< draft-ietf-httpbis-cdn-loop-00.txt		draft-ietf-httpbis-cdn-loop-01.txt >
	HTTP Working Group S. Ludin		HTTP Working Group S. Ludin
	Internet-Draft Akamai Technologies		Internet-Draft Akamai Technologies
	Intended status: Standards Track M. Nottingham		Intended status: Standards Track M. Nottingham
	Expires: February 17, 2019 Fastly		Expires: April 27, 2019 Fastly
	N. Sullivan		N. Sullivan
	Cloudflare		Cloudflare
	August 16, 2018		October 24, 2018
	CDN Loop Prevention		CDN Loop Prevention
	draft-ietf-httpbis-cdn-loop-00		draft-ietf-httpbis-cdn-loop-01
	Abstract		Abstract
	This specification defines the CDN-Loop request header field for		This specification defines the CDN-Loop request header field for
	HTTP.		HTTP.
	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.
	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 February 17, 2019.		This Internet-Draft will expire on April 27, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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
	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
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3		1.1. Relationship to Via . . . . . . . . . . . . . . . . . . . 2
	3. The CDN-Loop Request Header Field . . . . . . . . . . . . . . 3		1.2. Conventions and Definitions . . . . . . . . . . . . . . . 3
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 4		2. The CDN-Loop Request Header Field . . . . . . . . . . . . . . 3
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	6.1. Normative References . . . . . . . . . . . . . . . . . . 4		5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	6.2. Informative References . . . . . . . . . . . . . . . . . 5		5.1. Normative References . . . . . . . . . . . . . . . . . . 5
			5.2. Informative References . . . . . . . . . . . . . . . . . 5
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
	1. Introduction		1. Introduction
	In modern deployments of HTTP servers, it is common to interpose		In modern deployments of HTTP servers, it is common to interpose
	Content Delivery Networks (CDNs) to improve end-user perceived		Content Delivery Networks (CDNs) in front of origin servers to
	latency, reduce operational costs, and improve scalability and		improve end-user perceived latency, reduce operational costs, and
	reliability of services.		improve scalability and reliability of services.
	Often, more than one CDN is in use by any one server; this happens		Often, more than one CDN is in use by a given origin. This happens
	for a variety of reasons, such as cost savings, arranging for		for a variety of reasons, such as cost savings, arranging for
	failover should one CDN have issues, or to directly compare their		failover should one CDN have issues, or to directly compare their
	services.		services.
	As a result, it is not unknown for CDNs to be configured in a "loop"		As a result, it is not unknown for forwarding CDNs to be configured
	accidentally; because routing is achieved through a combination of		in a "loop" accidentally; because routing is achieved through a
	DNS and forwarding rules, and site configurations are sometimes		combination of DNS and forwarding rules, and site configurations are
	complex and managed by several parties.		sometimes complex and managed by several parties.
	When this happens, it is difficult to debug. Additionally, it		When this happens, it is difficult to debug. Additionally, it
	sometimes isn't accidental; loops between multiple CDNs be used as an		sometimes isn't accidental; loops between multiple CDNs be used as an
	attack vector (e.g., see [loop-attack]), especially if one CDN		attack vector (e.g., see [loop-attack]), especially if one CDN
	unintentionally strips the loop detection headers of another.		unintentionally strips the loop detection headers of another.
			This specification defines the CDN-Loop request header field for HTTP
			to enable secure interoperability of forwarding CDNs. Having a
			header that is guaranteed not to be modified by other CDNs that are
			used by a shared customer helps give each CDN additional confidence
			that any purpose (debugging, data gathering, enforcement) that they
			use this header for is free from tampering due to how that customer
			configured the other CDNs.
			1.1. Relationship to Via
	HTTP defines the Via header field in [RFC7230], Section 5.7.1 for		HTTP defines the Via header field in [RFC7230], Section 5.7.1 for
	"tracking message forwards, avoiding request loops, and identifying		"tracking message forwards, avoiding request loops, and identifying
	the protocol capabilities of senders along the request/response		the protocol capabilities of senders along the request/response
	chain."		chain."
	In theory, Via could be used to identify these loops. However, in		In theory, Via could be used to identify these loops. However, in
	practice it is not used in this fashion, because some HTTP servers		practice it is not used in this fashion, because some HTTP servers
	use Via for other purposes - in particular, some implementations		use Via for other purposes - in particular, some implementations
	disable some HTTP/1.1 features when the Via header is present.		disable some HTTP/1.1 features when the Via header is present.
	This specification defines the CDN-Loop request header field for		1.2. Conventions and Definitions
	HTTP, to address this shortcoming.
	2. Conventions and Definitions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	This specification uses the Augmented Backus-Naur Form (ABNF)		This specification uses the Augmented Backus-Naur Form (ABNF)
	notation of [RFC5234] with a list extension, defined in Section 7 of		notation of [RFC5234] with a list extension, defined in Section 7 of
	[RFC7230], that allows for compact definition of comma-separated		[RFC7230], that allows for compact definition of comma-separated
	lists using a '#' operator (similar to how the '*' operator indicates		lists using a '#' operator (similar to how the '*' operator indicates
	repetition). Additionally, it uses the OWS rule from [RFC7230] and		repetition). Additionally, it uses the OWS rule from [RFC7230] and
	the parameter rule from [RFC7231].		the parameter rule from [RFC7231].
