< draft-ietf-httpbis-alt-svc-02.txt		draft-ietf-httpbis-alt-svc-03.txt >
	HTTPbis Working Group M. Nottingham		HTTPbis Working Group M. Nottingham
	Internet-Draft Akamai		Internet-Draft Akamai
	Intended status: Standards Track P. McManus		Intended status: Standards Track P. McManus
	Expires: January 5, 2015 Mozilla		Expires: April 3, 2015 Mozilla
	J. Reschke		J. Reschke
	greenbytes		greenbytes
	July 4, 2014		September 30, 2014
	HTTP Alternative Services		HTTP Alternative Services
	draft-ietf-httpbis-alt-svc-02		draft-ietf-httpbis-alt-svc-03
	Abstract		Abstract
	This document specifies "alternative services" for HTTP, which allow		This document specifies "alternative services" for HTTP, which allow
	an origin's resources to be authoritatively available at a separate		an origin's resources to be authoritatively available at a separate
	network location, possibly accessed with a different protocol		network location, possibly accessed with a different protocol
	configuration.		configuration.
	Editorial Note (To be removed by RFC Editor)		Editorial Note (To be removed by RFC Editor)
	Discussion of this draft takes place on the HTTPBIS working group		Discussion of this draft takes place on the HTTPBIS working group
	mailing list (ietf-http-wg@w3.org), which is archived at		mailing list (ietf-http-wg@w3.org), which is archived at
	<https://lists.w3.org/Archives/Public/ietf-http-wg/>.		<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
	Working Group information can be found at		Working Group information can be found at
	<https://tools.ietf.org/wg/httpbis/> and <http://httpwg.github.io/>;		<https://tools.ietf.org/wg/httpbis/> and <http://httpwg.github.io/>;
	source code and issues list for tis draft can be found at		source code and issues list for this draft can be found at
	<https://github.com/httpwg/http-extensions>.		<https://github.com/httpwg/http-extensions>.
	The changes in this draft are summarized in Appendix A.		The changes in this draft are summarized in Appendix A.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 January 5, 2015.		This Internet-Draft will expire on April 3, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 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
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 31 ¶		skipping to change at page 2, line 31 ¶
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3
	2. Alternative Services Concepts . . . . . . . . . . . . . . . . 4		2. Alternative Services Concepts . . . . . . . . . . . . . . . . 4
	2.1. Host Authentication . . . . . . . . . . . . . . . . . . . 5		2.1. Host Authentication . . . . . . . . . . . . . . . . . . . 5
	2.2. Alternative Service Caching . . . . . . . . . . . . . . . 6		2.2. Alternative Service Caching . . . . . . . . . . . . . . . 6
	2.3. Requiring Server Name Indication . . . . . . . . . . . . . 6		2.3. Requiring Server Name Indication . . . . . . . . . . . . . 6
	2.4. Using Alternative Services . . . . . . . . . . . . . . . . 6		2.4. Using Alternative Services . . . . . . . . . . . . . . . . 6
	3. The Alt-Svc HTTP Header Field . . . . . . . . . . . . . . . . 7		3. The Alt-Svc HTTP Header Field . . . . . . . . . . . . . . . . 7
	3.1. Caching Alt-Svc Header Field Values . . . . . . . . . . . 9		3.1. Caching Alt-Svc Header Field Values . . . . . . . . . . . 9
	4. The ALTSVC HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 10		4. The ALTSVC HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 9
	5. The Alt-Svc-Used HTTP Header Field . . . . . . . . . . . . . . 11		5. The Alt-Svc-Used HTTP Header Field . . . . . . . . . . . . . . 11
	6. The 421 Not Authoritative HTTP Status Code . . . . . . . . . . 12		6. The 421 Not Authoritative HTTP Status Code . . . . . . . . . . 12
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	7.1. Header Field Registrations . . . . . . . . . . . . . . . . 12		7.1. Header Field Registrations . . . . . . . . . . . . . . . . 12
	7.2. The ALTSVC HTTP/2 Frame Type . . . . . . . . . . . . . . . 13		7.2. The ALTSVC HTTP/2 Frame Type . . . . . . . . . . . . . . . 13
	8. Internationalization Considerations . . . . . . . . . . . . . 13		8. Internationalization Considerations . . . . . . . . . . . . . 13
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 13		9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
