Network Working Group M. Kuehlewind
Internet-Draft B. Trammell
Intended status: Informational ETH Zurich
Expires: October 26, 2019 April 24, 2019
Manageability of the QUIC Transport Protocol
draft-ietf-quic-manageability-04
Abstract
This document discusses manageability of the QUIC transport protocol,
focusing on caveats impacting network operations involving QUIC
traffic. Its intended audience is network operators, as well as
content providers that rely on the use of QUIC-aware middleboxes,
e.g. for load balancing.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on October 26, 2019.
Copyright Notice
Copyright (c) 2019 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Features of the QUIC Wire Image . . . . . . . . . . . . . . . 3
2.1. QUIC Packet Header Structure . . . . . . . . . . . . . . 4
2.2. Coalesced Packets . . . . . . . . . . . . . . . . . . . . 6
2.3. Use of Port Numbers . . . . . . . . . . . . . . . . . . . 6
2.4. The QUIC handshake . . . . . . . . . . . . . . . . . . . 6
2.5. Integrity Protection of the Wire Image . . . . . . . . . 10
2.6. Connection ID and Rebinding . . . . . . . . . . . . . . . 10
2.7. Packet Numbers . . . . . . . . . . . . . . . . . . . . . 11
2.8. Version Negotiation and Greasing . . . . . . . . . . . . 11
3. Network-visible information about QUIC flows . . . . . . . . 11
3.1. Identifying QUIC traffic . . . . . . . . . . . . . . . . 11
3.1.1. Identifying Negotiated Version . . . . . . . . . . . 12
3.1.2. Rejection of Garbage Traffic . . . . . . . . . . . . 12
3.2. Connection confirmation . . . . . . . . . . . . . . . . . 12
3.3. Application Identification . . . . . . . . . . . . . . . 13
3.4. Flow association . . . . . . . . . . . . . . . . . . . . 13
3.5. Flow teardown . . . . . . . . . . . . . . . . . . . . . . 14
3.6. Flow symmetry measurement . . . . . . . . . . . . . . . . 14
3.7. Round-Trip Time (RTT) Measurement . . . . . . . . . . . . 14
3.7.1. Measuring initial RTT . . . . . . . . . . . . . . . . 14
3.7.2. Using the Spin Bit for Passive RTT Measurement . . . 15
4. Specific Network Management Tasks . . . . . . . . . . . . . . 16
4.1. Stateful treatment of QUIC traffic . . . . . . . . . . . 16
4.2. Passive network performance measurement and
troubleshooting . . . . . . . . . . . . . . . . . . . . . 16
4.3. Server cooperation with load balancers . . . . . . . . . 16
4.4. DDoS Detection and Mitigation . . . . . . . . . . . . . . 17
4.5. Distinguishing acknowledgment traffic . . . . . . . . . . 17
4.6. QoS support and ECMP . . . . . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
QUIC [QUIC-TRANSPORT] is a new transport protocol currently under
development in the IETF quic working group, focusing on support of
semantics as needed for HTTP/2 [QUIC-HTTP]. Based on current
deployment practices, QUIC is encapsulated in UDP and encrypted by
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default. The current version of QUIC integrates TLS [QUIC-TLS] to
encrypt all payload data and most control information.
Given that QUIC is an end-to-end transport protocol, all information
in the protocol header, even that which can be inspected, is not
meant to be mutable by the network, and is therefore integrity-
protected. While less information is visible to the network than for
TCP, integrity protection can also simplify troubleshooting because
none of the nodes on the network path can modify the transport layer
information.
This document provides guidance for network operation on the
management of QUIC traffic. This includes guidance on how to
interpret and utilize information that is exposed by QUIC to the
network as well as explaining requirement and assumptions that the
QUIC protocol design takes toward the expected network treatment. It
also discusses how common network management practices will be
impacted by QUIC.
Of course, 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.
QUIC is at the moment very much a moving target. This document
refers the state of the QUIC working group drafts as well as to
changes under discussion, via issues and pull requests in GitHub
current as of the time of writing.
1.1. Notational Conventions
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.
2. Features of the QUIC Wire Image
In this section, we discusses 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
QUIC's unencrypted wire image [WIRE-IMAGE], which we define as the
information available in the packet header in each QUIC packet, and
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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, at least the mechanism by which a
receiver can determine which version is used and the meaning and
location of fields used in the version negotiation process is
invariant [QUIC-INVARIANTS].
