Internet DRAFT - draft-ietf-masque-connect-udp
draft-ietf-masque-connect-udp
MASQUE D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track 17 June 2022
Expires: 19 December 2022
Proxying UDP in HTTP
draft-ietf-masque-connect-udp-15
Abstract
This document describes how to proxy UDP in HTTP, similar to how the
HTTP CONNECT method allows proxying TCP in HTTP. More specifically,
this document defines a protocol that allows an HTTP client to create
a tunnel for UDP communications through an HTTP server that acts as a
proxy.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://ietf-wg-
masque.github.io/draft-ietf-masque-connect-udp/draft-ietf-masque-
connect-udp.html. Status information for this document may be found
at https://datatracker.ietf.org/doc/draft-ietf-masque-connect-udp/.
Discussion of this document takes place on the MASQUE Working Group
mailing list (mailto: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."
Schinazi Expires 19 December 2022 [Page 1]
Internet-Draft Proxying UDP in HTTP June 2022
This Internet-Draft will expire on 19 December 2022.
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Client Configuration . . . . . . . . . . . . . . . . . . . . 3
3. Tunnelling UDP over HTTP . . . . . . . . . . . . . . . . . . 4
3.1. UDP Proxy Handling . . . . . . . . . . . . . . . . . . . 5
3.2. HTTP/1.1 Request . . . . . . . . . . . . . . . . . . . . 6
3.3. HTTP/1.1 Response . . . . . . . . . . . . . . . . . . . . 7
3.4. HTTP/2 and HTTP/3 Requests . . . . . . . . . . . . . . . 8
3.5. HTTP/2 and HTTP/3 Responses . . . . . . . . . . . . . . . 9
3.6. Note About Draft Versions . . . . . . . . . . . . . . . . 9
4. Context Identifiers . . . . . . . . . . . . . . . . . . . . . 9
5. HTTP Datagram Payload Format . . . . . . . . . . . . . . . . 10
6. Performance Considerations . . . . . . . . . . . . . . . . . 12
6.1. MTU Considerations . . . . . . . . . . . . . . . . . . . 12
6.2. Tunneling of ECN Marks . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8.1. HTTP Upgrade Token . . . . . . . . . . . . . . . . . . . 14
8.2. Well-Known URI . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
While HTTP provides the CONNECT method (see Section 9.3.6 of [HTTP])
for creating a TCP [TCP] tunnel to a proxy, prior to this
specification it lacked a method for doing so for UDP [UDP] traffic.
Schinazi Expires 19 December 2022 [Page 2]
Internet-Draft Proxying UDP in HTTP June 2022
This document describes a protocol for tunnelling UDP to a server
acting as a UDP-specific proxy over HTTP. UDP 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.
Unlike CONNECT, the UDP proxy itself is identified with an absolute
URL containing the traffic's destination. Clients generate those
URLs using a URI Template [TEMPLATE], as described in Section 2.
This protocol supports all existing versions of HTTP by using HTTP
Datagrams [HTTP-DGRAM]. When using HTTP/2 [HTTP/2] or HTTP/3
[HTTP/3], it uses HTTP Extended CONNECT as described in
[EXT-CONNECT2] and [EXT-CONNECT3]. When using HTTP/1.x [HTTP/1.1],
it uses HTTP Upgrade as defined in Section 7.8 of [HTTP].
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 "UDP proxy" to refer to the HTTP
server that acts upon the client's UDP tunnelling request to open a
UDP socket to a target server, and generates the response to this
request. If there are HTTP intermediaries (as defined in Section 3.7
of [HTTP]) between the client and the UDP 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. Client Configuration
HTTP clients are configured to use a UDP proxy with a URI Template
[TEMPLATE] that has the variables "target_host" and "target_port".
Examples are shown below:
https://example.org/.well-known/masque/udp/{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
The following requirements apply to the URI Template:
* The URI Template MUST be a level 3 template or lower.
Schinazi Expires 19 December 2022 [Page 3]
Internet-Draft Proxying UDP in HTTP June 2022
* The URI Template MUST be in absolute form, and MUST include non-
empty scheme, authority and path components.
* The path component of the URI Template MUST start with a slash
"/".
* All template variables MUST be within the path or query components
of the URI.
