QUIC-Aware Proxying Using CONNECT-UDP
draft-pauly-masque-quic-proxy-01
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Tommy Pauly
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David Schinazi
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2021-04-13
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MASQUE T. Pauly
Internet-Draft Apple Inc.
Intended status: Experimental D. Schinazi
Expires: 15 October 2021 Google LLC
13 April 2021
QUIC-Aware Proxying Using CONNECT-UDP
draft-pauly-masque-quic-proxy-01
Abstract
This document defines an extension to the CONNECT-UDP HTTP method
that adds specific optimizations for QUIC connections that are
proxied. 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 through the 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-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 15 October 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Required Proxy State . . . . . . . . . . . . . . . . . . . . 5
2.1. Datagram Flow ID Mapping . . . . . . . . . . . . . . . . 5
2.2. Server Connection ID Mapping . . . . . . . . . . . . . . 6
2.3. Client Connection ID Mappings . . . . . . . . . . . . . . 6
2.4. Detecting Connection ID Conflicts . . . . . . . . . . . . 6
3. Connection ID Headers for CONNECT-UDP . . . . . . . . . . . . 7
4. Client Request Behavior . . . . . . . . . . . . . . . . . . . 8
4.1. New Proxied Connection Setup . . . . . . . . . . . . . . 8
4.2. Adding New Client Connection IDs . . . . . . . . . . . . 9
4.3. Sending With Forwarded Mode . . . . . . . . . . . . . . . 10
4.4. Receiving With Forwarded Mode . . . . . . . . . . . . . . 10
4.5. Opting Out of Forwarded Mode . . . . . . . . . . . . . . 11
5. Proxy Response Behavior . . . . . . . . . . . . . . . . . . . 11
5.1. Removing Mapping State . . . . . . . . . . . . . . . . . 13
5.2. Handling Connection Migration . . . . . . . . . . . . . . 13
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Interactions with Load Balancers . . . . . . . . . . . . . . 14
8. Packet Size Considerations . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. HTTP Headers . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The CONNECT-UDP HTTP method [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 CONNECT-UDP HTTP method 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.
This extension is only defined for HTTP/3 [HTTP3] and not any earlier
versions.
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 CONNECT-
UDP.
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.
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* 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.
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.
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 CONNECT-UDP 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.
* Datagram flow ID: represents a flow of HTTP/3 DATAGRAMs [H3DGRAM]
specific to a single client <-> proxy QUIC connection.
* 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.
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* Server-facing socket: the socket used to communicate between the
proxy and the target.
* 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.
* Server 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 server-facing
sockets for multiple connections and support the forwarding mode of
proxying.
QUIC packets can be either tunnelled within an HTTP/3 proxy
connection using QUIC DATAGRAM frames [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. Datagram Flow ID Mapping
Each pair of client <-> proxy QUIC connection and datagram flow ID
MUST be mapped to a single server-facing socket.
(Client <-> Proxy QUIC connection + Datagram flow ID)
=> Server-facing socket
Multiple datagram flow IDs can map to the same server-facing socket,
but a single datagram flow ID cannot be mapped to multiple server-
facing sockets.
This mapping guarantees that any QUIC packet using the datagram flow
ID sent from the client to the proxy in tunnelled mode can be sent to
the correct target.
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2.2. Server Connection ID Mapping
Each pair of Server Connection ID and client-facing socket MUST map
to a single server-facing socket.
(Client-facing socket + Server Connection ID)
=> Server-facing socket
Multiple pairs of Connection IDs and sockets can map to the same
server-facing socket.
This mapping guarantees that any QUIC packet containing the Server
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 server-facing socket MUST map
to a single datagram flow ID on a single client <-> proxy QUIC
connection. Additionally, the pair of Client Connection ID and
server-facing socket MUST map to a single client-facing socket.
(Server-facing socket + Client Connection ID)
=> (Client <-> Proxy QUIC connection + Datagram flow ID)
(Server-facing socket + Client Connection ID)
=> Client-facing socket
Multiple pairs of Connection IDs and sockets can map to the same
datagram flow ID 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 server-facing socket for every client request with
a unique datagram flow ID. The mapping is critical for any case
where server-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.
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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
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 Headers for CONNECT-UDP
This document defines two headers that can be used in CONNECT-UDP
requests and responses. All other requirements defined for CONNECT-
UDP [CONNECT-UDP] still apply.
