Manageability of the QUIC Transport Protocol
draft-ietf-quic-manageability-11
The information below is for an old version of the document.
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| Authors | Mirja Kühlewind , Brian Trammell | ||
| Last updated | 2021-04-21 (Latest revision 2021-02-22) | ||
| Replaces | draft-kuehlewind-quic-manageability | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-quic-manageability-11
Network Working Group M. Kuehlewind
Internet-Draft Ericsson
Intended status: Informational B. Trammell
Expires: 23 October 2021 Google Switzerland GmbH
21 April 2021
Manageability of the QUIC Transport Protocol
draft-ietf-quic-manageability-11
Abstract
This document discusses manageability of the QUIC transport protocol,
focusing on the implications of QUIC's design and wire image on
network operations involving QUIC traffic. Its intended audience is
network operators and equipment vendors who rely on the use of
transport-aware network functions.
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
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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 23 October 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Features of the QUIC Wire Image . . . . . . . . . . . . . . . 4
2.1. QUIC Packet Header Structure . . . . . . . . . . . . . . 4
2.2. Coalesced Packets . . . . . . . . . . . . . . . . . . . . 6
2.3. Use of Port Numbers . . . . . . . . . . . . . . . . . . . 6
2.4. The QUIC Handshake . . . . . . . . . . . . . . . . . . . 7
2.5. Integrity Protection of the Wire Image . . . . . . . . . 11
2.6. Connection ID and Rebinding . . . . . . . . . . . . . . . 11
2.7. Packet Numbers . . . . . . . . . . . . . . . . . . . . . 12
2.8. Version Negotiation and Greasing . . . . . . . . . . . . 12
3. Network-Visible Information about QUIC Flows . . . . . . . . 12
3.1. Identifying QUIC Traffic . . . . . . . . . . . . . . . . 13
3.1.1. Identifying Negotiated Version . . . . . . . . . . . 13
3.1.2. First Packet Identification for Garbage Rejection . . 14
3.2. Connection Confirmation . . . . . . . . . . . . . . . . . 14
3.3. Distinguishing Acknowledgment Traffic . . . . . . . . . . 15
3.4. Server Name Indication (SNI) . . . . . . . . . . . . . . 15
3.4.1. Extracting Server Name Indication (SNI)
Information . . . . . . . . . . . . . . . . . . . . . 15
3.5. Flow Association . . . . . . . . . . . . . . . . . . . . 17
3.6. Flow Teardown . . . . . . . . . . . . . . . . . . . . . . 17
3.7. Flow Symmetry Measurement . . . . . . . . . . . . . . . . 17
3.8. Round-Trip Time (RTT) Measurement . . . . . . . . . . . . 18
3.8.1. Measuring Initial RTT . . . . . . . . . . . . . . . . 18
3.8.2. Using the Spin Bit for Passive RTT Measurement . . . 18
4. Specific Network Management Tasks . . . . . . . . . . . . . . 20
4.1. Passive Network Performance Measurement and
Troubleshooting . . . . . . . . . . . . . . . . . . . . 20
4.2. Stateful Treatment of QUIC Traffic . . . . . . . . . . . 20
4.3. Address Rewriting to Ensure Routing Stability . . . . . . 22
4.4. Server Cooperation with Load Balancers . . . . . . . . . 22
4.5. Filtering Behavior . . . . . . . . . . . . . . . . . . . 23
4.6. UDP Blocking or Throttling . . . . . . . . . . . . . . . 23
4.7. DDoS Detection and Mitigation . . . . . . . . . . . . . . 24
4.8. Quality of Service handling and ECMP . . . . . . . . . . 25
4.9. Handling ICMP Messages . . . . . . . . . . . . . . . . . 26
4.10. Guiding Path MTU . . . . . . . . . . . . . . . . . . . . 26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative References . . . . . . . . . . . . . . . . . . 28
9.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Distinguishing IETF QUIC and Google QUIC Versions . 32
A.1. Extracting the CRYPTO frame . . . . . . . . . . . . . . . 33
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
QUIC [QUIC-TRANSPORT] is a new transport protocol that is
encapsulated in UDP. QUIC integrates TLS [QUIC-TLS] to encrypt all
payload data and most control information. QUIC version 1 was
designed primarily as a transport for HTTP, with the resulting
protocol being known as HTTP/3 [QUIC-HTTP].
This document provides guidance for network operations that manage
QUIC traffic. This includes guidance on how to interpret and utilize
information that is exposed by QUIC to the network, requirements and
assumptions of the QUIC design with respect to network treatment, and
a description of how common network management practices will be
impacted by QUIC.
QUIC is an end-to-end transport protocol. No information in the
protocol header, even that which can be inspected, is meant to be
mutable by the network. This is achieved through integrity
protection of the wire image [WIRE-IMAGE]. Encryption of most
control signaling means that less information is visible to the
network than is the case with TCP.
Integrity protection can also simplify troubleshooting, because none
of the nodes on the network path can modify transport layer
information. However, it does imply that in-network operations that
depend on modification of data are not possible without the
cooperation of an QUIC endpoint. This might be possible with the
introduction of a proxy which authenticates as an endpoint. Proxy
operations are not in scope for this document.
Network management is not a one-size-fits-all endeavour: practices
considered necessary or even mandatory within enterprise networks
with certain compliance requirements, for example, would be
impermissible on other networks without those requirements. This
document therefore does not make any specific recommendations as to
which practices should or should not be applied; for each practice,
it describes what is and is not possible with the QUIC transport
protocol as defined.
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2. Features of the QUIC Wire Image
In this section, we discuss those aspects of the QUIC transport
protocol that have an impact on the design and operation of devices
that forward QUIC packets. Here, we are concerned primarily with the
unencrypted part of QUIC's wire image [WIRE-IMAGE], which we define
as the information available in the packet header in each QUIC
packet, and the dynamics of that information. Since QUIC is a
versioned protocol, the wire image of the header format can also
change from version to version. However, the field that identifies
the QUIC version in some packets, and the format of the Version
Negotiation Packet, are both inspectable and invariant
[QUIC-INVARIANTS].
This document describes version 1 of the QUIC protocol, whose wire
image is fully defined in [QUIC-TRANSPORT] and [QUIC-TLS]. Features
of the wire image described herein may change in future versions of
the protocol, except when specified as an invariant
[QUIC-INVARIANTS], and cannot be used to identify QUIC as a protocol
or to infer the behavior of future versions of QUIC.
Appendix A provides non-normative guidance on the identification of
QUIC version 1 packets compared to some pre-standard versions.
2.1. QUIC Packet Header Structure
QUIC packets may have either a long header or a short header. The
first bit of the QUIC header is the Header Form bit, and indicates
which type of header is present. The purpose of this bit is
invariant across QUIC versions.
The long header exposes more information. In version 1 of QUIC, it
is used during connection establishment, including version
negotiation, retry, and 0-RTT data. It contains a version number, as
well as source and destination connection IDs for grouping packets
belonging to the same flow. The definition and location of these
fields in the QUIC long header are invariant for future versions of
QUIC, although future versions of QUIC may provide additional fields
in the long header [QUIC-INVARIANTS].
Short headers contain only an optional destination connection ID and
the spin bit for RTT measurement. In version 1 of QUIC, they are
used after connection establishment.