* The URI template MUST contain the two variables "target_host" and
"target_port" and MAY contain other variables.
* The URI Template MUST NOT contain any non-ASCII unicode characters
and MUST only contain ASCII characters in the range 0x21-0x7E
inclusive (note that percent-encoding is allowed; see Section 2.1
of [URI]).
* The URI Template MUST NOT use Reserved Expansion ("+" operator),
Fragment Expansion ("#" operator), Label Expansion with Dot-
Prefix, Path Segment Expansion with Slash-Prefix, nor Path-Style
Parameter Expansion with Semicolon-Prefix.
Clients SHOULD validate the requirements above; however, clients MAY
use a general-purpose URI Template implementation that lacks this
specific validation. If a client detects that any of the
requirements above are not met by a URI Template, the client MUST
reject its configuration and abort the request without sending it to
the UDP proxy.
Since the original HTTP CONNECT method allowed conveying the target
host and port but not the scheme, proxy authority, path, nor query,
there exist clients with 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 MAY attempt to access UDP proxying capabilities
using the default template, which is defined as:
"https://$PROXY_HOST:$PROXY_PORT/.well-known/masque/
udp/{target_host}/{target_port}/" where $PROXY_HOST and $PROXY_PORT
are the configured host and port of the UDP proxy respectively. UDP
proxy deployments SHOULD offer service at this location if they need
to interoperate with such clients.
3. Tunnelling UDP over HTTP
To allow negotiation of a tunnel for UDP over HTTP, this document
defines the "connect-udp" HTTP Upgrade Token. The resulting UDP
tunnels use the Capsule Protocol (see Section 3.2 of [HTTP-DGRAM])
with HTTP Datagrams in the format defined in Section 5.
Schinazi Expires 19 December 2022 [Page 4]
Internet-Draft Proxying UDP in HTTP June 2022
To initiate a UDP tunnel associated with a single HTTP stream, a
client issues a request containing the "connect-udp" upgrade token.
The target of the tunnel is indicated by the client to the UDP proxy
via the "target_host" and "target_port" variables of the URI
Template, see Section 2. If the request is successful, the UDP proxy
commits to converting received HTTP Datagrams into UDP packets and
vice versa until the tunnel is closed.
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 IPv6 scoped addressing zone identifiers are not
supported. Also note that this URI Template expansion requires using
percent-encoding, so for example if the target_host is
"2001:db8::42", it will be encoded in the URI as
"2001%3Adb8%3A%3A42".
By virtue of the definition of the Capsule Protocol (see Section 3.2
of [HTTP-DGRAM]), UDP proxying requests do not carry any message
content. Similarly, successful UDP proxying responses also do not
carry any message content.
3.1. UDP Proxy Handling
Upon receiving a UDP proxying request:
* if the recipient is configured to use another HTTP proxy, it will
act as an intermediary: it forwards the request to another HTTP
server. Note that such intermediaries may need to reencode the
request if they forward it using a version of HTTP that is
different from the one used to receive it, as the request encoding
differs by version (see below).
* otherwise, the recipient will act as a UDP proxy: it 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 UDP 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 UDP proxy MUST perform DNS resolution before replying to the HTTP
request. If errors occur during this process, the UDP proxy MUST
reject the request and SHOULD send details using an appropriate
"Proxy-Status" header field [PROXY-STATUS] (for example, if DNS
resolution returns an error, the proxy can use the dns_error Proxy
Error Type from Section 2.3.2 of [PROXY-STATUS]).
Schinazi Expires 19 December 2022 [Page 5]
Internet-Draft Proxying UDP in HTTP June 2022
UDP proxies can use connected UDP sockets if their operating system
supports them, as that allows the UDP proxy to rely on the kernel to
only send it UDP packets that match the correct 5-tuple. If the UDP
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 UDP proxy.
The lifetime of the socket is tied to the request stream. The UDP
proxy MUST keep the socket open while the request stream is open. If
a UDP proxy is notified by its operating system that its socket is no
longer usable (for example, this can happen when an ICMP "Destination
Unreachable" message is received, see Section 3.1 of [ICMP6]), it
MUST close the request stream. UDP proxies MAY choose to close
sockets due to a period of inactivity, but they MUST close the
request stream when closing the socket. UDP 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 UDP 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.
