draft-ietf-quic-applicability-03.txt		draft-ietf-quic-applicability-04.txt
	Network Working Group M. Kuehlewind		Network Working Group M. Kuehlewind
	Internet-Draft B. Trammell		Internet-Draft B. Trammell
	Intended status: Informational ETH Zurich		Intended status: Informational ETH Zurich
	Expires: April 25, 2019 October 22, 2018		Expires: October 26, 2019 April 24, 2019
	Applicability of the QUIC Transport Protocol		Applicability of the QUIC Transport Protocol
	draft-ietf-quic-applicability-03		draft-ietf-quic-applicability-04
	Abstract		Abstract
	This document discusses the applicability of the QUIC transport		This document discusses the applicability of the QUIC transport
	protocol, focusing on caveats impacting application protocol		protocol, focusing on caveats impacting application protocol
	development and deployment over QUIC. Its intended audience is		development and deployment over QUIC. Its intended audience is
	designers of application protocol mappings to QUIC, and implementors		designers of application protocol mappings to QUIC, and implementors
	of these application protocols.		of these application protocols.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 34 ¶		skipping to change at page 1, line 34 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on April 25, 2019.		This Internet-Draft will expire on October 26, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2019 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
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	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
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	skipping to change at page 2, line 18 ¶		skipping to change at page 2, line 18 ¶
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
	2. The Necessity of Fallback . . . . . . . . . . . . . . . . . . 3		2. The Necessity of Fallback . . . . . . . . . . . . . . . . . . 3
	3. Zero RTT . . . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Zero RTT . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3.1. Thinking in Zero RTT . . . . . . . . . . . . . . . . . . 4		3.1. Thinking in Zero RTT . . . . . . . . . . . . . . . . . . 4
	3.2. Here There Be Dragons . . . . . . . . . . . . . . . . . . 4		3.2. Here There Be Dragons . . . . . . . . . . . . . . . . . . 4
	3.3. Session resumption versus Keep-alive . . . . . . . . . . 4		3.3. Session resumption versus Keep-alive . . . . . . . . . . 4
	4. Use of Streams . . . . . . . . . . . . . . . . . . . . . . . 6		4. Use of Streams . . . . . . . . . . . . . . . . . . . . . . . 6
	4.1. Stream versus Flow Multiplexing . . . . . . . . . . . . . 6		4.1. Stream versus Flow Multiplexing . . . . . . . . . . . . . 6
	4.2. Packetization and latency . . . . . . . . . . . . . . . . 7		4.2. Packetization and latency . . . . . . . . . . . . . . . . 7
	4.3. Prioritization . . . . . . . . . . . . . . . . . . . . . 7		4.3. Prioritization . . . . . . . . . . . . . . . . . . . . . 7
	5. Port Selection . . . . . . . . . . . . . . . . . . . . . . . 8		4.4. Flow Control Deadlocks . . . . . . . . . . . . . . . . . 8
	6. Graceful connection closure . . . . . . . . . . . . . . . . . 8		5. Port Selection . . . . . . . . . . . . . . . . . . . . . . . 9
	7. Information exposure and the Connection ID . . . . . . . . . 8		6. Graceful connection closure . . . . . . . . . . . . . . . . . 9
	7.1. Server-Generated Connection ID . . . . . . . . . . . . . 9		7. Information exposure and the Connection ID . . . . . . . . . 9
			7.1. Server-Generated Connection ID . . . . . . . . . . . . . 10
	7.2. Mitigating Timing Linkability with Connection ID		7.2. Mitigating Timing Linkability with Connection ID
	Migration . . . . . . . . . . . . . . . . . . . . . . . . 9		Migration . . . . . . . . . . . . . . . . . . . . . . . . 10
	7.3. Using Server Retry for Redirection . . . . . . . . . . . 9		7.3. Using Server Retry for Redirection . . . . . . . . . . . 11
	8. Use of Versions and Cryptographic Handshake . . . . . . . . . 10		8. Use of Versions and Cryptographic Handshake . . . . . . . . . 11
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10		9. Enabling New Versions . . . . . . . . . . . . . . . . . . . . 11
	10. Security Considerations . . . . . . . . . . . . . . . . . . . 10		10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10		11. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11		12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
	13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
	13.1. Normative References . . . . . . . . . . . . . . . . . . 11		14. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