The following information is exposed in QUIC packet headers in all
versions of QUIC:
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* version number: the version number is present in the long header,
and identifies the version used for that packet. During Version
Negotiation (see Section 17.2.1 of [QUIC-TRANSPORT] and
Section 2.8), the version number field has a special value
(0x00000000) that identifies the packet as a Version Negotiation
packet. QUIC version 1 uses version 0x00000001. Operators should
expect to observe packets with other version numbers as a result
of various Internet experiments, future standards, and greasing.
All deployed versions are maintained in an IANA registry (see
Section 22.2 of [QUIC-TRANSPORT]).
* source and destination connection ID: short and long packet
headers carry a destination connection ID, a variable-length field
that can be used to identify the connection associated with a QUIC
packet, for load-balancing and NAT rebinding purposes; see
Section 4.4 and Section 2.6. Long packet headers additionally
carry a source connection ID. The source connection ID
corresponds to the destination connection ID the source would like
to have on packets sent to it, and is only present on long packet
headers. On long header packets, the length of the connection IDs
is also present; on short header packets, the length of the
destination connection ID is implicit.
In version 1 of QUIC, the following additional information is
exposed:
* "fixed bit": The second-most-significant bit of the first octet of
most QUIC packets of the current version is set to 1, enabling
endpoints to demultiplex with other UDP-encapsulated protocols.
Even though this bit is fixed in the version 1 specification,
endpoints might use an extension that varies the bit. Therefore,
observers cannot reliably use it as an identifier for QUIC.
* latency spin bit: The third-most-significant bit of the first
octet in the short packet header for version 1. The spin bit is
set by endpoints such that tracking edge transitions can be used
to passively observe end-to-end RTT. See Section 3.8.2 for
further details.
* header type: The long header has a 2 bit packet type field
following the Header Form and fixed bits. Header types correspond
to stages of the handshake; see Section 17.2 of [QUIC-TRANSPORT]
for details.
* length: The length of the remaining QUIC packet after the length
field, present on long headers. This field is used to implement
coalesced packets during the handshake (see Section 2.2).
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* token: Initial packets may contain a token, a variable-length
opaque value optionally sent from client to server, used for
validating the client's address. Retry packets also contain a
token, which can be used by the client in an Initial packet on a
subsequent connection attempt. The length of the token is
explicit in both cases.
Retry (Section 17.2.5 of [QUIC-TRANSPORT]) and Version Negotiation
(Section 17.2.1 of [QUIC-TRANSPORT]) packets are not encrypted or
obfuscated in any way. For other kinds of packets, version 1 of QUIC
cryptographically obfuscates other information in the packet headers:
* packet number: All packets except Version Negotiation and Retry
packets have an associated packet number; however, this packet
number is encrypted, and therefore not of use to on-path
observers. The offset of the packet number is encoded in long
headers, while it is implicit (depending on destination connection
ID length) in short headers. The length of the packet number is
cryptographically obfuscated.
* key phase: The Key Phase bit, present in short headers, specifies
the keys used to encrypt the packet to support key rotation. The
Key Phase bit is cryptographically obfuscated.
2.2. Coalesced Packets
Multiple QUIC packets may be coalesced into a UDP datagram, with a
datagram carrying one or more long header packets followed by zero or
one short header packets. When packets are coalesced, the Length
fields in the long headers are used to separate QUIC packets; see
Section 12.2 of [QUIC-TRANSPORT]. The length header field is
variable length, and its position in the header is also variable
depending on the length of the source and destination connection ID;
see Section 17.2 of [QUIC-TRANSPORT].
2.3. Use of Port Numbers
Applications that have a mapping for TCP as well as QUIC are expected
to use the same port number for both services. However, as for all
other IETF transports [RFC7605], there is no guarantee that a
specific application will use a given registered port, or that a
given port carries traffic belonging to the respective registered
service, especially when application layer information is encrypted.
For example, [QUIC-HTTP] specifies the use of Alt-Svc for discovery
of HTTP/3 services on other ports.
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Further, as QUIC has a connection ID, it is also possible to maintain
multiple QUIC connections over one 5-tuple. However, if the
connection ID is zero-length, all packets of the 5-tuple belong to
the same QUIC connection.
2.4. The QUIC Handshake
New QUIC connections are established using a handshake, which is
distinguishable on the wire and contains some information that can be
passively observed.
To illustrate the information visible in the QUIC wire image during
the handshake, we first show the general communication pattern
visible in the UDP datagrams containing the QUIC handshake, then
examine each of the datagrams in detail.
The QUIC handshake can normally be recognized on the wire through at
least four datagrams we'll call "Client Initial", "Server Initial",
and "Client Completion", and "Server Completion", for purposes of
this illustration, as shown in Figure 1.
Packets in the handshake belong to three separate cryptographic and
transport contexts ("Initial", which contains observable payload, and
"Handshake" and "1-RTT", which do not). QUIC packets in separate
contexts during the handshake are generally coalesced (see
Section 2.2) in order to reduce the number of UDP datagrams sent
during the handshake.
As shown here, the client can send 0-RTT data as soon as it has sent
its Client Hello, and the server can send 1-RTT data as soon as it
has sent its Server Hello.
Client Server
| |
+----Client Initial----------------------->|
+----(zero or more 0RTT)------------------>|
| |
|<-----------------------Server Initial----+
|<---------(1RTT encrypted data starts)----+
| |
+----Client Completion-------------------->|
+----(1RTT encrypted data starts)--------->|
| |
|<--------------------Server Completion----+
| |
Figure 1: General communication pattern visible in the QUIC handshake
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A typical handshake starts with the client sending of a Client
Initial datagram as shown in Figure 2, which elicits a Server Initial
datagram as shown in Figure 3 typically containing three packets: an
Initial packet with the Server Initial, a Handshake packet with the
rest of the server's side of the TLS handshake, and initial 1-RTT
data, if present.
The Client Completion datagram contains at least one Handshake packet
and some also include an Initial packet.
Datagrams that contain a Client Initial Packet (Client Initial,
Server Initial, and some Client Completion) contain at least 1200
octets of UDP payload. This protects against amplification attacks
and verifies that the network path meets the requirements for the
minimum QUIC IP packet size; see Section 14 of [QUIC-TRANSPORT].
This is accomplished by either adding PADDING frames within the
Initial packet, coalescing other packets with the Initial packet, or
leaving unused payload in the UDP packet after the Initial packet. A
network path needs to be able to forward at least this size of packet
for QUIC to be used.
The content of Client Initial packets are encrypted using Initial
Secrets, which are derived from a per-version constant and the
client's destination connection ID; they are therefore observable by
any on-path device that knows the per-version constant. They are
therefore considered visible in this illustration. The content of
QUIC Handshake packets are encrypted using keys established during
the initial handshake exchange, and are therefore not visible.
Initial, Handshake, and the Short Header packets transmitted after
the handshake belong to cryptographic and transport contexts. The
Client Completion Figure 4 and the Server Completion Figure 5
datagrams finish these first two contexts, by sending the final
acknowledgment and finishing the transmission of CRYPTO frames.
+----------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+----------------------------------------------------------+
| QUIC long header (type = Initial, Version, DCID, SCID) (Length)
+----------------------------------------------------------+ |
| QUIC CRYPTO frame header | |
+----------------------------------------------------------+ |
| TLS Client Hello (incl. TLS SNI) | |
+----------------------------------------------------------+ |
| QUIC PADDING frames | |
+----------------------------------------------------------+<-+
Figure 2: Typical Client Initial datagram pattern without 0-RTT
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The Client Initial datagram exposes version number, source and
destination connection IDs without encryption. Information in the
TLS Client Hello frame, including any TLS Server Name Indication
(SNI) present, is obfuscated using the Initial secret. Note that the
location of PADDING is implementation-dependent, and PADDING frames
might not appear in a coalesced Initial packet.