	3. The CDN-Loop Request Header Field		2. The CDN-Loop Request Header Field
	The CDN-Loop request header field is intended to help a Content		The CDN-Loop request header field is intended to help a Content
	Delivery Network identify when an incoming request has already passed		Delivery Network identify when an incoming request has already passed
	through that CDN's servers, to prevent loops.		through that CDN's servers, to prevent loops.
	CDN-Loop = #cdn-id		CDN-Loop = #cdn-id
	cdn-id = token *( OWS ";" OWS parameter )		cdn-id = token *( OWS ";" OWS parameter )
	Conforming Content Delivery Networks SHOULD add a value to this		Conforming Content Delivery Networks SHOULD add a value to this
	header field to all requests they generate or forward (creating the		header field to all requests they generate or forward (creating the
	skipping to change at page 4, line 10 ¶		skipping to change at page 4, line 18 ¶
	Note that the token syntax does not allow whitespace, DQUOTE or any		Note that the token syntax does not allow whitespace, DQUOTE or any
	of the characters "(),/:;<=>?@[]{}". See [RFC7230], Section 3.2.6.		of the characters "(),/:;<=>?@[]{}". See [RFC7230], Section 3.2.6.
	Likewise, note the rules for when parameter values need to be quoted		Likewise, note the rules for when parameter values need to be quoted
	in [RFC7231], Section 3.1.1.		in [RFC7231], Section 3.1.1.
	To be effective, intermediaries - including Content Delivery Networks		To be effective, intermediaries - including Content Delivery Networks
	- MUST NOT remove this header field, or allow it to be removed (e.g.,		- MUST NOT remove this header field, or allow it to be removed (e.g.,
	through configuration) and servers (including intermediaries) SHOULD		through configuration) and servers (including intermediaries) SHOULD
	NOT use it for other purposes.		NOT use it for other purposes.
	4. Security Considerations		3. Security Considerations
			The threat model that the CDN-Loop header field addresses is a
			customer who is attempting to attack a service provider by
			configuring a forwarding loop by accident or malice. For it to
			function, CDNs cannot allow it to be modified by customers (see
			Section 2).
	The CDN-Loop header field can be generated by any client, and		The CDN-Loop header field can be generated by any client, and
	therefore its contents cannot be trusted. CDNs who modify their		therefore its contents cannot be trusted. CDNs who modify their
	behaviour based upon its contents should assure that this does not		behaviour based upon its contents should assure that this does not
	become an attack vector (e.g., for Denial-of-Service).		become an attack vector (e.g., for Denial-of-Service).
	It is possible to sign the contents of the header (either by putting		It is possible to sign the contents of the header (either by putting
	the signature directly into the field's content, or using another		the signature directly into the field's content, or using another
	header field), but such use is not defined (or required) by this		header field), but such use is not defined (or required) by this
	specification.		specification.
	5. IANA Considerations		4. IANA Considerations
	This document registers the "CDN-Loop" header field in the Permanent		This document registers the "CDN-Loop" header field in the Permanent
	Message Header Field Names registry.		Message Header Field Names registry.
	o Header Field Name: CDN-Loop		o Header Field Name: CDN-Loop
	o Protocol: http		o Protocol: http
	o Status: standard		o Status: standard
	o Reference: (this document)		o Reference: (this document)
	6. References		5. References
	6.1. Normative References		5.1. Normative References
	[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>.
	[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234,		Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC5234, January 2008,		DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc5234>.		<https://www.rfc-editor.org/info/rfc5234>.
	skipping to change at page 5, line 14 ¶		skipping to change at page 5, line 33 ¶
	[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Semantics and Content", RFC 7231,		Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
	DOI 10.17487/RFC7231, June 2014,		DOI 10.17487/RFC7231, June 2014,
	<https://www.rfc-editor.org/info/rfc7231>.		<https://www.rfc-editor.org/info/rfc7231>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	6.2. Informative References		5.2. Informative References
	[loop-attack]		[loop-attack]
	Chen, J., Jiang, J., Zheng, X., Duan, H., Liang, J., Li,		Chen, J., Jiang, J., Zheng, X., Duan, H., Liang, J., Li,
	K., Wan, T., and V. Paxson, "Forwarding-Loop Attacks in		K., Wan, T., and V. Paxson, "Forwarding-Loop Attacks in
	Content Delivery Networks", ISBN 1-891562-41-X,		Content Delivery Networks", ISBN 1-891562-41-X,
	DOI 10.14722/ndss.2016.23442, February 2016,		DOI 10.14722/ndss.2016.23442, February 2016,
	<http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>.		<http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>.
	Authors' Addresses		Authors' Addresses
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