Proxying Listener UDP in HTTP

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 8 January 2023.¶

Copyright Notice

Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

1. Introduction

The mechanism to proxy UDP in HTTP [CONNECT-UDP] allows proxying UDP payloads [UDP] to a fixed host and port. Combined with the HTTP CONNECT method (see Section 9.3.6 of [HTTP]), it allows proxying the majority of a Web Browser's HTTP traffic. However WebRTC [WebRTC] relies on ICE [ICE] to provide connectivity between two Web browsers, and that in turn relies on the ability to send and receive UDP packets to multiple hosts. While it would be possible in theory to accomplish this by using multiple UDP proxying HTTP requests, HTTP semantics [HTTP] do not guarantee that those distinct requests will be handled by the same server, which can lead to the UDP packets being sent from distinct IP addresses, which in turn prevents ICE from operating correctly. Because of this, UDP Proxying requests cannot enable WebRTC connectivity between peers.¶

This document describes an extension to UDP Proxying in HTTP that allows sending and receiving UDP payloads to multiple hosts within the scope of a single UDP proxying HTTP request.¶

2. Proxied UDP Listener Mechanism

In unextended UDP Proxying requests, the target host is encoded in the HTTP request path or query. For listener UDP proxying, it is instead conveyed in each HTTP Datagram, see Section 2.1.¶

When performing URI Template Exansion of the UDP proxying template (see Section 3 of [CONNECT-UDP]), the client sets both the target_host and the target_port variables to the '*' character (ASCII character 0x2A).¶

Before sending its UDP Proxying request to the proxy, the client allocates an even-numbered context ID, see Section 4 of [CONNECT-UDP]. The client then adds the "connect-udp-listen" header field to its proxying request, with the value equal to the context ID it has allocated, see Section 2.2.¶

Listener UDP Proxying HTTP Datagram Payload {
  IP Version (8),
  IP Address (32..128),
  UDP Port (16),
  UDP Payload (..),
}

3. Security Considerations

The security considerations described in Section 7 of [CONNECT-UDP] also apply here.¶

4. IANA Considerations

This document will request IANA to register the following entry in the "HTTP Field Name" registry maintained at <https://www.iana.org/assignments/http-fields>:¶

Field Name:

connect-udp-listen¶

Template:

None¶

Status:

provisional (permanent if this document is approved)¶

Reference:

This document¶

Comments:

None¶

Appendix A. Example

In the example below, the client is configured with URI Template "https://example.org/.well-known/masque/udp/{target_host}/{target_port}/" and wishes to use WebRTC to another browser over a listener UDP proxying tunnel. It then contacts a STUN server at 192.0.2.42. The STUN server then sends the proxy's IP address to the other browser at 203.0.113.33 leading that other browser to send a UDP packet to the proxy, and that packets gets proxied over HTTP back to the client.¶

 Client                                             Server

 STREAM(44): HEADERS            -------->
   :method = CONNECT
   :protocol = connect-udp
   :scheme = https
   :path = /.well-known/masque/udp/*/*/
   :authority = proxy.example.org
   connect-udp-listen = 2
   capsule-protocol = ?1

 DATAGRAM                       -------->
   Quarter Stream ID = 11
   Context ID = 2
   IP Version = 4
   IP Address = 192.0.2.42
   UDP Port = 1234
   UDP Payload = Encapsulated UDP Payload

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

/* Wait for STUN server to respond to UDP packet. */

            <--------  DATAGRAM
                         Quarter Stream ID = 11
                         Context ID = 2
                         IP Version = 4
                         IP Address = 192.0.2.42
                         UDP Port = 1234
                         UDP Payload = Encapsulated UDP Payload

/* Wait for the STUN server to send the proxy's IP and */
/* port to the other browser and for the other browser */
/* to send a UDP packet to the proxy. */

            <--------  DATAGRAM
                         Quarter Stream ID = 11
                         Context ID = 2
                         IP Version = 4
                         IP Address = 203.0.113.33
                         UDP Port = 4321
                         UDP Payload = Encapsulated UDP Payload

Appendix B. Comparison with CONNECT-IP

While the use-cases described in Section 1 could be solved using IP Proxying in HTTP [CONNECT-IP], that would require that every HTTP Datagram carry a complete IP header. This would not only cause inefficiencies in the wire encoding, it would additionally reduce the available Maximum Transmission Unit (MTU). Furthermore, it would require that Web browsers implement IPv4 and IPv6 header generation and parsing, alongside with validation and error handling.¶

Acknowledgments

This proposal is the result of many conversations with MASQUE working group participants.¶

Author's Address