+------------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+------------------------------------------------------------+
| QUIC long header (type = Initial, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| QUIC CRYPTO frame header | |
+------------------------------------------------------------+ |
| TLS Server Hello | |
+------------------------------------------------------------+ |
| QUIC ACK frame (acknowledging client hello) | |
+------------------------------------------------------------+<-+
| QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| encrypted payload (presumably CRYPTO frames) | |
+------------------------------------------------------------+<-+
| QUIC short header |
+------------------------------------------------------------+
| 1-RTT encrypted payload |
+------------------------------------------------------------+
Figure 3: Typical Server Initial datagram pattern
The Server Initial datagram also exposes version number, source and
destination connection IDs in the clear; information in the TLS
Server Hello message is obfuscated using the Initial secret.
+------------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+------------------------------------------------------------+
| QUIC long header (type = Initial, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| QUIC ACK frame (acknowledging Server Initial Initial) | |
+------------------------------------------------------------+<-+
| QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| encrypted payload (presumably CRYPTO/ACK frames) | |
+------------------------------------------------------------+<-+
| QUIC short header |
+------------------------------------------------------------+
| 1-RTT encrypted payload |
+------------------------------------------------------------+
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Figure 4: Typical Client Completion datagram pattern
The Client Completion datagram does not expose any additional
information; however, recognizing it can be used to determine that a
handshake has completed (see Section 3.2), and for three-way
handshake RTT estimation as in Section 3.8.
+------------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+------------------------------------------------------------+
| QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| encrypted payload (presumably ACK frame) | |
+------------------------------------------------------------+<-+
| QUIC short header |
+------------------------------------------------------------+
| 1-RTT encrypted payload |
+------------------------------------------------------------+
Figure 5: Typical Server Completion datagram pattern
Similar to Client Completion, Server Completion also exposes no
additional information; observing it serves only to determine that
the handshake has completed.
When the client uses 0-RTT connection resumption, 0-RTT data may also
be seen in the Client Initial datagram, as shown in Figure 6.
+----------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+----------------------------------------------------------+
| QUIC long header (type = Initial, Version, DCID, SCID) (Length)
+----------------------------------------------------------+ |
| QUIC CRYPTO frame header | |
+----------------------------------------------------------+ |
| TLS Client Hello (incl. TLS SNI) | |
+----------------------------------------------------------+<-+
| QUIC long header (type = 0RTT, Version, DCID, SCID) (Length)
+----------------------------------------------------------+ |
| 0-rtt encrypted payload | |
+----------------------------------------------------------+<-+
Figure 6: Typical 0-RTT Client Initial datagram pattern
In a 0-RTT Client Initial datagram, the PADDING frame is only present
if necessary to increase the size of the datagram with 0RTT data to
at least 1200 bytes. Additional datagrams containing only 0-RTT
protected long header packets may be sent from the client to the
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server after the Client Initial datagram, containing the rest of the
0-RTT data. The amount of 0-RTT protected data that can be sent in
the first round is limited by the initial congestion window,
typically around 10 packets (see Section 7.2 of [QUIC-RECOVERY]).
2.5. Integrity Protection of the Wire Image
As soon as the cryptographic context is established, all information
in the QUIC header, including exposed information, is integrity-
protected. Further, information that was exposed in packets sent
before the cryptographic context was established is validated during
the cryptographic handshake. Therefore, devices on path cannot alter
any information or bits in QUIC packets. Such alterations would
cause the integrity check to fail, which results in the receiver
discarding the packet. Some parts of Initial packets could be
altered by removing and re-applying the authenticated encryption
without immediate discard at the receiver. However, the
cryptographic handshake validates most fields and any modifications
in those fields will result in connection establishment failing later
on.
2.6. Connection ID and Rebinding
The connection ID in the QUIC packet headers allows association of
QUIC packets using information independent of the five-tuple. This
allows rebinding of a connection after one of one endpoint
experienced an address change - usually the client. Further it can
be used by in-network devices to ensure that related 5-tuple flows
are appropriately balanced together.
Client and server negotiate connection IDs during the handshake;
typically, however, only the server will request a connection ID for
the lifetime of the connection. Connection IDs for either endpoint
may change during the lifetime of a connection, with the new
connection ID being supplied via encrypted frames (see Section 5.1 of
[QUIC-TRANSPORT]). Therefore, observing a new connection ID does not
necessary indicate a new connection.
[QUIC_LB] specifies algorithms for encoding the server mapping in a
connection ID in order to share this information with selected on-
path devices such as load balancers. Server mappings should only be
exposed to selected entities. Uncontrolled exposure would allow
linkage of multiple IP addresses to the same host if the server also
supports migration which opens an attack vector on specific servers
or pools. The best way to obscure an encoding is to appear random to
any other observers, which is most rigorously achieved with
encryption. As a result any attempt to infer information from
specific parts of a connection ID is unlikely to be useful.
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2.7. Packet Numbers
The packet number field is always present in the QUIC packet header
in version 1; however, it is always encrypted. The encryption key
for packet number protection on handshake packets sent before
cryptographic context establishment is specific to the QUIC version,
while packet number protection on subsequent packets uses secrets
derived from the end-to-end cryptographic context. Packet numbers
are therefore not part of the wire image that is visible to on-path
observers.
2.8. Version Negotiation and Greasing
Version Negotiation packets are used by the server to indicate that a
requested version from the client is not supported (see Section 6 of
[QUIC-TRANSPORT]. Version Negotiation packets are not intrinsically
protected, but future QUIC versions will use later encrypted messages
to verify that they were authentic. Therefore any modification of
this list will be detected and may cause the endpoints to terminate
the connection attempt.
Also note that the list of versions in the Version Negotiation packet
may contain reserved versions. This mechanism is used to avoid
ossification in the implementation on the selection mechanism.
Further, a client may send a Initial Client packet with a reserved
version number to trigger version negotiation. In the Version
Negotiation packet, the connection IDs of the Client Initial packet
are reflected to provide a proof of return-routability. Therefore,
changing this information will also cause the connection to fail.
QUIC is expected to evolve rapidly, so new versions, both
experimental and IETF standard versions, will be deployed in the
Internet more often than with traditional Internet- and transport-
layer protocols. Using a particular version number to recognize
valid QUIC traffic is likely to persistently miss a fraction of QUIC
flows and completely fail in the near future, and is therefore not
recommended. In addition, due to the speed of evolution of the
protocol, devices that attempt to distinguish QUIC traffic from non-
QUIC traffic for purposes of network admission control should admit
all QUIC traffic regardless of version.
3. Network-Visible Information about QUIC Flows
This section addresses the different kinds of observations and
inferences that can be made about QUIC flows by a passive observer in
the network based on the wire image in Section 2. Here we assume a
bidirectional observer (one that can see packets in both directions
in the sequence in which they are carried on the wire) unless noted.
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3.1. Identifying QUIC Traffic
The QUIC wire image is not specifically designed to be
distinguishable from other UDP traffic.
The only application binding defined by the IETF QUIC WG is HTTP/3
[QUIC-HTTP] at the time of this writing; however, many other
applications are currently being defined and deployed over QUIC, so
an assumption that all QUIC traffic is HTTP/3 is not valid. HTTP/3
uses UDP port 443 by default, although URLs referring to resources
available over HTTP/3 may specify alternate port numbers. Simple
assumptions about whether a given flow is using QUIC based upon a UDP
port number may therefore not hold; see also Section 5 of [RFC7605].
