QUIC-Aware Proxying Using HTTP
draft-ietf-masque-quic-proxy-04
| Document | Type | Active Internet-Draft (masque WG) | |
|---|---|---|---|
| Authors | Tommy Pauly , Eric Rosenberg , David Schinazi | ||
| Last updated | 2024-10-18 | ||
| Replaces | draft-pauly-masque-quic-proxy | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-masque-quic-proxy-04
MASQUE T. Pauly
Internet-Draft E. Rosenberg
Intended status: Experimental Apple Inc.
Expires: 22 April 2025 D. Schinazi
Google LLC
19 October 2024
QUIC-Aware Proxying Using HTTP
draft-ietf-masque-quic-proxy-04
Abstract
This document extends UDP Proxying over HTTP to add optimizations for
proxied QUIC connections. Specifically, it allows a proxy to reuse
UDP 4-tuples for multiple proxied connections, and adds a mode of
proxying in which QUIC short header packets can be forwarded and
transformed through a HTTP/3 proxy rather than being fully re-
encapsulated and re-encrypted.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://ietf-wg-
masque.github.io/draft-ietf-masque-quic-proxy/draft-ietf-masque-quic-
proxy.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-masque-quic-proxy/.
Discussion of this document takes place on the MASQUE Working Group
mailing list (mailto:masque@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/masque/. Subscribe at
https://www.ietf.org/mailman/listinfo/masque/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-masque/draft-ietf-masque-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/.
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 22 April 2025.
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Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Connection ID Awareness . . . . . . . . . . . . . . . . . 7
2.2. Virtual Connection IDs . . . . . . . . . . . . . . . . . 8
2.3. Negotiating Modes and Connection IDs . . . . . . . . . . 10
3. Proxy-QUIC-Forwarding Header . . . . . . . . . . . . . . . . 11
4. Connection ID Capsules . . . . . . . . . . . . . . . . . . . 12
4.1. REGISTER_CLIENT_CID . . . . . . . . . . . . . . . . . . . 13
4.2. REGISTER_TARGET_CID . . . . . . . . . . . . . . . . . . . 14
4.3. ACK_CLIENT_CID . . . . . . . . . . . . . . . . . . . . . 14
4.4. ACK_TARGET_CID . . . . . . . . . . . . . . . . . . . . . 15
4.5. ACK_CLIENT_VCID . . . . . . . . . . . . . . . . . . . . . 17
4.6. CLOSE_CLIENT_CID and CLOSE_TARGET_CID . . . . . . . . . . 18
4.7. MAX_CONNECTION_IDS . . . . . . . . . . . . . . . . . . . 18
4.8. Detecting Conflicts . . . . . . . . . . . . . . . . . . . 18
4.9. Client Considerations . . . . . . . . . . . . . . . . . . 19
4.9.1. New Proxied Connection Setup . . . . . . . . . . . . 20
4.9.2. Adding New Client Connection IDs . . . . . . . . . . 20
4.10. Proxy Considerations . . . . . . . . . . . . . . . . . . 21
4.10.1. Closing Proxy State . . . . . . . . . . . . . . . . 22
5. Using Forwarded Mode . . . . . . . . . . . . . . . . . . . . 23
5.1. Sending With Forwarded Mode . . . . . . . . . . . . . . . 23
5.2. Receiving With Forwarded Mode . . . . . . . . . . . . . . 24
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5.3. Packet Transforms . . . . . . . . . . . . . . . . . . . . 24
5.3.1. The identify transform . . . . . . . . . . . . . . . 25
5.3.2. The scramble transform . . . . . . . . . . . . . . . 25
5.4. Connection Maintenance in Forwarded Mode . . . . . . . . 27
5.5. Handling Connection Migration . . . . . . . . . . . . . . 27
5.6. Handling ECN Marking . . . . . . . . . . . . . . . . . . 28
5.7. Stateless Resets for Forwarded Mode QUIC Packets . . . . 29
5.7.1. Stateless Resets from the Target . . . . . . . . . . 29
6. Example Exchange . . . . . . . . . . . . . . . . . . . . . . 30
7. Packet Size Considerations . . . . . . . . . . . . . . . . . 32
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33
8.1. Passive Attacks . . . . . . . . . . . . . . . . . . . . . 33
8.2. Active Attacks . . . . . . . . . . . . . . . . . . . . . 33
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
9.1. HTTP Header . . . . . . . . . . . . . . . . . . . . . . . 34
9.2. Proxy QUIC Forwarding Parameter Names . . . . . . . . . . 35
9.3. Packet Transform Names . . . . . . . . . . . . . . . . . 35
9.4. Capsule Types . . . . . . . . . . . . . . . . . . . . . . 36
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.1. Normative References . . . . . . . . . . . . . . . . . . 36
10.2. Informative References . . . . . . . . . . . . . . . . . 37
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
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.
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 server
hosting content, or another proxy for cases where proxies are chained
together.
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 one-to-one
mapping between QUIC connections and UDP 4-tuples (pairs of IP
addresses and ports).
Once a proxy is aware of QUIC Connection IDs, it can reuse UDP
4-tuples between itself and a target for multiple proxied QUIC
connections.
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For proxies that are themselves running on HTTP/3 [HTTP3], and thus
are accessed by clients over QUIC, QUIC Connection IDs can be used to
treat packets differently on the link between clients and proxies.
New QUIC Connection IDs can be assigned to perform transformations to
the packets that allow for efficient forwarding of packets that don't
require full re-encapsulation and re-encryption of proxied QUIC
packets within datagrams inside the QUIC connection between clients
and proxies.
This document defines two modes for proxying QUIC connections,
"tunnelled" and "forwarded":
1. Tunnelled is the default mode for UDP proxying, defined in
[CONNECT-UDP]. In this mode, packets in QUIC connection between
the client and target are encapsulated inside the QUIC connection
between the client and proxy. These packets use multiple layers
of encryption and congestion control.
2. Forwarded is the mode of proxying added by this document. In
this mode, packets in the QUIC connection between the client and
target are sent with dedicated QUIC Connection IDs between the
client and proxy, and use special-purpose tranforms instead of
full re-encapsulation and re-encryption.
QUIC long header packets between clients and targets MUST be proxied
in tunnelled mode. QUIC short header packets between clients and
targets MAY be proxied in forwarded mode, subject to negotiation
between a client and a proxy.
Forwarded mode is an optimization to reduce CPU and memory cost to
clients and proxies and avoid encapsulation overhead for packets on
the wire that reduce the effective MTU (Maximum Transmission Unit).
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 forwarded 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 links between client and proxy
and between proxy and target are not able to learn more about the
client-to-target communication than if no proxy was used.
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Forwarded mode does not prevent correlation of packets on the link
between client and proxy and the link between proxy and target by an
entity that can observe both links. The precise risks depend on the
negotiated transform (Section 5.3). See Section 8 for further
discussion.
Both clients and proxies can unilaterally choose to disable forwarded
mode for any client-to-target connection.
The forwarded mode of proxying is only defined for HTTP/3 [HTTP3] and
not any earlier versions of HTTP.