Both "Client-Connection-Id" and "Server-Connection-Id" are Item
Structured Headers [STRUCT]. Their value MUST be a Byte Sequence.
The byte sequence MAY be zero-length. The byte sequence length MUST
NOT exceed 255 bytes. The ABNF is:
Client-Connection-Id = sf-binary
Server-Connection-Id = sf-binary
"Client-Connection-Id" contains the client connection ID, whereas
"Server-Connection-Id" contains the server connection ID.
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Like the Datagram-Flow-Id header [CONNECT-UDP], the Client-
Connection-Id and Server-Connection-Id headers can only be supported
by an HTTP/3 proxy. If a proxy does not support HTTP/3 datagrams
[H3DGRAM], or it does not support the extension defined in this
document, it MUST NOT send the Client-Connection-Id and Server-
Connection-Id headers on any responses. If a proxy does support this
extension, it MUST echo the Client-Connection-Id and Server-
Connection-Id headers on any 2xx (Successful) responses. Clients
that do not receive an echoed Client-Connection-Id or Server-
Connection-Id header MUST fall back to using CONNECT-UDP without the
extended behavior defined in this document.
4. Client Request Behavior
A client sends new CONNECT-UDP requests when it wants to start a new
QUIC connection to a target, when it has received a new Server
Connection ID for the target, and before it advertises a new Client
Connection ID to the target.
Each request MUST contain a Datagram-Flow-Id header and an authority
pseudo-header identifying the target. All requests for the same QUIC
Connection between a client and a target MUST contain the same
authority, and SHOULD contain the same Datagram-Flow-Id. If there is
Datagram-Flow-Id mismatch, the proxy will treat the requests as
different proxied connections, which could appear as a migration or
NAT rebinding event to the target.
Each request MUST also contain exactly one connection ID header,
either Client-Connection-Id or Server-Connection-Id. Client-
Connection-Id requests define paths for receiving packets from the
target server to the client, and Server-Connection-Id requests define
paths for sending packets from the client to target server.
4.1. New Proxied Connection Setup
The first time that a client uses a proxy for a given QUIC
connection, it selects a new datagram flow ID with an even-numbered
value [H3DGRAM].
The first request the clients makes MUST contain the authority
pseudo-header, the Datagram-Flow-Id header, and the Client-
Connection-Id header. These respectively contain the authority of
the target, the selected datagram flow ID and the Client Connection
ID that will be used in the initial QUIC packets sent through the
proxy.
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The client can start sending packets tunnelled within DATAGRAM frames
as soon as this first CONNECT-UDP request for the datagram flow ID
has been sent, even in the same QUIC packet to the proxy. That is,
the QUIC packet sent from the client to the proxy MAY contain a
STREAM frame containing the CONNECT-UDP request, as well as a
DATAGRAM frame that contains a tunnelled QUIC packet to send to the
target. This is particularly useful for reducing round trips on
connection setup.
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 409 (Conflict)
status. 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.
Note that packets sent in DATAGRAM frames before the proxy has sent
its CONNECT-UDP response might be dropped if the proxy rejects the
request. Specifically, this can occur if the Client Connection ID
causes a conflict and the proxy returns a 409 (Conflict) error. Any
DATAGRAM frames that are sent in a separate QUIC packet from the
STREAM frame that contains the CONNECT-UDP request might also be
dropped in the case that the packet arrives at the proxy before the
packet containing the STREAM frame.
If the server rejects the first request that uses a specific datagram
flow ID, the client MUST retire that datagram flow ID. 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.
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Prior to informing the target of a new chosen client connection ID,
the client MUST send a CONNECT-UDP request with the Client-
Connection-Id header to the proxy, and only inform the target of the
new client connection ID once a 2xx (Successful) response is
received.
4.3. Sending With Forwarded Mode
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 request
containing the Server-Connection-Id header to request the ability to
forward packets. The client MUST wait for a successful (2xx)
response before using forwarded mode. Prior to receiving the server
response, the client MUST send short header packets tunnelled in
DATAGRAM frames. The client MAY also choose to tunnel some short
header packets even after receiving the successful response.
If the client's request that included the Server-Connection-Id is
rejected, for example with a 409 (Conflict) response, it MUST NOT
forward packets to the requested Server 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. For any
response code other than a 2xx success, the client MUST NOT retry a
request for the same Server Connection ID. For errors other than 409
(Conflict), clients SHOULD stop sending requests for other Server
Connection IDs in the future.