While the second-most-significant bit (0x40) of the first octet is
set to 1 in most QUIC packets of the current version (see Section 2.1
and Section 17 of [QUIC-TRANSPORT]), this method of recognizing QUIC
traffic is not reliable. First, it only provides one bit of
information and is prone to collision with UDP-based protocols other
than those considered in [RFC7983]. Second, this feature of the wire
image is not invariant [QUIC-INVARIANTS] and may change in future
versions of the protocol, or even be negotiated during the handshake
via the use of an extension.
Even though transport parameters transmitted in the client's Initial
packet are observable by the network, they cannot be modified by the
network without risking connection failure. Further, the reply from
the server cannot be observed, so observers on the network cannot
know which parameters are actually in use.
3.1.1. Identifying Negotiated Version
An in-network observer assuming that a set of packets belongs to a
QUIC flow can infer the version number in use by observing the
handshake: for QUIC version 1, if the version number in the Initial
packet from a client is the same as the version number in the Initial
packet of the server response, that version has been accepted by both
endpoints to be used for the rest of the connection.
The negotiated version cannot be identified for flows for which a
handshake is not observed, such as in the case of connection
migration; however, it might be possible to associate a flow with a
flow for which a version has been identified; see Section 3.5.
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3.1.2. First Packet Identification for Garbage Rejection
A related question is whether the first packet of a given flow on a
port known to be associated with QUIC is a valid QUIC packet. This
determination supports in-network filtering of garbage UDP packets
(reflection attacks, random backscatter, etc.). While heuristics
based on the first byte of the packet (packet type) could be used to
separate valid from invalid first packet types, the deployment of
such heuristics is not recommended, as bits in the first byte may
have different meanings in future versions of the protocol.
3.2. Connection Confirmation
This document focuses on QUIC version 1, and this section applies
only to packets belonging to QUIC version 1 flows; for purposes of
on-path observation, it assumes that these packets have been
identified as such through the observation of a version number
exchange as described above.
Connection establishment uses Initial and Handshake packets
containing a TLS handshake, and Retry packets that do not contain
parts of the handshake. Connection establishment can therefore be
detected using heuristics similar to those used to detect TLS over
TCP. A client initiating a connection may also send data in 0-RTT
packets directly after the Initial packet containing the TLS Client
Hello. Since these packets may be reordered in the network, 0-RTT
packets could be seen before the Initial packet.
Note that in this version of QUIC, clients send Initial packets
before servers do, servers send Handshake packets before clients do,
and only clients send Initial packets with tokens. Therefore, an
endpoint can be identified as a client or server by an on-path
observer. An attempted connection after Retry can be detected by
correlating the contents of the Retry packet with the Token and the
Destination Connection ID fields of the new Initial packet.
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3.3. Distinguishing Acknowledgment Traffic
Some deployed in-network functions distinguish pure-acknowledgment
(ACK) packets from packets carrying upper-layer data in order to
attempt to enhance performance, for example by queueing ACKs
differently or manipulating ACK signaling. Distinguishing ACK
packets is trivial in TCP, but not supported by QUIC, since
acknowledgment signaling is carried inside QUIC's encrypted payload,
and ACK manipulation is impossible. Specifically, heuristics
attempting to distinguish ACK-only packets from payload-carrying
packets based on packet size are likely to fail, and are not
recommended to use as a way to construe internals of QUIC's operation
as those mechanisms can change, e.g., due to the use of extensions.
3.4. Server Name Indication (SNI)
The client's TLS ClientHello may contain a Server Name Indication
(SNI) [RFC6066] extension, by which the client reveals the name of
the server it intends to connect to, in order to allow the server to
present a certificate based on that name. It may also contain an
Application-Layer Protocol Negotiation (ALPN) [RFC7301] extension, by
which the client exposes the names of application-layer protocols it
supports; an observer can deduce that one of those protocols will be
used if the connection continues.
Work is currently underway in the TLS working group to encrypt the
contents of the ClientHello in TLS 1.3 [TLS-ECH]. This would make
SNI-based application identification impossible by on-path
observation for QUIC and other protocols that use TLS.
3.4.1. Extracting Server Name Indication (SNI) Information
If the ClientHello is not encrypted, it can be derived from the
client's Initial packet by calculating the Initial secret to decrypt
the packet payload and parsing the QUIC CRYPTO Frame containing the
TLS ClientHello.
As both the derivation of the Initial secret and the structure of the
Initial packet itself are version-specific, the first step is always
to parse the version number (second to sixth bytes of the long
header). Note that only long header packets carry the version
number, so it is necessary to also check if the first bit of the QUIC
packet is set to 1, indicating a long header.
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Note that proprietary QUIC versions, that have been deployed before
standardization, might not set the first bit in a QUIC long header
packet to 1. To parse these versions, example code is provided in
the appendix (see Appendix A). However, it is expected that these
versions will gradually disappear over time.
When the version has been identified as QUIC version 1, the packet
type needs to be verified as an Initial packet by checking that the
third and fourth bits of the header are both set to 0. Then the
Destination Connection ID needs to be extracted to calculate the
Initial secret using the version-specific Initial salt, as described
in Section 5.2 of [QUIC-TLS]. The length of the connection ID is
indicated in the 6th byte of the header followed by the connection ID
itself.
To determine the end of the header and find the start of the payload,
the packet number length, the source connection ID length, and the
token length need to be extracted. The packet number length is
defined by the seventh and eight bits of the header as described in
Section 17.2 of [QUIC-TRANSPORT], but is obfuscated as described in
Section 5.4 of [QUIC-TLS]. The source connection ID length is
specified in the byte after the destination connection ID. The token
length, which follows the source connection ID, is a variable-length
integer as specified in Section 16 of [QUIC-TRANSPORT].
After decryption, the client's Initial packet can be parsed to detect
the CRYPTO frame that contains the TLS ClientHello, which then can be
parsed similarly to TLS over TCP connections. The client's Initial
packet may contain other frames, so the first bytes of each frame
need to be checked to identify the frame type, and if needed skip
over it. Note that the length of the frames is dependent on the
frame type. In QUIC version 1, the packet is expected to contain
only CRYPTO frames and optionally PADDING frames. PADDING frames,
each consisting of a single zero byte, may occur before, after, or
between CRYPTO frames. There might be multiple CRYPTO frames.
Finally, an extension might define additional frame types which could
be present.
Note that subsequent Initial packets might contain a Destination
Connection ID other than the one used to generate the Initial secret.
Therefore, attempts to decrypt these packets using the procedure
above might fail unless the Initial secret is retained by the
observer.
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3.5. Flow Association
The QUIC connection ID (see Section 2.6) is designed to allow a
coordinating on-path device, such as a load-balancer, to associate
two flows when one of the endpoints changes address or port. This
change can be due to NAT rebinding or address migration.
The connection ID must change upon intentional address change by an
endpoint, and connection ID negotiation is encrypted, so it is not
possible for a passive observer to link intended changes of address
using the connection ID.
When one endpoint unintentionally changes its address, as is the case
with NAT rebinding, an on-path observer may be able to use the
connection ID to associate the flow on the new address with the flow
on the old address.
A network function that attempts to use the connection ID to
associate flows must be robust to the failure of this technique.
Since the connection ID may change multiple times during the lifetime
of a connection, packets with the same five-tuple but different
connection IDs might or might not belong to the same connection.