QUIC proxies only need to understand the Header Form bit, and the
connection ID fields from packets in client-to-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-to-proxy 4-tuple: the UDP 4-tuple (client IP address,
client UDP port, proxy IP address, proxy UDP port) used to
communicate between the client and the proxy.
* Proxy-to-target 4-tuple: the UDP 4-tuple (proxy IP address, proxy
UDP port, target IP address, target UDP port) used to communicate
between the proxy and the target.
* Client Connection ID (CID): 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.
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* Target Connection ID (CID): 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.
* Virtual Connection ID (VCID): a fake QUIC Connection ID chosen by
the proxy that is used on the client-to-proxy 4-tuple in forwarded
mode.
* Client VCID: a VCID used by the proxy to send forwarded packets
from the target to the client.
* Target VCID: a VCID used by the client to send forwarded packets
to the target via the proxy.
* Packet Transform: the procedure used to modify packets before they
enter the client-proxy link.
2. Protocol Overview
QUIC-aware proxying involves a client, a proxy, and a target.
Although multiple proxies can be chained together in sequence (which
is a main motivation for enabling forwarded mode), each subsequent
proxy is just treated as a target by the preceding proxy.
+--------+ +-----------+ +--------+
| | | | | |
| Client +--------------+ Proxy +--------------+ Target |
| | | | | |
+--------+ +-----------+ +--------+
<----------- Client-to-target connection ----------->
<-- Client-to-proxy --> <-- Proxy-to-target -->
4-tuple 4-tuple
Figure 1: Diagram of roles in QUIC-aware proxying
All QUIC-aware proxying relies on the proxy learning information
about QUIC connection IDs on the client-to-target QUIC connection
(Section 2.1).
Forwarded mode adds the concept of Virtual Connection IDs that are
assigned by the proxy to use to identify packets on the client-to-
proxy 4-tuple (Section 2.2).
Negotation of modes and assignment of connection IDs is described in
Section 2.3.
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2.1. Connection ID Awareness
For a proxy to be aware of proxied QUIC connection IDs, it needs to
know and correlate three values:
1. The HTTP stream used to proxy a client-to-target QUIC connection
2. The client-chosen connection ID on the client-to-target QUIC
connection, or the "client CID"
3. The target-chosen connection ID on the client-to-target QUIC
connection, or the "target CID"
For example, consider a proxy using HTTP/3 that has two clients (A
and B) connected simultaneously, each client coming from a different
IP address and port. Each client makes a request to proxy a UDP flow
to "target.example.net" on port 443. If the proxy knows that client
A's connection to the target has negotiated a client CID AAAA0000 and
a target CID 0000AAAA, and client B's connection to the target has
negotiated a client CID BBBB0000 and a target CID 0000BBBB, then the
proxy would be able to use the same proxy-to-target 4-tuple for both
connections, because it can route packets from the target to the
correct client based on CID AAAA0000 or BBBB0000.
<---------- Client A-to-target connection ---------->
AAAA0000 0000AAAA
+--------+ +-----------+
| Client +--------------+ +
| A | | |
+--------+ | | +--------+
| | Shared | |
| Proxy +--------------+ Target |
| | 4-tuple | |
+--------+ | | +--------+
| Client | | |
| B +--------------+ |
+--------+ +-----------+
BBBB0000 0000BBBB
<---------- Client B-to-target connection ---------->
Figure 2: Example of sharing a proxy-to-target 4-tuple
In order to share a proxy-to-target 4-tuple between multiple proxied
connections, the proxy MUST guarantee that the client CIDs do not
conflict. See Section 4.8 for more discussion of handlng CID
conflicts.
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2.2. Virtual Connection IDs
Virtual Connection IDs (VCIDs) are QUIC Connection IDs used on the
link between a client and proxy that do not belong to the QUIC
connection between the client and proxy, but instead are aliases for
particular client-to-target connections. VCIDs are only used in
forwarded mode. They are established using HTTP capsules
[HTTP-CAPSULES] as described in Section 4.
For example, consider a proxy using HTTP/3 that has a single client
connected to it. The client-to-proxy QUIC connection has CCCC0000 as
the client CID and 0000CCCC as the proxy CID. The client has
connected to a single target through the proxy, and the client-to-
target QUIC connection has CCCC1111 as the client CID and 1111CCCC as
the target CID. In order to use forwarded mode, the proxy assigns
VCIDs to use on the client-to-proxy link to represent the client-to-
target connection. In this case, the VCIDs could be CCCC2222 for the
client's VCID and 2222CCCC for the proxy's VCID that it uses to
forward to the target.
+--------+ +-----------+ +--------+
| | | | | |
| Client +--------------+ Proxy +--------------+ Target |
| | | | | |
+--------+ +-----------+ +--------+
CCCC0000 0000CCCC
<-- Client-to-proxy -->
connection
CCCC1111 1111CCCC
<----------- Client-to-target connection ----------->
CCCC2222 (CCCC1111) 2222CCCC (1111CCCC)
<-- Client-to-proxy -->
VCIDs
Figure 3: Diagram of VCIDs in forwarded mode
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In order for a proxy to correctly route packets using VCIDs from
client-to-target and target-to-client, the proxy MUST guarantee that
the mappings between VCIDs, CIDs, and 4-tuples are unique.
Specifically, in order to route packets sent by the client, the proxy
needs to be able to observe the VCID and the client-to-proxy 4-tuple,
and map them to a specific target CID and proxy-to-target 4-tuple.
In order to route packets sent by a target, the proxy needs to be
able to observe the client CID and the proxy-to-target 4-tuple, and
map them to a specific VCID and client-to-proxy 4-tuple. Since
proxies choose the VCID values, they can ensure that the VCIDs are
distinguishable.
Servers receiving QUIC packets can employ load balancing strategies
such as those described in [QUIC-LB] that encode routing information
in the connection ID. When operating in forwarded mode, clients send
QUIC packets destined for the target directly to the proxy. Since
these packets are generated using the target CID, load balancers may
not have the necessary information to route packets to the correct
proxy. The target VCID is a VCID chosen by the proxy that the client
uses when sending forwarded mode packets. The proxy replaces the
target VCID with the target CID prior to forwarding the packet to the
target.
Similarly, QUIC requires that connection IDs aren't reused over
multiple network paths to avoid linkability. The client VCID is a
connection ID chosen by the proxy that the proxy uses when sending
forwarded mode packets. The proxy replaces the client CID with the
client VCID prior to forwarding the packet to the client. Clients
take advantage of this to avoid linkability when migrating a client
to proxy network path. The Virtual client CID allows the connection
ID bytes to change on the wire without requiring the connection IDs
on the client to target connection change. To reduce the likelihood
of connection ID conflicts, the proxy MUST choose a client VCID that
is at least as long as the original client CID. Similarly, clients
multiplexing connections on the same UDP 4-tuple SHOULD choose a
client CID that's sufficiently long to reduce the likelihood of a
conflict with the proxy-chosen client VCID. The client VCID MUST
either be constructed such that it is unpredictable to the client or
to guarantee no conflicts among all proxies sharing an IP address and
port. See Section 8 for more discussion on client VCID construction.