	9.1. Changing Ports . . . . . . . . . . . . . . . . . . . . . . 13		9.1. Changing Ports . . . . . . . . . . . . . . . . . . . . . . 13
	9.2. Changing Hosts . . . . . . . . . . . . . . . . . . . . . . 13		9.2. Changing Hosts . . . . . . . . . . . . . . . . . . . . . . 13
	9.3. Changing Protocols . . . . . . . . . . . . . . . . . . . . 14		9.3. Changing Protocols . . . . . . . . . . . . . . . . . . . . 14
	9.4. Tracking Clients Using Alternative Services . . . . . . . 14		9.4. Tracking Clients Using Alternative Services . . . . . . . 14
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15		10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15		11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
	11.1. Normative References . . . . . . . . . . . . . . . . . . . 15		11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
	11.2. Informative References . . . . . . . . . . . . . . . . . . 16		11.2. Informative References . . . . . . . . . . . . . . . . . . 16
	Appendix A. Change Log (to be removed by RFC Editor before		Appendix A. Change Log (to be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 16		publication) . . . . . . . . . . . . . . . . . . . . 16
	A.1. Since draft-nottingham-httpbis-alt-svc-05 . . . . . . . . 16		A.1. Since draft-nottingham-httpbis-alt-svc-05 . . . . . . . . 16
	A.2. Since draft-ietf-httpbis-alt-svc-00 . . . . . . . . . . . 16		A.2. Since draft-ietf-httpbis-alt-svc-00 . . . . . . . . . . . 16
	A.3. Since draft-ietf-httpbis-alt-svc-01 . . . . . . . . . . . 16		A.3. Since draft-ietf-httpbis-alt-svc-01 . . . . . . . . . . . 16
			A.4. Since draft-ietf-httpbis-alt-svc-02 . . . . . . . . . . . 16
	1. Introduction		1. Introduction
	HTTP [RFC7230] conflates the identification of resources with their		HTTP [RFC7230] conflates the identification of resources with their
	location. In other words, "http://" (and "https://") URLs are used		location. In other words, "http://" (and "https://") URLs are used
	to both name and find things to interact with.		to both name and find things to interact with.
	In some cases, it is desirable to separate these aspects; to be able		In some cases, it is desirable to separate these aspects; to be able
	to keep the same identifier for a resource, but interact with it		to keep the same identifier for a resource, but interact with it
	using a different location on the network.		using a different location on the network.
	skipping to change at page 5, line 18 ¶		skipping to change at page 5, line 18 ¶
	alternative. Likewise, the Host header field ([RFC7230], Section		alternative. Likewise, the Host header field ([RFC7230], Section
	5.4) is still derived from the origin, not the alternative service		5.4) is still derived from the origin, not the alternative service
	(just as it would if a CNAME were being used).		(just as it would if a CNAME were being used).
	The changes MAY, however, be made visible in debugging tools,		The changes MAY, however, be made visible in debugging tools,
	consoles, etc.		consoles, etc.
	Formally, an alternative service is identified by the combination of:		Formally, an alternative service is identified by the combination of:
	o An Application Layer Protocol Negotiation (ALPN) protocol, as per		o An Application Layer Protocol Negotiation (ALPN) protocol, as per
	[ALPN]		[RFC7301]
	o A host, as per [RFC3986], Section 3.2.2		o A host, as per [RFC3986], Section 3.2.2
	o A port, as per [RFC3986], Section 3.2.3		o A port, as per [RFC3986], Section 3.2.3
	Additionally, each alternative service MUST have:		Additionally, each alternative service MUST have:
	o A freshness lifetime, expressed in seconds; see Section 2.2		o A freshness lifetime, expressed in seconds; see Section 2.2
	There are many ways that a client could discover the alternative		There are many ways that a client could discover the alternative
	skipping to change at page 6, line 21 ¶		skipping to change at page 6, line 21 ¶
	Clients MAY choose to use an alternative service instead of the		Clients MAY choose to use an alternative service instead of the
	origin at any time when it is considered fresh; see Section 2.4 for		origin at any time when it is considered fresh; see Section 2.4 for
	specific recommendations.		specific recommendations.
