draft-ietf-cdni-request-routing-extensions-05.txt		draft-ietf-cdni-request-routing-extensions-06.txt
	Network Working Group O. Finkelman		Network Working Group O. Finkelman
	Internet-Draft Qwilt		Internet-Draft Qwilt
	Intended status: Standards Track S. Mishra		Intended status: Standards Track S. Mishra
	Expires: February 10, 2020 Verizon		Expires: March 26, 2020 Verizon
	August 9, 2019		September 23, 2019
	CDNI Request Routing Extensions		CDNI Request Routing Extensions
	draft-ietf-cdni-request-routing-extensions-05		draft-ietf-cdni-request-routing-extensions-06
	Abstract		Abstract
	The Open Caching working group of the Streaming Video Alliance is		Open Caching is a use case of Content Delivery Networks
	focused on the delegation of video delivery requests from commercial		Interconnetion (CDNI) in which the commercial Content Delivery
	CDNs to a caching layer at the ISP. In that aspect, Open Caching is		Network (CDN) is the upstream CDN (uCDN) and the ISP caching layer
	a specific use case of CDNI, where the commercial CDN is the upstream		serves as the downstream CDN (dCDN). The extensions specified in
	CDN (uCDN) and the ISP caching layer is the downstream CDN (dCDN).		this document to the CDNI Metadata and FCI interfaces are derived
	The extensions specified in this document to the CDNI Metadata and		from requirements raised by Open Caching but are also applicable to
	FCI interfaces are derived from requirements raised by Open Caching		CDNI use cases in general.
	but are applicable to CDNI use cases in general.
	Requirements Language		Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	document are to be interpreted as described in RFC 2119 [RFC2119].		"OPTIONAL" in this document are to be interpreted as described in BCP
			14 [RFC2119] [RFC8174] when, and only when, they appear in all
			capitals, as shown here.
	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 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 10, 2020.		This Internet-Draft will expire on March 26, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 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.
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	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
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	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Redirect Target Capability Object . . . . . . . . . . . . . . 3		2. Redirect Target Capability . . . . . . . . . . . . . . . . . 3
	2.1. Properties of Redirect Target Capability Object . . . . . 4		2.1. Properties of Redirect Target Capability Object . . . . . 5
	2.2. DnsTarget . . . . . . . . . . . . . . . . . . . . . . . . 6		2.2. DnsTarget . . . . . . . . . . . . . . . . . . . . . . . . 6
	2.3. HttpTarget . . . . . . . . . . . . . . . . . . . . . . . 6		2.3. HttpTarget . . . . . . . . . . . . . . . . . . . . . . . 7
	3. Fallback Target Address Metadata . . . . . . . . . . . . . . 8		2.4. Usage Example . . . . . . . . . . . . . . . . . . . . . . 9
	3.1. Properties Fallback Target Address Metadata Object . . . 9		3. Fallback Target Address Metadata . . . . . . . . . . . . . . 10
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		3.1. Properties of Fallback Target Address Metadata Object . . 11
	4.1. CDNI Payload Types . . . . . . . . . . . . . . . . . . . 9		3.2. Usage Example . . . . . . . . . . . . . . . . . . . . . . 12
	4.1.1. CDNI FCI RedirectTarget Payload Type . . . . . . . . 10		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
	4.1.2. CDNI MI FallbackTarget Payload Type . . . . . . . . . 10		4.1. CDNI Payload Types . . . . . . . . . . . . . . . . . . . 14
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 10		4.1.1. CDNI FCI RedirectTarget Payload Type . . . . . . . . 14
	5.1. Confidentiality and Privacy . . . . . . . . . . . . . . . 10		4.1.2. CDNI MI FallbackTarget Payload Type . . . . . . . . . 14
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10		5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		5.1. Confidentiality and Privacy . . . . . . . . . . . . . . . 15
	7.1. Normative References . . . . . . . . . . . . . . . . . . 11		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
	7.2. Informative References . . . . . . . . . . . . . . . . . 11		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12		7.1. Normative References . . . . . . . . . . . . . . . . . . 15
			7.2. Informative References . . . . . . . . . . . . . . . . . 16
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
	1. Introduction		1. Introduction
	This document defines objects needed for Open Caching request		The Open Caching working group of the Streaming Video Alliance (SVA)
	routing. For that purpose it extends CDNI metadata [RFC8006] and		is focused on the delegation of video delivery requests from
	CDNI Footprint and Capabilities [RFC8008]. For consistency, this		commercial CDNs to a caching layer at the Internet Service Provider's
	document follows the CDNI notation of uCDN (the commercial CDN) and		(ISP) network. Open Caching is a specific use case of CDNI where the
	dCDN (the ISP caching layer).		commercial CDN is the upstream CDN (uCDN) and the ISP caching layer
			is the downstream CDN (dCDN). This document defines and registers
			CDNI generic metadata object [RFC8006] and CDNI Footprint and
			Capabilities object [RFC8008] that are required for Open Caching
			request routing. For consistency with other CDNI documents this
			document follows the CDNI convention of uCDN (upstream CDN) and dCDN
			(downstream CDN) to represent the commerical CDN and ISP caching
			layer respectively.
