point-to-point, point-to-network, and network-to-network capabilities as described in [REQS].¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
In this document, we use the term "proxy" to refer to the HTTP server that responds to the CONNECT-IP request. If there are HTTP intermediaries (as defined in Section 2.3 of [RFC7230]) between the client and the proxy, those are referred to as "intermediaries" in this document.¶
The CONNECT-IP method establishes a stream to an endpoint server that then permits the exchange of control data, such as IP address information, reachable IP ranges, and other relevant information for successfully transmitting IP datagrams between hosts.¶
The request-target of a CONNECT-IP request is a URI [URI] which uses the "https" scheme and an immutable path of "/". When using HTTP/2 [H2] or later, CONNECT-IP requests use HTTP pseudo-headers with the following requirements:¶
A CONNECT-IP request that does not conform to these restrictions is malformed (see [H2], Section 8.1.2.6).¶
Any 2xx (Successful) response indicates that the proxy is willing to open an IP tunnel between it and the client. Any response other than a successful response indicates that the tunnel has not yet been formed.¶
A proxy MUST NOT send any Transfer-Encoding or Content-Length header fields in a 2xx (Successful) response to CONNECT-IP. A client MUST treat a successful response to CONNECT-IP containing any Content-Length or Transfer-Encoding header fields as malformed.¶
A payload within a CONNECT-IP request message has no defined semantics; a CONNECT-IP request with a non-empty payload is malformed. Note that the CONNECT-IP stream is used to convey control messages, but they are not semantically part of the request or response themselves.¶
Responses to the CONNECT-IP method are not cacheable.¶
The lifetime of the tunnel is tied to the CONNECT-IP stream. Closing the stream (via the FIN bit on a QUIC STREAM frame, or a QUIC RESET_STREAM frame) closes the associated tunnel.¶
When the HTTP connection supports HTTP/3 datagrams [H3DGRAM], IP packets can be sent using them. The HTTP/3 Datagram Payload contains a full IP packet, from the IP Version field until the last byte of the IP Payload.¶
Endpoints have the ability to advertise and reject routes using the ROUTE_ADVERTISEMENT (Section 6.4) and ROUTE_REJECTION (Section 6.4) messages. Note that these messages are purely informational: receipt of a ROUTE_ADVERTISEMENT message does not require the recipient to start routing traffic to its peer. Additionally, if an endpoint receives a ROUTE_REJECTION for a given prefix that it had previously received a ROUTE_ADVERTISEMENT message for, then the two cancel out and the endpoint MUST remove its state from the ROUTE_ADVERTISEMENT message instead of installing new state for the ROUTE_REJECTION message. Conversely, the same is true of a ROUTE_ADVERTISEMENT that matches a previous ROUTE_REJECTION. Routes are handled via longest-prefix-first preference, meaning that if a given IP prefix is covered by multiple route advertisement and route rejections, the one with the longest prefix is used.¶
The DATA stream tied to the bidirectional stream that the CONNECT-IP request was sent on is a sequence of CONNECT-IP Stream Chunks, which are defined as a sequence of type-length-value tuples using the following format (using the notation from the "Notational Conventions" section of [QUIC]):¶
CONNECT-IP Stream {
CONNECT-IP Stream Chunk (..) ...,
}
CONNECT-IP Stream Chunk {
CONNECT-IP Stream Chunk Type (i),
CONNECT-IP Stream Chunk Length (i),
CONNECT-IP Stream Chunk Value (..),
}
A variable-length integer indicating the Type of the CONNECT-IP Stream Chunk. Endpoints that receive a chunk with an unknown CONNECT-IP Stream Chunk Type MUST silently skip over that chunk.¶
The length of the CONNECT-IP Stream Chunk Value field following this field. Note that this field can have a value of zero.¶
The payload of this chunk. Its semantics are determined by the value of the CONNECT-IP Stream Chunk Type field.¶
The IP_PACKET message allows conveying IP Packets when HTTP/3 Datagrams are not available. This message uses a CONNECT-IP Stream Chunk Type of 0x00. Its value uses the following format:¶
IP_PACKET Message {
IP Packet (...),
}
A full IP packet, from the IP Version field until the last byte of the IP Payload.¶
Note that this message MAY still be used even when HTTP/3 datagrams are available.¶
The ADDRESS_ASSIGN message allows an endpoint to inform its peer that it has assigned an IP address to it. It allows assigning a prefix which can contain multiple addresses. This message uses a CONNECT-IP Stream Chunk Type of 0x01. Its value uses the following format:¶