Clients and Proxies not implementing forwarded mode do not need to
consider VCIDs since all client-to-target datagrams will be
encapsulated within the client-to-proxy connection.
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2.3. Negotiating Modes and Connection IDs
In order to support QUIC-aware proxying, both clients and proxies
need to support capsules [HTTP-CAPSULES], which is indicated by
including the "Capsule-Protocol" header field in requests and
responses. If this header field is not included, none of the
functionality in this document can be used.
capsule-protocol = ?1
To support forwarded mode, both clients and proxies need to include
the "Proxy-QUIC-Forwarding" header field, as defined in Section 3.
This indicates support for forwarded mode, and allows negotiation of
packet transforms to apply when forwarding (Section 5.3), along with
any parameters for specific transforms. Clients or proxies that
don't support forwarded mode will not include this header field.
proxy-quic-forwarding = ?1; accept-transform=scramble,identity; \
scramble-key=:abc...789=:
After negotiating support with header fields, clients and proxies use
the capsules defined in Section 4 to communicate information about
CIDs and VCIDs.
For QUIC-aware proxying without forwarded mode, the steps are as
follows:
1. The client sends the REGISTER_CLIENT_CID capsule once it selects
a CID that it will use for receiving packets from a target.
2. The proxy sends the ACK_CLIENT_CID capsule to acknowledge that
CID, with no associated client VCID; alternatively, the proxy can
send the CLOSE_CLIENT_CID if it detects a conflict with another
CID.
3. The client sends the REGISTER_TARGET_CID capsule as soon as it
learns the target CID on the client-to-target connection.
4. The proxy sends the ACK_TARGET_CID capsule to acknowledge that
CID, with no associated target VCID; alternatively, the proxy can
send the CLOSE_TARGET_CID if it detects a conflict with another
CID.
5. The proxy sends the MAX_CONNECTION_IDS capsule to allow
additional registration of new connection IDs via future
REGISTER_CLIENT_CID and REGISTER_TARGET_CID capsules.
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6. Whenever a client or target stops uses a particular CID, the
client sends a CLOSE_CLIENT_CID or CLOSE_TARGET_CID capsule. The
client can also initiate new REGISTER_CLIENT_CID or
REGISTER_TARGET_CID exchanges at any time.
For QUIC-aware proxying with forwarded mode, the steps are as
follows:
1. The client sends the REGISTER_CLIENT_CID capsule once it selects
a CID that it will use for receiving packets from a target.
2. The proxy sends the ACK_CLIENT_CID capsule to acknowledge that
CID, with a client VCID; alternatively, the proxy can send the
CLOSE_CLIENT_CID if it detects a conflict with another CID.
3. The client sends the ACK_CLIENT_VCID capsule to acknowledge the
client VCID, which allows forwarded packets for that VCID to be
used.
4. The client sends the REGISTER_TARGET_CID capsule as soon as it
learns the target CID on the client-to-target connection.
5. The proxy sends the ACK_TARGET_CID capsule to acknowledge that
CID, with a target VCID; alternatively, the proxy can send the
CLOSE_TARGET_CID if it detects a conflict with another CID. Once
the client receives the target VCID, it can start sending
forwarded packets using the target VCID.
6. The proxy sends the MAX_CONNECTION_IDS capsule to allow
additional registration of new connection IDs via future
REGISTER_CLIENT_CID and REGISTER_TARGET_CID capsules.
7. Whenever a client or target stops uses a particular CID, the
client sends a CLOSE_CLIENT_CID or CLOSE_TARGET_CID capsule. The
client can also initiate new REGISTER_CLIENT_CID or
REGISTER_TARGET_CID exchanges at any time.
3. Proxy-QUIC-Forwarding Header
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.
"Proxy-QUIC-Forwarding" is an Item Structured Header [RFC8941]. Its
value MUST be a Boolean.
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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
proxy-to-target 4-tuple, it sets the value to "?0".
The client MUST add an "accept-transform" parameter whose value is an
sf-string containing the supported packet transforms (Section 5.3) in
order of descending preference, separated by commas. If the proxy
receives a "Proxy-QUIC-Forwarding" header without the "accept-
transform" parameters, it MUST ignore the header and respond as if
the client had not sent the "Proxy-QUIC-Forwarding" header.
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 support this extension.
The proxy MUST include a "transform" parameter whose value is an sf-
string indicating the selected transform. If the proxy does not
recognize or accept any of the transforms offered by the client, it
MUST omit this parameter and set the header field value to "?0", or
omit the header entirely.
4. Connection ID Capsules
Connection ID awareness relies on using capsules [HTTP-CAPSULES] to
signal addition and removal of Connection IDs. Clients send capsules
to let proxies know when Connection IDs on the client-to-target QUIC
connection are changing. Proxies send capsules to acknowledge or
reject these Connection IDs, and in forwarded mode to let clients
know about Virtual Connection IDs to use on the client-to-proxy link.
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 REGISTER_CLIENT_CID (Section 4.1) and REGISTER_TARGET_CID
(Section 4.2) capsule types allow a client to inform the proxy about
a new client CID or a new target CID, respectively. These capsule
types MUST only be sent by a client. These capsule types share a
sequence number space which allows the proxy to limit the number of
active registrations. The first registration (of either client CID
or target CID) has sequence number 0, and subsequent registrations
increment the sequence number by 1.
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The ACK_CLIENT_CID (Section 4.3) and ACK_TARGET_CID (Section 4.4)
capsule types are sent by the proxy to the client to indicate that a
mapping was successfully created for a registered connection ID as
well as optionally provide the Virtual Connection IDs that can be
used in forwarded mode. These capsule types MUST only be sent by a
proxy.
The ACK_CLIENT_VCID (Section 4.5) capsule type MUST only be sent by
the client and only when forwarded mode is enabled. It is sent by
the client to the proxy in response to an ACK_CLIENT_CID capsule to
indicate that the client is ready to receive forwarded mode packets
with the specified virtual connection ID. The proxy MUST NOT send
forwarded mode packets to the client prior to receiving this
acknowledgement. This capsule also contains a Stateless Reset Token
the client may respond with when receiving forwarded mode packets
with the specified virtual connection ID.
The CLOSE_CLIENT_CID and CLOSE_TARGET_CID capsule types (Section 4.6)
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.
Similarly, if a client sends CLOSE_CLIENT_CID without having sent an
ACK_CLIENT_VCID capsule, the client is either rejecting the proxy-
chosen client VCID or no longer needs the connection ID registered.
The MAX_CONNECTION_IDS capsule type Section 4.7 MUST only be sent by
the proxy. It indicates to the client the maximum permitted sequence
number for connection ID registrations. This allows the proxy to
limit the number of active registrations. The initial maximum is 1,
allowing the client to send 2 registrations, one with sequence number
0 and another with sequence number 1. A proxy MUST NOT send a
MAX_CONNECTION_IDS capsule with a value less than 1. Clients
receiving a MAX_CONNECTION_IDS capsule with a value less than 1 MUST
reset the stream with H3_DATAGRAM_ERROR error code.
4.1. REGISTER_CLIENT_CID
The REGISTER_CLIENT_CID capsule is sent by the client and contains a
single connection ID that is the client-provided connection ID on the
client-to-target QUIC connection.
