Network Working Group M. Kuehlewind
Internet-Draft B. Trammell
Intended status: Informational ETH Zurich
Expires: April 28, 2018 October 25, 2017
Manageability of the QUIC Transport Protocol
draft-ietf-quic-manageability-01
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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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. Integrity Protection of the Wire Image . . . . . . . . . 5
2.3. Connection ID and Rebinding . . . . . . . . . . . . . . . 5
2.4. Packet Numbers . . . . . . . . . . . . . . . . . . . . . 6
2.5. Initial Handshake and PMTUD . . . . . . . . . . . . . . . 6
2.6. Version Negotiation and Greasing . . . . . . . . . . . . 6
3. Network-visible information about QUIC flows . . . . . . . . 6
3.1. Identifying QUIC traffic . . . . . . . . . . . . . . . . 7
3.1.1. Identifying Negotiated Version . . . . . . . . . . . 7
3.1.2. Rejection of Garbage Traffic . . . . . . . . . . . . 7
3.2. Connection confirmation . . . . . . . . . . . . . . . . . 7
3.3. Flow association . . . . . . . . . . . . . . . . . . . . 8
3.4. Flow teardown . . . . . . . . . . . . . . . . . . . . . . 8
3.5. Round-trip time measurement . . . . . . . . . . . . . . . 8
3.6. Packet loss measurement . . . . . . . . . . . . . . . . . 9
3.7. Flow symmetry measurement . . . . . . . . . . . . . . . . 9
4. Specific Network Management Tasks . . . . . . . . . . . . . . 9
4.1. Stateful treatment of QUIC traffic . . . . . . . . . . . 9
4.2. Passive network performance measurement and
troubleshooting . . . . . . . . . . . . . . . . . . . . . 9
4.3. Server cooperation with load balancers . . . . . . . . . 10
4.4. DDoS Detection and Mitigation . . . . . . . . . . . . . . 10
4.5. QoS support and ECMP . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
QUIC [QUIC] 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 default. The
current version of QUIC integrates TLS [QUIC-TLS] to encrypt all
payload data and most control information. Given QUIC is an end-to-
end transport protocol, all information in the protocol header, even
that which can be inspected, is is not meant to be mutable by the
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network, and will therefore be integrity-protected to the extent
possible.
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 words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
document. It's not shouting; when these words are capitalized, they
have a special meaning as defined in [RFC2119].
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, 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, also the
wire image of the header format can change. 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 need to be fixed.
This document is focused on the protocol as presently defined in
[QUIC] and [QUIC-TLS], and will change to track those documents.
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2.1. QUIC Packet Header Structure
The QUIC packet header is under active development; see section 5 of
[QUIC] for the present header structure.
The first bit of the QUIC header indicates the present of a long
header that exposes more information than the short header. The long
header is used during connection start including version negotiation,
server retry, and 0-RTT data while the short header is used after the
handshake and therefore on most data packets to limited unnecessary
header overhead. The fields and location of these fields as defined
by the current version of QUIC for the long header are fixed for all
future version as well. However, note that future versions of QUIC
may provide additional fields. In the current version of quic the
long header for all header types has a fixed length, containing,
besides the Header Form bit, a 7-bit header Type, a 64-bit Connection
ID, a 32-bit Packet Number, and a 32-bit Version. The short header
is variable length where bits after the Header Form bit indicate the
present on the Connection ID, and the length of the packet number.
The following information may be exposed in the packet header:
o header type: the long header has a 7-bit header type field
following the Header Form bit. The current version of QUIC
defines 6 header types, namely Version Negotiation, Client
Initial, Server Stateless Retry, Server Cleartext, Client
Cleartext, 0-RTT Protected.
o connection ID: The connection ID is always present on the long and
optionally present on the short header indicated by the Connection
ID Flag. If present at the short header it at the same position
then for the long header. The position and length pf the
congestion ID itself as well as the Connection ID flag in the
short header is fixed for all versions of QUIC. The connection ID
identifies the connection associated with a QUIC packet, for load-
balancing and NAT rebinding purposes; see Section 4.3 and
Section 2.3. Therefore it is also expected that the Connection ID
will either be present on all packets of a flow or none of the
short header packets. However, this field is under endpoint
control and there is no protocol mechanism that hinders the
sending endpoint to revise its decision about exposing the
Connection ID at any time during the connection.
o packet number: Every packet has an associated packet number. The
packet number increases with each packet, and the least-
significant bits of the packet number are present on each packet.
In the short header the length of the exposed packet number field
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is defined by the (short) header type and can either be 8, 16, or
32 bits. See Section 2.4.
o version number: The version number is present on the long headers
and identifies the version used for that packet, expect for the
Version negotiation packet. The version negotiation packet is
fixed for all version of QUIC and contains a list of versions that
is supported by the sender. The version in the version field of
the Version Negotiation packet is the reflected version of the
Client Initial packet and is therefore explicitly n ot supported
by the sender.
o key phase: The short header further has a Key Phase flag that is
used by the endpoint identify the right key that was used to
encrypt the packet.
2.2. Integrity Protection of the Wire Image
As soon as the cryptographic context is established, all information
in the QUIC header, including those exposed in the packet header, is
integrity protected. Further, information that were sent and exposed
in previous packets when the cryptographic context was established
yet, e.g. for the cryptographic initial handshake itself, will be
validated later during the cryptographic handshake, such as the
version number. Therefore, devices on path MUST NOT change any
information or bits in QUIC packet headers. As alteration of header
information would cause packet drop due to a failed integrity check
at the receiver, or can even lead to connection termination.