UDP proxies MUST NOT introduce fragmentation at the IP layer when
forwarding HTTP Datagrams onto a UDP socket; overly large datagrams
are silently dropped. In IPv4, the Don't Fragment (DF) bit MUST be
set if possible, to prevent fragmentation on the path. Future
extensions MAY remove these requirements.
Implementers of UDP proxies will benefit from reading the guidance in
[UDP-USAGE].
3.2. HTTP/1.1 Request
When using HTTP/1.1 [HTTP/1.1], a UDP proxying request will meet the
following requirements:
* the method SHALL be "GET".
* the request SHALL include a single "Host" header field containing
the origin of the UDP proxy.
* the request SHALL include a "Connection" header field with value
"Upgrade" (note that this requirement is case-insensitive as per
Section 7.6.1 of [HTTP]).
Schinazi Expires 19 December 2022 [Page 6]
Internet-Draft Proxying UDP in HTTP June 2022
* the request SHALL include an "Upgrade" header field with value
"connect-udp".
A UDP proxying request that does not conform to these restrictions is
malformed. The recipient of such a malformed request MUST respond
with an error, and SHOULD use the 400 (Bad Request) status code.
For example, if the client is configured with URI Template
"https://example.org/.well-known/masque/
udp/{target_host}/{target_port}/" and wishes to open a UDP proxying
tunnel to target 192.0.2.6:443, it could send the following request:
GET https://example.org/.well-known/masque/udp/192.0.2.6/443/ HTTP/1.1
Host: example.org
Connection: Upgrade
Upgrade: connect-udp
Capsule-Protocol: ?1
Figure 2: Example HTTP/1.1 Request
In HTTP/1.1, this protocol uses the GET method to mimic the design of
the WebSocket Protocol [WEBSOCKET].
3.3. HTTP/1.1 Response
The UDP proxy SHALL indicate a successful response by replying with
the following requirements:
* the HTTP status code on the response SHALL be 101 (Switching
Protocols).
* the reponse SHALL include a "Connection" header field with value
"Upgrade" (note that this requirement is case-insensitive as per
Section 7.6.1 of [HTTP]).
* the response SHALL include a single "Upgrade" header field with
value "connect-udp".
* the response SHALL meet the requirements of HTTP responses that
start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].
If any of these requirements are not met, the client MUST treat this
proxying attempt as failed and abort the connection.
For example, the UDP proxy could respond with:
Schinazi Expires 19 December 2022 [Page 7]
Internet-Draft Proxying UDP in HTTP June 2022
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: connect-udp
Capsule-Protocol: ?1
Figure 3: Example HTTP/1.1 Response
3.4. HTTP/2 and HTTP/3 Requests
When using HTTP/2 [HTTP/2] or HTTP/3 [HTTP/3], UDP proxying requests
use Extended CONNECT. This requires that servers send an HTTP
Setting as specified in [EXT-CONNECT2] and [EXT-CONNECT3], and that
requests use HTTP pseudo-header fields 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 UDP 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 8.1.1 of [HTTP/2] and Section 4.1.2 of
[HTTP/3]).
For example, if the client is configured with URI Template
"https://example.org/.well-known/masque/
udp/{target_host}/{target_port}/" and wishes to open a UDP proxying
tunnel to target 192.0.2.6:443, it could send the following request:
HEADERS
:method = CONNECT
:protocol = connect-udp
:scheme = https
:path = /.well-known/masque/udp/192.0.2.6/443/
:authority = example.org
capsule-protocol = ?1
Figure 4: Example HTTP/2 Request
Schinazi Expires 19 December 2022 [Page 8]
Internet-Draft Proxying UDP in HTTP June 2022
3.5. HTTP/2 and HTTP/3 Responses
The UDP proxy SHALL indicate a successful response by replying with
the following requirements:
* the HTTP status code on the response SHALL be in the 2xx
(Successful) range.
* the response SHALL meet the requirements of HTTP responses that
start the Capsule Protocol; see Section 3.2 of [HTTP-DGRAM].
If any of these requirements are not met, the client MUST treat this
proxying attempt as failed and abort the request.