Likewise, packets with the same connection ID but different five-
tuples might not belong to the same connection, either.
Connection IDs should be treated as opaque; see Section 4.4 for
caveats regarding connection ID selection at servers.
3.6. Flow Teardown
QUIC does not expose the end of a connection; the only indication to
on-path devices that a flow has ended is that packets are no longer
observed. Stateful devices on path such as NATs and firewalls must
therefore use idle timeouts to determine when to drop state for QUIC
flows; see Section 4.2.
3.7. Flow Symmetry Measurement
QUIC explicitly exposes which side of a connection is a client and
which side is a server during the handshake. In addition, the
symmetry of a flow (whether primarily client-to-server, primarily
server-to-client, or roughly bidirectional, as input to basic traffic
classification techniques) can be inferred through the measurement of
data rate in each direction. While QUIC traffic is protected and
ACKs may be padded, padding is not required.
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3.8. Round-Trip Time (RTT) Measurement
The round-trip time of QUIC flows can be inferred by observation once
per flow, during the handshake, as in passive TCP measurement; this
requires parsing of the QUIC packet header and recognition of the
handshake, as illustrated in Section 2.4. It can also be inferred
during the flow's lifetime, if the endpoints use the spin bit
facility described below and in Section 17.3.1 of [QUIC-TRANSPORT].
3.8.1. Measuring Initial RTT
In the common case, the delay between the client's Initial packet
(containing the TLS ClientHello) and the server's Initial packet
(containing the TLS ServerHello) represents the RTT component on the
path between the observer and the server. The delay between the
server's first Handshake packet and the Handshake packet sent by the
client represents the RTT component on the path between the observer
and the client. While the client may send 0-RTT packets after the
Initial packet during connection re-establishment, these can be
ignored for RTT measurement purposes.
Handshake RTT can be measured by adding the client-to-observer and
observer-to-server RTT components together. This measurement
necessarily includes any transport- and application-layer delay (the
latter mainly caused by the asymmetric crypto operations associated
with the TLS handshake) at both sides.
3.8.2. Using the Spin Bit for Passive RTT Measurement
The spin bit provides a version-specific method to measure per-flow
RTT from observation points on the network path throughout the
duration of a connection. See Section 17.4 of [QUIC-TRANSPORT] for
the definition of the spin bit in Version 1 of QUIC. Endpoint
participation in spin bit signaling is optional. That is, while its
location is fixed in this version of QUIC, an endpoint can
unilaterally choose to not support "spinning" the bit.
Use of the spin bit for RTT measurement by devices on path is only
possible when both endpoints enable it. Some endpoints may disable
use of the spin bit by default, others only in specific deployment
scenarios, e.g. for servers and clients where the RTT would reveal
the presence of a VPN or proxy. To avoid making these connections
identifiable based on the usage of the spin bit, all endpoints
randomly disable "spinning" for at least one eighth of connections,
even if otherwise enabled by default. An endpoint not participating
in spin bit signaling for a given connection can use a fixed spin
value for the duration of the connection, or can set the bit randomly
on each packet sent.
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When in use and a QUIC flow sends data continuously, the latency spin
bit in each direction changes value once per round-trip time (RTT).
An on-path observer can observe the time difference between edges
(changes from 1 to 0 or 0 to 1) in the spin bit signal in a single
direction to measure one sample of end-to-end RTT. This mechanism
follows the principles of protocol measurability laid out in [IPIM].
Note that this measurement, as with passive RTT measurement for TCP,
includes any transport protocol delay (e.g., delayed sending of
acknowledgements) and/or application layer delay (e.g., waiting for a
response to be generated). It therefore provides devices on path a
good instantaneous estimate of the RTT as experienced by the
application.
However, application-limited and flow-control-limited senders can
have application and transport layer delay, respectively, that are
much greater than network RTT. When the sender is application-
limited and e.g. only sends small amount of periodic application
traffic, where that period is longer than the RTT, measuring the spin
bit provides information about the application period, not the
network RTT.
Since the spin bit logic at each endpoint considers only samples from
packets that advance the largest packet number, signal generation
itself is resistant to reordering. However, reordering can cause
problems at an observer by causing spurious edge detection and
therefore inaccurate (i.e., lower) RTT estimates, if reordering
occurs across a spin-bit flip in the stream.
Simple heuristics based on the observed data rate per flow or changes
in the RTT series can be used to reject bad RTT samples due to lost
or reordered edges in the spin signal, as well as application or flow
control limitation; for example, QoF [TMA-QOF] rejects component RTTs
significantly higher than RTTs over the history of the flow. These
heuristics may use the handshake RTT as an initial RTT estimate for a
given flow. Usually such heuristics would also detect if the spin is
either constant or randomly set for a connection.
An on-path observer that can see traffic in both directions (from
client to server and from server to client) can also use the spin bit
to measure "upstream" and "downstream" component RTT; i.e, the
component of the end-to-end RTT attributable to the paths between the
observer and the server and the observer and the client,
respectively. It does this by measuring the delay between a spin
edge observed in the upstream direction and that observed in the
downstream direction, and vice versa.
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Raw RTT samples generated using these techniques can be processed in
various ways to generate useful network performance metrics. A
simple linear smoothing or moving minimum filter can be applied to
the stream of RTT samples to get a more stable estimate of
application-experienced RTT. RTT samples measured from the spin bit
can also be used to generate RTT distribution information, including
minimum RTT (which approximates network RTT over longer time windows)
and RTT variance (which approximates jitter as seen by the
application).
4. Specific Network Management Tasks
In this section, we review specific network management and
measurement techniques and how QUIC's design impacts them.
4.1. Passive Network Performance Measurement and Troubleshooting
Limited RTT measurement is possible by passive observation of QUIC
traffic; see Section 3.8. No passive measurement of loss is possible
with the present wire image. Extremely limited observation of
upstream congestion may be possible via the observation of CE
markings on ECN-enabled QUIC traffic.
4.2. Stateful Treatment of QUIC Traffic
Stateful treatment of QUIC traffic (e.g., at a firewall or NAT
middlebox) is possible through QUIC traffic and version
identification (Section 3.1) and observation of the handshake for
connection confirmation (Section 3.2). The lack of any visible end-
of-flow signal (Section 3.6) means that this state must be purged
either through timers or through least-recently-used eviction,
depending on application requirements.
While QUIC has no clear network-visible end-of-connection signal and
therefore does require timer-based state removal, the QUIC handshake
indicates confirmation by both ends of a valid bidirectional
transmission. As soon as the handshake completed, timers should be
set long enough to also allow for short idle time during a valid
transmission.
[RFC4787] requires a timeout that is not less than 2 minutes for most
UDP traffic. However, in practice, timers are sometimes lower, in
the range of 30 to 60 seconds. In contrast, [RFC5382] recommends a
timeout of more than 2 hours for TCP, given that TCP is a connection-
oriented protocol with well- defined closure semantics.
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Even though QUIC has explicitly been designed tolerate NAT
rebindings, decreasing the NAT timeout is not recommended, as it may
negatively impact application performance or incentivize endpoints to
send very frequent keep-alive packets. Instead it is recommended,
even when lower timers are used for other UDP traffic, to use a timer
of at least two minutes for QUIC traffic.
If state is removed too early, this could lead to black-holing of
incoming packets after a short idle period. To detect this
situation, a timer at the client needs to expire before a re-
establishment can happen (if at all), which would lead to unnecessary
long delays in an otherwise working connection.