2.3. Connection ID and Rebinding
The connection ID in the QUIC packer header is used to allow 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. The client set a Connection ID in the Initial
Client packet that will be used during the handshake. A new
connection ID is then provided by the server during connection
establishment, that will be used in the short header after the
handshake. Further a server might provide additional connection IDs
that can the used by the client at any time during the connection.
Therefore if a flow changes one of its IP addresses it may keep the
same connection ID, or the connection ID may also change together
with the IP address migration, avoiding linkability; see Section 7.6
of [QUIC].
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2.4. Packet Numbers
The packet number field is always present in the QUIC packet header.
The packet number exposes the least significant 32, 16, or 8 bits of
an internal packet counter per flow direction that increments with
each packet sent. This packet counter is initialized with a random
31-bit initial value at the start of a connection.
Unlike TCP sequence numbers, this packet number increases with every
packet, including those containing only acknowledgment or other
control information. Indeed, whether a packet contains user data or
only control information is intentionally left unexposed to the
network. The packet number increases with every packet but they
sender may skip packet numbers.
While loss detection in QUIC is based on packet numbers, congestion
control by default provides richer information than vanilla TCP does.
Especially, QUIC does not rely on duplicated ACKs, making it more
tolerant of packet re-ordering.
2.5. Initial Handshake and PMTUD
[Editor's note: text needed.]
2.6. 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
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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
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.
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: a Client Initial with a given version followed by Server
Cleartext 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 3.3.
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 requires cleartext packets and is using a
TLS handshake on stream 0. Therefore it is detectable using
heuristics similar to those used to detect TLS over TCP. 0-RTT
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connection may additional also send data packets, right after the
Client Initial with the TLS client hello. These data may be
reordered in the network, therefore it may be possible that 0-RTT
Protected data packets are seen before the Client Initial packet.
3.3. Flow association
The QUIC Connection ID (see Section 2.3) 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.
The connection ID to be used for a long-running flow is chosen by the
server (see [QUIC] section 5.6) during the handshake. This value
should be treated as opaque; see Section 4.3 for caveats regarding
connection ID selection at servers.
3.4. 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 are currently under discussion: see
https://github.com/quicwg/base-drafts/issues/602.
3.5. Round-trip time measurement
Round-trip time of QUIC flows can be inferred by observation once per
flow, during the handshake, as in passive TCP measurement. The delay
between the Client Initial packet and the Server Cleartext packet
sent back to the client represents the RTT component on the path
between the observer and the server, and the delay between this
packet and the Client Cleartext packet in reply represents the RTT
component on the path between the observer and the client. This
measurement necessarily includes any application delay at both sides.
Note that the Server's reply mayalso be a Version Negotiation or
Server Stateless Retry packet. In this case the Client will send
another Client Initial or the connection will fail.
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The lack of any acknowledgement information or timestamping
information in the QUIC wire image makes running passive RTT
estimation impossible.
Changes to this behavior are currently under discussion: see
https://github.com/quicwg/base-drafts/issues/631.
3.6. Packet loss measurement
All QUIC packets carry packet numbers in cleartext, and while the
protocol allows packet numbers to be skipped, skipping is not
recommended in the general case. This allows the trivial one-sided
estimation of packet loss and reordering between the sender and a
given observation point ("upstream loss"). However, since
retransmissions are not identifiable as such, loss between an
observation point and the receiver ("downstream loss") cannot be
reliably estimated.
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
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.
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 3.4) 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
Extremely limited loss and RTT measurement are possible by passive
observation of QUIC traffic; see Section 3.5 and Section 3.6.
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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.
Server-generated Connection IDs must not encode any information other
that that needed to route packets to the appropriate backend
server(s): typically the identity of the backend server or pool of
servers, if the data-center's load balancing system keeps "local"
state of all flows itself. Care must be exercised to ensure that the
information encoded in the Connection ID is not sufficient to
identify unique end users. Note that by encoding routing information
in the Connection ID, load balancers open up a new attack vector that
allows bad actors to direct traffic at a specific backend server or
pool. It is therefore recommended that Server-Generated Connection
ID includes a cryptographic MAC that the load balancer pool server
are able to identify and discard packets featuring an invalid MAC.
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. For traffic where the classification
step did not observe a QUIC handshake, the presence of packets
carrying the same Connection ID in both directions is a further
indication of legitimate traffic. Note that these classification
techniques help only against floods of garbage traffic, not against
DDoS attacks using legitimate QUIC clients.
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. 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. See also https://github.com/quicwg/base-drafts/issues/203
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4.5. 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
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 2.4), 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.
Some of the properties of the QUIC header used in network management
are irrelevant to application-layer protocol operation and/or user
privacy. For example, packet number exposure (and echo, as proposed
in this document), as well as connection establishment exposure for
1-RTT establishment, make no additional information about user
traffic available to devices on path.
At the other extreme, supporting current traffic classification
methods that operate through the deep packet inspection (DPI) of
application-layer headers are directly antithetical to QUIC's goal to
provide confidentiality to its application-layer protocol(s); in
these cases, alternatives must be found.
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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.
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
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>.
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] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-07 (work
in progress), October 2017.
[QUIC-HTTP]
Bishop, M., "Hypertext Transfer Protocol (HTTP) over
QUIC", draft-ietf-quic-http-07 (work in progress), October
2017.
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[QUIC-TLS]
Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-07 (work in
progress), October 2017.
[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>.
[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>.
Authors' Addresses
Mirja Kuehlewind
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: mirja.kuehlewind@tik.ee.ethz.ch
Brian Trammell
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: ietf@trammell.ch
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