ADDRESS_ASSIGN Message {
IP Version (8),
IP Address (32..128),
IP Prefix Length (8),
}
IP Version of this address assignment. MUST be either 4 or 6.¶
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.¶
Length of the IP Prefix assigned, in bits. MUST be lesser or equal to the length of the IP Address field, in bits.¶
The ADDRESS_REQUEST message allows an endpoint to request assignment of an IP address from its peer. It allows the endpoint to optionally indicate a preference for which address it would get assigned. This message uses a CONNECT-IP Stream Chunk Type of 0x02. Its value uses the following format:¶
ADDRESS_REQUEST Message {
IP Version (8),
IP Address (32..128),
IP Prefix Length (8),
}
IP Version of this address request. MUST be either 4 or 6.¶
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.¶
Length of the IP Prefix requested, in bits. MUST be lesser or equal to the length of the IP Address field, in bits.¶
Upon receiving the ADDRESS_REQUEST message, an endpoint SHOULD assign an IP address to its peer, and then respond with an ADDRESS_ASSIGN message to inform the peer of the assignment.¶
The ROUTE_ADVERTISEMENT message allows an endpoint to communicate to its peer that it is willing to route traffic to a given prefix. This message uses a CONNECT-IP Stream Chunk Type of 0x03. Its value uses the following format:¶
ROUTE_ADVERTISEMENT Message {
IP Version (8),
IP Address (32..128),
IP Prefix Length (8),
}
IP Version of this route advertisement. MUST be either 4 or 6.¶
IP address of the advertised route. 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.¶
Length of the IP Prefix of the advertised route, in bits. MUST be lesser or equal to the length of the IP Address field, in bits.¶
Upon receiving the ROUTE_ADVERTISEMENT message, an endpoint MAY start routing IP packets in that prefix to its peer.¶
The ROUTE_REJECTION message allows an endpoint to communicate to its peer that it is not willing to route traffic to a given prefix. This message uses a CONNECT-IP Stream Chunk Type of 0x04. Its value uses the following format:¶
ROUTE_REJECTION Message {
IP Version (8),
IP Address (32..128),
IP Prefix Length (8),
}
IP Version of this route rejection. MUST be either 4 or 6.¶
IP address of the rejected route. 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.¶
Length of the IP Prefix of the advertised route, in bits. MUST be lesser or equal to the length of the IP Address field, in bits.¶
Upon receiving the ROUTE_REJECTION message, an endpoint MUST stop routing IP packets in that prefix to its peer. Note that this message can be reordered with DATAGRAM frames, and therefore an endpoint that receives packets for routes it has rejected MUST NOT treat that as an error.¶
The ROUTE_RESET message allows an endpoint to cancel any routes it had previously advertised or denied. This message uses a CONNECT-IP Stream Chunk Type of 0x05. Its value uses the following format:¶
ROUTE_RESET Message {
}
Upon receiving the ROUTE_RESET message, an endpoint MUST stop routing IP packets to its peer. Note that this message can be reordered with DATAGRAM frames, and therefore an endpoint that receives packets for routes it has rejected MUST NOT treat that as an error.¶
The main purpose of the ROUTE_RESET message is to allow endpoints to not have to remember the full list of routes they have shared with their peer. In practice, it is expected that ROUTE_RESET messages will be closely followed by ROUTE_ADVERTISEMENT messages that will refill the routing table that was just cleared.¶
The SHUTDOWN message allows an endpoint to communicate to its peer that it is about to close the CONNECT-IP stream, with a string explaining the reason for the shutdown. This message uses a CONNECT-IP Stream Chunk Type of 0x06. Its value uses the following format:¶
SHUTDOWN Message {
Reason Phrase (..),
}
Additional diagnostic information for the shutdown. This SHOULD be a UTF-8 encoded string [UTF8], though the frame does not carry information, such as language tags, that would aid comprehension by any entity other than the one that created the text.¶
Note that the SHUTDOWN message is informational, the tunnel is only closed when its corresponding CONNECT-IP stream is closed. Endpoints MAY close the tunnel with a reason phrase by sending the SHUTDOWN message with the FIN bit set on the underlying QUIC STREAM frame that carried it.¶
The ATOMIC_START message allows an endpoint to create an atomic set of messages. This message uses a CONNECT-IP Stream Chunk Type of 0x07. Its value uses the following format:¶
ATOMIC_START Message {
}
