MASQUE T. Pauly
Internet-Draft Apple Inc.
Intended status: Experimental D. Schinazi
Expires: 6 September 2022 Google LLC
5 March 2022
QUIC-Aware Proxying Using HTTP
draft-pauly-masque-quic-proxy-03
Abstract
This document defines an extension to UDP Proxying over HTTP that
adds specific optimizations for proxied QUIC connections. This
extension allows a proxy to reuse UDP 4-tuples for multiple
connections. It also defines a mode of proxying in which QUIC short
header packets can be forwarded using an HTTP/3 proxy rather than
being re-encapsulated and re-encrypted.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/tfpauly/quic-proxy (https://github.com/tfpauly/
quic-proxy).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 6 September 2022.
Copyright Notice
Copyright (c) 2022 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 . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Required Proxy State . . . . . . . . . . . . . . . . . . . . 5
2.1. Stream Mapping . . . . . . . . . . . . . . . . . . . . . 5
2.2. Target Connection ID Mapping . . . . . . . . . . . . . . 5
2.3. Client Connection ID Mappings . . . . . . . . . . . . . . 6
2.4. Detecting Connection ID Conflicts . . . . . . . . . . . . 6
3. Connection ID Capsule Types . . . . . . . . . . . . . . . . . 7
4. Client Request Behavior . . . . . . . . . . . . . . . . . . . 8
4.1. New Proxied Connection Setup . . . . . . . . . . . . . . 9
4.2. Adding New Client Connection IDs . . . . . . . . . . . . 9
4.3. Sending With Forwarded Mode . . . . . . . . . . . . . . . 9
4.4. Receiving With Forwarded Mode . . . . . . . . . . . . . . 10
5. Proxy Response Behavior . . . . . . . . . . . . . . . . . . . 11
5.1. Removing Mapping State . . . . . . . . . . . . . . . . . 12
5.2. Handling Connection Migration . . . . . . . . . . . . . . 13
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Interactions with Load Balancers . . . . . . . . . . . . . . 15
8. Packet Size Considerations . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. HTTP Header . . . . . . . . . . . . . . . . . . . . . . 16
10.2. Capsule Types . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
UDP Proxying over HTTP [CONNECT-UDP] defines a way to send datagrams
through an HTTP proxy, where UDP is used to communicate between the
proxy and a target server. This can be used to proxy QUIC
connections [QUIC], since QUIC runs over UDP datagrams.
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This document uses the term "target" to refer to the server that a
client is accessing via a proxy. This target may be an origin
hosting content, or another proxy.
This document extends the UDP proxying protocol to add signalling
about QUIC Connection IDs. QUIC Connection IDs are used to identify
QUIC connections in scenarios where there is not a strict
bidirectional mapping between one QUIC connection and one UDP 4-tuple
(pairs of IP addresses and ports). A proxy that is aware of
Connection IDs can reuse UDP 4-tuples between itself and a target for
multiple proxied QUIC connections.
Awareness of Connection IDs also allows a proxy to avoid re-
encapsulation and re-encryption of proxied QUIC packets once a
connection has been established. When this functionality is present,
the proxy can support two modes for handling QUIC packets:
1. Tunnelled, in which client <-> target QUIC packets are
encapsulated inside client <-> proxy QUIC packets. These packets
use multiple layers of encryption and congestion control. QUIC
long header packets MUST use this mode. QUIC short header
packets MAY use this mode. This is the default mode for UDP
proxying.
2. Forwarded, in which client <-> target QUIC packets are sent
directly over the client <-> proxy UDP socket. These packets are
only encrypted using the client-target keys, and use the client-
target congestion control. This mode MUST only be used for QUIC
short header packets.
Forwarding is defined as an optimization to reduce CPU processing on
clients and proxies, as well as avoiding MTU overhead for packets on
the wire. This makes it suitable for deployment situations that
otherwise relied on cleartext TCP proxies, which cannot support QUIC
and have inferior security and privacy properties.
The properties provided by the forwarding mode are as follows:
* All packets sent between the client and the target traverse
through the proxy device.
* The target server cannot know the IP address of the client solely
based on the proxied packets the target receives.