	This document also registers CDNI Payload Types [RFC7736] for the		This document also registers CDNI Payload Types [RFC7736] for the
	defined objects:		defined objects:
	o Redirect Target Capability (for dCDN advertising redirect target		o Redirect Target Capability (for dCDN advertising redirect target
	address)		address)
	o Fallback Target Metadata (for uCDN configuring fallback target		o Fallback Target Metadata (for uCDN configuring fallback target
	address)		address)
	1.1. Terminology		1.1. Terminology
	This document reuses the terminology defined in [RFC6707], [RFC8006],		The following terms are used throughout this document:
	[RFC8007], and [RFC8008].
	Additionally, the following terms are used throughout this document		o FQDN - Fully Qualified Domain Name
	and are defined as follows:
	o RR - Request Router		o CDN - Content Delivery Network
	o CP - Content Provider		Additionaly, this document reuses the terminology defined in
			[RFC6707], [RFC7336], [RFC8006], [RFC8007], and [RFC8008].
			Specifically, we use the following CDNI acronyms:
	2. Redirect Target Capability Object		o FCI - Footprint and Capability Interface (see [RFC8008])
	Iterative request redirect as defined in section 1.1 of [RFC7336]		o MI - Metadata Interface (see [RFC8006])
	requries the provisioning of a redirect target address to be used by
	the uCDN in order to redirect to the dCDN. Redirect target addresses		o uCDN, dCDN - Upstream CDN and Downstream CDN respectively (see
	can vary between different footprints, for example, between different		[RFC7336])
	regions, and they may also change over time, for example as a result
	of network problems. Given this variable and dynamic nature of the		o RT - Redirection Target. Endpoint for redirection from uCDN to
	redirect target, it may not be suitable to advertise it during		dCDN.
	bootstrap. A more dynamic and footprint oriented interface is
	required. Therefore, we have chosen to use the CDNI Footprint and		o RR - Request Router. An element responsible for routing user
	Capabilities interface for redirect target advertisement.		requests.
			2. Redirect Target Capability
			Iterative request redirection is defined in Section 1.1 of [RFC7336]
			and elaborated by examples in Sections 3.2 and 3.4 of [RFC7336]. A
			Redirection Target (RT) is defined in Section 2 of [RFC7975] for
			Recursive Request Redirection as:
			"The endpoint to which the User Agent is redirected. In CDNI, a
			RT may point to a number of different components, some examples
			include a surrogate in the same CDN as the request router, a
			request router in a dCDN, or a surrogate in a dCDN".