For example, the UDP proxy could respond with:
HEADERS
:status = 200
capsule-protocol = ?1
Figure 5: Example HTTP/2 Response
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 field. 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 UDP proxy, it
contains a single draft number selected by the UDP proxy from the
list provided by the client (e.g., "connect-udp-version: 2").
Sending this header field is RECOMMENDED but not required. The
"connect-udp-version" header field is a List Structured Field
(https://www.rfc-editor.org/rfc/rfc8941#section-3.1). Each list
member MUST be an Integer.
4. Context Identifiers
The mechanism for proxying UDP in HTTP defined in this document
allows future extensions to exchange HTTP Datagrams that carry
different semantics from UDP payloads. Some of these extensions can
augment UDP payloads with additional data, while others can exchange
data that is completely separate from UDP payloads. In order to
accomplish this, all HTTP Datagrams associated with UDP Proxying
request streams start with a context ID, see Section 5.
Schinazi Expires 19 December 2022 [Page 9]
Internet-Draft Proxying UDP in HTTP June 2022
Context IDs are 62-bit integers (0 to 2^62-1). Context IDs are
encoded as variable-length integers, see Section 16 of [QUIC]. The
context ID value of 0 is reserved for UDP payloads, while non-zero
values are dynamically allocated: non-zero even-numbered context IDs
are client-allocated, and odd-numbered context IDs are proxy-
allocated. The context ID namespace is tied to a given HTTP request:
it is possible for a context ID with the same numeric value to be
simultaneously allocated in distinct requests, potentially with
different semantics. Context IDs MUST NOT be re-allocated within a
given HTTP namespace but MAY be allocated in any order. The context
ID allocation restrictions to the use of even-numbered and odd-
numbered context IDs exist in order to avoid the need for
synchronisation between endpoints. However, once a context ID has
been allocated, those restrictions do not apply to the use of the
context ID: it can be used by any client or UDP proxy, independent of
which endpoint initially allocated it.
Registration is the action by which an endpoint informs its peer of
the semantics and format of a given context ID. This document does
not define how registration occurs. Future extensions MAY use HTTP
header fields or capsules to register contexts. Depending on the
method being used, it is possible for datagrams to be received with
Context IDs which have not yet been registered, for instance due to
reordering of the packet containing the datagram and the packet
containing the registration message during transmission.
5. HTTP Datagram Payload Format
When HTTP Datagrams (see Section 2 of [HTTP-DGRAM]) are associated
with UDP proxying request streams, the HTTP Datagram Payload field
has the format defined in Figure 6. Note that when HTTP Datagrams
are encoded using QUIC DATAGRAM frames [DGRAM], the Context ID field
defined below directly follows the Quarter Stream ID field which is
at the start of the QUIC DATAGRAM frame payload (see Section 2.1 of
[HTTP-DGRAM]).
UDP Proxying HTTP Datagram Payload {
Context ID (i),
Payload (..),
}
Figure 6: UDP Proxying HTTP Datagram Format
Context ID: A variable-length integer (see Section 16 of [QUIC])
Schinazi Expires 19 December 2022 [Page 10]
Internet-Draft Proxying UDP in HTTP June 2022
that contains the value of the Context ID. If an HTTP/3 Datagram
which carries an unknown Context ID is received, the receiver
SHALL either drop that datagram silently or buffer it temporarily
(on the order of a round trip) while awaiting the registration of
the corresponding Context ID.
Payload: The payload of the datagram, whose semantics depend on
value of the previous field. Note that this field can be empty.
UDP packets are encoded using HTTP Datagrams with the Context ID set
to zero. When the Context ID is set to zero, the Payload field
contains the unmodified payload of a UDP packet (referred to as "data
octets" in [UDP]).
By virtue of the definition of the UDP header [UDP], it is not
possible to encode UDP payloads longer than 65527 bytes. Therefore,
endpoints MUST NOT send HTTP Datagrams with a Payload field longer
than 65527 using Context ID zero. An endpoint that receives an HTTP
Datagram using Context ID zero whose Payload field is longer than
65527 MUST abort the corresponding stream. If a UDP proxy knows it
can only send out UDP packets of a certain length due to its
underlying link MTU, it has no choice but to discard incoming HTTP
Datagrams using Context ID zero whose Payload field is longer than
that limit. If the discarded HTTP Datagram was transported by a
DATAGRAM capsule, the receiver SHOULD discard that capsule without
buffering the capsule contents.
