UDP Proxying Support for HTTP
draft-ietf-masque-connect-udp-06
MASQUE D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track 25 October 2021
Expires: 28 April 2022
UDP Proxying Support for HTTP
draft-ietf-masque-connect-udp-06
Abstract
This document describes how to proxy UDP over HTTP. Similar to how
the CONNECT method allows proxying TCP over HTTP, this document
defines a new mechanism to proxy UDP. It is built using HTTP
Extended CONNECT.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the MASQUE WG 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/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-
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 28 April 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Configuration of Clients . . . . . . . . . . . . . . . . . . 3
3. HTTP Exchanges . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Proxy Handling . . . . . . . . . . . . . . . . . . . . . 4
3.2. HTTP Request over HTTP/1.1 . . . . . . . . . . . . . . . 5
3.3. HTTP Response over HTTP/1.1 . . . . . . . . . . . . . . . 5
3.4. HTTP Request over HTTP/2 and HTTP/3 . . . . . . . . . . . 6
3.5. HTTP Response over HTTP/2 and HTTP/3 . . . . . . . . . . 7
3.6. Note About Draft Versions . . . . . . . . . . . . . . . . 7
4. Encoding of Proxied UDP Packets . . . . . . . . . . . . . . . 7
5. Performance Considerations . . . . . . . . . . . . . . . . . 8
5.1. MTU Considerations . . . . . . . . . . . . . . . . . . . 9
5.2. Tunneling of ECN Marks . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.1. HTTP Upgrade Token . . . . . . . . . . . . . . . . . . . 10
7.2. Datagram Format Type . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This document describes how to proxy UDP over HTTP. Similar to how
the CONNECT method (see Section 9.3.6 of [SEMANTICS]) allows proxying
TCP [TCP] over HTTP, this document defines a new mechanism to proxy
UDP [UDP].
UDP Proxying supports all versions of HTTP and uses HTTP Datagrams
[HTTP-DGRAM]. When using HTTP/2 or HTTP/3, UDP proxying uses HTTP
Extended CONNECT as described in [EXT-CONNECT2] and [EXT-CONNECT3].
When using HTTP/1.x, UDP proxying uses HTTP Upgrade as defined in
Section 7.8 of [SEMANTICS].
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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.
In this document, we use the term "proxy" to refer to the HTTP server
that opens the UDP socket and responds to the UDP proxying request.
If there are HTTP intermediaries (as defined in Section 3.7 of
[SEMANTICS]) 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.
2. Configuration of Clients
Clients are configured to use UDP Proxying over HTTP via an URI
Template [TEMPLATE]. The URI template MUST contain exactly two
variables: "target_host" and "target_port". Examples are shown
below:
https://masque.example.org/{target_host}/{target_port}/
https://proxy.example.org:4443/masque?h={target_host}&p={target_port}
https://proxy.example.org:4443/masque{?target_host,target_port}
Figure 1: URI Template Examples
Since the original HTTP CONNECT method allowed conveying the target
host and port but not the scheme, proxy authority, path, nor query,
there exist proxy configuration interfaces that only allow the user
to configure the proxy host and the proxy port. Client
implementations of this specification that are constrained by such
limitations MUST use the default template which is defined as:
"https://$PROXY_HOST:$PROXY_PORT/{target_host}/{target_port}/" where
$PROXY_HOST and $PROXY_PORT are the configured host and port of the
proxy respectively. Proxy deployments SHOULD use the default
template to facilitate interoperability with such clients.
3. HTTP Exchanges
This document defines the "connect-udp" HTTP Upgrade Token. "connect-
udp" uses the Capsule Protocol as defined in [HTTP-DGRAM].
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A "connect-udp" request requests that the recipient establish a
tunnel over a single HTTP stream to the destination target server
identified by the "target_host" and "target_port" variables of the
URI template (see Section 2). If the request is successful, the
proxy commits to converting received HTTP Datagrams into UDP packets
and vice versa until the tunnel is closed. Tunnels are commonly used
to create an end-to-end virtual connection, which can then be secured
using QUIC [QUIC] or another protocol running over UDP.
When sending its UDP proxying request, the client SHALL perform URI
template expansion to determine the path and query of its request.
target_host supports using DNS names, IPv6 literals and IPv4
literals. Note that this URI template expansion requires using pct-
encoding, so for example if the target_host is "2001:db8::42", it
will be encoded in the URI as "2001%3Adb8%3A%3A42".
A payload within a UDP proxying request message has no defined
semantics; a UDP proxying request with a non-empty payload is
malformed.
Responses to UDP proxying requests are not cacheable.
3.1. Proxy Handling
Upon receiving a UDP proxying request, the recipient proxy extracts
the "target_host" and "target_port" variables from the URI it has
reconstructed from the request headers, and establishes a tunnel by
directly opening a UDP socket to the requested target.
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 request without waiting for a
packet from the target. However, if the target_host is a DNS name,
the proxy MUST perform DNS resolution before replying to the HTTP
request. If DNS resolution fails, the proxy MUST fail the request
and SHOULD send details using the Proxy-Status header [PROXY-STATUS].