	Clients with existing connections to alternative services are not		Clients with existing connections to alternative services are not
	needed to fall back to the origin when its freshness lifetime ends;		needed to fall back to the origin when its freshness lifetime ends;
	i.e., the caching mechanism is intended for limiting how long an		i.e., the caching mechanism is intended for limiting how long an
	alternative service can be used for establishing new requests, not		alternative service can be used for establishing new requests, not
	limiting the use of existing ones.		limiting the use of existing ones.
	To mitigate risks associated with caching compromised values (see		Clients ought to consider that changes in network configurations can
	Section 9.2 for details), user agents SHOULD examine cached		result in suboptimal or compromised cached alternative services.
	alternative services when they detect a change in network
	configuration, and remove any that could be compromised (for example,
	those whose association with the trust root is questionable). UAs
	that do not have a means of detecting network changes SHOULD place an
	upper bound on their lifetime.
	2.3. Requiring Server Name Indication		2.3. Requiring Server Name Indication
	A client MUST only use a TLS-based alternative service if the client		A client MUST only use a TLS-based alternative service if the client
	also supports TLS Server Name Indication (SNI). This supports the		also supports TLS Server Name Indication (SNI). This supports the
	conservation of IP addresses on the alternative service host.		conservation of IP addresses on the alternative service host.
	2.4. Using Alternative Services		2.4. Using Alternative Services
	By their nature, alternative services are OPTIONAL: clients do not		By their nature, alternative services are OPTIONAL: clients do not
	need to use them. However, it is advantageous for clients to behave		need to use them. However, it is advantageous for clients to behave
	in a predictable way when they are used by servers (e.g., for load		in a predictable way when they are used by servers (e.g., for load
	balancing).		balancing).
	Therefore, if a client becomes aware of an alternative service, the		Therefore, if a client becomes aware of an alternative service, the
	client SHOULD use that alternative service for all requests to the		client SHOULD use that alternative service for all requests to the
	associated origin as soon as it is available, provided that the		associated origin as soon as it is available, provided that the
	security properties of the alternative service protocol are		security properties of the alternative service protocol are
	desirable, as compared to the existing connection.		desirable, as compared to the existing connection.
			If a client becomes aware of multiple alternative services, it MAY
			choose the most suitable according to its own criteria (again,
			keeping security properties in mind). For example, an origin might
			advertise multiple alternative services to notify clients of support
			for multiple versions of HTTP; or, an alternative service might
			itself advertise an alternative.
	When a client uses an alternate service, it MUST emit the Alt-Svc-		When a client uses an alternate service, it MUST emit the Alt-Svc-
	Used header field (Section 5) on every request using that alternate		Used header field (Section 5) on every request using that alternate
	service.		service.
	The client does not need to block requests; the origin's connection		The client does not need to block requests; the origin's connection
	can be used until the alternative connection is established.		can be used until the alternative connection is established.
	However, if the security properties of the existing connection are		However, if the security properties of the existing connection are
	weak (e.g. cleartext HTTP/1.1) then it might make sense to block		weak (e.g. cleartext HTTP/1.1) then it might make sense to block
	until the new connection is fully available in order to avoid		until the new connection is fully available in order to avoid
	information leakage.		information leakage.
	skipping to change at page 7, line 24 ¶		skipping to change at page 7, line 26 ¶
	3. The Alt-Svc HTTP Header Field		3. The Alt-Svc HTTP Header Field
	An HTTP(S) origin server can advertise the availability of		An HTTP(S) origin server can advertise the availability of
	alternative services to clients by adding an Alt-Svc header field to		alternative services to clients by adding an Alt-Svc header field to
	responses.		responses.