If a UDP proxy receives an HTTP Datagram before it has received the
corresponding request, it SHALL either drop that HTTP Datagram
silently or buffer it temporarily (on the order of a round trip)
while awaiting the corresponding request.
Note that buffering datagrams (either because the request was not yet
received, or because the Context ID is not yet known) consumes
resources. Receivers that buffer datagrams SHOULD apply buffering
limits in order to reduce the risk of resource exhaustion occuring.
For example, receivers can limit the total number of buffered
datagrams, or the cumulative size of buffered datagrams, on a per-
stream, per-context, or per-connection basis.
A client MAY optimistically start sending UDP packets in HTTP
Datagrams before receiving the response to its UDP proxying request.
However, implementers should note that such proxied packets may not
be processed by the UDP proxy if it responds to the request with a
failure, or if the proxied packets are received by the UDP proxy
before the request and the UDP proxy chooses to not buffer them.
Schinazi Expires 19 December 2022 [Page 11]
Internet-Draft Proxying UDP in HTTP June 2022
6. Performance Considerations
Bursty traffic can often lead to temporally correlated packet losses,
which in turn can lead to suboptimal responses from congestion
controllers in protocols running over UDP. To avoid this, UDP
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. 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 UDP proxy with a connection containing a UDP proxying
request stream disables congestion control, it MUST NOT signal
Explicit Congestion Notification (ECN) [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 QUIC ACK_ECN
frames or the TCP "ECE" bit, as the peer may not have disabled
congestion control.
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, UDP proxying
SHOULD be performed over HTTP/3 to allow leveraging the QUIC DATAGRAM
frame.
6.1. 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 UDP 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 UDP 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 [DPLPMTUD]. In this scenario, the UDP proxy
SHOULD drop the UDP payload and send an ICMP "Packet Too Big" message
to the target, see Section 3.2 of [ICMP6].
Schinazi Expires 19 December 2022 [Page 12]
Internet-Draft Proxying UDP in HTTP June 2022
6.2. Tunneling of ECN Marks
UDP proxying does not create an IP-in-IP tunnel, so the guidance in
[ECN-TUNNEL] 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 UDP
proxy sends to the target, nor can UDP proxies communicate the
markings of each UDP packet from target to UDP proxy.
A UDP proxy MUST ignore ECN bits in the IP header of UDP packets
received from the target, and MUST set the ECN bits to Not-ECT on UDP
packets it sends to the target. These do not relate to the ECN
markings of packets sent between client and UDP proxy in any way.
7. Security Considerations
There are significant risks in allowing arbitrary clients to
establish a tunnel to arbitrary targets, as that could allow bad
actors to send traffic and have it attributed to the UDP proxy. HTTP
servers that support UDP proxying ought to restrict its use to
authenticated users.
There exist software and network deployments that perform access
control checks based on the source IP address of incoming requests.
For example, some software allows unauthenticated configuration
changes if they originated from 127.0.0.1. Such software could be
running on the same host as the UDP proxy, or in the same broadcast
domain. Proxied UDP traffic would then be received with a source IP
address belonging to the UDP proxy. If this source address is used
for access control, UDP proxying clients could use the UDP proxy to
escalate their access privileges beyond those they might otherwise
have. This could lead to unauthorized access by UDP proxying clients
unless the UDP proxy disallows UDP proxying requests to vulnerable
targets, such as the UDP proxy's own addresses and localhost, link-
local, multicast, and broadcast addresses. UDP proxies can use the
destination_ip_prohibited Proxy Error Type from Section 2.3.5 of
[PROXY-STATUS] when rejecting such requests.
