Applicability of the QUIC Transport Protocol
draft-ietf-quic-applicability-02
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| Document | Type | Active Internet-Draft (quic WG) | |
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| Authors | Mirja Kühlewind , Brian Trammell | ||
| Last updated | 2018-07-02 (Latest revision 2017-10-25) | ||
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draft-ietf-quic-applicability-02
Network Working Group M. Kuehlewind
Internet-Draft B. Trammell
Intended status: Informational ETH Zurich
Expires: January 3, 2019 July 02, 2018
Applicability of the QUIC Transport Protocol
draft-ietf-quic-applicability-02
Abstract
This document discusses the applicability of the QUIC transport
protocol, focusing on caveats impacting application protocol
development and deployment over QUIC. Its intended audience is
designers of application protocol mappings to QUIC, and implementors
of these application protocols.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The Necessity of Fallback . . . . . . . . . . . . . . . . . . 3
3. Zero RTT . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Thinking in Zero RTT . . . . . . . . . . . . . . . . . . 4
3.2. Here There Be Dragons . . . . . . . . . . . . . . . . . . 4
3.3. Session resumption versus Keep-alive . . . . . . . . . . 4
4. Use of Streams . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Stream versus Flow Multiplexing . . . . . . . . . . . . . 5
4.2. Packetization and latency . . . . . . . . . . . . . . . . 6
4.3. Prioritization . . . . . . . . . . . . . . . . . . . . . 6
5. Graceful connection closure . . . . . . . . . . . . . . . . . 6
6. Information exposure and the Connection ID . . . . . . . . . 7
6.1. Server-Generated Connection ID . . . . . . . . . . . . . 7
6.2. Using Server Retry for Redirection . . . . . . . . . . . 8
7. Use of Versions and Cryptographic Handshake . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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] such as stream-multiplexing to avoid
head-of-line blocking. Based on current deployment practices, QUIC
is encapsulated in UDP. The version of QUIC that is currently under
development will integrate TLS 1.3 [TLS13] to encrypt all payload
data and most control information.
This document provides guidance for application developers that want
to use the QUIC protocol without implementing it on their own. This
includes general guidance for application use of HTTP/2 over QUIC as
well as the use of other application layer protocols over QUIC. For
specific guidance on how to integrate HTTP/2 with QUIC, see
[QUIC-HTTP].
In the following sections we discuss specific caveats to QUIC's
applicability, and issues that application developers must consider
when using QUIC as a transport for their application.
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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. The Necessity of Fallback
QUIC uses UDP as a substrate for userspace implementation and port
numbers for NAT and middlebox traversal. While there is no evidence
of widespread, systematic disadvantage of UDP traffic compared to TCP
in the Internet [Edeline16], somewhere between three [Trammell16] and
five [Swett16] percent of networks simply block UDP traffic. All
applications running on top of QUIC must therefore either be prepared
to accept connectivity failure on such networks, or be engineered to
fall back to some other transport protocol. This fallback SHOULD
provide TLS 1.3 or equivalent cryptographic protection, if available,
in order to keep fallback from being exploited as a downgrade attack.
In the case of HTTP, this fallback is TLS 1.3 over TCP.
These applications must operate, perhaps with impaired functionality,
in the absence of features provided by QUIC not present in the
fallback protocol. For fallback to TLS over TCP, the most obvious
difference is that TCP does not provide stream multiplexing and
therefore stream multiplexing would need to be implemented in the
application layer if needed. Further, TCP without the TCP Fast Open
extension does not support 0-RTT session resumption. TCP Fast Open
can be requested by the connection initiator but might no be
supported by the far end or could be blocked on the network path.
Note that there is some evidence of middleboxes blocking SYN data
even if TFO was successfully negotiated (see [PaaschNanog]).
Any fallback mechanism is likely to impose a degradation of
performance; however, fallback MUST not silently violate the
application's expectation of confidentiality or integrity of its
payload data.
Moreover, while encryption (in this case TLS) is inseparably
integrated with QUIC, TLS negotiation over TCP can be blocked. In
case it is RECOMMENDED to abort the connection, allowing the
application to present a suitable prompt to the user that secure
communication is unavailable.
3. Zero RTT
QUIC provides for 0-RTT connection establishment (see section 3.2 of
[QUIC]). This presents opportunities and challenges for applications
using QUIC.
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3.1. Thinking in Zero RTT
A transport protocol that provides 0-RTT connection establishment to
recently contacted servers is qualitatively different than one that
does not from the point of view of the application using it.
Relative trade-offs between the cost of closing and reopening a
connection and trying to keep it open are different; see Section 3.3.
Applications must be slightly rethought in order to make best use of
0-RTT resumption. Most importantly, application operations must be
divided into idempotent and non-idempotent operations, as only
idempotent operations may appear in 0-RTT packets. This implies that
the interface between the application and transport layer exposes
idempotence either explicitly or implicitly.
