draft-ietf-httpbis-cdn-loop-02.txt		draft-ietf-httpbis-cdn-loop-latest.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: August 8, 2019 Fastly		Expires: April 12, 2026 Fastly
	N. Sullivan		N. Sullivan
	Cloudflare		Cloudflare
	February 04, 2019		October 09, 2025
	CDN Loop Detection		Loop Detection in Content Delivery Networks (CDNs)
	draft-ietf-httpbis-cdn-loop-02		draft-ietf-httpbis-cdn-loop-latest
	Abstract		Abstract
	This document defines the CDN-Loop request header field for HTTP.		This document defines the CDN-Loop request header field for HTTP.
	CDN-Loop addresses an operational need that occurs when an HTTP		CDN-Loop addresses an operational need that occurs when an HTTP
	request is intentionally forwarded between Content Delivery Networks		request is intentionally forwarded between Content Delivery Networks
	(CDNs), but is then accidentally or maliciously re-routed back into		(CDNs), but is then accidentally or maliciously re-routed back into
	the original CDN causing a non-terminating loop. The new header		the original CDN causing a non-terminating loop. The new header
	field can be used to identify the error and terminate the loop.		field can be used to identify the error and terminate the loop.
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	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 August 8, 2019.		This Internet-Draft will expire on April 12, 2026.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2025 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
	skipping to change at page 2, line 26 ¶		skipping to change at page 2, line 26 ¶
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	5.1. Normative References . . . . . . . . . . . . . . . . . . 5		5.1. Normative References . . . . . . . . . . . . . . . . . . 5
	5.2. Informative References . . . . . . . . . . . . . . . . . 6		5.2. Informative References . . . . . . . . . . . . . . . . . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
	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) in front of origin servers to		Content Delivery Networks (CDNs) in front of origin servers to
	improve end-user perceived latency, reduce operational costs, and		improve latency perceived by end users, reduce operational costs, and
	improve scalability and reliability of services.		improve scalability and reliability of services.
	Often, more than one CDN is in use by a given origin. 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 direct comparison of the
	services.		CDNs' services.
	As a result, it is not unknown for forwarding CDNs to be configured		As a result, it is possible for forwarding CDNs to be configured in a
	in a "loop" accidentally; because routing is achieved through a		"loop" accidentally; because routing is achieved through a
	combination of DNS and forwarding rules, and site configurations are		combination of DNS and forwarding rules, and site configurations are
	sometimes 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 can be used		sometimes isn't accidental; loops between multiple CDNs can be used
	as an attack vector (e.g., see [loop-attack]), especially if one CDN		as an 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 HTTP request header field to		This specification defines the CDN-Loop HTTP request header field to
	help detect such attacks and accidents among implementing forwarding		help detect such attacks and accidents among forwarding CDNs that
	CDNs, by disallowing its modification by their customers.		have implemented it; the header field may not be modified by their
			customers.
	1.1. Relationship to Via		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 Section 5.7.1 of [RFC7230] 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.
	1.2. Conventions and Definitions		1.2. 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 token, OWS, uri-host and port		repetition). Additionally, it uses a token (OWS), uri-host, and port
	rules from [RFC7230] and the parameter rule from [RFC7231].		rules from [RFC7230] and the parameter rule from [RFC7231].
	2. 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 detect loops.		through that CDN's servers to detect loops.
	CDN-Loop = #cdn-info		CDN-Loop = #cdn-info
	cdn-info = cdn-id *( OWS ";" OWS parameter )		cdn-info = cdn-id *( OWS ";" OWS parameter )
	cdn-id = ( uri-host [ ":" port ] ) / pseudonym		cdn-id = ( uri-host [ ":" port ] ) / pseudonym
	pseudonym = token		pseudonym = token
	The cdn-id identifies the CDN using either a hostname under its		The cdn-id identifies the CDN using either a hostname under its
	control or a pseudonym. Hostnames are preferred, to help avoid		control or a pseudonym. Hostnames are preferred, to help avoid
	accidental collisions. If a pseudonym is used, unintentional		accidental collisions. If a pseudonym is used, unintentional
	collisions are more likely, and therefore values should be carefully		collisions are more likely, and therefore values should be carefully
	chosen to prevent them; for example, using a well-known value (such		chosen to prevent them; for example, using a well-known value (such
	as the recognized name of the CDN in question), or a generated value		as the recognized name of the CDN in question), or a generated value
	with enough entropy to make collisions unlikely (such as a UUID		with enough entropy to make collisions unlikely (such as a UUID
	[RFC4122]).		[RFC4122]).
	Optionally, cdn-info can have semicolon-separated key/value		Optionally, cdn-info can have semicolon-separated key/value
	parameters, to accommodate additional information for the CDN's use.		parameters to accommodate additional information for the CDN's use.
	Conforming Content Delivery Networks SHOULD add a cdn-info to this		Conforming Content Delivery Networks SHOULD add a cdn-info to this
	header field in all requests they generate or forward (creating the		header field in all requests they generate or forward (creating the
	header field if necessary).		header field if necessary).