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 request. Packets that do not match MUST be discarded by the
proxy.
The lifetime of the socket is tied to the request stream. The proxy
MUST keep the socket open while the request stream is open. If a
proxy is notified by its operating system that its socket is no
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longer usable, it MUST close the request stream. Proxies MAY choose
to close sockets due to a period of inactivity, but they MUST close
the request stream before closing the socket. Proxies that close
sockets after a period of inactivity SHOULD NOT use a period lower
than two minutes, see Section 4.3 of [BEHAVE].
A successful response (as defined in Section 3.3 and Section 3.5)
indicates that the proxy has opened a socket to the requested target
and is willing to proxy UDP payloads. Any response other than a
successful response indicates that the request has failed, and the
client MUST therefore abort the request.
3.2. HTTP Request over HTTP/1.1
When using HTTP/1.1, a UDP proxying request will meet the following
requirements:
* the method SHALL be "CONNECT".
* the request-target SHALL use absolute-form (see Section 3.2.2 of
[MESSAGING]).
* the request SHALL include a single Host header containing the
origin of the proxy.
* the request SHALL include a single "Connection" header with value
"Upgrade".
* the request SHALL include a single "Upgrade" header with value
"connect-udp".
For example, if the client is configured with URI template
"https://proxy.example.org/{target_host}/{target_port}/" and wishes
to open a UDP proxying tunnel to target 192.0.2.42:443, it could send
the following request:
CONNECT https://proxy.example.org/192.0.2.42/443/ HTTP/1.1
Host: proxy.example.org
Connection: upgrade
Upgrade: connect-udp
Figure 2: Example HTTP Request over HTTP/1.1
3.3. HTTP Response over HTTP/1.1
The proxy SHALL indicate a successful response by replying with the
following requirements:
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* the HTTP status code on the response SHALL be 101 (Switching
Protocols).
* the reponse SHALL include a single "Connection" header with value
"Upgrade".
* the response SHALL include a single "Upgrade" header with value
"connect-udp".
* the response SHALL NOT include any Transfer-Encoding or Content-
Length header fields.
If any of these requirements are not met, the client MUST treat this
proxying attempt as failed and abort the connection.
For example, the proxy could respond with:
HTTP/1.1 101 Switching Protocols
Connection: upgrade
Upgrade: connect-udp
Figure 3: Example HTTP Response over HTTP/1.1
3.4. HTTP Request over HTTP/2 and HTTP/3
When using HTTP/2 [H2] or HTTP/3 [H3], UDP proxying requests use HTTP
pseudo-headers with the following requirements:
* The ":method" pseudo-header field SHALL be "CONNECT".
* The ":protocol" pseudo-header field SHALL be "connect-udp".
* The ":authority" pseudo-header field SHALL contain the authority
of the 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.
A UDP proxying request that does not conform to these restrictions is
malformed (see Section 8.1.2.6 of [H2]).
For example, if the client is configured with URI template
"https://proxy.example.org/{target_host}/{target_port}/" and wishes
to open a UDP proxying tunnel to target 192.0.2.42:443, it could send
the following request:
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HEADERS
:method = CONNECT
:protocol = connect-udp
:scheme = https
:path = /192.0.2.42/443/
:authority = proxy.example.org
Figure 4: Example HTTP Request over HTTP/2
3.5. HTTP Response over HTTP/2 and HTTP/3
The proxy SHALL indicate a successful response by replying with any
2xx (Successful) HTTP status code, without any Transfer-Encoding or
Content-Length header fields.
If any of these requirements are not met, the client MUST treat this
proxying attempt as failed and abort the request.
For example, the proxy could respond with:
HEADERS
:status = 200
Figure 5: Example HTTP Response over HTTP/2
3.6. Note About Draft Versions
[[RFC editor: please remove this section before publication.]]
In order to allow implementations to support multiple draft versions
of this specification during its development, we introduce the
"connect-udp-version" header. When sent by the client, it contains a
list of draft numbers supported by the client (e.g., "connect-udp-
version: 0, 2"). When sent by the proxy, it contains a single draft
number selected by the proxy from the list provided by the client
(e.g., "connect-udp-version: 2"). Sending this header is RECOMMENDED
but not required.
4. Encoding of Proxied UDP Packets
UDP packets are encoded using HTTP Datagrams [HTTP-DGRAM] with the
UDP_PAYLOAD HTTP Datagram Format Type (see value in Section 7.2).
When using the UDP_PAYLOAD HTTP Datagram Format Type, the payload of
a UDP packet (referred to as "data octets" in [UDP]) is sent
unmodified in the "HTTP Datagram Payload" field of an HTTP Datagram.
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In order to use HTTP Datagrams, the client will first decide whether
or not it will attempt to use HTTP Datagram Contexts and then
register its context ID (or lack thereof) using the corresponding
registration capsule, see [HTTP-DGRAM].
When sending a registration capsule using the "Datagram Format Type"
set to UDP_PAYLOAD, the "Datagram Format Additional Data" field SHALL
be empty. Servers MUST NOT register contexts using the UDP_PAYLOAD
HTTP Datagram Format Type. Clients MUST NOT register more than one
context using the UDP_PAYLOAD HTTP Datagram Format Type. Endpoints
MUST NOT close contexts using the UDP_PAYLOAD HTTP Datagram Format
Type. If an endpoint detects a violation of any of these
requirements, it MUST abort the stream.
