wdiff rfc9298v1.txt rfc9298.txt

Internet Engineering Task Force (IETF) D. Schinazi
Request for Comments: 9298 Google LLC
Category: Standards Track August 2022
ISSN: 2070-1721

Proxying UDP in HTTP

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.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9298.

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
1.1. Conventions and Definitions
2. Client Configuration
3. Tunneling UDP over HTTP
3.1. UDP Proxy Handling
3.2. HTTP/1.1 Request
3.3. HTTP/1.1 Response
3.4. HTTP/2 and HTTP/3 Requests
3.5. HTTP/2 and HTTP/3 Responses
4. Context Identifiers
5. HTTP Datagram Payload Format
6. Performance Considerations
6.1. MTU Considerations
6.2. Tunneling of ECN Marks
7. Security Considerations
8. IANA Considerations
8.1. HTTP Upgrade Token
8.2. Well-Known URI
9. References
9.1. Normative References
9.2. Informative References
Acknowledgments
Author's Address

1. Introduction

While HTTP provides the CONNECT method (see Section 9.3.6 of [HTTP])
for creating a TCP [TCP] tunnel to a proxy, it lacked a method for
doing so for UDP [UDP] traffic prior to this specification.

This document describes a protocol for tunneling 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 HTTP CONNECT method, 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 tunneling request to open a
UDP socket to a target server and that 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.

* 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

The original HTTP CONNECT method allowed conveying for the conveyance of the
target host and port port, but not the scheme, proxy authority, path, nor query,
there exist or
query. Thus, clients with proxy configuration interfaces that only
allow the user to configure the proxy host and the proxy port. port exist.
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. Tunneling UDP over HTTP

To allow negotiation of a tunnel for UDP over HTTP, this document
defines the "connect-udp" HTTP Upgrade Token. 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.

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. This URI Template expansion requires Using the terms IPv6address, IPv4address, reg-name, and
port from [URI], the "target_host" and "target_port" variables MUST
adhere to the format in Figure 2, using percent-
encoding. notation from [ABNF].
Additionally:

* both the "target_host" and "target_port" variables MUST NOT be
empty.

* if "target_host" contains an IPv6 literal, the colons (":") MUST
be percent-encoded. For example, if the "target_host" target host is
"2001:db8::42", it will be encoded in the URI as
"2001%3Adb8%3A%3A42".

* "target_port" MUST represent an integer between 1 and 65535
inclusive.

target_host = IPv6address / IPv4address / reg-name
target_port = port

Figure 2: URI Template Variable Format

When sending its UDP proxying request, the client SHALL perform URI
Template expansion to determine the path and query of its request.

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.

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 by forwarding the request to another HTTP
server. Note that such intermediaries may need to re-encode 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 headers, decodes their percent-
encoding, and establishes a tunnel by directly opening a UDP
socket to the requested target.

Unlike TCP, UDP is connectionless. 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"
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].

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, it MUST close the request stream. For example, this
can happen when an ICMP "Destination Unreachable" Destination Unreachable message is
received, received;
see Section 3.1 of [ICMP6]) [ICMP6]. 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, minutes;
see Section 4.3 of [BEHAVE].

A successful response (as defined in Sections 3.3 and 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; thus, the client MUST
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" Host header field containing
the origin of the UDP proxy.

* the request SHALL include a "Connection" Connection header field with value
"Upgrade" (note that this requirement is case insensitive case-insensitive as per
Section 7.6.1 of [HTTP]).

* the request SHALL include an "Upgrade" 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: 3: 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 response SHALL include a "Connection" Connection header field with value
"Upgrade" (note that this requirement is case insensitive case-insensitive as per
Section 7.6.1 of [HTTP]).

* the response SHALL include a single "Upgrade" 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:

HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: connect-udp
Capsule-Protocol: ?1

Figure 3: 4: 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 HTTP Extended CONNECT. This requires that servers send an HTTP
Setting as specified in [EXT-CONNECT2] and [EXT-CONNECT3] and that
requests use HTTP pseudoheader pseudo-header fields with the following
requirements:

* The ":method" pseudoheader :method pseudo-header field SHALL be "CONNECT".

* The ":protocol" pseudoheader :protocol pseudo-header field SHALL be "connect-udp".

* The ":authority" pseudoheader :authority pseudo-header field SHALL contain the authority of
the UDP proxy.

* The ":path" :path and ":scheme" pseudoheader :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]).

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: 5: Example HTTP/2 Request

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: 6: Example HTTP/2 Response

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; Context ID field; see Section 5.