UDP proxies share many similarities to TCP CONNECT proxies when
considering them as infrastructure for abuse to enable denial of
service attacks. Both can obfuscate the attacker's source address
from the attack target. In the case of a stateless volumetric attack
(e.g., a TCP SYN flood or a UDP flood), both types of proxies pass
the traffic to the target host. With stateful volumetric attacks
(e.g., HTTP flooding) being sent over a TCP CONNECT proxy, the proxy
Schinazi Expires 19 December 2022 [Page 13]
Internet-Draft Proxying UDP in HTTP June 2022
will only send data if the target has indicated its willingness to
accept data by responding with a TCP SYN-ACK. Once the path to the
target is flooded, the TCP CONNECT proxy will no longer receive
replies from the target and will stop sending data. Since UDP does
not establish shared state between the UDP proxy and the target, the
UDP proxy could continue sending data to the target in such a
situation. While a UDP proxy could potentially limit the number of
UDP packets it is willing to forward until it has observed a response
from the target, that provides limited protection against denial of
service attacks when attacks target open UDP ports where the protocol
running over UDP would respond, and that would be interpreted as
willingness to accept UDP by the UDP proxy. Such a packet limit
could also cause issues for valid traffic.
The security considerations described in Section 4 of [HTTP-DGRAM]
also apply here. Since it is possible to tunnel IP packets over UDP,
the guidance in [TUNNEL-SECURITY] can apply.
8. IANA Considerations
8.1. HTTP Upgrade Token
This document will request IANA to register "connect-udp" in the
"HTTP Upgrade Tokens" 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
8.2. Well-Known URI
This document will request IANA to register "masque" in the "Well-
Known URIs" registry maintained at <https://www.iana.org/assignments/
well-known-uris>.
URI Suffix: masque
Change Controller: IETF
Reference: This document
Status: permanent (if this document is approved)
Related Information: Includes all resources identified with the path
prefix "/.well-known/masque/udp/"
9. References
9.1. Normative References
Schinazi Expires 19 December 2022 [Page 14]
Internet-Draft Proxying UDP in HTTP June 2022
[DGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[ECN] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/rfc/rfc3168>.
[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",
RFC 9220, DOI 10.17487/RFC9220, June 2022,
<https://www.rfc-editor.org/rfc/rfc9220>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", Work in Progress, Internet-Draft,
draft-ietf-masque-h3-datagram-11, 17 June 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
h3-datagram-11>.
[HTTP/1.1] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
[HTTP/2] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
[HTTP/3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[PROXY-STATUS]
Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
Response Header Field", RFC 9209, DOI 10.17487/RFC9209,
June 2022, <https://www.rfc-editor.org/rfc/rfc9209>.
Schinazi Expires 19 December 2022 [Page 15]
Internet-Draft Proxying UDP in HTTP June 2022
[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>.
[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>.
[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>.
9.2. 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>.
[DPLPMTUD] 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>.
[ECN-TUNNEL]
Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/rfc/rfc6040>.
Schinazi Expires 19 December 2022 [Page 16]
Internet-Draft Proxying UDP in HTTP June 2022
[ICMP6] 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>.
[TUNNEL-SECURITY]
Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169,
DOI 10.17487/RFC6169, April 2011,
<https://www.rfc-editor.org/rfc/rfc6169>.
[UDP-USAGE]
Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/rfc/rfc8085>.
[URI] 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/rfc/rfc3986>.
[WEBSOCKET]
Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/rfc/rfc6455>.
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 HELIUM (https://www.ietf.org/archive/id/draft-
schwartz-httpbis-helium-00.txt) by Ben Schwartz, HiNT
(https://www.ietf.org/archive/id/draft-pardue-httpbis-http-network-
tunnelling-00.txt) by Lucas Pardue, and the original MASQUE Protocol
(https://www.ietf.org/archive/id/draft-schinazi-masque-00.txt) by the
author of this document.
The author would like to thank Eric Rescorla for suggesting the use
of an HTTP method to proxy UDP. The author is indebted to Mark
Nottingham and Lucas Pardue for the many improvements they
contributed to this document. The extensibility design in this
document came out of the HTTP Datagrams Design Team, whose members
were Alan Frindell, Alex Chernyakhovsky, Ben Schwartz, Eric Rescorla,
Lucas Pardue, Marcus Ihlar, Martin Thomson, Mike Bishop, Tommy Pauly,
Victor Vasiliev, and the author of this document.
Schinazi Expires 19 December 2022 [Page 17]
Internet-Draft Proxying UDP in HTTP June 2022
Author's Address
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: dschinazi.ietf@gmail.com
Schinazi Expires 19 December 2022 [Page 18]