* Observers of either or both of the client <-> proxy link and the
proxy <-> target are not able to learn more about the client <->
target communication than if no proxy was used.
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It is not a goal of forwarding mode to prevent correlation between
client <-> proxy and the proxy <-> target packets from an entity that
can observe both links. See Section 9 for further discussion.
Both clients and proxies can unilaterally choose to disable forwarded
mode for any client <-> target connection.
The forwarding mode of this extension is only defined for HTTP/3
[HTTP3] and not any earlier versions of HTTP. The forwarding mode
also requires special handling in order to be compatible with
intermediaries or load balancers (see Section 7).
QUIC proxies only need to understand the Header Form bit, and the
connection ID fields from packets in client <-> target QUIC
connections. Since these fields are all in the QUIC invariants
header [INVARIANTS], QUIC proxies can proxy all versions of QUIC.
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.
1.2. Terminology
This document uses the following terms:
* Client: the client of all QUIC connections discussed in this
document.
* Proxy: the endpoint that responds to the UDP proxying request.
* Target: the server that a client is accessing via a proxy.
* Client <-> Proxy QUIC connection: a single QUIC connection
established from the client to the proxy.
* Socket: a UDP 4-tuple (local IP address, local UDP port, remote IP
address, remote UDP port). In some implementations, this is
referred to as a "connected" socket.
* Client-facing socket: the socket used to communicate between the
client and the proxy.
* Target-facing socket: the socket used to communicate between the
proxy and the target.
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* Client Connection ID: a QUIC Connection ID that is chosen by the
client, and is used in the Destination Connection ID field of
packets from the target to the client.
* Target Connection ID: a QUIC Connection ID that is chosen by the
target, and is used in the Destination Connection ID field of
packets from the client to the target.
2. Required Proxy State
In the methods defined in this document, the proxy is aware of the
QUIC Connection IDs being used by proxied connections, along with the
sockets used to communicate with the client and the target. Tracking
Connection IDs in this way allows the proxy to reuse target-facing
sockets for multiple connections and support the forwarding mode of
proxying.
QUIC packets can be either tunnelled within an HTTP proxy connection
using HTTP Datagram frames [HTTP-DGRAM], or be forwarded directly
alongside an HTTP/3 proxy connection on the same set of IP addresses
and UDP ports. The use of forwarded mode requires the consent of
both the client and the proxy.
In order to correctly route QUIC packets in both tunnelled and
forwarded modes, the proxy needs to maintain mappings between several
items. There are three required unidirectional mappings, described
below.
2.1. Stream Mapping
Each pair of client <-> proxy QUIC connection and an HTTP stream MUST
be mapped to a single target-facing socket.
(Client <-> Proxy QUIC connection + Stream)
=> Target-facing socket
Multiple streams can map to the same target-facing socket, but a
single stream cannot be mapped to multiple target-facing sockets.
This mapping guarantees that any HTTP Datagram using a stream sent
from the client to the proxy in tunnelled mode can be sent to the
correct target.
2.2. Target Connection ID Mapping
Each pair of Target Connection ID and client-facing socket MUST map
to a single target-facing socket.
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(Client-facing socket + Target Connection ID)
=> Target-facing socket
Multiple pairs of Connection IDs and sockets can map to the same
target-facing socket.
This mapping guarantees that any QUIC packet containing the Target
Connection ID sent from the client to the proxy in forwarded mode can
be sent to the correct target. Thus, a proxy that does not allow
forwarded mode does not need to maintain this mapping.
2.3. Client Connection ID Mappings
Each pair of Client Connection ID and target-facing socket MUST map
to a single stream on a single client <-> proxy QUIC connection.
Additionally, the pair of Client Connection ID and target-facing
socket MUST map to a single client-facing socket.
(Target-facing socket + Client Connection ID)
=> (Client <-> Proxy QUIC connection + Stream)
(Target-facing socket + Client Connection ID)
=> Client-facing socket
Multiple pairs of Connection IDs and sockets can map to the same
stream or client-facing socket.