Register CID Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i),
Connection ID (0..2040),
}
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Figure 4: Register CID Capsule Format
Connection ID: A connection ID being registered, 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.
4.2. REGISTER_TARGET_CID
The REGISTER_TARGET_CID capsule is sent by the client and includes
the target-provided connection ID on the client-to-target QUIC
connection, and the corresponding Stateless Reset Token.
Register Target CID Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i),
Connection ID Length (i)
Connection ID (0..2040),
Stateless Reset Token Length (i),
Stateless Reset Token (..),
}
Figure 5: Register Target CID Capsule Format
Connection ID Length The length of the connection ID being
registered, which is between 0 and 255. Note that in QUICv1, the
length of the Connection ID is limited to 20 bytes, but QUIC
invariants allow up to 255 bytes.
Connection ID A connection ID being registered whose length is equal
to Connection ID Length. This is the real target CID.
Stateless Reset Token Length The length of the target-provided
Stateless Reset Token.
Stateless Reset Token The target-provided Stateless Reset token
allowing the proxy to correctly recognize Stateless Reset packets
to be tunnelled to the client.
4.3. ACK_CLIENT_CID
The ACK_CLIENT_CID capsule is sent by the proxy in response to a
REGISTER_CLIENT_CID capsule. It optionally assigns a Virtual
Connection ID when forwarded mode is supported.
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Acknowledge Client CID Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i)
Connection ID Length (i)
Connection ID (0..2040),
Virtual Connection ID Length (i)
Virtual Connection ID (0..2040),
}
Figure 6: Acknowledge Client CID Capsule Format
Connection ID Length The length of the connection ID being
acknowledged, which is between 0 and 255. Note that in QUICv1,
the length of the Connection ID is limited to 20 bytes, but QUIC
invariants allow up to 255 bytes.
Connection ID A connection ID being acknowledged whose length is
equal to Connection ID Length. This is the real Cilent Connection
ID.
Virtual Connection ID Length The length of the client VCID being
provided. This MUST be a valid connection ID length for the QUIC
version used in the client-to-proxy QUIC connection. When
forwarded mode is not negotiated, the length MUST be zero. The
Virtual Connection ID Length and Connection ID Length SHOULD be
equal when possible to avoid the need to resize packets during
replacement. The client VCID Length MUST be at least as large as
the Connection ID to reduce the likelihood of connection ID
conflicts.
Virtual Connection ID The proxy-chosen connection ID that the proxy
MUST use when sending in forwarded mode. The proxy rewrites
forwarded mode packets to contain the correct client VCID prior to
sending them to the client.
4.4. ACK_TARGET_CID
The ACK_TARGET_CID capsule is sent by the proxy in response to a
REGISTER_TARGET_CID capsule. It optionally assigns a Virtual
Connection ID and Stateless Reset Token if forwarded mode is enabled.
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Acknowledge Target CID Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i)
Connection ID Length (i)
Connection ID (0..2040),
Virtual Connection ID Length (i)
Virtual Connection ID (0..2040),
Stateless Reset Token Length (i),
Stateless Reset Token (..),
}
Figure 7: Acknowledge Target CID Capsule Format
Connection ID Length The length of the connection ID being
acknowledged, which is between 0 and 255. Note that in QUICv1,
the length of the Connection ID is limited to 20 bytes, but QUIC
invariants allow up to 255 bytes.
Connection ID A connection ID being acknowledged whose length is
equal to Connection ID Length. This is the real target CID.
Virtual Connection ID Length The length of the target VCID being
provided. This MUST be a valid connection ID length for the QUIC
version used in the client-to-proxy QUIC connection. When
forwarded mode is not negotiated, the length MUST be zero. The
Virtual Connection ID Length and Connection ID Length SHOULD be
equal when possible to avoid the need to resize packets during
replacement.
Virtual Connection ID The proxy-chosen connection ID that the client
MUST use when sending in forwarded mode. The proxy rewrites
forwarded mode packets to contain the correct target CID prior to
sending them.
Stateless Reset Token Length The length of the Stateless Reset Token
sent by the proxy in response to forwarded mode packets in order
to reset the client-to-target QUIC connection. When forwarded
mode is not negotiated, the length MUST be zero. Proxies choosing
not to support stateless resets MAY set the length to zero.
Clients receiving a zero-length stateless reset token MUST ignore
it.
Stateless Reset Token A Stateless Reset Token allowing reset of the
client-to-target connection in response to client-to-target
forwarded mode packets.
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4.5. ACK_CLIENT_VCID
The ACK_CLIENT_VCID capsule type is sent by the client in response to
an ACK_TARGET_CID capsule that contains a virtual connection ID.
Acknowledge Client VCID Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i)
Connection ID Length (i)
Connection ID (0..2040),
Virtual Connection ID Length (i)
Virtual Connection ID (0..2040),
Stateless Reset Token Length (i),
Stateless Reset Token (..),
}
Figure 8: Acknowledge Client VCID Capsule Format
Connection ID Length The length of the connection ID being
acknowledged, which is between 0 and 255. Note that in QUICv1,
the length of the Connection ID is limited to 20 bytes, but QUIC
invariants allow up to 255 bytes.
Connection ID A connection ID being acknowledged whose length is
equal to Connection ID Length. This is the real Cilent Connection
ID.
Virtual Connection ID Length The length of the client VCID being
acknowledged.
Virtual Connection ID The proxy-chosen virtual connection ID being
acknowledged whose length is equal to Virtual Connection ID
Length.
Stateless Reset Token Length The length of the Stateless Reset Token
that may be sent by the client in response to forwarded mode
packets to reset the client-to-target connection. Clients
choosing not to support stateless resets MAY set the length to
zero. Proxies receiving a zero-length stateless reset token MUST
ignore it.
Stateless Reset Token A Stateless Reset Token allowing reset of the
target-to-client forwarding rule in response to target-to-client
forwarded mode packets.
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4.6. CLOSE_CLIENT_CID and CLOSE_TARGET_CID
CLOSE_CLIENT_CID and CLOSE_TARGET_CID capsule types include a single
connection ID to close. They can be sent by either clients or
proxies.
Close CID Capsule {
Type (i) = see {{iana}} for the values of the capsule types
Length (i),
Connection ID (0..2040),
}
Figure 9: Close CID Capsule Format
Connection ID: A connection ID being closed, 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.
4.7. MAX_CONNECTION_IDS
The MAX_CONNECTION_IDS capsule is sent by the proxy to permit
additional connection ID registrations.
Maximum Connection IDs Capsule {
Type (i) = see {{iana}} for the value of the capsule type
Length (i)
Maximum Sequence Number (i)
}
Figure 10: Maximum Connection IDs Capsule Format
Maximum Sequence Number The maximum permitted sequence number for
connection ID registrations. This MUST NOT be less than 1.
4.8. Detecting Conflicts
In order to be able to route packets correctly in both tunnelled and
forwarded mode, proxies check for conflicts before creating a new CID
mapping. If a conflict is detected, the proxy will reject the
client's request using a CLOSE_CLIENT_CID or CLOSE_TARGET_CID
capsule.