	13.2. Informative References . . . . . . . . . . . . . . . . . 11		14.1. Normative References . . . . . . . . . . . . . . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13		14.2. Informative References . . . . . . . . . . . . . . . . . 14
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	QUIC [QUIC] is a new transport protocol currently under development		QUIC [QUIC] is a new transport protocol currently under development
	in the IETF quic working group, focusing on support of semantics as		in the IETF quic working group, focusing on support of semantics as
	needed for HTTP/2 [QUIC-HTTP] such as stream-multiplexing to avoid		needed for HTTP/2 [QUIC-HTTP] such as stream-multiplexing to avoid
	head-of-line blocking. Based on current deployment practices, QUIC		head-of-line blocking. Based on current deployment practices, QUIC
	is encapsulated in UDP. The version of QUIC that is currently under		is encapsulated in UDP. The version of QUIC that is currently under
	development will integrate TLS 1.3 [TLS13] to encrypt all payload		development will integrate TLS 1.3 [TLS13] to encrypt all payload
	data and most control information.		data and most control information.
	skipping to change at page 8, line 7 ¶		skipping to change at page 8, line 7 ¶
	before new data, unless indicated differently by the application.		before new data, unless indicated differently by the application.
	Currently, QUIC only provides fully reliable stream transmission,		Currently, QUIC only provides fully reliable stream transmission,
	which means that prioritization of retransmissions will be beneficial		which means that prioritization of retransmissions will be beneficial
	in most cases, by filling in gaps and freeing up the flow control		in most cases, by filling in gaps and freeing up the flow control
	window. For partially reliable or unreliable streams, priority		window. For partially reliable or unreliable streams, priority
	scheduling of retransmissions over data of higher-priority streams		scheduling of retransmissions over data of higher-priority streams
	might not be desirable. For such streams, QUIC could either provide		might not be desirable. For such streams, QUIC could either provide
	an explicit interface to control prioritization, or derive the		an explicit interface to control prioritization, or derive the
	prioritization decision from the reliability level of the stream.		prioritization decision from the reliability level of the stream.
			4.4. Flow Control Deadlocks
			Flow control provides a means of managing access to the limited
			buffers endpoints have for incoming data. This mechanism limits the
			amount of data that can be in buffers in endpoints or in transit on
			the network. However, there are several ways in which limits can
			produce conditions that can cause a connection to either perform
			suboptimally or deadlock.
			Deadlocks in flow control are possible for any protocol that uses
			QUIC, though whether they become a problem depends on how
			implementations consume data and provide flow control credit.
			Understanding what causes deadlocking might help implementations
			avoid deadlocks.
			Large messages can produce deadlocking if the recipient does not
			process the message incrementally. If the message is larger than
			flow control credit available and the recipient does not release
			additional flow control credit until the entire message is received
			and delivered, a deadlock can occur. This is possible even where
			stream flow control limits are not reached because connection flow
			control limits can be consumed by other streams.
			A common flow control implementation technique is for a receiver to
			extend credit to the sender as a the data consumer reads data. In
			this setting, a length-prefixed message format makes it easier for
			the data consumer to leave data unread in the receiver's buffers and
			thereby withhold flow control credit. If flow control limits prevent
			the remainder of a message from being sent, a deadlock will result.
			A length prefix might also enable the detection of this sort of
			deadlock. Where protocols have messages that might be processed as a
			single unit, reserving flow control credit for the entire message
			atomically ensures that this style of deadlock is less likely.
			A data consumer can read all data as it becomes available to cause
			the receiver to extend flow control credit to the sender and reduce
			the chances of a deadlock. However, releasing flow control credit
			might mean that the data consumer might need other means for holding
			a peer accountable for the state it keeps for partially processed
			messages.