Furthermore, not all endpoints use routing architectures where
connections will survive a port or address change. So even when the
client revives the connection, a NAT rebinding can cause a routing
mismatch where a packet is not even delivered to the server that
might support address migration. For these reasons, the limits in
[RFC4787] are important to avoid black-holing of packets (and hence
avoid interrupting the flow of data to the client), especially where
devices are able to distinguish QUIC traffic from other UDP payloads.
The QUIC header optionally contains a connection ID which could
provide additional entropy beyond the 5-tuple. The QUIC handshake
needs to be observed in order to understand whether the connection ID
is present and what length it has. However, connection IDs may be
renegotiated after the handshake, and this renegotiation is not
visible to the path. Therefore using the connection ID as a flow key
field for stateful treatment of flows is not recommended as
connection ID changes will cause undetectable and unrecoverable loss
of state in the middle of a connection. Specially, the use of the
connection ID for functions that require state to make a forwarding
decison is not viable as it will break connectivity or at minimum
cause long timeout-based delays before this problem is detected by
the endpoints and the connection can potentially be re-established.
Use of connection IDs is specifically discouraged for NAT
applications. If a NAT hits an operational limit, it is recommended
to rather drop the initial packets of a flow (see also Section 4.5),
which potentially triggers a fallback to TCP. Use of the connection
ID to multiplex multiple connections on the same IP address/port pair
is not a viable solution as it risks connectivity breakage, in case
the connection ID changes.
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4.3. Address Rewriting to Ensure Routing Stability
While QUIC's migration capability makes it possible for an server to
survive address changes, this does not work if the routers or
switches in the server infrastructure route using the address-port
4-tuple. If infrastructure routes on addresses only, NAT rebinding
or address migration will cause packets to be delivered to the wrong
server. [QUIC_LB] describes a way to addresses this problem by
coordinating the selection and use of connection IDs between load-
balancers and servers.
Applying address translation at a middlebox to maintain a stable
address-port mapping for flows based on connection ID might seem like
a solution to this problem. However, hiding information about the
change of the IP address or port conceals important and security-
relevant information from QUIC endpoints and as such would facilitate
amplification attacks (see Section 9 of [QUIC-TRANSPORT]). A NAT
function that hides peer address changes prevents the other end from
detecting and mitigating attacks as the endpoint cannot verify
connectivity to the new address using QUIC PATH_CHALLENGE and
PATH_RESPONSE frames.
In addition, a change of IP address or port is also an input signal
to other internal mechanisms in QUIC. When a path change is
detected, path-dependent variables like congestion control parameters
will be reset protecting the new path from overload.
Therefore, the use of address rewriting to ensure routing stability
can open QUIC up to various attacks, as it conceals client address
changes, and as such masks important signals that drive security
mechanisms.
4.4. Server Cooperation with Load Balancers
In the case of networking architectures that include load balancers,
the connection ID can be used as a way for the server to signal
information about the desired treatment of a flow to the load
balancers. Guidance on assigning connection IDs is given in
[QUIC-APPLICABILITY]. [QUIC_LB] describes a system for coordinating
selection and use of connection IDs between load-balancers and
servers.
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4.5. Filtering Behavior
[RFC4787] describes possible packet filtering behaviors that relate
to NATs but is often also used is other scenarios where packet
filtering is desired. Though the guidance there holds, a
particularly unwise behavior is to admit a handful of UDP packets and
then make a decision as to whether or not to filter it. QUIC
applications are encouraged to fail over to TCP if early packets do
not arrive at their destination [I-D.ietf-quic-applicability], as
QUIC is based on UDP and there are known blocks of UDP traffic (see
Section 4.6). Admitting a few packets allows the QUIC endpoint to
determine that the path accepts QUIC. Sudden drops afterwards will
result in slow and costly timeouts before abandoning the connection.
4.6. UDP Blocking or Throttling
Today, UDP is the most prevalent DDoS vector, since it is easy for
compromised non-admin applications to send a flood of large UDP
packets (while with TCP the attacker gets throttled by the congestion
controller) or to craft reflection and amplification attacks. Some
networks therefore block UDP traffic. With increased deployment of
QUIC, there is also an increased need to allow UDP traffic on ports
used for QUIC. However, if UDP is generally enabled on these ports,
UDP flood attacks may also use the same ports. One possible response
to this threat is to throttle UDP traffic on the network, allocating
a fixed portion of the network capacity to UDP and blocking UDP
datagrams over that cap. As the portion of QUIC traffic compared to
TCP is also expected to increase over time, using such a limit is not
recommended but if done, limits might need to be adapted dynamically.
Further, if UDP traffic is desired to be throttled, it is recommended
to block individual QUIC flows entirely rather than dropping packets
randomly. When the handshake is blocked, QUIC-capable applications
may failover to TCP However, blocking a random fraction of QUIC
packets across 4-tuples will allow many QUIC handshakes to complete,
preventing a TCP failover, but the connections will suffer from
severe packet loss (see also Section 4.5). Therefore UDP throttling
should be realized by per-flow policing as opposed to per-packet
policing. Note that this per-flow policing should be stateless to
avoid problems with stateful treatment of QUIC flows (see
Section 4.2), for example blocking a portion of the space of values
of a hash function over the addresses and ports in the UDP datagram.
While QUIC endpoints are often able to survive address changes, e.g.
by NAT rebindings, blocking a portion of the traffic based on 5-tuple
hashing increases the risk of black-holing an active connection when
the address changes.
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4.7. DDoS Detection and Mitigation
On-path observation of the transport headers of packets can be used
for various security functions. For example, Denial of Service (DOS)
and Distributed DOS (DDOS) attacks against the infrastructure or
against an endpoint can be detected and mitigated by characterising
anomalous traffic. Other uses include support for security audits
(e.g., verifying the compliance with ciphersuites); client and
application fingerprinting for inventory; and to provide alerts for
network intrusion detection and other next generation firewall
functions.
Current practices in detection and mitigation of DDoS attacks
generally involve classification of incoming traffic (as packets,
flows, or some other aggregate) into "good" (productive) and "bad"
(DDoS) traffic, and then differential treatment of this traffic to
forward only good traffic. This operation is often done in a
separate specialized mitigation environment through which all traffic
is filtered; a generalized architecture for separation of concerns in
mitigation is given in [DOTS-ARCH].
Efficient classification of this DDoS traffic in the mitigation
environment is key to the success of this approach. Limited first-
packet garbage detection as in Section 3.1.2 and stateful tracking of
QUIC traffic as in Section 4.2 above may be useful during
classification.
Note that the use of a connection ID to support connection migration
renders 5-tuple based filtering insufficient to detect active flows
and requires more state to be maintained by DDoS defense systems if
support of migration of QUIC flows is desired. For the common case
of NAT rebinding, where the client's address changes without the
client's intent or knowledge, DDoS defense systems can detect a
change in the client's endpoint address by linking flows based on the
server's connection IDs. However, QUIC's linkability resistance
ensures that a deliberate connection migration is accompanied by a
change in the connection ID. In this case, the connection ID can not
be used to distinguish valid, active traffic from new attack traffic.
It is also possible for endpoints to directly support security
functions such as DoS classification and mitigation. Endpoints can
cooperate with an in-network device directly by e.g. sharing
information about connection IDs.
Another potential method could use an on-path network device that
relies on pattern inferences in the traffic and heuristics or machine
learning instead of processing observed header information.