Two 4-tuples 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 4-tuple, 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.
4.9. Client Considerations
The client sends a REGISTER_CLIENT_CID capsule whenever it advertises
a new client CID to the target, and a REGISTER_TARGET_CID capsule
when it has received a new target CID for the target. In order to
change the connection ID bytes on the wire, a client can solicit new
virtual connection IDs by re-registering the same connection IDs.
The client may solicit a new target VCID by sending a
REGISTER_TARGET_CID capsule with a previously registered target CID.
Similarly, the client may solicit a new client VCID by sending a
REGISTER_CLIENT_CID with a previously registered client CID. The
client MUST acknowledge the new client VCID with an ACK_CLIENT_VCID
capsule or close the registration. The proxy MUST NOT send in
forwarded mode until ACK_CLIENT_VCID has been received. Clients are
responsible for changing Virtual Connection IDs when the HTTP
stream's network path changes to avoid linkability across network
paths. Note that initial REGISTER_CLIENT_CID capsules MAY be sent
prior to receiving an HTTP response from the proxy.
Connection ID registrations are subject to a proxy-advertised limit.
Each registration has a corresponding sequence number. The client
MUST NOT send a registration capsule with a sequence number greater
than what the proxy advertises via the MAX_CONNECTION_IDS capsule.
The initial MAX_CONNECTION_IDS value is 1, allowing both sequence
numbers 0 and 1 for a total of two registrations without receiving a
MAX_CONNECTION_IDS capsule from the proxy.
Clients that cannot register new connection IDs within a reasonable
time due to the MAX_CONNECTION_IDS limit SHOULD abort the proxied
connection by resetting the HTTP stream with error code NO_ERROR.
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This may happen, for example, if the target server sends a
NEW_CONNECTION_ID frame with Sequence Number and Retire Prior To
equal to the same value.
4.9.1. New Proxied Connection Setup
To initiate QUIC-aware proxying, the client sends a
REGISTER_CLIENT_CID capsule containing the initial client CID 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 client CID that was
requested as well as a client VCID that the client MUST use when
sending forwarded mode packets, assuming forwarded mode is supported.
If forwarded mode is supported, the client MUST respond with an
ACK_CLIENT_VCID to signal to the proxy that it may start sending
forwarded mode packets. If forwarded mode is not supported, an
ACK_CLIENT_VCID capsule MUST NOT be sent.
Since clients are always aware whether or not they are using a QUIC
proxy, clients are expected to cooperate with proxies in selecting
client CIDs. A proxy detects a conflict when it is not able to
create a unique mapping using the client CID (Section 4.8). 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 CIDs of at least 8
bytes in length with unpredictable values. A client also SHOULD NOT
select a client CID 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 CID, 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.
4.9.2. 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 CID, the client
MUST send a REGISTER_CLIENT_CID capsule to the proxy containing the
new client CID.
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The client should only inform the target of the new client CID once
an ACK_CLIENT_CID capsule is received that contains the echoed
connection ID.
If forwarded mode is enabled, the client MUST reply to the
ACK_CLIENT_CID with an ACK_CLIENT_VCID capsule with the real and
virtual connection IDs along with an optional Stateless Reset Token.
4.10. Proxy Considerations
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 proxy-to-target 4-tuple 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 proxy-to-target 4-tuple to the authority. The proxy-to-
target 4-tuple might already be open due to a previous request from
this client, or another. If the 4-tuple is not already created, the
proxy creates a new one. Proxies can choose to reuse proxy-to-target
4-tuples across multiple UDP proxying requests, or have a unique
proxy-to-target 4-tuple for every UDP proxying request.
If a proxy reuses proxy-to-target 4-tuples, it SHOULD store which
authorities (which could be a domain name or IP address literal) are
being accessed over a particular proxy-to-target 4-tuple 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.
Proxy-to-target 4-tuples 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 proxy-
to-target 4-tuple used for proxying QUIC that does not correspond to
a known CID MUST be dropped.
When the proxy recieves a REGISTER_CLIENT_CID capsule, it is
receiving a request to be able to route traffic matching the client
CID back to the client using. If the pair of this client CID and the
selected proxy-to-target 4-tuple does not create a conflict, the
proxy creates the mapping and responds with an ACK_CLIENT_CID
capsule. If forwarded mode is enabled, the capsule contains a proxy-
chosen client VCID. If forwarded mode is enabled, and after
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receiving an ACK_CLIENT_VCID capsule from the client, any packets
received by the proxy from the proxy-to-target 4-tuple that match the
client CID can to be sent to the client after the proxy has replaced
the CID with the client VCID. If forwarded mode is not supported,
the proxy MUST NOT send a client VCID by setting the length to zero.
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. The proxy generates a target VCID for the client to use when
sending packets in forwarded mode. If forwarded mode is not
supported, the proxy MUST NOT send a target VCID by setting the
length to zero. If forwarded mode is supported, the proxy MUST use a
target VCID that does not introduce a conflict with any other
Connection ID on the client-to-proxy 4-tuple. The proxy creates the
mapping and responds with an ACK_TARGET_CID capsule. Once the
successful response is sent, the proxy will forward any short header
packets received on the client-to-proxy 4-tuple that use the target
VCID using the correct proxy-to-target 4-tuple after first rewriting
the target VCID to be the correct target CID.
Proxies MUST choose unpredictable client and target VCIDs to avoid
forwarding loop attacks.
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 VCIDs. Packets sent by the client that are
forwarded SHOULD be considered as activity for restarting QUIC's Idle
Timeout [QUIC].
In order to permit the client to change client-to-target connection
IDs, the proxy SHOULD send MAX_CONNECTION_IDS capsules allowing the
client additional connection ID registrations.
4.10.1. Closing Proxy State
For any registration capsule for which the proxy has sent an
acknowledgement, any mappings 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.
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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 proxy-to-target 4-tuple once all UDP proxying
requests mapped to that 4-tuple have been removed.
5. Using Forwarded Mode
All packets sent in forwarded mode use a transform in which CIDs are
switched into VCIDs, and the contents of packets are either left the
same, or modified (Section 5.3).
Forwarded mode also raises special considerations for handling
connection maintenance (Section 5.4), connection migration
(Section 5.5), ECN markings (Section 5.6), and stateless resets
(Section 5.7).
5.1. Sending With Forwarded Mode
Support for forwarded mode is determined by the "Proxy-QUIC-
Forwarding" header, see Section 3.
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 CID to request the
ability to forward packets.
The client MUST wait for an ACK_TARGET_CID capsule that contains the
echoed connection ID and target VCID 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 CID registration is rejected, for example with a
CLOSE_TARGET_CID capsule, it MUST NOT forward packets to the
requested target CID, 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.
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When forwarding, the client sends a QUIC packet with the target VCID
in the QUIC short header, using the same 4-tuple between client and
proxy that was used for the main QUIC connection between client and
proxy.
When forwarding, the proxy sends a QUIC packet with the client VCID
in the QUIC short header, using the same 4-tuple between client and
proxy that was used for the main QUIC connection between client and
proxy.