Upon receiving an ATOMIC_START message, an endpoint MUST buffer all incoming known messages until it receives an ATOMIC_END message. Endpoints MUST NOT send two ATOMIC_START messages without an ATOMIC_END message between them.¶
Endpoints MUST NOT buffer unknown messages. Endpoints MAY choose to immediately process IP_PACKET and SHUTDOWN messages instead of buffering them. Extensions that register new message types MAY specify that it is allowed to skip buffering for them.¶
The purpose of this frame is to avoid timing issues where an endpoint installs a route before an important route rejection was received. Endpoints SHOULD group their initial configuration into an atomic block to allow their peer to mark the tunnel as operational once the whole block is parsed.¶
The ATOMIC_END message allows an endpoint to end an atomic set of messages. This message uses a CONNECT-IP Stream Chunk Type of 0x08. Its value uses the following format:¶
ATOMIC_END Message {
}
Upon receiving an ATOMIC_END message, an endpoint MUST parse all previously buffered messages, in order of receipt. Endpoints MUST NOT send an ATOMIC_END message without a preceding ATOMIC_START message.¶
CONNECT-IP can be extended via multiple mechanisms to increase functionality. There are two main ways to extend CONNECT-IP: HTTP headers and CONNECT-IP Stream Chunk Types. For example, an authentication extension could define an HTTP header that allows endpoints to send authentication credentials to their peer during the creation of the tunnel. Alternatively, one could specify an extension that defines a new CONNECT-IP Stream Chunk Type which allows exchanging DNS configuration between endpoints.¶
There are significant risks in allowing arbitrary clients to establish a tunnel to arbitrary servers, as that could allow bad actors to send traffic and have it attributed to the proxy. Proxies that support CONNECT-IP SHOULD restrict its use to authenticated users. The HTTP Authorization header [AUTH] MAY be used to authenticate clients. More complex authentication schemes are out of scope for this document but can be implemented using CONNECT-IP extensions.¶
This document will request IANA to register "CONNECT-IP" in the HTTP Method Registry (IETF review) maintained at <https://www.iana.org/assignments/http-methods>.¶
+-------------+------+------------+---------------+ | Method Name | Safe | Idempotent | Reference | +-------------+------+------------+---------------+ | CONNECT-IP | no | no | This document | +-------------+------+------------+---------------+¶
This document will request IANA to create a "CONNECT-IP Stream Chunk Type" registry. This registry governs a 62-bit space, and follows the registration policy for QUIC registries as defined in [QUIC]. In addition to the fields required by the QUIC policy, registrations in this registry MUST include the following fields:¶
A short mnemonic for the type.¶
A brief description of the type semantics, which MAY be a summary if a specification reference is provided.¶
The initial contents of this registry are:¶
+-------+---------------------+---------------------+---------------+ | Value | Type | Description | Reference | +-------+---------------------+---------------------+---------------+ | 0x00 | IP_PACKET | Full IP packet | This document | | 0x01 | ADDRESS_ASSIGN | Address Assignment | This document | | 0x02 | ADDRESS_REQUEST | Address Request | This document | | 0x03 | ROUTE_ADVERTISEMENT | Route Advertisement | This document | | 0x04 | ROUTE_REJECTION | Route Rejection | This document | | 0x05 | ROUTE_RESET | Route Reset | This document | | 0x06 | SHUTDOWN | Shutdown Reason | This document | | 0x07 | ATOMIC_START | Atomic Start | This document | | 0x08 | ATOMIC_END | Atomic End | This document | +-------+---------------------+---------------------+---------------+¶
Each value of the format 41 * N + 29 for integer values of N (that is, 29,
70, 111, ...) are reserved; these values MUST NOT be assigned by IANA and MUST
NOT appear in the listing of assigned values.¶
In this scenario, the client will typically receive a single IP address that the proxy has picked from a pool of addresses it maintains. The client will route all traffic through the tunnel. The exchange could look as follows:¶
Client Server
ADDRESS_REQUEST -------->
IP Version = 4
IP Address = 0.0.0.0
IP Prefix Length = 0
<-------- ADDRESS_ASSIGN
IP Version = 4
IP Address = 192.0.2.42
IP Prefix Length = 32
<-------- ROUTE_ADVERTISEMENT
IP Version = 4
IP Address = 0.0.0.0
IP Prefix Length = 0
¶
The design of CONNECT-IP was inspired by discussions in the MASQUE working group around [REQS]. The authors would like to thank participants in those discussions for their feedback.¶