These mappings guarantee that any QUIC packet sent from a target to
the proxy can be sent to the correct client, in either tunnelled or
forwarded mode. Note that this mapping becomes trivial if the proxy
always opens a new target-facing socket for every client request with
a unique stream. The mapping is critical for any case where target-
facing sockets are shared or reused.
2.4. Detecting Connection ID Conflicts
In order to be able to route packets correctly in both tunnelled and
forwarded mode, proxies check for conflicts before creating a new
mapping. If a conflict is detected, the proxy will reject the
client's request, as described in Section 5.
Two sockets conflict if and only if all members of the 4-tuple (local
IP address, local UDP port, remote IP address, and remote UDP port)
are identical.
Two Connection IDs conflict if and only if one Connection ID is equal
to or a prefix of another. For example, a zero-length Connection ID
conflicts with all connection IDs. This definition of a conflict
originates from the fact that QUIC short headers do not carry the
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length of the Destination Connection ID field, and therefore if two
short headers with different Destination Connection IDs are received
on a shared socket, one being a prefix of the other prevents the
receiver from identifying which mapping this corresponds to.
The proxy treats two mappings as being in conflict when a conflict is
detected for all elements on the left side of the mapping diagrams
above.
Since very short Connection IDs are more likely to lead to conflicts,
particularly zero-length Connection IDs, a proxy MAY choose to reject
all requests for very short Connection IDs as conflicts, in
anticipation of future conflicts. Note that a request that doesn't
contain any Connection ID is equivalent to a request for a zero-
length Connection ID, and similarly would cause conflicts when
forwarding.
3. Connection ID Capsule Types
Proxy awareness of QUIC Connection IDs relies on using capsules
([HTTP-DGRAM]) to signal the addition and removal of client and
Target Connection IDs.
Note that these capsules do not register contexts. QUIC packets are
encoded using HTTP Datagrams with the context ID set to zero as
defined in [CONNECT-UDP].
The capsules used for QUIC-aware proxying allow a client to register
connection IDs with the proxy, and for the proxy to acknowledge or
reject the connection ID mappings.
The REGISTER_CLIENT_CID and REGISTER_TARGET_CID capsule types (see
Section 10.2 for the capsule type values) allow a client to inform
the proxy about a new Client Connection ID or a new Target Connection
ID, respectively. These capsule types MUST only be sent by a client.
The ACK_CLIENT_CID and ACK_TARGET_CID capsule types (see Section 10.2
for the capsule type values) are sent by the proxy to the client to
indicate that a mapping was successfully created for a registered
connection ID. These capsule types MUST only be sent by a proxy.
The CLOSE_CLIENT_CID and CLOSE_TARGET_CID capsule types (see
Section 10.2 for the capsule type values) allow either a client or a
proxy to remove a mapping for a connection ID. These capsule types
MAY be sent by either a client or the proxy. If a proxy sends a
CLOSE_CLIENT_CID without having sent an ACK_CLIENT_CID, or if a proxy
sends a CLOSE_TARGET_CID without having sent an ACK_TARGET_CID, it is
rejecting a Connection ID registration.
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All Connection ID capsule types share the same format:
Connection ID Capsule {
Type (i) = 0xffe100..0xffe103,
Length (i),
Connection ID (0..2040),
}
Figure 1: Connection ID Capsule Format
Connection ID: A connection ID being registered or acknowledged,
which is between 0 and 255 bytes in length. The length of the
connection ID is implied by the length of the capsule. Note that
in QUICv1, the length of the Connection ID is limited to 20 bytes,
but QUIC invariants allow up to 255 bytes.
4. Client Request Behavior
A client initiates UDP proxying via a CONNECT request as defined in
[CONNECT-UDP]. Within its request, it includes the "Proxy-QUIC-
Forwarding" header to indicate whether or not the request should
support forwarding. If this header is not included, the client MUST
NOT send any connection ID capsules.
The "Proxy-QUIC-Forwarding" is an Item Structured Header [RFC8941].
Its value MUST be a Boolean. Its ABNF is:
Proxy-QUIC-Forwarding = sf-boolean
If the client wants to enable QUIC packet forwarding for this
request, it sets the value to "?1". If it doesn't want to enable
forwarding, but instead only provide information about QUIC
Connection IDs for the purpose of allowing the proxy to share a
target-facing socket, it sets the value to "?0".