Prior to sending a forwarded mode packet, the sender MUST replace the
Connection ID with the Virtual Connection ID. If the Virtual
Connection ID is larger than the Connection ID, the sender MUST
extend the length of the packet by the difference between the two
lengths, to include the entire Virtual Connection ID. If the Virtual
Connection ID is smaller than the Connection ID, the sender MUST
shrink the length of the packet by the difference between the two
lengths.
Clients and proxies supporting forwarded mode MUST be able to handle
Virtual Connection IDs of different lengths than the corresponding
Connection IDs.
5.2. Receiving With Forwarded Mode
If the client has indicated support for forwarded mode with the
"Proxy-QUIC-Forwarding" header, the proxy MAY use forwarded mode for
any client CID for which it has a valid mapping.
Once a client has sent an ACK_CLIENT_VCID capsule to the proxy, it
MUST be prepared to receive forwarded short header packets on the
4-tuple between itself and the proxy for the specified client VCID.
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. The client replaces the client
VCID with the real client CID before processing the packet further.
5.3. Packet Transforms
A packet transform is the procedure applied to encode packets as they
are sent on the link between the client and proxy, along with the
inverse decode step applied on receipt. Simple transforms can be
modeled as a function as follows:
Inputs:
1. A QUIC short header packet (after Connection ID remapping).
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2. The mode (encode or decode).
3. The direction (client-to-proxy or proxy-to-client).
4. Any configuration information negotiated at startup.
Output:
* A UDP payload that conforms to the QUIC invariants [RFC8999] and
does not modify the Connection ID.
More complex transform behaviors could have internal state, but no
such transforms are presented here.
Packet transforms are identified by an IANA-registered name, and
negotiated in the HTTP headers (see Section 3). This document
defines two initial transforms: the identity transform and the
scramble transform.
5.3.1. The identify transform
The identity transform does not modify the packet in any way. When
this transform is in use, a global passive adversary can trivially
correlate pairs of packets that crossed the forwarder, providing a
compact proof that a specific client was communicating to a specific
target.
The identity transform is identified by the value "identity"
Section 9.3.
Use of this transform is NOT RECOMMENDED if the scramble transform is
supported by both the client and the proxy. Implementations MAY
choose to not implement or support the identity transform, depending
on the use cases and privacy requirements of the deployment.
5.3.2. The scramble transform
The scramble transform implements length-preserving unauthenticated
re-encryption of QUIC packets while preserving the QUIC invariants.
When the scramble transform is in use, a global passive adversary
cannot simply compare the packet contents on both sides of the proxy
to link the client and target. However, the scramble transform does
not defend against analysis of packet sizes and timing, nor does it
protect privacy against an active attacker.
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Deployments that implement the version of the scramble transform
defined in this document MUST use the value "scramble-dt". The
finalized version is expected to use the reserved value "scramble"
Section 9.3.
The scramble transform is initialized using a 32-byte random
symmetric key. When offering or selecting this transform, the client
and server each generate the key that they will use to encrypt
scrambled packets and MUST add it to the "Proxy-QUIC-Transform"
header in an sf-binary parameter named "scramble-key". If either
side receives a scramble transform without the "scramble-key"
parameter, forwarded mode MUST be disabled.
This transform relies on the AES-128 block cipher, which is
represented by the syntax AES-ECB(key, plaintext_block) as in
[RFC9001]. The corresponding decryption operation is written here as
AES-ECB-inv(key, ciphertext_block). It also uses AES in Counter Mode
([SP800-38A], Section 6.5), which is represented by the syntax AES-
CTR(key, iv, input) for encryption and decryption (which are
identical). In this syntax, iv is an array of 16 bytes containing
the initial counter block. The counter is incremented by the
standard incrementing function ([SP800-38A], Appendix B.1) on the
full block width.
In brief, the transform applies AES in counter mode (AES-CTR) using
an initialization vector drawn from the packet, then encrypts the
initialization vector with AES-ECB. The detailed procedure is as
follows:
1. Let k1, k2 = scramble_key[:16], scramble_key[16:32].
2. Let L be the Connection ID length.
3. Let cid = packet[1:L+1], i.e., the Connection ID.
4. Let iv = packet[L+1:L+17], i.e., the 16 bytes following the
Connection ID.
5. Let ctr_input = packet[0] | packet[L+17:].
6. Let ctr_output = AES-CTR(k1, iv, ctr_input).
7. Let header = ctr_output[0] & 0x7F. This ensures that the Header
Form bit is zero, as required by the QUIC invariants ([RFC8999],
Section 5.2).
8. Encrypt iv with the block cipher: encrypted_iv = AES-ECB(k2, iv).
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9. Produce the output packet as:
header | cid | encrypted_iv | ctr_output[1:].
The inverse transform operates as follows:
1. Decrypt the AES-CTR initialization vector:
iv = AES-ECB-inv(k2, packet[L+1:L+17]).
2. Compute the other variables exactly as in the forward transform.
(AES-CTR encryption and decryption are identical.)
3. Produce the output: header | cid | iv | ctr_output[1:].
The encryption keys used in this procedure do not depend on the
packet contents, so each party only needs to perform AES
initialization once for each connection.
NOTE: The security of this arrangement relies on every short-header
QUIC packet containing a distinct 16 bytes following the Connection
ID. This is true for the original ciphersuites of QUICv1, but it is
not guaranteed by the QUIC Invariants. Future ciphersuites and QUIC
versions could in principle produce packets that are too short or
repeat the values at this location. When using the scramble
transform, clients MUST NOT offer any configuration that could cause
the client or target to violate this requirement.
5.4. Connection Maintenance in Forwarded Mode
When a client and proxy are using forwarded mode, it is possible that
there can be long periods of time in which no ack-eliciting packets
(see Section 2 of [QUIC-RETRANSMISSION]) are exchanged between the
client and proxy. If these periods extend beyond the effective idle
timeout for the client-to-proxy QUIC connection (see Section 10.1 of
[QUIC]), the QUIC connection might be closed by the proxy if the
proxy does not use forwarded packets as an explicit liveness signal.
To avoid this, clients SHOULD send keepalive packets to the proxy
before the idle timeouts would be reached, which can be done using a
PING frame or another ack-eliciting frame as described in
Section 10.1.1 of [QUIC].
5.5. 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
forwarded packets on a new path prior to path validation.
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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.
When operating in forwarded mode, the proxy reconfigures or removes
forwarding rules as the network path between the client and proxy
changes. In the event of passive migration, the proxy automatically
reconfigures forwarding rules to use the latest active and validated
network path for the HTTP stream. In the event of active migration,
the proxy removes forwarding rules in order to not send packets with
the same connection ID bytes over multiple network paths. After
initiating active migration, clients are no longer able to send
forwarded mode packets since the proxy will have removed forwarding
rules. Clients can proceed with tunnelled mode or can request new
forwarding rules via REGISTER_CLIENT_CID and REGISTER_TARGET_CID
capsules. Each of the acknowledging capsules will contain new
virtual connection IDs to prevent packets with the same connection ID
bytes being used over multiple network paths. Note that the client
CID and target CID can stay the same while the target VCID and client
VCID change.