3.2. Here There Be Dragons
Retransmission or (malicious) replay of data contained in 0-RTT
resumption packets could cause the server side to receive two copies
of the same data. This is further described in [HTTP-RETRY]. Data
sent during 0-RTT resumption also cannot benefit from perfect forward
secrecy (PFS).
Data in the first flight sent by the client in a connection
established with 0-RTT MUST be idempotent (as specified in section
3.2 in [QUIC-TLS]). Applications MUST be designed, and their data
MUST be framed, such that multiple reception of idempotent data is
recognized as such by the receiverApplications that cannot treat data
that may appear in a 0-RTT connection establishment as idempotent
MUST NOT use 0-RTT establishment. For this reason the QUIC transport
SHOULD provide an interface for the application to indicate if 0-RTT
support is in general desired or a way to indicate whether data is
idempotent, and/or whether PFS is a hard requirement for the
application.
3.3. Session resumption versus Keep-alive
[EDITOR'S NOTE: see https://github.com/quicwg/ops-drafts/issues/6]
4. Use of Streams
QUIC's stream multiplexing feature allows applications to run
multiple streams over a single connection, without head-of-line
blocking between streams, associated at a point in time with a single
five-tuple. Stream data is carried within Frames, where one (UDP)
packet on the wire can carry one of multiple stream frames.
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Stream can be independently open and closed, gracefully or by error.
If a critical stream for the application is closed, the application
can generate respective error messages on the application layer to
inform the other end or the higher layer and eventually indicate quic
to reset the connection. QUIC, however, does not need to know which
streams are critical, and does not provide an interface to
exceptional handling of any stream. There are special streams in
QUIC that are used for control on the QUIC connection, however, these
streams are not exposed to the application.
Mapping of application data to streams is application-specific and
described for HTTP/s in [QUIC-HTTP]. In general data that can be
processed independently, and therefore would suffer from head of line
blocking, if forced to be received in order, should be transmitted
over different streams. If there is a logical grouping of those data
chunks or messages, stream can be reused, or a new stream can be
opened for each chunk/message. If a QUIC receiver has maximum
allowed concurrent streams open and the sender on the other end
indicates that more streams are needed, it doesn't automatically lead
to an increase of the maximum number of streams by the receiver.
Therefore it can be valuable to expose maximum number of allowed,
currently open and currently used streams to the application to make
the mapping of data to streams dependent on this information.
Further, streams have a maximum number of bytes that can be sent on
one stream. This number is high enough (2^64) that this will usually
not be reached with current applications. Applications that send
chunks of data over a very long period of time (such as days, months,
or years), should rather utilize the 0-RTT session resumption ability
provided by QUIC, than trying to maintain one connection open.
4.1. Stream versus Flow Multiplexing
Streams are meaningful only to the application; since stream
information is carried inside QUIC's encryption boundary, no
information about the stream(s) whose frames are carried by a given
packet is visible to the network. Therefore stream multiplexing is
not intended to be used for differentiating streams in terms of
network treatment. Application traffic requiring different network
treatment SHOULD therefore be carried over different five-tuples
(i.e. multiple QUIC connections). Given QUIC's ability to send
application data in the first RTT of a connection (if a previous
connection to the same host has been successfully established to
provide the respective credentials), the cost for establishing
another connection are extremely low.
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4.2. Packetization and latency
Quic provides an interface that provides multiple streams to the
application, however, the application usually doesn't have control
how the data transmitted over one stream is mapped into frame and how
frames are bundled into packets. By default QUIC will try to
maximally pack packets to minimize bandwidth consumption and
computational costs with one or multiple same data frames. If not
enough data available to send QUIC may even wait for a short time,
trading of latency and bandwidth efficiency. This time might either
be pre-configured or can the dynamically adjusted based on the
observed sending pattern of the application. If the application
requires low latency, with only small chunks of data to send, it may
be valuable to indicate to QUIC that all data should be send out
immediately. Or if a certain sending pattern is know by the
application, it might also provide valuable guidance to QUIC how long
it should wait to bundle frame into a packet.
4.3. Prioritization
Stream prioritization is not exposed to the network, nor to the
receiver. Prioritization can be realized by the sender and the QUIC
transport should provide an interface for applications to prioritize
streams [QUIC]. Further applications can implement their own
prioritization scheme on top of QUIC: (an application) protocol that
runs on top of QUIC can define explicit messages for signaling
priority, such as those defined for HTTP/2; it can define rules that
allow an endpoint to determine priority based on context; or it can
provide a higher level interface and leave the determination to the
application on top.
Priority handling of retransmissions can be implemented by the sender
in the transport layer. [QUIC] recommends to retransmit lost data
before new data, unless indicated differently by the application.
Currently QUIC only provides fully reliable stream transmission, and
as such prioritization of retransmissions likely beneficial in most
cases, as gaps that get filled up and thereby free up flow control.
For not fully reliable streams priority scheduling of retransmissions
over data of higher-priority streams might not be desired. In this
case QUIC could also provide an interface or derive the
prioritization decision from the reliability level of the stream.