			In this document we adopt the same defintion of the RT for the
			Iterative Request Redirect use case. This use case requires the
			provisioning of the RT address to be used by the uCDN in order to
			redirect to the dCDN. RT addresses can vary between different
			footprints, for example, between different regions, and they may also
			change over time, for example as a result of network problems. Given
			this variable and dynamic nature of the redirect target address, it
			may not be suitable to advertise it during bootstrap. A more dynamic
			and footprint oriented interface is required. Section 4.3 of
			[RFC7336] suggests that it could be one of the roles of the FCI
			[RFC8008]. Following this suggestion we have, therefore, chosen to
			use the CDNI Footprint and Capabilities interface for redirect target
			address advertisement.
	Use cases		Use cases
	o Footprint: The dCDN may want to have a different target per		o Footprint: The dCDN may want to have a different target per
	footprint. Note that a dCDN may spread across multiple		footprint. Note that a dCDN may spread across multiple
	geographies. This makes it easier to route client requests to a		geographies. This makes it easier to route client requests to a
	nearby request router. Though this can be achieved using a single		nearby request router. Though this can be achieved using a single
	canonical name and Geo DNS, that approach has limitations; for		canonical name and Geo DNS, that approach has limitations; for
	example a client may be using a third party DNS resolver, making		example a client may be using a third party DNS resolver, making
	it impossible for the redirector to detect where the client is		it impossible for the redirector to detect where the client is
	skipping to change at page 4, line 12 ¶		skipping to change at page 4, line 47 ¶
	by deploying more request routers in new locations and advertise		by deploying more request routers in new locations and advertise
	them via an updatable interface like the FCI.		them via an updatable interface like the FCI.
	The Redirect Target capability object is used to indicate the target		The Redirect Target capability object is used to indicate the target
	address the uCDN should use in order to redirect a client to the		address the uCDN should use in order to redirect a client to the
	dCDN. A target may be attached to a specific uCDN host, a list of		dCDN. A target may be attached to a specific uCDN host, a list of
	uCDN hosts, or used globally for all the hosts of the uCDN.		uCDN hosts, or used globally for all the hosts of the uCDN.
	When a dCDN is attaching the redirect target to a specific uCDN host		When a dCDN is attaching the redirect target to a specific uCDN host
	or a list of uCDN hosts, the dCDN MUST advertise the hosts within the		or a list of uCDN hosts, the dCDN MUST advertise the hosts within the
	Redirect Target capability object as "redirecting-hosts". In that		Redirect Target capability object as "redirecting-hosts". In this
	case, the uCDN can redirect to that dCDN address, only if the request		case, the uCDN can redirect to that dCDN address, only if the User
	was directed to one of those uCDN hosts.		Agent request was to one of these uCDN hosts.
	A redirect target for DNS redirection is an IP address used as an A		A redirect target for DNS redirection is an IPv4 address used as an A
	record response or a FQDN used as an alias in a CNAME record response		record response, an IPv6 address used as an AAAA record response or a
	(see [RFC1034]) of the uCDN DNS router. Note that DNS routers make		FQDN used as an alias in a CNAME record response (see [RFC1034]) of
	routing decisions based on either the DNS resolver's IP address or		the uCDN DNS router. Note that DNS routers make routing decisions
	the client IP address when EDNS0 client-subnet is used (see		based on either the DNS resolver's IP address or the client IP
	[RFC7871]). The dCDN may choose to advertise redirect targets and		address when EDNS0 client-subnet is used (see [RFC7871]). The dCDN
	footprints to cover both cases. A uCDN DNS router implemenation		may choose to advertise redirect targets and footprints to cover both
	SHOULD prefer routing based on client IP address when it is		cases. A uCDN DNS router implemenation SHOULD prefer routing based
	available.		on client IP address when it is available.
	A redirect target for HTTP redirection is the URI to be used as the		A redirect target for HTTP redirection is the URI to be used as the
	value for the Location header of a HTTP redirect 3xx response,		value for the Location header of a HTTP redirect 3xx response,
	typically a 302 (Found) (see section 7.1.2 of [RFC7231] and section		typically a 302 (Found) (see Section 7.1.2 of [RFC7231] and section
	6.4 of [RFC7231]).		6.4 of [RFC7231]).