5.6. Handling ECN Marking
Explicit Congestion Notification marking [ECN] uses two bits in the
IP header to signal congestion from a network to endpoints. When
using forwarded mode, the proxy replaces IP headers for packets
exchanged between the client and target; these headers can include
ECN markings. Proxies SHOULD preserve ECN markings on forwarded
packets in both directions, to allow ECN to function end-to-end. If
the proxy does not preserve ECN markings, it MUST set ECN marks to
zero on the IP headers it generates.
Forwarded mode does not create an IP-in-IP tunnel, so the guidance in
[ECN-TUNNEL] about transferring ECN markings between inner and outer
IP headers does not apply.
A proxy MAY additionally add ECN markings to signal congestion being
experienced on the proxy itself.
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5.7. Stateless Resets for Forwarded Mode QUIC Packets
While the lifecycle of forwarding rules are bound to the lifecycle of
the client-to-proxy HTTP stream, a peer may not be aware that the
stream has terminated. If the above mappings are lost or removed
without the peer's knowledge, they may send forwarded mode packets
even though the client or proxy no longer has state for that
connection. To allow the client or proxy to reset the client-to-
target connection in the absence of the mappings above, a stateless
reset token corresponding to the Virtual Connection ID can be
provided.
Consider a proxy that initiates closure of a client-to-proxy QUIC
connection. If the client is temporarily unresponsive or
unreachable, the proxy might have considered the connection closed
and removed all connection state (including the stream mappings used
for forwarding). If the client never learned about the closure, it
might send forwarded mode packets to the proxy, assuming the stream
mappings and client-to-proxy connection are still intact. The proxy
will receive these forwarded mode packets, but won't have any state
corresponding to the destination connection ID in the packet. If the
proxy has provided a stateless reset token for the target VCID, it
can send a stateless reset packet to quickly notify the client that
the client-to-target connection is broken.
5.7.1. Stateless Resets from the Target
Reuse of proxy-to-target 4-tuples is only possible because QUIC
connection IDs allow distinguishing packets for multiple QUIC
connections received with the same 5-tuple. One exception to this is
Stateless Reset packets, in which the connection ID is not used, but
rather populated with unpredictable bits followed by a Stateless
Reset token, to make it indistinguishable from a regular packet with
a short header. In order for the proxy to correctly recognize
Stateless Reset packets, the client SHOULD share the Stateless Reset
token for each registered target CID. When the proxy receives a
Stateless Reset packet, it can send the packet to the client as a
tunnelled datagram. Although Stateless Reset packets look like short
header packets, they are not technically short header packets and do
not contain negotiated connection IDs, and thus are not eligible for
forwarded mode.
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6. Example Exchange
Consider a client that is establishing a new QUIC connection through
the proxy. In this example, the client prefers the scramble
transform, but also offers the identity transform. It has selected a
client CID of 0x31323334. In order to inform a proxy of the new QUIC
client CID, 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.
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; accept-transform=scramble,identity; \
scramble-key=:abc...789=:
capsule-protocol = ?1
STREAM(44): DATA -------->
Capsule Type = REGISTER_CLIENT_CID
Connection ID = 0x31323334
Stateless Reset Token = Token
<-------- STREAM(44): DATA
Capsule Type = MAX_CONNECTION_IDS
Maximum Sequence Number = 3
DATAGRAM -------->
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated QUIC initial
<-------- STREAM(44): HEADERS
:status = 200
proxy-quic-forwarding = ?1; \
transform=scramble; \
scramble-key=:ABC...321=:
capsule-protocol = ?1
<-------- STREAM(44): DATA
Capsule Type = ACK_CLIENT_CID
Connection ID = 0x31323334
Virtual CID = 0x62646668
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The proxy has acknowledged the client CID and provided a client VCID.
Even if there were Short Header packets to send, the proxy cannot
send forwarded mode packets because the client hasn't acknowledged
the client VCID.
The proxy indicates to the client that it will allow connection ID
registrations with sequence numbers 0-3, allowing for registrations
beyond the initial maximum of 1.
STREAM(44): DATA -------->
Capsule Type = ACK_CLIENT_VCID
Connection ID = 0x31323334
Virtual CID = 0x62646668
Stateless Reset Token = Token
The client acknowledges the client VCID. The proxy still doesn't
have any Short Header Packets to send, but, if it did, it would be
able to send with forwarded mode.
/* Wait for target server to respond to UDP packet. */
<-------- DATAGRAM
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated QUIC initial
/* All Client -> Target QUIC packets must still be encapsulated */
DATAGRAM -------->
Quarter Stream ID = 11
Context ID = 0
Payload = Encapsulated QUIC packet
/* Forwarded mode packets possible in Target -> Client direction */
<-------- UDP Datagram
Payload = Forwarded QUIC SH packet
The client may receive forwarded mode packets from the proxy with a
Virtual client CID of 0x62646668 which it will replace with the real
client CID of 0x31323334. All forwarded mode packets sent by the
proxy will have been modified to contain the client VCID instead of
the client CID, and processed by the negotiated "scramble" packet
transform. However, in the unlikely event that a forwarded packet
arrives before the proxy's HTTP response, the client will not know
which transform the proxy selected. In this case, the client will
have to ignore the packet or buffer it until the HTTP response is
received.
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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:
STREAM(44): DATA -------->
Capsule Type = REGISTER_TARGET_CID
Connection ID = 0x61626364
<-------- STREAM(44): DATA
Capsule Type = ACK_TARGET_CID
Connection ID = 0x61626364
Virtual Connection ID = 0x123412341234
Stateless Reset Token = Token
/* Client -> Target QUIC short header packets may use forwarded mode */
UDP Datagram -------->
Payload = Forwarded QUIC SH packet
Upon receiving an ACK_TARGET_CID capsule, the client starts sending
Short Header packets with a Destination Connection ID of
0x123412341234 directly to the proxy (not tunnelled), and these are
rewritten by the proxy to have the Destination Connection ID
0x61626364 prior to being forwarded directly to the target. In the
reverse direction, Short Header packets from the target with a
Destination Connection ID of 0x31323334 are modified to replace the
Destination Connection ID with the client VCID of 0x62646668 and
forwarded directly to the client.
7. 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
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.
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8. 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 clients to additional information exposure and
deanonymization attacks which need to be carefully considered.
Analysis should consider both passive and active attackers which may
be global or localized to the network paths used on one side of the
proxy. The following sections highlight deanonymization risks with
using forwarded mode.
8.1. Passive Attacks
A passive attacker aims to deanonymize a client by correlating
traffic across both sides of the proxy. When using forwarded mode
with the identity packet transform (see Section 5.3.1), such
correlation is trivial by matching a subset of QUIC packet bytes as
packets enter the proxy on one side and exit on the other. Packet
transforms such as scramble mitigate this by cryptographically
preventing such byte comparisons (see Section 5.3.2).
Regardless of which packet transform is used, both tunnelled and
forwarded mode are still vulnerable to size and timing attacks,
without the addition of techniques that go beyond the analysis in
this document, such as padding and adding chaff packets. Such
techniques could be supported in future packet transforms, subject to
additional security analysis.