	Alt-Svc = 1#( alternative *( OWS ";" OWS parameter ) )		Alt-Svc = 1#( alternative *( OWS ";" OWS parameter ) )
	alternative = protocol-id "=" alt-authority		alternative = protocol-id "=" alt-authority
	protocol-id = token ; percent-encoded ALPN protocol identifier		protocol-id = token ; percent-encoded ALPN protocol identifier
	alt-authority = token / quoted-string		alt-authority = quoted-string ; containing [ uri-host ] ":" port
	; containing [ uri-host ] ":" port
	ALPN protocol names are octet sequences with no additional		ALPN protocol names are octet sequences with no additional
	constraints on format. Octets not allowed in tokens ([RFC7230],		constraints on format. Octets not allowed in tokens ([RFC7230],
	Section 3.2.6) MUST be percent-encoded as per Section 2.1 of		Section 3.2.6) MUST be percent-encoded as per Section 2.1 of
	[RFC3986]. Consequently, the octet representing the percent		[RFC3986]. Consequently, the octet representing the percent
	character "%" (hex 25) MUST be percent-encoded as well.		character "%" (hex 25) MUST be percent-encoded as well.
	In order to have precisely one way to represent any ALPN protocol		In order to have precisely one way to represent any ALPN protocol
	name, the following additional constraints apply:		name, the following additional constraints apply:
	skipping to change at page 8, line 7 ¶		skipping to change at page 8, line 7 ¶
	With these constraints, recipients can apply simple string comparison		With these constraints, recipients can apply simple string comparison
	to match protocol identifiers.		to match protocol identifiers.
	The "alt-authority" component consists of an OPTIONAL uri-host		The "alt-authority" component consists of an OPTIONAL uri-host
	("host" in Section 3.2.2 of [RFC3986]), a colon (":"), and a port		("host" in Section 3.2.2 of [RFC3986]), a colon (":"), and a port
	number.		number.
	For example:		For example:
	Alt-Svc: http2=":8000"		Alt-Svc: h2=":8000"
	This indicates the "http2" protocol on the same host using the		This indicates the "h2" protocol ([HTTP2]) on the same host using the
	indicated port 8000.		indicated port 8000.
	An example involving a change of host:		An example involving a change of host:
	Alt-Svc: http2="new.example.org:80"		Alt-Svc: h2="new.example.org:80"
	This indicates the "http2" protocol on the host "new.example.org",		This indicates the "h2" protocol on the host "new.example.org",
	running on port 80. Note that the "quoted-string" syntax needs to be		running on port 80. Note that the "quoted-string" syntax needs to be
	used when a host is specified in addition to a port (":" is not an		used because ":" is not an allowed character in "token".
	allowed character in "token").
	Examples for protocol name escaping:		Examples for protocol name escaping:
	+--------------------+-------------+---------------------+		+--------------------+-------------+---------------------+
	| ALPN protocol name | protocol-id | Note |		| ALPN protocol name | protocol-id | Note |
	+--------------------+-------------+---------------------+		+--------------------+-------------+---------------------+
	| http2 | http2 | No escaping needed |		| h2 | h2 | No escaping needed |
	+--------------------+-------------+---------------------+		+--------------------+-------------+---------------------+
	| w=x:y#z | w%3Dx%3Ay#z | "=" and ":" escaped |		| w=x:y#z | w%3Dx%3Ay#z | "=" and ":" escaped |
	+--------------------+-------------+---------------------+		+--------------------+-------------+---------------------+
	| x%y | x%25y | "%" needs escaping |		| x%y | x%25y | "%" needs escaping |
	+--------------------+-------------+---------------------+		+--------------------+-------------+---------------------+
	Alt-Svc MAY occur in any HTTP response message, regardless of the		Alt-Svc MAY occur in any HTTP response message, regardless of the
	status code.		status code.
	Alt-Svc does not allow advertisement of alternative services on other
	hosts, to protect against various header-based attacks.