This document is focused on the protocol as presently defined in
[QUIC-TRANSPORT] and [QUIC-TLS], and will change to track those
documents.
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 indicates which type of header is
present.
The long header exposes more information. 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 are used after connection establishment, and contain
only an optional destination connection ID and the spin bit for RTT
measurement.
The following information is exposed in QUIC packet headers:
o demux bit: the second most significant bit of the first octet
every QUIC packet of the current version is set to 1, for
demultiplexing with other UDP-encapsulated protocols.
o latency spin bit: the third most significant bit of first octet in
the short packet header. The spin bit is set by endpoints such
that tracking edge transitions can be used to passively observe
end-to-end RTT. See Section 3.7.2 for further details.
o header type: the long header has a 2 bit packet type field
following the Header Form bit. Header types correspond to stages
of the handshake; see Section 17.2 of [QUIC-TRANSPORT].
o version number: the version number present in the long header, and
identifies the version used for that packet. Note that during
Version Negotiation (see Section 2.8, and Section 17.2.1 of
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[QUIC-TRANSPORT], the version number field has a special value
(0x00000000) that identifies the packet as a Version Negotiation
packet.
o 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 4.3 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.
o 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).
o 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 and Version Negotiation packets are not encrypted or obfuscated
in any way. For other kinds of packets, other information in the
packet headers is cryptographically obfuscated:
o packet number: Most packets (with the exception of 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 the header for packets with long headers, while it is implicit
(depending on Destination Connection ID length) in short header
packets. The length of the packet number is cryptographically
obfuscated.
o key phase: The Key Phase bit, present in short headers, specifies
the keys used to encrypt the packet, supporting key rotation. The
Key Phase bit is cryptographically obfuscated.
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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. The
length header field is variable length and its position in the header
is also variable depending on the length of the source and
destionation connection ID. See Section 4.6 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 with TCP-
based services, especially when application layer information is
encrypted, there is no guarantee that a specific application will use
the registered port, or the used port is carrying traffic belonging
to the respective registered service. For example, [QUIC-TRANSPORT]
specifies the use of Alt-Svc for discovery of QUIC/HTTP services on
other ports.
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 not present in the packet header, 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 datagams containing the QUIC handshake, then
examine each of the datagrams in detail.
In the nominal case, the QUIC handshake can be recognized on the wire
through at least four datagrams we'll call "QUIC Client Hello", "QUIC
Server Hello", and "Initial Completion", and "Handshake 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.
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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
| |
+----QUIC Client Hello-------------------->|
+----(zero or more 0RTT)------------------>|
| |
|<--------------------QUIC Server Hello----+
|<---------(1RTT encrypted data starts)----+
| |
+----Initial Completion------------------->|
+----(1RTT encrypted data starts)--------->|
| |
|<-----------------Handshake Completion----+
| |
Figure 1: General communication pattern visible in the QUIC handshake
A typical handshake starts with the client sending of a QUIC Client
Hello datagram as shown in Figure 2, which elicits a QUIC Server
Hello datagram as shown in Figure 3 typically containing three
packets: an Initial packet with the Server Hello, a Handshake packet
with the rest of the server's side of the TLS handshake, and initial
1-RTT data, if present.
The content of QUIC 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; we therefore
consider these as visible in our 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
Initial Completion Figure 4 and the Handshake Completion Figure 5
datagrams finish these first two contexts, by sending the final
acknowledgment and finishing the transmission of CRYPTO frames.
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+----------------------------------------------------------+
| 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 frame | |
+----------------------------------------------------------+<-+
Figure 2: Typical 1-RTT QUIC Client Hello datagram pattern
The Client Hello datagram exposes version number, source and
destination connection IDs, and information in the TLS Client Hello
message, including any TLS Server Name Indication (SNI) present, in
the clear. The QUIC PADDING frame shown here may be present to
ensure the Client Hello datagram has a minumum size of 1200 octets,
to mitigate the possibility of handshake amplification. Note that
the location of PADDING is implementation-dependent, and PADDING
frames may not appear in the Initial packet in a coalesced 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 QUIC Server Hello datagram pattern
The Server Hello datagram exposes version number, source and
destination connection IDs, and information in the TLS Server Hello
message.