If the proxy supports QUIC-aware proxying, it will include the
"Proxy-QUIC-Forwarding" header in successful HTTP responses. The
value indicates whether or not the proxy supports forwarding. If the
client does not receive this header in responses, the client SHALL
assume that the proxy does not understand how to parse Connection ID
capsules, and MUST NOT send any Connection ID capsules.
The client sends a REGISTER_CLIENT_CID capsule whenever it advertises
a new Client Connection ID to the target, and a REGISTER_TARGET_CID
capsule when it has received a new Target Connection ID for the
target. Note that the initial REGISTER_CLIENT_CID capsule MAY be
sent prior to receiving an HTTP response from the proxy.
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4.1. New Proxied Connection Setup
To initiate QUIC-aware proxying, the client sends a
REGISTER_CLIENT_CID capsule containing the initial Client Connection
ID that the client has advertised to the target.
If the mapping is created successfully, the client will receive a
ACK_CLIENT_CID capsule that contains the same connection ID that was
requested.
Since clients are always aware whether or not they are using a QUIC
proxy, clients are expected to cooperate with proxies in selecting
Client Connection IDs. A proxy detects a conflict when it is not
able to create a unique mapping using the Client Connection ID
(Section 2.4). It can reject requests that would cause a conflict
and indicate this to the client by replying with a CLOSE_CLIENT_CID
capsule. In order to avoid conflicts, clients SHOULD select Client
Connection IDs of at least 8 bytes in length with unpredictable
values. A client also SHOULD NOT select a Client Connection ID that
matches the ID used for the QUIC connection to the proxy, as this
inherently creates a conflict.
If the rejection indicated a conflict due to the Client Connection
ID, the client MUST select a new Connection ID before sending a new
request, and generate a new packet. For example, if a client is
sending a QUIC Initial packet and chooses a Connection ID that
conflicts with an existing mapping to the same target server, it will
need to generate a new QUIC Initial.
4.2. Adding New Client Connection IDs
Since QUIC connection IDs are chosen by the receiver, an endpoint
needs to communicate its chosen connection IDs to its peer before the
peer can start using them. In QUICv1, this is performed using the
NEW_CONNECTION_ID frame.
Prior to informing the target of a new chosen client connection ID,
the client MUST send a REGISTER_CLIENT_CID capsule request containing
the new Client Connection ID.
The client should only inform the target of the new Client Connection
ID once an ACK_CLIENT_CID capsule is received that contains the
echoed connection ID.
4.3. Sending With Forwarded Mode
Support for forwarding mode is determined by the "Proxy-QUIC-
Forwarding" header, see Section 5.
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Once the client has learned the target server's Connection ID, such
as in the response to a QUIC Initial packet, it can send a
REGISTER_TARGET_CID capsule containing the Target Connection ID to
request the ability to forward packets.
The client MUST wait for an ACK_TARGET_CID capsule that contains the
echoed connection ID before using forwarded mode.
Prior to receiving the proxy server response, the client MUST send
short header packets tunnelled in HTTP Datagram frames. The client
MAY also choose to tunnel some short header packets even after
receiving the successful response.
If the Target Connection ID registration is rejected, for example
with a CLOSE_TARGET_CID capsule, it MUST NOT forward packets to the
requested Target Connection ID, but only use tunnelled mode. The
request might also be rejected if the proxy does not support
forwarded mode or has it disabled by policy.
QUIC long header packets MUST NOT be forwarded. These packets can
only be tunnelled within HTTP Datagram frames to avoid exposing
unnecessary connection metadata.
When forwarding, the client sends a QUIC packet with the target
server's Connection ID in the QUIC short header, using the same
socket between client and proxy that was used for the main QUIC
connection between client and proxy.
4.4. Receiving With Forwarded Mode
If the client has indicated support for forwarding with the "Proxy-
QUIC-Forwarding" header, the proxy MAY use forwarded mode for any
Client Connection ID for which it has a valid mapping.