5. Graceful connection closure
[EDITOR'S NOTE: give some guidance here about the steps an
application should take; however this is still work in progress]
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6. Information exposure and the Connection ID
QUIC exposes some information to the network in the unencrypted part
of the header, either before the encryption context is established,
because the information is intended to be used by the network. QUIC
has a long header that is used during connection establishment and
for other control processes, and a short header that may be used for
data transmission in an established connection. While the long
header is fixed and exposes some information, the short header only
exposes the packet number by default and may optionally expose a
connection ID.
Given that exposing this information may make it possible to
associate multiple addresses with a single client during rebinding,
which has privacy implications, an application may indicate to not
support exposure of certain information after the handshake.
Specifically, an application that has additional information that the
client is not behind a NAT and the server is not behind a load
balancer, and therefore it is unlikely that the addresses will be re-
bound, may indicate to the transport that is wishes to not expose a
connection ID.
6.1. Server-Generated Connection ID
QUIC supports a server-generated Connection ID, transmitted to the
client during connection establishment: see Section 5.7 of [QUIC].
Servers behind load balancers should propose a Connection ID during
the handshake, encoding the identity of the server or information
about its load balancing pool, in order to support stateless load
balancing. Once the server generates a Connection ID that encodes
its identity, every CDN load balancer would be able to forward the
packets to that server without needing information about every
specific flow it is forwarding.
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 is
able to identify and discard packets featuring an invalid MAC.
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6.2. Using Server Retry for Redirection
QUIC provides a Server Retry packet that can be sent by a server in
response to the Client Initial packet. The server may choose a new
connection ID in that packet and the client will retry by sending
another Client Initial packet with the server-selected connection ID.
This mechanism can be used to redirect a connection to a different
server, e.g. due to performance reasons or when servers in a server
pool are upgraded gradually, and therefore may support different
versions of QUIC. In this case, it is assumed that all servers
belonging to a certain pool are served in cooperation with load
balancers that forward the traffic based on the connection ID. A
server can chose the connection ID in the Server Retry packet such
that the load balancer will redirect the next Client Initial packet
to a different server in that pool.
7. Use of Versions and Cryptographic Handshake
Versioning in QUIC may change the protocol's behavior completely,
except for the meaning of a few header fields that have been declared
to be fixed. As such version of QUIC with a higher version number
does not necessarily provide a better service, but might simply
provide a very different service, so an application needs to be able
to select which versions of QUIC it wants to use.
A new version could use an encryption scheme other than TLS 1.3 or
higher. [QUIC] specifies requirements for the cryptographic
handshake as currently realized by TLS 1.3 and described in a
separate specification [QUIC-TLS]. This split is performed to enable
light-weight versioning with different cryptographic handshakes.
8. IANA Considerations
This document has no actions for IANA.
9. Security Considerations
See the security considerations in [QUIC] and [QUIC-TLS]; the
security considerations for the underlying transport protocol are
relevant for applications using QUIC, as well.
Application developers should note that any fallback they use when
QUIC cannot be used due to network blocking of UDP SHOULD guarantee
the same security properties as QUIC; if this is not possible, the
connection SHOULD fail to allow the application to explicitly handle
fallback to a less-secure alternative. See Section 2.
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10. Contributors
Igor Lubashev contributed text to Section 6 on server-selected
connection IDs.
11. 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.
12. References
12.1. Normative References
[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-13 (work
in progress), June 2018.
[QUIC-TLS]
Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-13 (work in
progress), June 2018.
[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>.
[TLS13] Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-13 (work in
progress), June 2018.
12.2. Informative References
[Edeline16]
Edeline, K., Kuehlewind, M., Trammell, B., Aben, E., and
B. Donnet, "Using UDP for Internet Transport Evolution
(arXiv preprint 1612.07816)", December 2016,
<https://arxiv.org/abs/1612.07816>.
[HTTP-RETRY]
Nottingham, M., "Retrying HTTP Requests", draft-
nottingham-httpbis-retry-01 (work in progress), February
2017.
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[I-D.nottingham-httpbis-retry]
Nottingham, M., "Retrying HTTP Requests", draft-
nottingham-httpbis-retry-01 (work in progress), February
2017.
[PaaschNanog]
Paasch, C., "Network Support for TCP Fast Open (NANOG 67
presentation)", June 2016,
<https://www.nanog.org/sites/default/files/
Paasch_Network_Support.pdf>.
[QUIC-HTTP]
Bishop, M., "Hypertext Transfer Protocol (HTTP) over
QUIC", draft-ietf-quic-http-13 (work in progress), June
2018.
[Swett16] Swett, I., "QUIC Deployment Experience at Google (IETF96
QUIC BoF presentation)", July 2016,
<https://www.ietf.org/proceedings/96/slides/slides-96-
quic-3.pdf>.
[Trammell16]
Trammell, B. and M. Kuehlewind, "Internet Path
Transparency Measurements using RIPE Atlas (RIPE72 MAT
presentation)", May 2016, <https://ripe72.ripe.net/wp-
content/uploads/presentations/86-atlas-udpdiff.pdf>.
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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