	It can, however, have multiple values:		It can, however, have multiple values:
	Alt-Svc: h2c=":8000", h2=":443"		Alt-Svc: h2c=":8000", h2=":443"
	The value(s) advertised by Alt-Svc can be used by clients to open a		The value(s) advertised by Alt-Svc can be used by clients to open a
	new connection to one or more alternative services immediately, or		new connection to one or more alternative services immediately, or
	simultaneously with subsequent requests on the same connection.		simultaneously with subsequent requests on the same connection.
	To reduce the ability of servers to track individual clients over		To reduce the ability of servers to track individual clients over
	time (see Section 9.4), an alternative service indication sent by a		time (see Section 9.4), an alternative service indication sent by a
	client SHOULD NOT include any alternative service information other		client SHOULD NOT include any alternative service information other
	than the protocol, host and port.		than the protocol, host and port.
	When using HTTP/2 ([HTTP2]), clients SHOULD instead send an ALTSVC		When using HTTP/2 ([HTTP2]), servers SHOULD instead send an ALTSVC
	frame. A single ALTSVC frame can be sent for a connection; a new		frame (Section 4). A single ALTSVC frame can be sent for a
	frame is not needed for every request.		connection; a new frame is not needed for every request.
	Note that all field elements that allow "quoted-string" syntax MUST		Note that all field elements that allow "quoted-string" syntax MUST
	be processed as per Section 3.2.6 of [RFC7230].		be processed as per Section 3.2.6 of [RFC7230].
	3.1. Caching Alt-Svc Header Field Values		3.1. Caching Alt-Svc Header Field Values
	When an alternative service is advertised using Alt-Svc, it is		When an alternative service is advertised using Alt-Svc, it is
	considered fresh for 24 hours from generation of the message. This		considered fresh for 24 hours from generation of the message. This
	can be modified with the 'ma' (max-age) parameter;		can be modified with the 'ma' (max-age) parameter;
	skipping to change at page 11, line 18 ¶		skipping to change at page 11, line 14 ¶
	Host-Len: An unsigned, 8-bit integer indicating the length, in		Host-Len: An unsigned, 8-bit integer indicating the length, in
	octets, of the Host header field.		octets, of the Host header field.
	Host: A sequence of characters (length determined by "Host-Len")		Host: A sequence of characters (length determined by "Host-Len")
	containing an ASCII string indicating the host that the		containing an ASCII string indicating the host that the
	alternative service is available upon.		alternative service is available upon.
	Origin: An OPTIONAL sequence of characters (length determined by		Origin: An OPTIONAL sequence of characters (length determined by
	subtracting the length of all preceding fields from the frame		subtracting the length of all preceding fields from the frame
	length) containing the ASCII serialisation of an origin		length) containing the ASCII serialization of an origin
	([RFC6454], Section 6.2) that the alternate service is applicable		([RFC6454], Section 6.2) that the alternate service is applicable
	to.		to.
	The ALTSVC frame does not define any flags.		The ALTSVC frame does not define any flags.
	The ALTSVC frame is intended for receipt by clients; a server that		The ALTSVC frame is intended for receipt by clients; a server that
	receives an ALTSVC frame MUST treat it as a connection error of type		receives an ALTSVC frame MUST treat it as a connection error of type
	PROTOCOL_ERROR.		PROTOCOL_ERROR.
	The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT		The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT
	forward ALTSVC frames, though it can use the information contained in		forward ALTSVC frames, though it can use the information contained in
	ALTSVC frames in forming new ALTSVC frames to send to its own		ALTSVC frames in forming new ALTSVC frames to send to its own
	clients.		clients.
	5. The Alt-Svc-Used HTTP Header Field		5. The Alt-Svc-Used HTTP Header Field
	The Alt-Svc-Used HTTP header field is used in requests to indicate		The Alt-Svc-Used HTTP header field is used in requests to indicate
	that an alternate service is in use.		that an alternate service is in use.