			If the redirect target capability object does not contain a target or
			the target is empty, the uCDN MUST interpret it as "no target
			available for these uCDN hosts for the specified footprint". In case
			such a target was already advertised in a previous FCI object, the
			uCDN MUST interperet it as an update that deletes the previous
			redirect target.
	2.1. Properties of Redirect Target Capability Object		2.1. Properties of Redirect Target Capability Object
	The Redirect Target capability object consists of the following		The Redirect Target capability object consists of the following
	properties:		properties:
	Property: redirecting-hosts		Property: redirecting-hosts
	Description: One or more uCDN hosts to which this redirect		Description: One or more uCDN hosts to which this redirect
	target is attached. A redirecting host SHOULD be a host that		target is attached. A redirecting host SHOULD be a host that
	was published in a HostMatch object by the uCDN as defined in		was published in a HostMatch object by the uCDN as defined in
	section 4.1.2 of [RFC8006].		Section 4.1.2 of [RFC8006].
	Type: A list of Endpoint objects (see section 4.3.3 of		Type: A list of Endpoint objects (see Section 4.3.3 of
	[RFC8006])		[RFC8006])
	Mandatory-to-Specify: No. If not present, or empty, the		Mandatory-to-Specify: No. If not present, or empty, the
	redirect target applies to all hosts of the redirecting uCDN.		redirect target applies to all hosts of the redirecting uCDN.
	Property: dns-target		Property: dns-target
	Description: Target address for a DNS A record or CNAME record.		Description: Target address for a DNS A record, AAAA record or
			CNAME record.
	Type: DnsTarget object (see Section 2.2)		Type: DnsTarget object (see Section 2.2)
	Mandatory-to-Specify: No. but at least one of "dns-target" or		Mandatory-to-Specify: No. If the dns-target is not present or
	"http-target" MUST be present and non-empty.		empty the uCDN MUST interpret it as "no dns-target available".
	Property: http-target		Property: http-target
	Description: Target URI for a HTTP redirect.		Description: Target URI for a HTTP redirect.
	Type: HttpTarget object (see Section 2.3)		Type: HttpTarget object (see Section 2.3)
	Mandatory-to-Specify: No, but at least one of "dns-target" or		Mandatory-to-Specify: No. If the http-target is not present or
	"http-target" MUST be present and non-empty.		empty the uCDN MUST interpret it as "no http-target available".
	The following is an example of a Redirect Target capability object		The following is an example of a Redirect Target capability object
	serialization that advertises a dCDN target address that is attached		serialization that advertises a dCDN target address that is attached
	to a specific list of uCDN "redirecting-hosts". A uCDN host that is		to a specific list of uCDN "redirecting-hosts". A uCDN host that is
	included in that list can redirect to the advertised dCDN redirect		included in that list can redirect to the advertised dCDN redirect
	target.		target. The capabilities object is serialized as a JSON object as
			defined in Section 5 of [RFC8008]
	{		{
	"capabilities": [		"capabilities": [
	{		{
	"capability-type": "FCI.RedirectTarget",		"capability-type": "FCI.RedirectTarget",
	"capability-value": {		"capability-value": {
	"redirecting-hosts": [		"redirecting-hosts": [
	"a.service123.ucdn.example.com",		"a.service123.ucdn.example.com",
	"b.service123.ucdn.example.com"		"b.service123.ucdn.example.com"
	],		],
	skipping to change at page 6, line 11 ¶		skipping to change at page 7, line 4 ¶
	}		}
	]		]
	}		}
	2.2. DnsTarget		2.2. DnsTarget
	The DnsTarget object gives the target address for the DNS response to		The DnsTarget object gives the target address for the DNS response to
	delegate from the uCDN to the dCDN.		delegate from the uCDN to the dCDN.
	Property: host		Property: host
	Description: The host property is a hostname or an IP address,		Description: The host property is a hostname or an IP address,
	without a port number.		without a port number.
	Type: Endpoint object as defined in section 4.3.3 of [RFC8006]		Type: Endpoint object as defined in Section 4.3.3 of [RFC8006]
	with the limitation that it SHOULD NOT include a port number		with the limitation that it SHOULD NOT include a port number
	and, in case a port number is present, the uCDN MUST ignore it.		and, in case a port number is present, the uCDN MUST ignore it.
