| Internet-Draft | The Other-Transport Extension | January 2021 |
| Duke | Expires 29 July 2021 | [Page] |
This document describes an extension to the HTTP CONNECT-UDP method [CONNECTUDP] that supports tunneling of other transport protocols, as long as the first four octets of those protocols encode the source and destination ports.¶
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 29 July 2021.¶
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
The HTTP CONNECT method (section 4.3.6 of [RFC7231]) has long provided a means of tunneling a TCP connection over an HTTP stream. The CONNECT-UDP method [CONNECTUDP] extends this capability to include UDP datagrams over a stream.¶
As CONNECT-UDP delivers discrete datagrams to each endpoint, it can extend conceptually to any packetized protocol. The Other-Transport extension allows a CONNECT-UDP proxy to tunnel packets with non-TCP, non-UDP protocol numbers, as long as the corresponding protocol meets minimal formatting requirements.¶
Specifically, any protocol header where the first four octets encode the source and destination ports can be tunneled using this framework. The client and proxy include all other protocol header information in the datagrams delivered over the tunnel. For example, 33 (DCCP, [RFC4330]); 132 (SCTP, [RFC4960]); and 136 (UDPLite, [RFC3828]) would all be valid candidates for Other-Transport.¶
In principle, TCP can be proxied using this extension as well. This might provide advantages over traditional HTTP CONNECT if the client's TCP implementation has features lacking at the proxy.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
In this document, we use the term "proxy" to refer to the HTTP server that opens the UDP socket and responds to the CONNECT-UDP 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.¶
"Other-Transport" is an Item Structured Header [HDRSTRUCT]. Its ABNF is:¶
Other-Transport = sf-integer¶
The value MUST be between 0 and 255, inclusive. Any other value is malformed. This value indicates the value of the Protocol Number (IPv4) or Next Header (IPv6) in IP headers corresponding to the CONNECT-UDP stream.¶
An Other-Transport header is ignored in any method other than CONNECT-UDP.¶
A client that sends this header MUST include the entire transport header, with the exception of the first four octets, in each HTTP/3 DATAGRAM or Stream Chunk payload it sends. It MUST process incoming datagrams with the same assumption.¶
When a client sends the Other-Transport header field, it MUST use a value that corresponds to a protocol whose first four octets of each packet correspond to the source and destination ports. For example, 33 (DCCP, [RFC4330]); 132 (SCTP, [RFC4960]); and 136 (UDPLite, [RFC3828]) would all be valid choices.¶
A proxy MUST NOT include this header unless it will prepend and strip port numbers instead of entire UDP headers, and use the Protocol Number in IP headers for both packets to the server and for demultiplexing incoming server packets.¶
A proxy MAY choose not to send the header due to policy regarding specific protocol numbers.¶
This extension is said to have been negotiated when both client and proxy indicate support for it in their CONNECT-UDP request and response using the same value.¶
If the server responds without the Other-Transport header, the client may either proceed with UDP datagrams or close the stream.¶
A response with a Other-Transport value other than that provided by the client is malformed.¶
All DATAGRAM frames corresponding to the negotiated Datagram-Flow-Id headers are processed in accordance with the Other-Transport extension, if negotiated.¶
All DATAGRAM frames MUST include the entire IP payload with the exception of the first four octets.¶
If a client sent an Other-Transport header, it MUST NOT send DATAGRAM frames until it confirms this extension has been negotiated. If the proxy does not support Other-Transport, it will interpret DATAGRAM frames as UDP payloads, with unpredictable results.¶
Endpoints use the 0x10 Stream Chunk Type to encode datagrams.¶
Clients MAY send payloads using Stream Chunks before negotiation is complete. Proxies that do not support the extension will simply ignore these chunks.¶
HTTP Intermediaries that discover that an upstream proxy does not support the Other-Transport header MUST abort the stream in the direction of the client.¶
CONNECT-UDP streams that use the Other-Transport header have similar security properties to other CONNECT-UDP streams, as described in [CONNECTUDP].¶
However, as more of the transport header originates at the server, and the tunneled protocols are less ubiquitous than UDP, these headers may serve to fingerprint the protocol implementation that generated them.¶
Furthermore, additional control over packet headers enhances the ability of clients to induce the proxy to generate certain packets, which might have undesirable effects in the network while being less traceable to the client.¶
This document requests that IANA registers the "Other-Transport" header in the "Permanent Message Header Field Names" registry maintained at <https://www.iana.org/assignments/message-headers>.¶
+-------------------+----------+--------+---------------+ | Header Field Name | Protocol | Status | Reference | +-------------------+----------+--------+---------------+ | Other-Transport | http | std | This document | +-------------------+----------+--------+---------------+¶
This document will request IANA to register the following entry in the "CONNECT-UDP Stream Chunk Type" registry [CONNECTUDP]:¶
+-------+-----------------+-------------------------+---------------+ | Value | Type | Description | Reference | +-------+-----------------+-------------------------+---------------+ | 0x10 | OTHER_TRANSPORT | Other Transport Protocol| This document | +-------+-----------------+-------------------------+---------------+¶