Once a client has sent "Proxy-QUIC-Forwarding" with a value of "?1",
it MUST be prepared to receive forwarded short header packets on the
socket between itself and the proxy for any Client Connection ID that
it has registered with a REGISTER_CLIENT_CID capsule. The client
uses the Destination Connection ID field of the received packet to
determine if the packet was originated by the proxy, or merely
forwarded from the target.
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5. Proxy Response Behavior
Upon receipt of a CONNECT request that includes the "Proxy-QUIC-
Forwarding" header, the proxy indicates to the client that it
supports QUIC-aware proxying by including a "Proxy-QUIC-Forwarding"
header in a successful response. If it supports QUIC packet
forwarding, it sets the value to "?1"; otherwise, it sets it to "?0".
Upon receipt of a REGISTER_CLIENT_CID or REGISTER_TARGET_CID capsule,
the proxy validates the registration, tries to establish the
appropriate mappings as described in Section 2.
The proxy MUST reply to each REGISTER_CLIENT_CID capsule with either
an ACK_CLIENT_CID or CLOSE_CLIENT_CID capsule containing the
Connection ID that was in the registration capsule.
Similarly, the proxy MUST reply to each REGISTER_TARGET_CID capsule
with either an ACK_TARGET_CID or CLOSE_TARGET_CID capsule containing
the Connection ID that was in the registration capsule.
The proxy then determines the target-facing socket to associate with
the client's request. This will generally involve performing a DNS
lookup for the target hostname in the CONNECT request, or finding an
existing target-facing socket to the authority. The target-facing
socket might already be open due to a previous request from this
client, or another. If the socket is not already created, the proxy
creates a new one. Proxies can choose to reuse target-facing sockets
across multiple UDP proxying requests, or have a unique target-facing
socket for every UDP proxying request.
If a proxy reuses target-facing sockets, it SHOULD store which
authorities (which could be a domain name or IP address literal) are
being accessed over a particular target-facing socket so it can avoid
performing a new DNS query and potentially choosing a different
target server IP address which could map to a different target
server.
Target-facing sockets MUST NOT be reused across QUIC and non-QUIC UDP
proxy requests, since it might not be possible to correctly
demultiplex or direct the traffic. Any packets received on a target-
facing socket used for proxying QUIC that does not correspond to a
known Connection ID MUST be dropped.
When the proxy recieves a REGISTER_CLIENT_CID capsule, it is
receiving a request to be able to route traffic back to the client
using that Connection ID. If the pair of this Client Connection ID
and the selected target-facing socket does not create a conflict, the
proxy creates the mapping and responds with a ACK_CLIENT_CID capsule.
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After this point, any packets received by the proxy from the target-
facing socket that match the Client Connection ID can to be sent to
the client. The proxy MUST use tunnelled mode (HTTP Datagram frames)
for any long header packets. The proxy SHOULD forward directly to
the client for any matching short header packets if forwarding is
supported by the client, but the proxy MAY tunnel these packets in
HTTP Datagram frames instead. If the mapping would create a
conflict, the proxy responds with a CLOSE_CLIENT_CID capsule.
When the proxy recieves a REGISTER_TARGET_CID capsule, it is
receiving a request to allow the client to forward packets to the
target. If the pair of this Target Connection ID and the client-
facing socket on which the request was received does not create a
conflict, the proxy creates the mapping and responds with a
ACK_TARGET_CID capsule. Once the successful response is sent, the
proxy will forward any short header packets received on the client-
facing socket that use the Target Connection ID using the correct
target-facing socket. If the pair is not unique, the proxy responds
with a CLOSE_TARGET_CID capsule. If this occurs, traffic for that
Target Connection ID can only use tunnelled mode, not forwarded.
If the proxy does not support forwarded mode, or does not allow
forwarded mode for a particular client or authority by policy, it can
reject all REGISTER_TARGET_CID requests with CLOSE_TARGET_CID
capsule.
The proxy MUST only forward non-tunnelled packets from the client
that are QUIC short header packets (based on the Header Form bit) and
have mapped Target Connection IDs. Packets sent by the client that
are forwarded SHOULD be considered as activity for restarting QUIC's
Idle Timeout [QUIC].