	As with all HTTP header fields defined using the "#" rule, the CDN-		As with all HTTP header fields defined using the "#" rule, the CDN-
	Loop header field can be added to by comma-separating values, or by		Loop header field can be added to by comma-separating values, or by
	creating a new header field with the desired value.		creating a new header field with the desired value.
	For example:		For example:
	GET /image.jpg HTTP/1.1		GET /image.jpg HTTP/1.1
	Host: cdn-customer.example		Host: cdn-customer.example
	User-Agent: ExampleBrowser/5		User-Agent: ExampleBrowser/5
	CDN-Loop: foo123.foocdn.example, barcdn.example; trace="abcdef"		CDN-Loop: foo123.foocdn.example, barcdn.example; trace="abcdef"
	CDN-Loop: AnotherCDN; abc=123; def="456"		CDN-Loop: AnotherCDN; abc=123; def="456"
	Note that the pseudonym syntax does not allow whitespace, DQUOTE or		Note that the pseudonym syntax does not allow whitespace, DQUOTE, or
	any of the characters "(),/:;<=>?@[]{}". See [RFC7230],		any of the characters "(),/:;<=>?@[]{}". See Section 3.2.6 of
	Section 3.2.6. Likewise, note the rules for when parameter values		[RFC7230]. Likewise, note the rules for when parameter values need
	need to be quoted in [RFC7231], Section 3.1.1.		to be quoted in Section 3.1.1 of [RFC7231].
	The effectiveness of this mechanism relies on all intermediaries		The effectiveness of this mechanism relies on all intermediaries
	preserving the header field, since removing (or allowing it to be		preserving the header field, since removing (or allowing it to be
	removed, e.g., by customer configuration) would prevent downstream		removed, e.g., by customer configuration) would prevent downstream
	CDNs from using it to detect looping. In general, unknown header		CDNs from using it to detect looping. In general, unknown header
	fields are not removed by intermediaries, but there may be need to		fields are not removed by intermediaries, but there may be a need to
	add CDN-Loop to an implementation's list of header fields that are		add CDN-Loop to an implementation's list of header fields that are
	not to be removed under any circumstances. The header field SHOULD		not to be removed under any circumstances. The header field SHOULD
	NOT be used for other purposes.		NOT be used for other purposes.
	3. Security Considerations		3. Security Considerations
	The threat model that the CDN-Loop header field addresses is a		The threat model that the CDN-Loop header field addresses is a
	customer who is attacking a service provider by configuring a		customer who is attacking a service provider by configuring a
	forwarding loop by accident or malice. For it to function, CDNs		forwarding loop by accident or malice. For it to function, CDNs
	cannot allow customers to modify or remove it in their configuration		cannot allow customers to modify or remove it in their configuration
	skipping to change at page 5, line 12 ¶		skipping to change at page 5, line 12 ¶
	remains an attack vector against both implementing and non-		remains an attack vector against both implementing and non-
	implementing CDNs.		implementing CDNs.
	A CDN's use of the CDN-Loop header field might expose its presence.		A CDN's use of the CDN-Loop header field might expose its presence.
	For example, if CDN A is configured to forward its requests to CDN B		For example, if CDN A is configured to forward its requests to CDN B
	for a given origin, CDN B's presence can be revealed if it behaves		for a given origin, CDN B's presence can be revealed if it behaves
	differently based upon the presence of the CDN-Loop header field.		differently based upon the presence of the CDN-Loop header field.
	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		behavior 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 field (either by		It is possible to sign the contents of the header field (either by
	putting the signature directly into the field's content, or using		putting the signature directly into the field's content or using
	another header field), but such use is not defined (or required) by		another header field), but such use is not defined (or required) by
	this specification.		this specification.
	Depending on how it is used, CDN-Loop can expose information about		Depending on how it is used, CDN-Loop can expose information about
	the internal configuration of the CDN; for example, the number of		the internal configuration of the CDN; for example, the number of
	hops inside the CDN, and the hostnames of nodes.		hops inside the CDN, and the hostnames of nodes.
	4. 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: RFC 8586
	5. References		5. References
	5.1. 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>.
	skipping to change at page 6, line 24 ¶		skipping to change at page 6, line 24 ¶
	[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>.
	5.2. 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", DOI 10.14722/ndss.2016.23442,		Content Delivery Networks", February 2016,
	February 2016,
	<http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>.		<http://www.icir.org/vern/papers/cdn-loops.NDSS16.pdf>.
	[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally		[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
	Unique IDentifier (UUID) URN Namespace", RFC 4122,		Unique IDentifier (UUID) URN Namespace", RFC 4122,
	DOI 10.17487/RFC4122, July 2005,		DOI 10.17487/RFC4122, July 2005,
	<https://www.rfc-editor.org/info/rfc4122>.		<https://www.rfc-editor.org/info/rfc4122>.
	Authors' Addresses		Authors' Addresses
	Stephen Ludin		Stephen Ludin
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