QUIC long header packets MUST NOT be forwarded. These packets can
only be tunnelled within 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
A proxy MUST NOT forward packets from the target to the client until
after the client has sent at least one packet in forwarded mode.
Once this occurs, the proxy MAY use forwarded mode for any Client
Connection ID for which it has a valid mapping.
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If a client has started using forwarding mode, it MUST be prepared to
receive forwarded short header packets on the socket between itself
and the proxy for any Client Connection ID that has been accepted by
the proxy. The client uses the received Connection ID to determine
if a packet was originated by the proxy, or merely forwarded from the
target.
4.5. Opting Out of Forwarded Mode
The use of forwarded mode is initiated by the client sending a
request with the Server-Connection-Id header and sending at least one
forwarded packet to the proxy. A client that does not wish to accept
forwarded packets from the proxy when communicating with a specific
target can simply not start forwarding packets to the proxy.
5. Proxy Response Behavior
Upon receipt of a CONNECT-UDP request that contains a Client-
Connection-Id or Server-Connection-Id header, the proxy validates the
request, tries to establish the appropriate mappings as described in
Section 2, and establishes a new server-facing socket if necessary.
The proxy MUST validate that the request only contains one of either
the Client-Connection-Id or the Server-Connection-Id header, along
with a Datagram-Flow-Id header and an authority pseudo-header. If
any of these conditions is not met, the proxy MUST reject the request
with a 400 (Bad Request) response. The proxy also MUST reject the
request if the requested datagram flow ID has already been used on
that client <-> proxy QUIC connection with a different requested
authority.
The proxy then determines the server-facing socket to associate with
the client's datagram flow. This will generally involve performing a
DNS lookup for the hostname in the request authority, or finding an
existing server-facing socket to the authority. The server-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 server-facing sockets
across multiple datagram flows, or have a unique server-facing socket
for every datagram flow.
If a proxy reuses server-facing sockets, it SHOULD store which
authorities (which could be a domain name or IP address literal) are
being accessed over a particular server-facing socket so it can avoid
performing a new DNS query and potentially choosing a different
server IP address which could map to a different server.
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Server-facing sockets MUST NOT be reused across QUIC and non-QUIC
CONNECT-UDP requests, since it might not be possible to correctly
demultiplex or direct the traffic. Any packets received on a server-
facing socket used for proxying QUIC that does not correspond to a
known Connection ID MUST be dropped.
If the request includes a Client-Connection-Id header, the proxy 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 server-facing socket does not create a conflict, the
proxy creates the mapping and responds with a 200 (OK) response.
After this point, any packets received by the proxy from the server-
facing socket that match the Client Connection ID can to be sent to
the client. The proxy MUST use tunnelled mode (DATAGRAM frames) on
the correct datagram flow for any long header packets. The proxy
SHOULD forward directly to the client for any matching short header
packets, but MAY tunnel them in DATAGRAM frames. If the pair is not
unique, or the proxy chooses not to support zero-length Client
Connection IDs, the proxy responds with a 409 (Conflict) response.
If this occurs on the first request for a given datagram flow, the
proxy removes any mapping for that datagram flow.
If the request includes a Server-Connection-Id header, the proxy is
receiving a request to allow the client to forward packets to the
target. If the pair of this Server 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 200 (OK)
response. Once the successful response is sent, the proxy will
forward any short header packets received on the client-facing socket
that use the Server Connection ID using the correct server-facing
socket. If the pair is not unique, the server responds with a 409
(Conflict) response. If this occurs, traffic for that Server
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 requests that include the Server-Connection-Id header with a
response to indicate the error, such as 403 (Forbidden).
Any successful (2xx) response MUST also echo any Client-Connection-
Id, Server-Connection-Id, and Datagram-Flow-Id headers included in
the request.
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 Server Connection IDs. Packets sent by the client that
are forwarded SHOULD be considered as activity for restarting QUIC's
Idle Timeout [QUIC].
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5.1. Removing Mapping State
Each CONNECT-UDP request consumes one bidirectional HTTP/3 stream
[HTTP3]. For any stream on which the proxy has sent a response
indicating success, any mappings for the request last as long as the
stream is open.
A client that no longer wants a given Connection ID to be forwarded
by the proxy, for either direction, MUST cancel its CONNECT-UDP
HTTP/3 request by closing the corresponding stream.
