The CONNECT-UDP HTTP Method
draft-ietf-masque-connect-udp-01
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (masque WG) | |
|---|---|---|---|
| Author | David Schinazi | ||
| Last updated | 2020-12-12 (Latest revision 2020-08-28) | ||
| Replaces | draft-schinazi-masque-connect-udp | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-masque-connect-udp-01
Network Working Group D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track 12 December 2020
Expires: 15 June 2021
The CONNECT-UDP HTTP Method
draft-ietf-masque-connect-udp-01
Abstract
This document describes the CONNECT-UDP HTTP method. CONNECT-UDP is
similar to the HTTP CONNECT method, but it uses UDP instead of TCP.
Discussion of this work is encouraged to happen on the MASQUE IETF
mailing list masque@ietf.org or on the GitHub repository which
contains the draft: https://github.com/ietf-wg-masque/draft-ietf-
masque-connect-udp.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-masque/draft-ietf-masque-connect-udp.
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-
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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 15 June 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 2
2. Supported HTTP Versions . . . . . . . . . . . . . . . . . . . 3
3. The CONNECT-UDP Method . . . . . . . . . . . . . . . . . . . 3
4. Datagram Encoding of Proxied UDP Packets . . . . . . . . . . 4
5. Stream Encoding of Proxied UDP Packets . . . . . . . . . . . 5
6. Proxy Handling . . . . . . . . . . . . . . . . . . . . . . . 6
7. HTTP Intermediaries . . . . . . . . . . . . . . . . . . . . . 6
8. Performance Considerations . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10.1. HTTP Method . . . . . . . . . . . . . . . . . . . . . . 8
10.2. URI Scheme Registration . . . . . . . . . . . . . . . . 8
10.3. Stream Chunk Type Registration . . . . . . . . . . . . . 8
11. Normative References . . . . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This document describes the CONNECT-UDP HTTP method. CONNECT-UDP is
similar to the HTTP CONNECT method (see section 4.3.6 of [RFC7231]),
but it uses UDP [UDP] instead of TCP [TCP].
Discussion of this work is encouraged to happen on the MASQUE IETF
mailing list masque@ietf.org or on the GitHub repository which
contains the draft: https://github.com/ietf-wg-masque/draft-ietf-
masque-connect-udp.
1.1. 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.
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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.
2. Supported HTTP Versions
The CONNECT-UDP method is defined for all versions of HTTP. When the
HTTP version used runs over QUIC [QUIC], UDP payloads can be sent
over QUIC DATAGRAM frames [DGRAM]. Otherwise they are sent on the
stream where the CONNECT-UDP request was made. Note that, when the
HTTP version in use does not support multiplexing streams (such as
HTTP/1.1), then any reference to "stream" in this document is meant
to represent the entire connection.
3. The CONNECT-UDP Method
The CONNECT-UDP method requests that the recipient establish a tunnel
over a single HTTP stream to the destination origin server identified
by the request-target and, if successful, thereafter restrict its
behavior to blind forwarding of packets, in both directions, until
the tunnel is closed. Tunnels are commonly used to create an end-to-
end virtual connection, which can then be secured using QUIC or
another protocol running over UDP.
The request-target of a CONNECT-UDP request is a URI [RFC3986] which
uses the "masque" scheme and an immutable path of "/". For example:
CONNECT-UDP masque://target.example.com:443/ HTTP/1.1
Host: target.example.com:443
When using HTTP/2 [H2] or later, CONNECT-UDP requests use HTTP
pseudo-headers with the following requirements:
* The ":method" pseudo-header field is set to "CONNECT-UDP".
* The ":scheme" pseudo-header field is set to "masque".
* The ":path" pseudo-header field is set to "/".
* The ":authority" pseudo-header field contains the host and port to
connect to (similar to the authority-form of the request-target of
CONNECT requests; see [RFC7230], Section 5.3).
A CONNECT-UDP request that does not conform to these restrictions is
malformed (see [H2], Section 8.1.2.6).
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The recipient proxy establishes a tunnel by directly opening a UDP
socket to the request-target. Any 2xx (Successful) response
indicates that the proxy has opened a socket to the request-target
and is willing to proxy UDP payloads. 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-UDP. A client MUST
treat a response to CONNECT-UDP containing any Content-Length or
Transfer-Encoding header fields as malformed.
A payload within a CONNECT-UDP request message has no defined
semantics; a CONNECT-UDP request with a non-empty payload is
malformed. Note that the CONNECT-UDP stream is used to convey UDP
packets, but they are not semantically part of the request or
response themselves.
Responses to the CONNECT-UDP method are not cacheable.