	Alt-Svc-Used = ("1" / "0") *( OWS ";" OWS Alt-Svc-Used-Ext )		Alt-Svc-Used = use-flag *( OWS ";" OWS ext-param )
	Alt-Svc-Used-Ext = token "=" ( token / quoted-string )		use-flag = "1" / "0"
			ext-param = token "=" ( token / quoted-string )
	Alt-Svc-Used is intended to allow alternate services to avoid sending		Alt-Svc-Used is intended to allow alternate services to avoid sending
	alternative service indications where there is a risk of generating a		alternative service indications where there is a risk of generating a
	loops. It also allows a service to identify requests for accounting		loops. It also allows a service to identify requests for accounting
	and load balancing purposes.		and load balancing purposes.
	When using an alternative service, clients MUST include a Alt-Svc-		When using an alternative service, clients MUST include a Alt-Svc-
	Used header field in all requests.		Used header field in all requests.
			A flag value of "1" indicates that an alternate service was used,
			while "0" means it was not.
	For example:		For example:
	GET /thing HTTP/1.1		GET /thing HTTP/1.1
	Host: origin.example.com		Host: origin.example.com
	Alt-Svc-Used: 1		Alt-Svc-Used: 1
	The extension parameters (Alt-Svc-Used-Ext) are reserved for future		The extension parameters (ext-param) are reserved for future use;
	use; specifications that want to define an extension will need to		specifications that want to define an extension will need to update
	update this document (and ought to introduce an extension registry).		this document (and ought to introduce an extension registry).
	6. The 421 Not Authoritative HTTP Status Code		6. The 421 Not Authoritative HTTP Status Code
	The 421 (Not Authoritative) status code is defined in [HTTP2],		The 421 (Not Authoritative) status code is defined in [HTTP2],
	Section 9.1.2 to indicate that the current server instance is not		Section 9.1.2 to indicate that the current server instance is not
	authoritative for the requested resource. This can be used to		authoritative for the requested resource. This can be used to
	indicate that an alternative service is not authoritative; see		indicate that an alternative service is not authoritative; see
	Section 2).		Section 2).
	Clients receiving 421 (Not Authoritative) from an alternative service		Clients receiving 421 (Not Authoritative) from an alternative service
	skipping to change at page 14, line 23 ¶		skipping to change at page 14, line 23 ¶
	known exploits to make an attacker's certificate appear as		known exploits to make an attacker's certificate appear as
	legitimate.		legitimate.
	Alternative services could be used to persist such an attack; for		Alternative services could be used to persist such an attack; for
	example, an intermediary could man-in-the-middle TLS-protected		example, an intermediary could man-in-the-middle TLS-protected
	communication to a target, and then direct all traffic to an		communication to a target, and then direct all traffic to an
	alternative service with a large freshness lifetime, so that the user		alternative service with a large freshness lifetime, so that the user
	agent still directs traffic to the attacker even when not using the		agent still directs traffic to the attacker even when not using the
	intermediary.		intermediary.
	As a result, there is a requirement in Section 2.2 to examine cached
	alternative services when a network change is detected.
	9.3. Changing Protocols		9.3. Changing Protocols
	When the ALPN protocol is changed due to the use of an alternative		When the ALPN protocol is changed due to the use of an alternative
	service, the security properties of the new connection to the origin		service, the security properties of the new connection to the origin
	can be different from that of the "normal" connection to the origin,		can be different from that of the "normal" connection to the origin,
	because the protocol identifier itself implies this.		because the protocol identifier itself implies this.
	For example, if a "https://" URI had a protocol advertised that does		For example, if a "https://" URI had a protocol advertised that does
	not use some form of end-to-end encryption (most likely, TLS), it		not use some form of end-to-end encryption (most likely, TLS), it
	violates the expectations for security that the URI scheme implies.		violates the expectations for security that the URI scheme implies.
	skipping to change at page 15, line 11 ¶		skipping to change at page 15, line 7 ¶
	Clients that do not wish to be tracked MAY choose to ignore		Clients that do not wish to be tracked MAY choose to ignore
	alternative service advertisements.		alternative service advertisements.
	In a browser, any alternative service information MUST be removed		In a browser, any alternative service information MUST be removed
	when origin-specific data is cleared (for instance, when cookies are		when origin-specific data is cleared (for instance, when cookies are
	cleared).		cleared).