Unlike tunnelled mode where packets are fully encapsulated in the
client-to-proxy connection, clients using forwarded mode to access
multiple target servers over the same client-to-proxy connection
expose the number of target servers they are communicating with on
each connection to passive attackers that can observe the client-to-
proxy traffic. This additional metadata revealed on each packet
simplifies size and timing attacks.
8.2. Active Attacks
An active attacker is an adversary that can inject, modify, drop, and
view packets in the network. Some active attacks have different
effects between forwarded mode and tunnelled mode, but active attacks
can be used to correlate flows in either mode.
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Both tunnelled mode and forwarded mode (regardless of packet
transform) are vulnerable to packet injection in the target-to-client
direction. An attacker can inject a burst of packets with a known
QUIC Connection ID and see which Connection ID is used for the
corresponding burst on the proxy-to-client network path.
Packet injection with a known QUIC Connection ID can also happen in
the client-to-proxy direction, which only affects forwarded mode
since tunnelled mode sends packets within an authenticated and
integrity protected QUIC connection to the proxy (see [RFC9001]).
None of the packet transforms defined in this document provide
integrity protection. Even if a packet transform did provide
integrity protection, attackers can inject replayed packets.
Protection against replayed packets is similarly provided by QUIC in
tunnelled mode, but not provided by any of the forwarded mode packet
transforms defined in this document.
An active attacker can modify packets in the client-to-proxy
direction, which would cause a tunnelling proxy to silently drop
packets, while a forwarding proxy would forward the packets. In this
way, forwarded mode is less vulnerable to flow recognition based on
corrupting a portion of packets in a burst.
Chaining of proxies using forwarded mode introduces the risk of
forwarding loop attacks. Preventing client VCID conflicts across
proxies sharing an IP address and port mitigates one such forwarding
loop attack. Conflicts can be avoided by partitioning the client
VCID space across proxies, using sufficiently long and random values,
or by other means.
9. IANA Considerations
9.1. HTTP Header
This document registers the "Proxy-QUIC-Forwarding" header in the
"Hypertext Transfer Protocol (HTTP) Field Name Registry"
<https://www.iana.org/assignments/http-fields>.
+-----------------------+----------+--------+---------------+
| Header Field Name | Protocol | Status | Reference |
+-----------------------+----------+--------+---------------+
| Proxy-QUIC-Forwarding | http | exp | This document |
+-----------------------+----------+--------+---------------+
Figure 11: Registered HTTP Header
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9.2. Proxy QUIC Forwarding Parameter Names
This document establishes a new registry, "Proxy QUIC Forwarding
Parameter Names", for parameter names to use with the "Proxy-QUIC-
Forwarding" header field, in
<https://www.iana.org/assignments/masque/masque.xhtml>.
Registrations in this registry are assigned using the Specification
Required policy (Section 4.6 of [IANA-POLICY]).
+-----------------------+-------------------------------------+---------------+--------------------------------+
| Parameter Name | Description | Reference | Notes |
+-----------------------+-------------------------------------+---------------+--------------------------------+
| accept-transform | contains supported transforms | This document | Section {{forwarding-header}} |
+-----------------------+-------------------------------------+---------------+--------------------------------+
| transform | indicates selected transforms | This document | Section {{forwarding-header}} |
+-----------------------+-------------------------------------+---------------+--------------------------------+
| scramble-key | contains key for scramble transform | This document | Section {{scramble-transform}} |
+-----------------------+-------------------------------------+---------------+--------------------------------+
Figure 12: Initial Proxy QUIC Forwarding Parameter Names
9.3. Packet Transform Names
This document establishes a new registry for packet transform names
in <https://www.iana.org/assignments/masque/masque.xhtml> and defines
two initial transforms: "identity" and "scramble". Prior to
finalization, deployments that implement the version of the scramble
transform defined in this document should use the value "scramble-
dt". Once the design team proposal is adopted and a new draft is
submitted, the wire identifier will become "scramble-XX" where XX is
the draft number. Registrations in this registry are assigned using
the Specification Required policy (Section 4.6 of [IANA-POLICY]).
+===========+================+===============+===============+
| Transform | Description | Specification | Notes |
| Name | | | |
+===========+================+===============+===============+
| identity | no | This Document | Section |
| | transformation | | Section 5.3.1 |
+-----------+----------------+---------------+---------------+
| scramble | Reserved (will | This Document | Section |
| | be used for | | Section 5.3.2 |
| | final version) | | |
+-----------+----------------+---------------+---------------+
Table 1: Initial Packet Transform Names
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9.4. Capsule Types
This document registers six new values in the "HTTP Capsule Types"
registry established by [HTTP-CAPSULES]. Note that the codepoints
below will be replaced with lower values before publication.
+=====================+==========+===============+
| Capule Type | Value | Specification |
+=====================+==========+===============+
| REGISTER_CLIENT_CID | 0xffe600 | This Document |
+---------------------+----------+---------------+
| REGISTER_TARGET_CID | 0xffe601 | This Document |
+---------------------+----------+---------------+
| ACK_CLIENT_CID | 0xffe602 | This Document |
+---------------------+----------+---------------+
| ACK_CLIENT_VCID | 0xffe603 | This Document |
+---------------------+----------+---------------+
| ACK_TARGET_CID | 0xffe604 | This Document |
+---------------------+----------+---------------+
| CLOSE_CLIENT_CID | 0xffe605 | This Document |
+---------------------+----------+---------------+
| CLOSE_TARGET_CID | 0xffe606 | This Document |
+---------------------+----------+---------------+
| MAX_CONNECTION_IDS | 0xffe607 | This Document |
+---------------------+----------+---------------+
Table 2: Registered Capsule Types
All of these new entries use the following values for these fields:
Status: provisional (permanent when this document is published)
Reference: This document
Change Controller: IETF
Contact: masque@ietf.org
Notes: None
10. References
10.1. Normative References
[CONNECT-UDP]
Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>.
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[ECN] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/rfc/rfc3168>.
[HTTP-CAPSULES]
Schinazi, D. and L. Pardue, "HTTP Datagrams and the
Capsule Protocol", RFC 9297, DOI 10.17487/RFC9297, August
2022, <https://www.rfc-editor.org/rfc/rfc9297>.
[HTTP3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[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>.
[QUIC-RETRANSMISSION]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", RFC 9002, DOI 10.17487/RFC9002,
May 2021, <https://www.rfc-editor.org/rfc/rfc9002>.
[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. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[SP800-38A]
Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Methods and Techniques", 1 December 2001,
<https://nvlpubs.nist.gov/nistpubs/legacy/sp/
nistspecialpublication800-38a.pdf>.
10.2. Informative References
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[ECN-TUNNEL]
Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/rfc/rfc6040>.
[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-19, 5 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
load-balancers-19>.
[RFC8999] Thomson, M., "Version-Independent Properties of QUIC",
RFC 8999, DOI 10.17487/RFC8999, May 2021,
<https://www.rfc-editor.org/rfc/rfc8999>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
Acknowledgments
Thanks to Lucas Pardue, Ryan Hamilton, and Mirja Kühlewind 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
Eric Rosenberg
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Email: eric_rosenberg@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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