			Deadlocking can also occur if data on different streams is
			interdependent. Suppose that data on one stream arrives before the
			data on a second stream on which it depends. A deadlock can occur if
			the first stream is left unread, preventing the receiver from
			extending flow control credit for the second stream. To reduce the
			likelihood of deadlock for interdependent data, the sender should
			ensure that dependent data is not sent until the data it depends on
			has been accounted for in both stream- and connection- level flow
			control credit.
			Some deadlocking scenarios might be resolved by cancelling affected
			streams with STOP_SENDING or RST_STREAM. Cancelling some streams
			results in the connection being terminated in some protocols.
	5. Port Selection		5. Port Selection
	As QUIC is a general purpose transport protocol, there are no		As QUIC is a general purpose transport protocol, there are no
	requirements that servers use a particular UDP port for QUIC in		requirements that servers use a particular UDP port for QUIC in
	general. Instead, the same port number is used as would be used for		general. Instead, the same port number is used as would be used for
	the same application over TCP. In the case of HTTP the expectation		the same application over TCP. In the case of HTTP the expectation
	is that port 443 is used, which has already been registered for "http		is that port 443 is used, which has already been registered for "http
	protocol over TLS/SSL". However, [QUIC-HTTP] also specifies the use		protocol over TLS/SSL". However, [QUIC-HTTP] also specifies the use
	of Alt-Svc for HTTP/QUIC discovery which allows the server to use and		of Alt-Svc for HTTP/QUIC discovery which allows the server to use and
	announce a different port number.		announce a different port number.
	skipping to change at page 9, line 9 ¶		skipping to change at page 10, line 12 ¶
	for other control processes, and a short header that may be used for		for other control processes, and a short header that may be used for
	data transmission in an established connection. While the long		data transmission in an established connection. While the long
	header always exposes some information (such as the version and		header always exposes some information (such as the version and
	Connection IDs), the short header exposes at most only a single		Connection IDs), the short header exposes at most only a single
	Connection ID.		Connection ID.
	7.1. Server-Generated Connection ID		7.1. Server-Generated Connection ID
	QUIC supports a server-generated Connection ID, transmitted to the		QUIC supports a server-generated Connection ID, transmitted to the
	client during connection establishment (see Section 6.1 of [QUIC]).		client during connection establishment (see Section 6.1 of [QUIC]).
	Servers behind load balancers may need to propose a Connection ID		Servers behind load balancers may need to change the Connection ID
	during the handshake, encoding the identity of the server or		during the handshake, encoding the identity of the server or
	information about its load balancing pool, in order to support		information about its load balancing pool, in order to support
	stateless load balancing. Once the server generates a Connection ID		stateless load balancing. Once the server generates a Connection ID
	that encodes its identity, every CDN load balancer would be able to		that encodes its identity, every CDN load balancer would be able to
	forward the packets to that server without retaining connection		forward the packets to that server without retaining connection
	state.		state.
	Server-generated connection IDs should seek to obscure any encoding,		Server-generated connection IDs should seek to obscure any encoding,
	of routing identities or any other information. Exposing the server		of routing identities or any other information. Exposing the server
	mapping would allow linkage of multiple IP addresses to the same host		mapping would allow linkage of multiple IP addresses to the same host
	skipping to change at page 10, line 28 ¶		skipping to change at page 11, line 37 ¶
	might simply provide a different feature set. As such, an		might simply provide a different feature set. As such, an
	application needs to be able to select which versions of QUIC it		application needs to be able to select which versions of QUIC it
	wants to use.		wants to use.
	A new version could use an encryption scheme other than TLS 1.3 or		A new version could use an encryption scheme other than TLS 1.3 or
	higher. [QUIC] specifies requirements for the cryptographic		higher. [QUIC] specifies requirements for the cryptographic
	handshake as currently realized by TLS 1.3 and described in a		handshake as currently realized by TLS 1.3 and described in a
	separate specification [QUIC-TLS]. This split is performed to enable		separate specification [QUIC-TLS]. This split is performed to enable
	light-weight versioning with different cryptographic handshakes.		light-weight versioning with different cryptographic handshakes.