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+------------------------------------------------------------+
| UDP header (source and destination UDP ports) |
+------------------------------------------------------------+
| QUIC long header (type = Initial, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| QUIC ACK frame (acknowledging Server Hello Initial) | |
+------------------------------------------------------------+<-+
| QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
+------------------------------------------------------------+ |
| encrypted payload (presumably CRYPTO/ACK frames) | |
+------------------------------------------------------------+<-+
| QUIC short header |
+------------------------------------------------------------+
| 1-RTT encrypted payload |
+------------------------------------------------------------+
Figure 4: Typical QUIC Initial Completion datagram pattern
The Initial 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 3.7.
+------------------------------------------------------------+
| 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 QUIC Handshake Completion datagram pattern
Similar to Initial Competion, Handshake 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 QUIC Client Hello datagram, as shown in Figure 6.
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+----------------------------------------------------------+
| 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 QUIC Client Hello datagram pattern
In a 0-RTT QUIC Client Hello 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 server after the Client Hello datagram, containing the rest of
the 0-RTT data. The amount of 0-RTT protected data is limited by the
initial congestion window, typically around 10 packets [RFC6928].
2.5. Integrity Protection of the Wire Image
As soon as the cryptographic context is established, all information
in the QUIC header, including information exposed in the packet
header, is integrity protected. Further, information that was sent
and exposed in handshake packets sent before the cryptographic
context was established are validated later during the cryptographic
handshake. Therefore, devices on path MUST NOT change any
information or bits in QUIC packet headers, since alteration of
header information will lead to a failed integrity check at the
receiver, and can even lead to connection termination.
2.6. Connection ID and Rebinding
The connection ID in the QUIC packet headers allows routing of QUIC
packets at load balancers on other than five-tuple information,
ensuring that related flows are appropriately balanced together; and
to allow rebinding of a connection after one of the endpoint's
addresses changes - usually the client's, in the case of the HTTP
binding. 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
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the new connection ID being negotiated via encrypted frames. See
Section 5.1 of [QUIC-TRANSPORT].
2.7. Packet Numbers
The packet number field is always present in the QUIC packet header;
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 useful to on-path observers.
2.8. Version Negotiation and Greasing
Version negotiation is not protected, given the used protection
mechanism can change with the version. However, the choices provided
in the list of version in the Version Negotiation packet will be
validated as soon as the cryptographic context has been established.
Therefore any manipulation of this list will be detected and will
cause the endpoints to terminate the connection.
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 ID and packet number of the Client
Initial packet are reflected to provide a proof of return-
routability. Therefore changing these information will also cause
the connection to fail.
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.
3.1. Identifying QUIC traffic
The QUIC wire image is not specifically designed to be
distinguishable from other UDP traffic.
The only application binding currently defined for QUIC is HTTP
[QUIC-HTTP]. HTTP over QUIC uses UDP port 443 by default, although
URLs referring to resources available over HTTP over QUIC may specify
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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 [RFC7605] section 5.
While the second most significant bit (0x40) of the first octet is
always set to 1 in QUIC packets of the current version, this is not a
recommended method of recognizing QUIC traffic, as it only provides
one bit of information and is quite prone to collide with UDP-based
protocols other than those that this static bit is meant to allow
multiplexing with.
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: an Initial packet with a given version from a client to
which a server responds with an Initial packet with the same version
implies acceptance of that version.
Negotiated version cannot be identified for flows for which a
handshake is not observed, such as in the case of NAT rebinding;
however, these flows can be associated with flows for which a version
has been identified; see Section 3.4.
In the rest of this section, we discuss only packets belonging to
Version 1 QUIC flows, and assume that these packets have been
identified as such through the observation of a version negotiation.
3.1.2. Rejection of Garbage Traffic
A related question is whether a first packet of a given flow on known
QUIC-associated port is a valid QUIC packet, in order to support in-
network filtering of garbage UDP packets (reflection attacks, random
backscatter). 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 packet types may have different meanings in future versions of the
protocol.