4. Datagram Encoding of Proxied UDP Packets
When the HTTP connection supports HTTP/3 datagrams [H3DGRAM], UDP
packets can be encoded using QUIC DATAGRAM frames. This support is
ascertained by checking the received value of the H3_DATAGRAM
SETTINGS Parameter.
If the client has both sent and received the H3_DATAGRAM SETTINGS
Parameter with value 1 on this connection, it SHOULD attempt to use
HTTP/3 datagrams. This is accomplished by requesting a datagram flow
identifier from the flow identifier allocation service [H3DGRAM].
That service generates an even flow identifier, and the client sends
it to the proxy by using the "Datagram-Flow-Id" header; see
[H3DGRAM]. A CONNECT-UDP request with an odd flow identifier is
malformed.
The proxy that is creating the UDP socket to the destination responds
to the CONNECT-UDP request with a 2xx (Successful) response, and
indicates it supports datagram encoding by echoing the "Datagram-
Flow-Id" header. Once the client has received the "Datagram-Flow-Id"
header on the successful response, it knows that it can use the
HTTP/3 datagram encoding to send proxied UDP packets for this
particular request. It then encodes the payload of UDP datagrams
into the payload of HTTP/3 datagrams. Is the CONNECT-UDP response
does not carry the "Datagram-Flow-Id" header, then the datagram
encoding is not available for this request. A CONNECT-UDP response
that carries the "Datagram-Flow-Id" header but with a different flow
identifier than the one sent on the request is malformed.
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When the proxy processes a new CONNECT-UDP request, it MUST ensure
that the datagram flow identifier is not equal to flow identifiers
from other requests: if it is, the proxy MUST reject the request with
a 4xx (Client Error) status code. Extensions MAY weaken or remove
this requirement.
Clients MAY optimistically start sending proxied UDP packets before
receiving the response to its CONNECT-UDP request, noting however
that those may not be processed by the proxy if it responds to the
CONNECT-UDP request with a failure or without echoing the "Datagram-
Flow-Id" header, or if the datagrams arrive before the CONNECT-UDP
request.
Note that a proxy can send the H3_DATAGRAM SETTINGS Parameter with a
value of 1 while disabling datagrams on a particular request by not
echoing the "Datagram-Flow-Id" header. If the proxy does this, it
MUST NOT treat receipt of datagrams as an error, because the client
could have sent them optimistically before receiving the response.
In this scenario, the proxy MUST discard those datagrams.
Extensions to CONNECT-UDP MAY leverage parameters on the "Datagram-
Flow-Id" header (parameters are defined in Section 3.1.2 of
[STRUCT-HDR]). Proxies MUST NOT echo parameters on the "Datagram-
Flow-Id" header if it does not understand their semantics.
5. Stream Encoding of Proxied UDP Packets
If HTTP/3 datagrams are not supported, the stream is used to convey
UDP payloads, by using the following format (using the notation from
the "Notational Conventions" section of [QUIC]):
CONNECT-UDP Stream Chunk {
CONNECT-UDP Stream Chunk Type (i) = 0x00,
UDP Payload Length (i),
UDP Payload (..),
}
Figure 1: CONNECT-UDP Stream Chunk Format
CONNECT-UDP Stream Chunk Type: A variable-length integer indicating
the Type of the CONNECT-UDP Stream Chunk, set to 0x00 to indicate
a UDP Payload.
UDP Payload Length: The length of the UDP Payload field following
this field.
UDP Payload: The payload of the UDP datagram.
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The bidirectional stream that the CONNECT-UDP request was sent on is
a sequence of CONNECT-UDP Stream Chunks. The CONNECT-UDP Stream
Chunk Type is designed to allow future extensibility. Endpoints that
receive a chunk with an unknown CONNECT-UDP Stream Chunk Type MUST
silently skip over that chunk.
6. Proxy Handling
Unlike TCP, UDP is connection-less. The proxy that opens the UDP
socket has no way of knowing whether the destination is reachable.
Therefore it needs to respond to the CONNECT-UDP request without
waiting for a TCP SYN-ACK.
Proxies can use connected UDP sockets if their operating system
supports them, as that allows the proxy to rely on the kernel to only
send it UDP packets that match the correct 5-tuple. If the proxy
uses a non-connected socket, it MUST validate the IP source address
and UDP source port on received packets to ensure they match the
client's CONNECT-UDP request. Packets that do not match MUST be
discarded by the proxy.
The lifetime of the socket is tied to the CONNECT-UDP stream. The
proxy MUST keep the socket open while the CONNECT-UDP stream is open.
Proxies MAY choose to close sockets due to a period of inactivity,
but they MUST close the CONNECT-UDP stream before closing the socket.
7. HTTP Intermediaries
HTTP/3 DATAGRAM flow identifiers are specific to a given HTTP/3
connection. However, in some cases, an HTTP request may travel
across multiple HTTP connections if there are HTTP intermediaries
involved; see Section 2.3 of [RFC7230].