	9. IANA Considerations		9. Enabling New Versions
			QUIC provides integrity protection for its version negotiation
			process. This process assumes that the set of versions that a server
			supports is fixed. This complicates the process for deploying new
			QUIC versions or disabling old versions when servers operate in
			clusters.
			A server that rolls out a new version of QUIC can do so in three
			stages. Each stage is completed across all server instances before
			moving to the next stage.
			In the first stage of deployment, all server instances start
			accepting new connections with the new version. The new version can
			be enabled progressively across a deployment, which allows for
			selective testing. This is especially useful when the new version is
			compatible with an old version, because the new version is more
			likely to be used.
			While enabling the new version, servers do not advertise the new
			version in any Version Negotiation packets they send. This prevents
			clients that receive a Version Negotiation packet from attempting to
			connect to server instances that might not have the new version
			enabled.
			During the initial deployment, some clients will have received
			Version Negotiation packets that indicate that the server does not
			support the new version. Other clients might have successfully
			connected with the new version and so will believe that the server
			supports the new version. Therefore, servers need to allow for this
			ambiguity when validating the negotiated version.
			The second stage of deployment commences once all server instances
			are able accept new connections with the new version. At this point,
			all servers can start sending the new version in Version Negotiation
			packets.
			During the second stage, the server still allows for the possibility
			that some clients believe the new version to be available and some do
			not. This state will persist only for as long as any Version
			Negotiation packets take to be transmitted and responded to. So the
			third stage can follow after a relatively short delay.
			The third stage completes the process by enabling validation of the
			negotiation version as though the new version were disabled.
			The process for disabling an old version or rolling back the
			introduction of a new version uses the same process in reverse.
			Servers disable validation of the old version, stop sending the old
			version in Version Negotiation packets, then the old version is no
			longer accepted.
			10. IANA Considerations
	This document has no actions for IANA.		This document has no actions for IANA.
	10. Security Considerations		11. Security Considerations
	See the security considerations in [QUIC] and [QUIC-TLS]; the		See the security considerations in [QUIC] and [QUIC-TLS]; the
	security considerations for the underlying transport protocol are		security considerations for the underlying transport protocol are
	relevant for applications using QUIC, as well.		relevant for applications using QUIC, as well.
	Application developers should note that any fallback they use when		Application developers should note that any fallback they use when
	QUIC cannot be used due to network blocking of UDP SHOULD guarantee		QUIC cannot be used due to network blocking of UDP SHOULD guarantee
	the same security properties as QUIC; if this is not possible, the		the same security properties as QUIC; if this is not possible, the
	connection SHOULD fail to allow the application to explicitly handle		connection SHOULD fail to allow the application to explicitly handle
	fallback to a less-secure alternative. See Section 2.		fallback to a less-secure alternative. See Section 2.
	11. Contributors		12. Contributors
	Igor Lubashev contributed text to Section 7 on server-selected		Igor Lubashev contributed text to Section 7 on server-selected
	Connection IDs.		Connection IDs.
	12. Acknowledgments		13. Acknowledgments
	This work is partially supported by the European Commission under		This work is partially supported by the European Commission under
	Horizon 2020 grant agreement no. 688421 Measurement and Architecture		Horizon 2020 grant agreement no. 688421 Measurement and Architecture
	for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat		for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
	for Education, Research, and Innovation under contract no. 15.0268.		for Education, Research, and Innovation under contract no. 15.0268.
	This support does not imply endorsement.		This support does not imply endorsement.
	13. References		14. References
	13.1. Normative References		14.1. Normative References
	[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed		[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
	and Secure Transport", draft-ietf-quic-transport-15 (work		and Secure Transport", draft-ietf-quic-transport-20 (work
	in progress), October 2018.		in progress), April 2019.
	[QUIC-INVARIANTS]		[QUIC-INVARIANTS]
	Thomson, M., "Version-Independent Properties of QUIC",		Thomson, M., "Version-Independent Properties of QUIC",
	draft-ietf-quic-invariants-03 (work in progress), October		draft-ietf-quic-invariants-04 (work in progress), April
	2018.		2019.