3.2. Connection confirmation
Connection establishment uses Initial, Handshake, and Retry packets
containing a TLS handshake. Connection establishment can therefore
be detected using heuristics similar to those used to detect TLS over
TCP. A client using 0-RTT connection may also send data packets in
0-RTT Protected packets directly after the Initial packet containing
the TLS Client Hello. Since these packets may be reordered in the
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network, note that 0-RTT Protected data packets may be seen before
the Initial packet.
Note that clients send Initial packets before servers do, servers
send Handshake packets before clients do, and only clients send
Initial packets with tokens, so the sides of a connection can be
generally be confirmed by an on-path observer. An attempted
connection after Retry can be detected by correlating the token on
the Retry with the token on the subsequent Initial packet.
3.3. Application Identification
The cleartext TLS handshake may contain Server Name Indication (SNI)
[RFC6066], 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 information from
Application-Layer Protocol Negotiation (ALPN) [RFC7301], 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
SNI in TLS 1.3 [TLS-ENCRYPT-SNI], reducing the information available
in the SNI to the name of a fronting service, which can generally be
identified by the IP address of the server anyway. If used with
QUIC, this would make SNI-based application identification impossible
through passive measurement.
3.4. Flow association
The QUIC Connection ID (see Section 2.6) is designed to allow an on-
path device such as a load-balancer to associate two flows as
identified by five-tuple when the address and port of one of the
endpoints changes; e.g. due to NAT rebinding or server IP address
migration. An observer keeping flow state can associate a connection
ID with a given flow, and can associate a known flow with a new flow
when when observing a packet sharing a connection ID and one endpoint
address (IP address and port) with the known flow.
However, since the connection ID may change multiple times during the
lifetime of a flow, and the negotiation of connection ID changes is
encrypted, packets with the same 5-tuple but different connection IDs
may or may not belong to the same connection.
The connection ID value should be treated as opaque; see Section 4.3
for caveats regarding connection ID selection at servers.
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3.5. Flow teardown
The 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.
Changes to this behavior have been discussed in the working group,
but there is no current proposal to implement these changes: see
https://github.com/quicwg/base-drafts/issues/602.
3.6. 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
symmerty 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.
3.7. Round-Trip Time (RTT) Measurement
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 [QUIC-TRANSPORT], section 17.3.1.
3.7.1. Measuring initial RTT
In the common case, the delay between the Initial packet containing
the TLS Client Hello and the Handshake packet containing the TLS
Server Hello represents the RTT component on the path between the
observer and the server. The delay between the TLS Server Hello and
the Handshake packet containing the TLS Finished message sent by the
client represents the RTT component on the path between the observer
and the client. While the client may send 0-RTT Protected packets
after the Initial packet during 0-RTT 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 at
both sides.
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3.7.2. Using the Spin Bit for Passive RTT Measurement
The spin bit provides an additional method to measure per-flow RTT
from observation points on the network path throughout the duration
of a connection. Endpoint participation in spin bit signaling is
optional in QUIC. 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 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. In order to not
make these connections identifiable based on the usage of the spin
bit, it is recommended that all endpoints disable "spinning" randomly
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.
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.
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. A simple linear smoothing or moving minimum filter can
be applied to the stream of RTT information to get a more stable
estimate.
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 low RTT estimates, if reordering occurs across a spin-bit
flip in the stream.
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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.
4. Specific Network Management Tasks
In this section, we address specific network management and
measurement techniques and how QUIC's design impacts them.
4.1. Stateful treatment of QUIC traffic
Stateful treatment of QUIC traffic 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 3.5) means that this state must
be purged either through timers or through least-recently-used
eviction, depending on application requirements.
4.2. Passive network performance measurement and troubleshooting
Limited RTT measurement is possible by passive observation of QUIC
traffic; see Section 3.7. 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.
4.3. Server cooperation with load balancers
In the case of content distribution networking architectures
including load balancers, the connection ID provides 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].
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4.4. DDoS Detection and Mitigation
Current practices in detection and mitigation of Distributed Denial
of Service (DDoS) attacks generally involve passive measurement using
network flow data [RFC7011], classification of traffic into "good"
(productive) and "bad" (DoS) flows, and filtering of these bad flows
in a "scrubbing" environment. Key to successful DDoS mitigation is
efficient classification of this traffic.
Limited first-packet garbage detection as in Section 3.1.2 and
stateful tracking of QUIC traffic as in Section 4.1 above can be used
in this classification step.