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Intermediaries that support both CONNECT-UDP and HTTP/3 datagrams
MUST negotiate flow identifiers separately on the client-facing and
server-facing connections. This is accomplished by having the
intermediary parse the "Datagram-Flow-Id" header on all CONNECT-UDP
requests it receives, and sending the same value in the "Datagram-
Flow-Id" header on the response. The intermediary then ascertains
whether it can use datagrams on the server-facing connection. If
they are supported (as indicated by the H3_DATAGRAM SETTINGS
parameter), the intermediary uses its own flow identifier allocation
service to allocate a flow identifier for the server-facing
connection, and waits for the server's reply to see if the server
sent the "Datagram-Flow-Id" header on the response. The intermediary
then translates datagrams between the two connections by using the
flow identifier specific to that connection. An intermediary MAY
also choose to use datagrams on only one of the two connections, and
translate between datagrams and streams.
8. Performance Considerations
Proxies SHOULD strive to avoid increasing burstiness of UDP traffic:
they SHOULD NOT queue packets in order to increase batching.
When the protocol running over UDP that is being proxied uses
congestion control (e.g., [QUIC]), the proxied traffic will incur at
least two nested congestion controllers. This can reduce performance
but the underlying HTTP connection MUST NOT disable congestion
control unless it has an out-of-band way of knowing with absolute
certainty that the inner traffic is congestion-controlled.
When the protocol running over UDP that is being proxied uses loss
recovery (e.g., [QUIC]), and the underlying HTTP connection runs over
TCP, the proxied traffic will incur at least two nested loss recovery
mechanisms. This can reduce performance as both can sometimes
independently retransmit the same data. To avoid this, HTTP/3
datagrams SHOULD be used.
9. Security Considerations
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-UDP SHOULD restrict its use to authenticated
users.
Because the CONNECT method creates a TCP connection to the target,
the target has to indicate its willingness to accept TCP connections
by responding with a TCP SYN-ACK before the proxy can send it
application data. UDP doesn't have this property, so a CONNECT-UDP
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proxy could send more data to an unwilling target than a CONNECT
proxy. However, in practice denial of service attacks target open
TCP ports so the TCP SYN-ACK does not offer much protection in real
scenarios. Proxies MUST NOT introspect the contents of UDP payloads
as that would lead to ossification of UDP-based protocols by proxies.
10. IANA Considerations
10.1. HTTP Method
This document will request IANA to register "CONNECT-UDP" in the HTTP
Method Registry (IETF review) maintained at
<https://www.iana.org/assignments/http-methods>.
+-------------+------+------------+---------------+
| Method Name | Safe | Idempotent | Reference |
+-------------+------+------------+---------------+
| CONNECT-UDP | no | no | This document |
+-------------+------+------------+---------------+
10.2. URI Scheme Registration
This document will request IANA to register the URI scheme "masque".
The syntax definition below uses Augmented Backus-Naur Form (ABNF)
[RFC5234]. The definitions of "host" and "port" are adopted from
[RFC3986]. The syntax of a MASQUE URI is:
masque-URI = "masque:" "//" host ":" port "/"
The "host" and "port" component MUST NOT be empty, and the "port"
component MUST NOT be 0.
10.3. Stream Chunk Type Registration
This document will request IANA to create a "CONNECT-UDP 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:
Type: A short mnemonic for the type.
Description: 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:
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+-------+------------+-----------------------+---------------+
| Value | Type | Description | Reference |
+-------+------------+-----------------------+---------------+
| 0x00 | UDP_PACKET | Payload of UDP packet | This document |
+-------+------------+-----------------------+---------------+
Each value of the format "37 * N + 23" for integer values of N (that
is, 23, 60, 97, ...) are reserved; these values MUST NOT be assigned
by IANA and MUST NOT appear in the listing of assigned values.
11. Normative References
[DGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-ietf-quic-datagram-01, 24 August 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
datagram-01.txt>.
[H2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[H3DGRAM] Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in
Progress, Internet-Draft, draft-schinazi-masque-h3-
datagram-01, 12 December 2020, <http://www.ietf.org/
internet-drafts/draft-schinazi-masque-h3-datagram-01.txt>.
[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-32, 20 October 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
transport-32.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[STRUCT-HDR]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-header-structure-19, 3 June 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
header-structure-19.txt>.
[TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
Acknowledgments
This proposal was inspired directly or indirectly by prior work from
many people. The author would like to thank Eric Rescorla for
suggesting to use an HTTP method to proxy UDP. Thanks to Lucas
Pardue for their inputs on this document.
Author's Address
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Email: dschinazi.ietf@gmail.com
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