	[QUIC-TLS]		[QUIC-TLS]
	Thomson, M. and S. Turner, "Using Transport Layer Security		Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
	(TLS) to Secure QUIC", draft-ietf-quic-tls-15 (work in		draft-ietf-quic-tls-20 (work in progress), April 2019.
	progress), October 2018.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.		[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
	Cheshire, "Internet Assigned Numbers Authority (IANA)		Cheshire, "Internet Assigned Numbers Authority (IANA)
	Procedures for the Management of the Service Name and		Procedures for the Management of the Service Name and
	Transport Protocol Port Number Registry", BCP 165,		Transport Protocol Port Number Registry", BCP 165,
	RFC 6335, DOI 10.17487/RFC6335, August 2011,		RFC 6335, DOI 10.17487/RFC6335, August 2011,
	<https://www.rfc-editor.org/info/rfc6335>.		<https://www.rfc-editor.org/info/rfc6335>.
	[TLS13] Thomson, M. and S. Turner, "Using Transport Layer Security		[TLS13] Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
	(TLS) to Secure QUIC", draft-ietf-quic-tls-15 (work in		draft-ietf-quic-tls-20 (work in progress), April 2019.
	progress), October 2018.
	13.2. Informative References		14.2. Informative References
	[Edeline16]		[Edeline16]
	Edeline, K., Kuehlewind, M., Trammell, B., Aben, E., and		Edeline, K., Kuehlewind, M., Trammell, B., Aben, E., and
	B. Donnet, "Using UDP for Internet Transport Evolution		B. Donnet, "Using UDP for Internet Transport Evolution
	(arXiv preprint 1612.07816)", December 2016,		(arXiv preprint 1612.07816)", December 2016,
	<https://arxiv.org/abs/1612.07816>.		<https://arxiv.org/abs/1612.07816>.
	[Hatonen10]		[Hatonen10]
	Hatonen, S., Nyrhinen, A., Eggert, L., Strowes, S.,		Hatonen, S., Nyrhinen, A., Eggert, L., Strowes, S.,
	Sarolahti, P., and M. Kojo, "An experimental study of home		Sarolahti, P., and M. Kojo, "An experimental study of home
	skipping to change at page 12, line 34 ¶		skipping to change at page 14, line 36 ¶
	nottingham-httpbis-retry-01 (work in progress), February		nottingham-httpbis-retry-01 (work in progress), February
	2017.		2017.
	[PaaschNanog]		[PaaschNanog]
	Paasch, C., "Network Support for TCP Fast Open (NANOG 67		Paasch, C., "Network Support for TCP Fast Open (NANOG 67
	presentation)", June 2016,		presentation)", June 2016,
	<https://www.nanog.org/sites/default/files/		<https://www.nanog.org/sites/default/files/
	Paasch_Network_Support.pdf>.		Paasch_Network_Support.pdf>.
	[QUIC-HTTP]		[QUIC-HTTP]
	Bishop, M., "Hypertext Transfer Protocol (HTTP) over		Bishop, M., "Hypertext Transfer Protocol Version 3
	QUIC", draft-ietf-quic-http-15 (work in progress), October		(HTTP/3)", draft-ietf-quic-http-20 (work in progress),
	2018.		April 2019.
	[Swett16] Swett, I., "QUIC Deployment Experience at Google (IETF96		[Swett16] Swett, I., "QUIC Deployment Experience at Google (IETF96
	QUIC BoF presentation)", July 2016,		QUIC BoF presentation)", July 2016,
	<https://www.ietf.org/proceedings/96/slides/		<https://www.ietf.org/proceedings/96/slides/
	slides-96-quic-3.pdf>.		slides-96-quic-3.pdf>.
	[Trammell16]		[Trammell16]
	Trammell, B. and M. Kuehlewind, "Internet Path		Trammell, B. and M. Kuehlewind, "Internet Path
	Transparency Measurements using RIPE Atlas (RIPE72 MAT		Transparency Measurements using RIPE Atlas (RIPE72 MAT
	presentation)", May 2016, <https://ripe72.ripe.net/wp-		presentation)", May 2016, <https://ripe72.ripe.net/wp-
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