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However, it is questionable whether connection migrations must be
supported during a DDoS attack. While unintended migration without a
connection ID change can be more easily supported, it might be
acceptable to not support migrations of active QUIC connections that
are not visible to the network functions performing the DDoS
detection. As soon as the connection blocking is detected by the
client, the client may be able to rely on the fast resumption
mechanism provided by QUIC. When clients migrate to a new path, they
should be prepared for the migration to fail and attempt to reconnect
quickly.
Beyond in-network DDoS protection mechanisms, TCP syncookies
[RFC4937] are a well-established method of mitigating some kinds of
TCP DDoS attacks. QUIC Retry packets are the functional analogue to
syncookies, forcing clients to prove possession of their IP address
before committing server state. However, there are safeguards in
QUIC against unsolicited injection of these packets by intermediaries
who do not have consent of the end server. See [QUIC_LB] for
standard ways for intermediaries to send Retry packets on behalf of
consenting servers.
4.8. Quality of Service handling and ECMP
It is expected that any QoS handling in the network, e.g. based on
use of DiffServ Code Points (DSCPs) [RFC2475] as well as Equal-Cost
Multi-Path (ECMP) routing, is applied on a per flow-basis (and not
per-packet) and as such that all packets belonging to the same QUIC
connection get uniform treatment. Using ECMP to distribute packets
from a single flow across multiple network paths or any other non-
uniform treatment of packets belong to the same connection could
result in variations in order, delivery rate, and drop rate. As
feedback about loss or delay of each packet is used as input to the
congestion controller, these variations could adversely affect
performance.
Depending of the loss recovery mechanism implemented, QUIC may be
more tolerant of packet re-ordering than traditional TCP traffic (see
Section 2.7). However, it cannot be known by the network which exact
recovery mechanism is used and therefore reordering tolerance should
be considered as unknown.
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4.9. Handling ICMP Messages
Datagram Packetization Layer PMTU Discovery (PLPMTUD) can be used by
QUIC to probe for the supported PMTU. PLPMTUD optionally uses ICMP
messages (e.g., IPv6 Packet Too Big messages). Given known attacks
with the use of ICMP messages, the use of PLPMTUD in QUIC has been
designed to safely use but not rely on receiving ICMP feedback (see
Section 14.2.1. of [QUIC-TRANSPORT]).
Networks are recommended to forward these ICMP messages and retain as
much of the original packet as possible without exceeding the minimum
MTU for the IP version when generating ICMP messages as recommended
in [RFC1812] and [RFC4443].
4.10. Guiding Path MTU
Some networks support 1500-byte packets, but can only do so by
fragmenting at a lower layer before traversing a smaller MTU segment,
and then reassembling. This is permissible even when the IP layer is
IPv6 or IPv4 with the DF bit set, because it occurs below the IP
layer. However, this process can add to compute and memory costs,
leading to a bottleneck that limits network capacity. In such
networks this generates a desire to influence a majority of senders
to use smaller packets, so that the limited reassembly capacity is
not exceeded.
For TCP, MSS clamping (Section 3.2 of [RFC4459]) is often used to
change the sender's maximum TCP segment size, but QUIC requires a
different approach. Section 14 of [QUIC-TRANSPORT] advises senders
to probe larger sizes using Datagram Packetization Layer PMTU
Discovery ([DPLPMTUD]) or Path Maximum Transmission Unit Discovery
(PMTUD: [RFC1191] and [RFC8201]). This mechanism will encourage
senders to approach the maximum size, which could cause fragmentation
with a network segment that they may not be aware of.
If path performance is limited when sending larger packets, an on-
path device should support a maximum packet size for a specific
transport flow and then consistently drop all packets that exceed the
configured size when the inner IPv4 packet has DF set, or IPv6 is
used. Endpoints can cache PMTU information between IP flows, in the
IP-layer cache, so short-term consistency between the PMTU for flows
can help avoid an endpoint using a PMTU that is inefficient.
Networks with configurations that would lead to fragmentation of
large packets should drop such packets rather than fragmenting them.
Network operators who plan to implement a more selective policy may
start by focussing on QUIC. QUIC flows cannot always be easily
distinguished from other UDP traffic, but we assume at least some
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portion of QUIC traffic can be identified (see Section 3.1). For
QUIC endpoints using DPLPMTUD it is recommended for the path to drop
a packet larger than the supported size. A QUIC probe packet is used
to discover the PMTU. If lost, this does not impact the flow of QUIC
data.
IPv4 routers generate an ICMP message when a packet is dropped
because the link MTU was exceeded. [RFC8504] specifies how an IPv6
node generates an ICMPv6 Packet Too Big message (PTB) in this case.
PMTUD relies upon an endpoint receiving such PTB messages [RFC8201],
whereas DPLPMTUD does not reply upon these messages, but still can
optionally use these to improve performance Section 4.6 of
[DPLPMTUD].
Since a network cannot know in advance which discovery method a QUIC
endpoint is using, it should always send a PTB message in addition to
dropping the oversized packet. A generated PTB message should be
compliant with the validation requirements of Section 14.2.1 of
[QUIC-TRANSPORT], otherwise it will be ignored by DPLPMTUD. This
will likely provide the right signal for the endpoint to keep the
packet size small and thereby avoid network fragmentation for that
flow entirely.
5. IANA Considerations
This document has no actions for IANA.
6. Security Considerations
QUIC is an encrypted and authenticated transport. That means, once
the cryptographic handshake is complete, QUIC endpoints discard most
packets that are not authenticated, greatly limiting the ability of
an attacker to interfere with existing connections.
However, some information is still observerable, as supporting
manageability of QUIC traffic inherently involves tradeoffs with the
confidentiality of QUIC's control information; this entire document
is therefore security-relevant.
More security considerations for QUIC are discussed in
[QUIC-TRANSPORT] and [QUIC-TLS], generally considering active or
passive attackers in the network as well as attacks on specific QUIC
mechanism.
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Version Negotiation packets do not contain any mechanism to prevent
version downgrade attacks. However, future versions of QUIC that use
Version Negotiation packets are require to define a mechanism that is
robust against version downgrade attacks. Therefore a network node
should not attempt to impact version selection, as version downgrade
may result in connection failure.
7. Contributors
The following people have contributed text to sections of this
document:
* Dan Druta
* Martin Duke
* Igor Lubashev
* David Schinazi
* Gorry Fairhurst
* Chris Box
8. Acknowledgments
Thanks to Thomas Fossati, Jana Iygengar, Marcus Ihlar for their early
reviews and feedback. Special thanks also to Martin Thomson and
Martin Duke for their detailed reviews and input. And thanks to Sean
Turner, Mike Bishop, Ian Swett, and Nick Banks for their last call
reviews.
This work is partially supported by the European Commission under
Horizon 2020 grant agreement no. 688421 Measurement and Architecture
for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
for Education, Research, and Innovation under contract no. 15.0268.
This support does not imply endorsement.
9. References
9.1. Normative References
[QUIC-TLS] Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
Work in Progress, Internet-Draft, draft-ietf-quic-tls-34,
14 January 2021,
<https://tools.ietf.org/html/draft-ietf-quic-tls-34>.
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[QUIC-TRANSPORT]
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,
<https://tools.ietf.org/html/draft-ietf-quic-transport-
34>.
9.2. Informative References
[DOTS-ARCH]
Mortensen, A., Reddy, T., Andreasen, F., Teague, N., and
R. Compton, "DDoS Open Threat Signaling (DOTS)
Architecture", Work in Progress, Internet-Draft, draft-
ietf-dots-architecture-18, 6 March 2020,
<https://tools.ietf.org/html/draft-ietf-dots-architecture-
18>.