Note that the use of a connection ID to support connection migration
renders 5-tuple based filtering insufficient, and requires more state
to be maintained by DDoS defense systems, and linkability resistance
in connection ID update mechanisms means that a connection ID aware
DDoS defense system must have the same information about flows as the
load balancer.
However, it is questionable if connection migrations needs to be
supported in a DDOS attack. If the connection migration is not
visible to the network that performs the DDoS detection, an active,
migrated QUIC connection may be blocked by such a system under
attack. However, a defense system might simply rely on the fast
resumption mechanism provided by QUIC.
4.5. 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 emphatically
NOT RECOMMENDED.
4.6. QoS support and ECMP
[EDITOR'S NOTE: this is a bit speculative; keep?]
QUIC does not provide any additional information on requirements on
Quality of Service (QoS) provided from the network. QUIC assumes
that all packets with the same 5-tuple {dest addr, source addr,
protocol, dest port, source port} will receive similar network
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treatment. That means all stream that are multiplexed over the same
QUIC connection require the same network treatment and are handled by
the same congestion controller. If differential network treatment is
desired, multiple QUIC connections to the same server might be used,
given that establishing a new connection using 0-RTT support is cheap
and fast.
QoS mechanisms in the network MAY also use the connection ID for
service differentiation, as a change of connection ID is bound to a
change of address which anyway is likely to lead to a re-route on a
different path with different network characteristics.
Given that QUIC is more tolerant of packet re-ordering than TCP (see
Section 2.7), Equal-cost multi-path routing (ECMP) does not
necessarily need to be flow based. However, 5-tuple (plus eventually
connection ID if present) matching is still beneficial for QoS given
all packets are handled by the same congestion controller.
5. IANA Considerations
This document has no actions for IANA.
6. Security Considerations
Supporting manageability of QUIC traffic inherently involves
tradeoffs with the confidentiality of QUIC's control information;
this entire document is therefore security-relevant.
7. Contributors
Dan Druta contributed text to Section 4.4. Igor Lubashev contributed
text to Section 4.3 on the use of the connection ID for load
balancing. Marcus Ilhar contributed text to Section 3.7 on the use
of the spin bit.
8. Acknowledgments
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
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9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[Ding2015]
Ding, H. and M. Rabinovich, "TCP Stretch Acknowledgments
and Timestamps - Findings and Impliciations for Passive
RTT Measurement (ACM Computer Communication Review)", July
2015, <http://www.sigcomm.org/sites/default/files/ccr/
papers/2015/July/0000000-0000002.pdf>.
[IPIM] Allman, M., Beverly, R., and B. Trammell, "In-Protocol
Internet Measurement (arXiv preprint 1612.02902)",
December 2016, <https://arxiv.org/abs/1612.02902>.
[QUIC-APPLICABILITY]
Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
Transport Protocol", draft-ietf-quic-applicability-03
(work in progress), October 2018.
[QUIC-HTTP]
Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", draft-ietf-quic-http-20 (work in progress),
April 2019.
[QUIC-INVARIANTS]
Thomson, M., "Version-Independent Properties of QUIC",
draft-ietf-quic-invariants-04 (work in progress), April
2019.
[QUIC-TLS]
Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
draft-ietf-quic-tls-20 (work in progress), April 2019.
[QUIC-TRANSPORT]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-20 (work
in progress), April 2019.
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[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6928] Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
"Increasing TCP's Initial Window", RFC 6928,
DOI 10.17487/RFC6928, April 2013,
<https://www.rfc-editor.org/info/rfc6928>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[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/info/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/info/rfc7605>.
[TLS-ENCRYPT-SNI]
Huitema, C. and E. Rescorla, "Issues and Requirements for
SNI Encryption in TLS", draft-ietf-tls-sni-encryption-04
(work in progress), November 2018.
[TMA-QOF] Trammell, B., Gugelmann, D., and N. Brownlee, "Inline Data
Integrity Signals for Passive Measurement (in Proc. TMA
2014)", April 2014.
[WIRE-IMAGE]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", draft-trammell-wire-image-04 (work in
progress), April 2018.
Authors' Addresses
Mirja Kuehlewind
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: mirja.kuehlewind@tik.ee.ethz.ch
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Brian Trammell
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: ietf@trammell.ch
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