Network Working Group M. Kuehlewind
Internet-Draft B. Trammell
Intended status: Informational ETH Zurich
Expires: January 4, 2018 D. Druta
AT&T
July 03, 2017
Manageability of the QUIC Transport Protocol
draft-ietf-quic-manageability-00
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.
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This Internet-Draft will expire on January 4, 2018.
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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 . . . . . . . . . . . . . . 3
2.2. Integrity Protection of the Wire Image . . . . . . . . . 5
2.3. Connection ID and Rebinding . . . . . . . . . . . . . . . 5
2.4. Packet Numbers . . . . . . . . . . . . . . . . . . . . . 5
2.5. Initial Handshake and PMTUD . . . . . . . . . . . . . . . 6
2.6. Version Negotiation and Greasing . . . . . . . . . . . . 6
3. Specific Network Management Tasks . . . . . . . . . . . . . . 6
3.1. Stateful Treatment of QUIC Traffic . . . . . . . . . . . 6
3.2. Measurement of QUIC Traffic . . . . . . . . . . . . . . . 7
3.3. DDoS Detection and Mitigation . . . . . . . . . . . . . . 8
3.4. QoS support and ECMP . . . . . . . . . . . . . . . . . . 8
3.5. Load Balancing using the Connection ID . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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
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
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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.
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 typically used during connection start or for other control
processes while the short header will be used on most data packets to
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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 7 header types, namely Version Negotiation, Client
Initial, Server Stateless Retry, Server Cleartext, Client
Cleartext, 0-RTT Protected, 1-RTT Protected (key phase 0), 1-RTT
Protected (key phase 1), and Public Reset.
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 3.5 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 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
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 lit of versions that
is supported by the sender. However the version in the version
field of the header is the reflected version of the clients
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initial packet and is therefore explicitly not 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. Different key phases are indicated with the
use of the long header by using to different header types for
protected long header packets.
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
validate 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 connection ID is proposed by the server during
connection establishment, and 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].
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
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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. Specific Network Management Tasks
In this section, we address specific network management and
measurement techniques and how QUIC's design impacts them.
3.1. Stateful Treatment of QUIC Traffic
Stateful network devices such as firewalls use exposed header
information to support state setup and tear-down. [STATEFULNESS]
provides a general model for in-network state management on these
devices, independent of transport protocol. Features already present
in QUIC may be used for state maintenance in this model. Here, there
are two important goals: distinguishing valid QUIC connection
establishment from other traffic, in order to establish state; and
determining the end of a QUIC connection, in order to tear that state
down.
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Both, 1-RTT and O-RTT connection establishment, using a TLS handshake
on stream 0, is detectable using heuristics similar to those used to
detect TLS over TCP. 0-RTT connection may additional also send data
packets, right after the client hello. These data may be reorder in
the network, therefore it may be possible that 0-RTT Protected data
packet are seen before the Client Initial packet.
Exposure of connection shutdown is currently under discussion; see
https://github.com/quicwg/base-drafts/issues/353 and
https://github.com/quicwg/base-drafts/pull/20.
3.2. Measurement of QUIC Traffic
Passive measurement of TCP performance parameters is commonly
deployed in access and enterprise networks to aid troubleshooting and
performance monitoring without requiring the generation of active
measurement traffic.
The presence of packet numbers on all QUIC packets allows the trivial
one-sided estimation of packet loss and reordering between the sender
and a given observation point. However, since retransmissions are
not identifiable as such, loss between an observation point and the
receiver cannot be reliably estimated.
The lack of any acknowledgement information or timestamping
information in the QUIC packet header makes running passive
estimation of latency via round trip time (RTT) impossible. RTT can
only be measured at connection establishment time, by observing the
Client Initial packet and the Server's reply to this packet which
maybe a Server Cleartext, Version Negotiation, or Server Stateless
Retry packet.
Note that adding a packet number echo (as in
https://github.com/quicwg/base-drafts/pull/367 or
https://github.com/quicwg/base-drafts/pull/368) to the public header
would allow passive RTT measurement at on-path observation points.