	10. Acknowledgements		10. Acknowledgements
	Thanks to Eliot Lear, Stephen Farrell, Guy Podjarny, Stephen Ludin,		Thanks to Adam Langley, Eliot Lear, Erik Nygren, Guy Podjarny, Paul
	Erik Nygren, Paul Hoffman, Adam Langley, Will Chan and Richard Barnes		Hoffman, Richard Barnes, Stephen Farrell, Stephen Ludin, and Will
	for their feedback and suggestions.		Chan for their feedback and suggestions.
	The Alt-Svc header field was influenced by the design of the		The Alt-Svc header field was influenced by the design of the
	Alternate-Protocol header field in SPDY.		Alternate-Protocol header field in SPDY.
	11. References		11. References
	11.1. Normative References		11.1. Normative References
	[ALPN] Friedl, S., Popov, A., Langley, A., and S. Emile,
	"Transport Layer Security (TLS) Application Layer Protocol
	Negotiation Extension", draft-ietf-tls-applayerprotoneg-05
	(work in progress), March 2014.
	[HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext		[HTTP2] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
	Transfer Protocol version 2", draft-ietf-httpbis-http2-13		Transfer Protocol version 2", draft-ietf-httpbis-http2-14
	(work in progress), June 2014.		(work in progress), July 2014.
	[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, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66,		Resource Identifier (URI): Generic Syntax", STD 66,
	RFC 3986, January 2005.		RFC 3986, January 2005.
	[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax		[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234, January 2008.		Specifications: ABNF", STD 68, RFC 5234, January 2008.
	skipping to change at page 16, line 10 ¶		skipping to change at page 15, line 50 ¶
	December 2011.		December 2011.
	[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Message Syntax and Routing",		Protocol (HTTP/1.1): Message Syntax and Routing",
	RFC 7230, June 2014.		RFC 7230, June 2014.
	[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,		[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
	Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",		Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
	RFC 7234, June 2014.		RFC 7234, June 2014.
			[RFC7301] Friedl, S., Popov, A., Langley, A., and S. Emile,
			"Transport Layer Security (TLS) Application-Layer Protocol
			Negotiation Extension", RFC 7301, July 2014.
	11.2. Informative References		11.2. Informative References
	[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration		[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
	Procedures for Message Header Fields", BCP 90, RFC 3864,		Procedures for Message Header Fields", BCP 90, RFC 3864,
	September 2004.		September 2004.
	[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security		[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
	(TLS) Protocol Version 1.2", RFC 5246, August 2008.		(TLS) Protocol Version 1.2", RFC 5246, August 2008.
	Appendix A. Change Log (to be removed by RFC Editor before publication)		Appendix A. Change Log (to be removed by RFC Editor before publication)
	skipping to change at page 17, line 5 ¶		skipping to change at page 16, line 47 ¶
	Note that ALTSVC frame is preferred to Alt-Svc header field		Note that ALTSVC frame is preferred to Alt-Svc header field
	(<https://github.com/http2/http2-spec/pull/503>).		(<https://github.com/http2/http2-spec/pull/503>).
	Incorporate ALTSRV frame		Incorporate ALTSRV frame
	(<https://github.com/http2/http2-spec/pull/507>).		(<https://github.com/http2/http2-spec/pull/507>).
	Moved definition of status code 421 to HTTP/2.		Moved definition of status code 421 to HTTP/2.
	Partly resolved <https://github.com/httpwg/http-extensions/issues/5>.		Partly resolved <https://github.com/httpwg/http-extensions/issues/5>.
			A.4. Since draft-ietf-httpbis-alt-svc-02
			Updated ALPN reference.
			Resolved <https://github.com/httpwg/http-extensions/issues/2>.
	Authors' Addresses		Authors' Addresses
	Mark Nottingham		Mark Nottingham
	Akamai		Akamai
	EMail: mnot@mnot.net		EMail: mnot@mnot.net
	URI: https://www.mnot.net/		URI: https://www.mnot.net/
	Patrick McManus		Patrick McManus
	Mozilla		Mozilla
End of changes. 29 change blocks.
	48 lines changed or deleted		52 lines changed or added
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