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
Context ID value of 0 is reserved for UDP payloads, while non-zero
values are dynamically allocated. Non-zero even-numbered context Context IDs
are client allocated, client-allocated, and odd-numbered context Context IDs are proxy proxy-
allocated. The context Context ID namespace is tied to a given HTTP request,
and request;
it is possible for a context Context ID with the same numeric value to be
simultaneously allocated in distinct requests, potentially with
different semantics. Context IDs MUST NOT be reallocated re-allocated within a
given HTTP namespace but MAY be allocated in any order. The context Context
ID allocation restrictions to the use of even-numbered and odd-
numbered context Context IDs exist in order to avoid the need for
synchronization between endpoints. However, once a context Context ID has
been allocated, those restrictions do not apply to the use of the
context
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 Context ID. This document does
not define how registration occurs. Future extensions MAY use HTTP
header fields or capsules to register contexts. Context IDs. Depending on the
method being used, it is possible for datagrams to be received with
Context IDs that have not yet been registered. For instance, this
can be 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. 7, using notation from Section 1.3
of [QUIC]. Note that when HTTP Datagrams are encoded using QUIC
DATAGRAM frames [DGRAM], [QUIC-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),
UDP Proxying Payload (..),
}

Figure 6: 7: UDP Proxying HTTP Datagram Format

Context ID: A variable-length integer (see Section 16 of [QUIC])
that contains the value of the Context ID. If an HTTP/3 Datagram
that 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.
UDP Proxying Payload: The payload of the datagram, whose semantics
depend on the value of the previous field. Note that this field
can be empty.

UDP packets are encoded using HTTP Datagrams with the Context ID
field set to zero. When the Context ID field is set to zero, the UDP
Proxying Payload field contains the unmodified payload of a UDP
packet (referred to as "data
octets" 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 UDP Proxying Payload
field longer than 65527 using Context ID zero. An endpoint that
receives an HTTP Datagram using Context ID zero whose UDP Proxying
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 UDP
Proxying 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 occurring.
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 choose chooses to not buffer them.

6. Performance Considerations

Bursty traffic can often lead to temporally correlated packet losses;
in turn, this 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 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" 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], [QUIC-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
(PMTU). 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 PMTU
Discovery (DPLPMTUD) depend on [DPLPMTUD]. In this scenario, the UDP
proxy SHOULD drop the UDP payload and send an ICMP "Packet Packet Too Big" Big
message to the target; see Section 3.2 of [ICMP6].

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.

In this specification, note that UDP proxying clients do not have the
ability 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 it 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 with TCP CONNECT proxies when
considering them as infrastructure for abuse to enable denial-of-
service (DoS) 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 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 DoS 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

IANA has registered "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: RFC 9298

8.2. Well-Known URI

IANA has registered "masque" in the "Well-Known URIs" registry
maintained at <https://www.iana.org/assignments/well-known-uris>.

URI Suffix: masque
Change Controller: IETF
Reference: RFC 9298
Status: permanent
Related Information: Includes all resources identified with the path
prefix "/.well-known/masque/udp/"

9. References

9.1. Normative References

[DGRAM] Pauly, T., Kinnear, E.,

[ABNF] Crocker, D., Ed. and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 9221, 2234, DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/info/rfc9221>. 10.17487/RFC2234,
November 1997, <https://www.rfc-editor.org/info/rfc2234>.

[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/info/rfc3168>.

[EXT-CONNECT2]
McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/info/rfc8441>.

[EXT-CONNECT3]
Hamilton, R., "Bootstrapping WebSockets with HTTP/3",
RFC 9220, DOI 10.17487/RFC9220, June 2022,
<https://www.rfc-editor.org/info/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/info/rfc9110>.

[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August
2022, <https://www.rfc-editor.org/info/rfc9297>.

[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/info/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/info/rfc9113>.

[HTTP/3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/info/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/info/rfc9209>.

[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/info/rfc9000>.

[QUIC-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/info/rfc9221>.

[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>.

[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>.

[TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/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/info/rfc6570>.

[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.

[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/info/rfc3986>.

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/info/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/info/rfc8899>.

[ECN-TUNNEL]
Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/info/rfc6040>.

[HELIUM] Schwartz, B. M., "Hybrid Encapsulation Layer for IP and
UDP Messages (HELIUM)", Work in Progress, Internet-Draft,
draft-schwartz-httpbis-helium-00, 25 June 2018,
<https://datatracker.ietf.org/doc/html/draft-schwartz-
httpbis-helium-00>.

[HiNT] Pardue, L., "HTTP-initiated Network Tunnelling (HiNT)",
Work in Progress, Internet-Draft, draft-pardue-httpbis-
http-network-tunnelling-00, 2 July 2018,
<https://datatracker.ietf.org/doc/html/draft-pardue-
httpbis-http-network-tunnelling-00>.

[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/info/rfc4443>.

[MASQUE]

[MASQUE-ORIGINAL]
Schinazi, D., "The MASQUE Protocol", Work in Progress,
Internet-Draft, draft-schinazi-masque-00, 28 February
2019, <https://datatracker.ietf.org/doc/html/draft-
schinazi-masque-00>.

[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/info/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/info/rfc8085>.

[WEBSOCKET]
Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>.

Acknowledgments

This document is a product of the MASQUE Working Group, and the
author thanks all MASQUE enthusiasts for their contributions. This
proposal was inspired directly or indirectly by prior work from many
people, in particular [HELIUM] by Ben Schwartz, [HiNT] by Lucas
Pardue, and the original MASQUE Protocol [MASQUE] [MASQUE-ORIGINAL] 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.

Author's Address

David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: dschinazi.ietf@gmail.com