If the proxy rejects a CONNECT-UDP request by sending a status code
of 300 or higher, it MUST close the corresponding stream and remove
any associated mappings.
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 server-facing socket once all datagram flows
mapped to that socket have been removed.
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. It
selects the next open datagram flow ID (2). In order to inform a
proxy of the new QUIC Client Connection ID, and binds that connection
ID to datagram flow ID 2, the client sends the following CONNECT-UDP
request:
HEADERS
:method = CONNECT-UDP
:authority = target.example.com:443
client-connection-id = :MTIzNA==:
datagram-flow-id = 2
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The client will also send the initial QUIC packet with the Long
Header form in a DATAGRAM frame with flow ID 2.
Once the proxy sends a 200 response indicating success, packets
received by the proxy that match the Connection ID 0x31323334 will be
directly forwarded to the client. The proxy will also forward the
initial QUIC packet received on DATAGRAM flow ID 2 to
target.example.com:443.
When the proxy receives a response from target.example.com:443 that
has 0x31323334 as the Destination Connection ID, the proxy will
forward that packet to the client on DATAGRAM flow ID 2.
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. In this case, that ID is 0x61626364. The client sends the
following request:
HEADERS
:method = CONNECT-UDP
:authority = target.example.com:443
server-connection-id = :YWJjZA==:
datagram-flow-id = 2
The client also sends its reply to the target server in a DATAGRAM
frame on flow ID 2 after sending the new request.
Once the proxy sends a 200 response indicating success, packets sent
by the client that match the Connection ID 0x61626364 will be
forwarded to the target server, i.e., without proxy decryption.
Upon receiving the response, 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
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Destination Connection IDs that belong to the end 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 CONNECT-UDP 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 sending 2xx
(Successful) responses to clients.
QUIC-aware CONNECT-UDP 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
DATAGRAM frames that are used for a QUIC-aware CONNECT-UDP 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
packet within a 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 packets 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 DATAGRAM contents are written to the target.)
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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 Headers
This document registers the "Client-Connection-Id" and "Server-
Connection-Id" headers in the "Permanent Message Header Field Names"
<https://www.iana.org/assignments/message-headers>.
+----------------------+----------+--------+---------------+
| Header Field Name | Protocol | Status | Reference |
+----------------------+----------+--------+---------------+
| Client-Connection-Id | http | exp | This document |
+----------------------+----------+--------+---------------+
| Server-Connection-Id | http | exp | This document |
+----------------------+----------+--------+---------------+
11. References
11.1. Normative References
[CONNECT-UDP]
Schinazi, D., "The CONNECT-UDP HTTP Method", Work in
Progress, Internet-Draft, draft-ietf-masque-connect-udp-
03, 5 January 2021, <http://www.ietf.org/internet-drafts/
draft-ietf-masque-connect-udp-03.txt>.
[DGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-ietf-quic-datagram-01, 24 August 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
datagram-01.txt>.
[H3DGRAM] Schinazi, D., "Using QUIC Datagrams with HTTP/3", Work in
Progress, Internet-Draft, draft-schinazi-quic-h3-datagram-
05, 12 October 2020, <http://www.ietf.org/internet-drafts/
draft-schinazi-quic-h3-datagram-05.txt>.
[HTTP3] Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-33, 15 December 2020, <http://www.ietf.org/
internet-drafts/draft-ietf-quic-http-33.txt>.
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[INVARIANTS]
Thomson, M., "Version-Independent Properties of QUIC",
Work in Progress, Internet-Draft, draft-ietf-quic-
invariants-13, 14 January 2021, <http://www.ietf.org/
internet-drafts/draft-ietf-quic-invariants-13.txt>.
[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", Work in Progress, Internet-Draft,
draft-ietf-quic-transport-34, 14 January 2021,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-
transport-34.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[STRUCT] Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-header-structure-19, 3 June 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
header-structure-19.txt>.
11.2. Informative References
[QUIC-LB] Duke, M. and N. Banks, "QUIC-LB: Generating Routable QUIC
Connection IDs", Work in Progress, Internet-Draft, draft-
ietf-quic-load-balancers-05, 30 October 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-quic-load-
balancers-05.txt>.
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
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Email: tpauly@apple.com
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043,
United States of America
Email: dschinazi.ietf@gmail.com
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