Clients MAY optimistically start sending proxied UDP packets before
receiving the response to its UDP proxying request, noting however
that those may not be processed by the proxy if it responds to the
request with a failure, or if the datagrams are received by the proxy
before the request.
Extensions to this mechanism MAY define new HTTP Datagram Format
Types in order to use different semantics or encodings for UDP
payloads.
5. 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.
If a client or proxy with a connection containing a UDP proxying
request stream disables congestion control, it MUST NOT signal ECN
support on that connection. That is, it MUST mark all IP headers
with the Not-ECT codepoint. It MAY continue to report ECN feedback
via ACK_ECN frames, as the peer may not have disabled congestion
control.
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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.
5.1. MTU Considerations
When using HTTP/3 with the QUIC Datagram extension [DGRAM], UDP
payloads are transmitted in QUIC DATAGRAM frames. Since those cannot
be fragmented, they can only carry payloads up to a given length
determined by the QUIC connection configuration and the path MTU. If
a proxy is using QUIC DATAGRAM frames and it receives a UDP payload
from the target that will not fit inside a QUIC DATAGRAM frame, the
proxy SHOULD NOT send the UDP payload in a DATAGRAM capsule, as that
defeats the end-to-end unreliability characteristic that methods such
as Datagram Packetization Layer Path MTU Discovery (DPLPMTUD) depend
on [RFC8899]. In this scenario, the proxy SHOULD drop the UDP
payload and send an ICMP "Packet Too Big" message to the target
[RFC4443].
5.2. Tunneling of ECN Marks
UDP proxying does not create an IP-in-IP tunnel, so the guidance in
[RFC6040] about transferring ECN marks between inner and outer IP
headers does not apply. There is no inner IP header in UDP proxying
tunnels.
Note that UDP proxying clients do not have the ability in this
specification to control the ECN codepoints on UDP packets the proxy
sends to the server, nor can proxies communicate the markings of each
UDP packet from server to proxy.
A UDP proxy MUST ignore ECN bits in the IP header of UDP packets
received from the server, and MUST set the ECN bits to Not-ECT on UDP
packets it sends to the server. These do not relate to the ECN
markings of packets sent between client and proxy in any way.
6. 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 UDP proxying SHOULD restrict its use to authenticated
users.
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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 UDP 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.
7. IANA Considerations
7.1. HTTP Upgrade Token
This document will request IANA to register "connect-udp" in the HTTP
Upgrade Token Registry maintained at
<https://www.iana.org/assignments/http-upgrade-tokens>.
Value: connect-udp
Description: Proxying of UDP Payloads.
Expected Version Tokens: None.
Reference: This document.
7.2. Datagram Format Type
This document will request IANA to register UDP_PAYLOAD in the "HTTP
Datagram Format Types" registry established by [HTTP-DGRAM].
+=============+==========+===============+
| Type | Value | Specification |
+=============+==========+===============+
| UDP_PAYLOAD | 0xff6f00 | This Document |
+-------------+----------+---------------+
Table 1: Registered Datagram Format Type
8. References
8.1. 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-06, 5 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
datagram-06>.
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[EXT-CONNECT2]
McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/rfc/rfc8441>.
[EXT-CONNECT3]
Hamilton, R., "Bootstrapping WebSockets with HTTP/3", Work
in Progress, Internet-Draft, draft-ietf-httpbis-h3-
websockets-00, 9 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
h3-websockets-00>.
[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/rfc/rfc7540>.
[H3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "Using Datagrams with HTTP",
Work in Progress, Internet-Draft, draft-ietf-masque-h3-
datagram-05, 25 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
h3-datagram-05>.
[MESSAGING]
Fielding, R. T., Nottingham, M., and J. Reschke,
"HTTP/1.1", Work in Progress, Internet-Draft, draft-ietf-
httpbis-messaging-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
messaging-19>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<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, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
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[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/rfc/rfc8174>.
[SEMANTICS]
Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
[TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<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, March 2012,
<https://www.rfc-editor.org/rfc/rfc6570>.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/rfc/rfc768>.
8.2. Informative References
[BEHAVE] Audet, F., Ed. and C. Jennings, "Network Address
Translation (NAT) Behavioral Requirements for Unicast
UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, <https://www.rfc-editor.org/rfc/rfc4787>.
[PROXY-STATUS]
Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
Response Header Field", Work in Progress, Internet-Draft,
draft-ietf-httpbis-proxy-status-08, 13 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
proxy-status-08>.
[RFC4443] 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, March 2006,
<https://www.rfc-editor.org/rfc/rfc4443>.
[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/rfc/rfc6040>.
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[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/rfc/rfc8899>.
Acknowledgments
This document is a product of the MASQUE Working Group, and the
author thanks all MASQUE enthusiasts for their contibutions. This
proposal was inspired directly or indirectly by prior work from many
people. In particular, 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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