5.1. Removing Mapping State
For any connection ID for which the proxy has sent an
acknowledgement, any mappings for the connection ID last until either
endpoint sends a close capsule or the either side of the HTTP stream
closes.
A client that no longer wants a given Connection ID to be forwarded
by the proxy sends a CLOSE_CLIENT_CID or CLOSE_TARGET_CID capsule.
If a client's connection to the proxy is terminated for any reason,
all mappings associated with all requests are removed.
A proxy can close its target-facing socket once all UDP proxying
requests mapped to that socket have been removed.
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5.2. Handling Connection Migration
If a proxy supports QUIC connection migration, it needs to ensure
that a migration event does not end up sending too many tunnelled or
proxied packets on a new path prior to path validation.
Specifically, the proxy MUST limit the number of packets that it will
proxy to an unvalidated client address to the size of an initial
congestion window. Proxies additionally SHOULD pace the rate at
which packets are sent over a new path to avoid creating
unintentional congestion on the new path.
6. Example
Consider a client that is establishing a new QUIC connection through
the proxy. It has selected a Client Connection ID of 0x31323334. In
order to inform a proxy of the new QUIC Client Connection ID, the
client also sends a REGISTER_CLIENT_CID capsule.
The client will also send the initial QUIC packet with the Long
Header form in an HTTP datagram.
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Client Server
STREAM(44): HEADERS -------->
:method = CONNECT
:protocol = connect-udp
:scheme = https
:path = /target.example.com/443/
:authority = proxy.example.org
proxy-quic-forwarding = ?1
capsule-protocol = ?1
STREAM(44): DATA -------->
Capsule Type = REGISTER_CLIENT_CID
Connection ID = 0x31323334
DATAGRAM -------->
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated QUIC initial
<-------- STREAM(44): HEADERS
:status = 200
proxy-quic-forwarding = ?1
capsule-protocol = ?1
<-------- STREAM(44): DATA
Capsule Type = ACK_CLIENT_CID
Connection ID = 0x31323334
/* Wait for target server to respond to UDP packet. */
<-------- DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated QUIC initial
Once the client learns which Connection ID has been selected by the
target server, it can send a new request to the proxy to establish a
mapping for forwarding. In this case, that ID is 0x61626364. The
client sends the following capsule:
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STREAM(44): DATA -------->
Capsule Type = REGISTER_TARGET_CID
Connection ID = 0x61626364
<-------- STREAM(44): DATA
Capsule Type = ACK_TARGET_CID
Connection ID = 0x61626364
Upon receiving an ACK_TARGET_CID capsule, the client starts sending
Short Header packets with a Destination Connection ID of 0x61626364
directly to the proxy (not tunnelled), and these are forwarded
directly to the target by the proxy. Similarly, Short Header packets
from the target with a Destination Connection ID of 0x31323334 are
forwarded directly to the client.
7. Interactions with Load Balancers
Some QUIC servers are accessed using load balancers, as described in
[QUIC-LB]. These load balancers route packets to servers based on
the server's Connection ID. These Connection IDs are generated in a
way that can be coordinated between servers and their load balancers.
If a proxy that supports this extension is itself running behind a
load balancer, extra complexity arises once clients start using
forwarding mode and sending packets to the proxy that have
Destination Connection IDs that belong to the target servers, not the
proxy. If the load balancer is not aware of these Connection IDs, or
the Connection IDs conflict with other Connection IDs used by the
load balancer, packets can be routed incorrectly.
QUIC-aware proxies that use forwarding mode generally SHOULD NOT be
run behind load balancers; and if they are, they MUST coordinate
between the proxy and the load balancer to create mappings for
proxied Connection IDs prior to the proxy ACK_CLIENT_CID or
ACK_TARGET_CID capsules to clients.
QUIC-aware proxies that do not allow forwarding mode can function
unmodified behind QUIC load balancers.
8. Packet Size Considerations
Since Initial QUIC packets must be at least 1200 bytes in length, the
HTTP Datagram frames that are used for a QUIC-aware proxy MUST be
able to carry at least 1200 bytes.