For efficiency purposes, this packet number echo need not be carried
on every packet, and could be made optional, allowing endpoints to
make a measurability/efficiency tradeoff; see section 4 of [IPIM].
Note further that this facility would have significantly better
measurability characteristics than sequence-acknowledgement-based RTT
measurement currently available in TCP on typical asymmetric flows,
as adequate samples will be available in both directions, and packet
number echo would be decoupled from the underlying acknowledgment
machinery; see e.g. [Ding2015]
Note in-network devices can inspect and correlate connection IDs for
partial tracking of mobility events.
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3.3. DDoS Detection and Mitigation
For enterprises and network operators one of the biggest management
challenges is dealing with Distributed Denial of Service (DDoS)
attacks. Some network operators offer Security as a Service (SaaS)
solutions that detect attacks by monitoring, analyzing and filtering
traffic. These approaches generally utilize network flow data
[RFC7011]. If any flows pose a threat, usually they are routed to a
"scrubbing environment" where the traffic is filtered, allowing the
remaining "good" traffic to continue to the customer environment.
This type of DDoS mitigation is fundamentally based on tracking state
for flows (see Section 3.1) that have receiver confirmation and a
proof of return-routability, and classifying flows as legitimate or
DoS traffic. The QUIC packet header currently does not support an
explicit mechanism to easily distinguish legitimate QUIC traffic from
other UDP traffic. However, the first packet in a QUIC connection
will usually be a Client Initial packet. This can be used to
identify the first packet of the connection.
If the QUIC handshake was not observed by the defense system, the
connection ID can be used as a confirmation signal as per
[STATEFULNESS] if present in both directions.
Further, 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. This problem is also related to these issues under discussion:
https://github.com/quicwg/base-drafts/issues/203
3.4. QoS support and ECMP
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 connection to the same server might be used,
given that establishing a new connection using 0-RTT support is cheap
and fast.
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QoS mechanisms in the network MAY also use the connection ID for
service differentiation as usually a change of connection ID is bind
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.
3.5. Load Balancing using the Connection ID
The Connection ID is used in part to support load balancing in
content distribution networks (CDNs), which operate complex,
geographically distributed pools of back-end servers, fronted by load
balancing systems. These load balancers are responsible for
identifying the most appropriate server for each connection and for
routing all packets belonging to that connection to the chosen
server.
Load balancers are often deployed in pools for redundancy and load
sharing. For high availability, it is important that when packets
belonging to a flow start to arrive at a different load balancer in
the load balancer pool, the packets continue to be forwarded to the
original server in the server pool.
Support for seamless connection migration is an important design goal
of QUIC - a necessity due to the proliferation of mobile connected
devices. This connection persistence provides an additional
challenge for multi-homed anycast-based services often employed by
large content owners and CDNs. The challenge is that a migration to
a different network in the middle of the connection greatly increases
the chances of the packets routed to a different anycast point of
presence (POP) due to the new network's different connectivity and
Internet peering arrangements. The load balancer in the new POP,
potentially thousands of miles away, will not have information about
the established flow and would not be able to route it back to the
original POP.
Load balancers may cooperate with servers or server pools behind them
to use a server-generated Connection ID value, in order to support
stateless load balancing, even across NAT rebinding or other address
change events (see Section 2.3). See section 5.7 of [QUIC].
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
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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. IANA Considerations
This document has no actions for IANA.
5. 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.
6. Contributors
Igor Lubashev contributed text to Section 3.5 on the use of the
connection ID for load balancing.
7. 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.
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8. References
8.1. Normative References
[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-04 (work
in progress), June 2017.
[QUIC-HTTP]
Bishop, M., "Hypertext Transfer Protocol (HTTP) over
QUIC", draft-ietf-quic-http-04 (work in progress), June
2017.
[QUIC-TLS]
Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-04 (work in
progress), June 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. 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>.
[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,
<http://www.rfc-editor.org/info/rfc7011>.
[STATEFULNESS]
Kuehlewind, M., Trammell, B., and J. Hildebrand,
"Transport-Independent Path Layer State Management",
draft-trammell-plus-statefulness-03 (work in progress),
March 2017.
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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
Dan Druta
AT&T
Email: dd5826@att.com
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