[DPLPMTUD] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/rfc/rfc8899>.
[I-D.ietf-quic-applicability]
Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
Transport Protocol", Work in Progress, Internet-Draft,
draft-ietf-quic-applicability-11, 21 April 2021,
<https://tools.ietf.org/html/draft-ietf-quic-
applicability-11>.
[IPIM] Allman, M., Beverly, R., and B. Trammell, "In-Protocol
Internet Measurement (arXiv preprint 1612.02902)", 9
December 2016, <https://arxiv.org/abs/1612.02902>.
[QUIC-APPLICABILITY]
Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
Transport Protocol", Work in Progress, Internet-Draft,
draft-ietf-quic-applicability-11, 21 April 2021,
<https://tools.ietf.org/html/draft-ietf-quic-
applicability-11>.
[QUIC-HTTP]
Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-34, 2 February 2021,
<https://tools.ietf.org/html/draft-ietf-quic-http-34>.
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[QUIC-INVARIANTS]
Thomson, M., "Version-Independent Properties of QUIC",
Work in Progress, Internet-Draft, draft-ietf-quic-
invariants-13, 14 January 2021,
<https://tools.ietf.org/html/draft-ietf-quic-invariants-
13>.
[QUIC-RECOVERY]
Iyengar, J. and I. Swett, "QUIC Loss Detection and
Congestion Control", Work in Progress, Internet-Draft,
draft-ietf-quic-recovery-34, 14 January 2021,
<https://tools.ietf.org/html/draft-ietf-quic-recovery-34>.
[QUIC_LB] Duke, M. and N. Banks, "QUIC-LB: Generating Routable QUIC
Connection IDs", Work in Progress, Internet-Draft, draft-
ietf-quic-load-balancers-06, 4 February 2021,
<https://tools.ietf.org/html/draft-ietf-quic-load-
balancers-06>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/rfc/rfc1191>.
[RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers",
RFC 1812, DOI 10.17487/RFC1812, June 1995,
<https://www.rfc-editor.org/rfc/rfc1812>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/rfc/rfc2475>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/rfc/rfc4443>.
[RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the-
Network Tunneling", RFC 4459, DOI 10.17487/RFC4459, April
2006, <https://www.rfc-editor.org/rfc/rfc4459>.
[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
Translation (NAT) Behavioral Requirements for Unicast
UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, <https://www.rfc-editor.org/rfc/rfc4787>.
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[RFC4937] Arberg, P. and V. Mammoliti, "IANA Considerations for PPP
over Ethernet (PPPoE)", RFC 4937, DOI 10.17487/RFC4937,
June 2007, <https://www.rfc-editor.org/rfc/rfc4937>.
[RFC5382] Guha, S., Ed., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, DOI 10.17487/RFC5382, October 2008,
<https://www.rfc-editor.org/rfc/rfc5382>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/rfc/rfc6066>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC7605] Touch, J., "Recommendations on Using Assigned Transport
Port Numbers", BCP 165, RFC 7605, DOI 10.17487/RFC7605,
August 2015, <https://www.rfc-editor.org/rfc/rfc7605>.
[RFC7983] Petit-Huguenin, M. and G. Salgueiro, "Multiplexing Scheme
Updates for Secure Real-time Transport Protocol (SRTP)
Extension for Datagram Transport Layer Security (DTLS)",
RFC 7983, DOI 10.17487/RFC7983, September 2016,
<https://www.rfc-editor.org/rfc/rfc7983>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/rfc/rfc8201>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/rfc/rfc8504>.
[TLS-ECH] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-10, 8 March 2021,
<https://tools.ietf.org/html/draft-ietf-tls-esni-10>.
[TMA-QOF] Trammell, B., Gugelmann, D., and N. Brownlee, "Inline Data
Integrity Signals for Passive Measurement (in Proc. TMA
2014)", April 2014.
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[WIRE-IMAGE]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/rfc/rfc8546>.
Appendix A. Distinguishing IETF QUIC and Google QUIC Versions
This section contains algorithms that allows parsing versions from
both Google QUIC and IETF QUIC. These mechanisms will become
irrelevant when IETF QUIC is fully deployed and Google QUIC is
deprecated.
Note that other than this appendix, nothing in this document applies
to Google QUIC. And the purpose of this appendix is merely to
distinguish IETF QUIC from any versions of Google QUIC.
This appendix uses the following conventions: * array[i] - one byte
at index i of array * array[i:j] - subset of array starting with
index i (inclusive) up to j-1 (inclusive) * array[i:] - subset of
array starting with index i (inclusive) up to the end of the array
Conceptually, a Google QUIC version is an opaque 32bit field. When
we refer to a version with four printable characters, we use its
ASCII representation: for example, Q050 refers to {'Q', '0', '5',
'0'} which is equal to {0x51, 0x30, 0x35, 0x30}. Otherwise, we use
its hexadecimal representation: for example, 0xff00001d refers to
{0xff, 0x00, 0x00, 0x1d}.
QUIC versions that start with 'Q' or 'T' followed by three digits are
Google QUIC versions. Versions up to and including 43 are documented
by <https://docs.google.com/document/d/
1WJvyZflAO2pq77yOLbp9NsGjC1CHetAXV8I0fQe-B_U/preview>. Versions
Q046, Q050, T050, and T051 are not fully documented, but this
appendix should contain enough information to allow parsing Client
Hellos for those versions.
To extract the version number itself, one needs to look at the first
byte of the QUIC packet, in other words the first byte of the UDP
payload.
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first_byte = packet[0]
first_byte_bit1 = ((first_byte & 0x80) != 0)
first_byte_bit2 = ((first_byte & 0x40) != 0)
first_byte_bit3 = ((first_byte & 0x20) != 0)
first_byte_bit4 = ((first_byte & 0x10) != 0)
first_byte_bit5 = ((first_byte & 0x08) != 0)
first_byte_bit6 = ((first_byte & 0x04) != 0)
first_byte_bit7 = ((first_byte & 0x02) != 0)
first_byte_bit8 = ((first_byte & 0x01) != 0)
if (first_byte_bit1) {
version = packet[1:5]
} else if (first_byte_bit5 && !first_byte_bit2) {
if (!first_byte_bit8) {
abort("Packet without version")
}
if (first_byte_bit5) {
version = packet[9:13]
} else {
version = packet[5:9]
}
} else {
abort("Packet without version")
}
A.1. Extracting the CRYPTO frame
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counter = 0
while (payload[counter] == 0) {
counter += 1
}
first_nonzero_payload_byte = payload[counter]
fnz_payload_byte_bit3 = ((first_nonzero_payload_byte & 0x20) != 0)
if (first_nonzero_payload_byte != 0x06) {
abort("Unexpected frame")
}
if (payload[counter+1] != 0x00) {
abort("Unexpected crypto stream offset")
}
counter += 2
if ((payload[counter] & 0xc0) == 0) {
crypto_data_length = payload[counter]
counter += 1
} else {
crypto_data_length = payload[counter:counter+2]
counter += 2
}
crypto_data = payload[counter:counter+crypto_data_length]
ParseTLS(crypto_data)
Authors' Addresses
Mirja Kuehlewind
Ericsson
Email: mirja.kuehlewind@ericsson.com
Brian Trammell
Google Switzerland GmbH
Gustav-Gull-Platz 1
CH- 8004 Zurich
Switzerland
Email: ietf@trammell.ch
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