Additionally, clients that connect to a proxy for purpose of proxying
QUIC SHOULD start their connection with a larger packet size than
1200 bytes, to account for the overhead of tunnelling an Initial QUIC
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packet within an HTTP Datagram frame. If the client does not begin
with a larger packet size than 1200 bytes, it will need to perform
Path MTU (Maximum Transmission Unit) discovery to discover a larger
path size prior to sending any tunnelled Initial QUIC packets.
Once a proxied QUIC connections moves into forwarded mode, the client
SHOULD initiate Path MTU discovery to increase its end-to-end MTU.
9. Security Considerations
Proxies that support this extension SHOULD provide protections to
rate-limit or restrict clients from opening an excessive number of
proxied connections, so as to limit abuse or use of proxies to launch
Denial-of-Service attacks.
Sending QUIC packets by forwarding through a proxy without tunnelling
exposes some QUIC header metadata to onlookers, and can be used to
correlate packet flows if an attacker is able to see traffic on both
sides of the proxy. Tunnelled packets have similar inference
problems. An attacker on both sides of the proxy can use the size of
ingress and egress packets to correlate packets belonging to the same
connection. (Absent client-side padding, tunneled packets will
typically have a fixed amount of overhead that is removed before
their HTTP Datagram contents are written to the target.)
Since proxies that forward QUIC packets do not perform any
cryptographic integrity check, it is possible that these packets are
either malformed, replays, or otherwise malicious. This may result
in proxy targets rate limiting or decreasing the reputation of a
given proxy.
10. IANA Considerations
10.1. HTTP Header
This document registers the "Proxy-QUIC-Forwarding" header in the
"Permanent Message Header Field Names"
<https://www.iana.org/assignments/message-headers>.
+-----------------------+----------+--------+---------------+
| Header Field Name | Protocol | Status | Reference |
+-----------------------+----------+--------+---------------+
| Proxy-QUIC-Forwarding | http | exp | This document |
+-----------------------+----------+--------+---------------+
Figure 2: Registered HTTP Header
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10.2. Capsule Types
This document registers six new values in the "HTTP Capsule Types"
registry established by [HTTP-DGRAM].
+=====================+==========+===============+
| Capule Type | Value | Specification |
+=====================+==========+===============+
| REGISTER_CLIENT_CID | 0xffe100 | This Document |
+---------------------+----------+---------------+
| REGISTER_TARGET_CID | 0xffe101 | This Document |
+---------------------+----------+---------------+
| ACK_CLIENT_CID | 0xffe102 | This Document |
+---------------------+----------+---------------+
| ACK_TARGET_CID | 0xffe103 | This Document |
+---------------------+----------+---------------+
| CLOSE_CLIENT_CID | 0xffe104 | This Document |
+---------------------+----------+---------------+
| CLOSE_TARGET_CID | 0xffe105 | This Document |
+---------------------+----------+---------------+
Table 1: Registered Capsule Types
11. References
11.1. Normative References
[CONNECT-UDP]
Schinazi, D., "UDP Proxying Support for HTTP", Work in
Progress, Internet-Draft, draft-ietf-masque-connect-udp-
07, 4 March 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-masque-connect-udp-07>.
[HTTP-DGRAM]
Schinazi, D. and L. Pardue, "Using Datagrams with HTTP",
Work in Progress, Internet-Draft, draft-ietf-masque-h3-
datagram-06, 4 March 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-masque-
h3-datagram-06>.
[HTTP3] 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>.
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[INVARIANTS]
Thomson, M., "Version-Independent Properties of QUIC",
RFC 8999, DOI 10.17487/RFC8999, May 2021,
<https://www.rfc-editor.org/rfc/rfc8999>.
[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>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
11.2. Informative References
[QUIC-LB] Duke, M., Banks, N., and C. Huitema, "QUIC-LB: Generating
Routable QUIC Connection IDs", Work in Progress, Internet-
Draft, draft-ietf-quic-load-balancers-12, 11 February
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
quic-load-balancers-12>.
Acknowledgments
Thanks to Lucas Pardue, Ryan Hamilton, and Mirja Kuehlewind for their
inputs on this document.
Authors' Addresses
Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Email: tpauly@apple.com
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David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Email: dschinazi.ietf@gmail.com
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