	Mandatory-to-Specify: Yes.		Mandatory-to-Specify: Yes.
	The following is an example of DnsTarget object:		The following is an example of DnsTarget object:
	{		{
	"host": "service123.ucdn.dcdn.example.com"		"host": "service123.ucdn.dcdn.example.com"
	}		}
	skipping to change at page 6, line 48 ¶		skipping to change at page 7, line 40 ¶
	2.3. HttpTarget		2.3. HttpTarget
	The HttpTarget object gives the necessary information to construct		The HttpTarget object gives the necessary information to construct
	the target Location URI for HTTP redirection.		the target Location URI for HTTP redirection.
	Property: host		Property: host
	Description: Hostname or IP address and an optional port, i.e.,		Description: Hostname or IP address and an optional port, i.e.,
	the host and port of the authority component of the URI as		the host and port of the authority component of the URI as
	described in section 3.2 of [RFC3986].		described in Section 3.2 of [RFC3986].
	Type: Endpoint object as defined in section 4.3.3 of [RFC8006].		Type: Endpoint object as defined in Section 4.3.3 of [RFC8006].
	Mandatory-to-Specify: Yes.		Mandatory-to-Specify: Yes.
	Property: path-prefix		Property: path-prefix
	Description: A path prefix for the HTTP redirect Location		Description: A path prefix for the HTTP redirect Location
	header. The original path is appended after this prefix.		header. The original path is appended after this prefix.
	Type: A prefix of a path-absolute as defined in section 3.3 of		Type: A prefix of a path-absolute as defined in Section 3.3 of
	[RFC3986]. The prefix MUST end with a trailing slash, to		[RFC3986]. The prefix MUST end with a trailing slash, to
	indicate the end of the last path segment in the prefix.		indicate the end of the last path segment in the prefix.
	Mandatory-to-Specify: No. If this property is absent or empty,		Mandatory-to-Specify: No. If this property is absent or empty,
	the uCDN MUST NOT prepend a path prefix to the original content		the uCDN MUST NOT prepend a path prefix to the original content
	path, i.e., the original path MUST appear in the location URI		path, i.e., the original path MUST appear in the location URI
	right after the authority component.		right after the authority component.
	Property: include-redirecting-host		Property: include-redirecting-host
	skipping to change at page 8, line 14 ¶		skipping to change at page 9, line 5 ¶
	Request:		Request:
	GET /vod/1/movie.mp4 HTTP/1.1		GET /vod/1/movie.mp4 HTTP/1.1
	Host: a.service123.ucdn.example.com		Host: a.service123.ucdn.example.com
	Response:		Response:
	HTTP/1.1 302 Found		HTTP/1.1 302 Found
	Location: http://us-east1.dcdn.example.com/cache/1/		Location: http://us-east1.dcdn.example.com/cache/1/
	a.service123.ucdn.example.com/vod/1/movie.mp4		a.service123.ucdn.example.com/vod/1/movie.mp4
			2.4. Usage Example
			Before requests can be routed from the uCDN to the dCDN the CDNs must
			exchange service configurations between them. Using the MI the uCDN
			advertises out-of-band its hosts to the dCDN, each host is designated
			by a host name and has its own specific metadata (see Section 4.1.2
			of [RFC8006]. The dCDN, using the FCI, advertises, also out-of-band,
			the redirect target address object defined in Section 2.1 for the
			relevant uCDN hosts. The following is a generalized example of the
			message flow between an upstream CDN and a downstream dCDN. For
			simplicity, we focus on the sequence of messages between the uCDN and
			dCDN and not on how they are passed.
			dCDN uCDN
			+ +
			| |
			(1) | MI: host: s123.ucdn.example.com |
			| host-metadata: < metadata > |
			<-------------------------------------------------------+
			| |
			(2) | FCI: capability-type: FCI.RedirectTarget |
			| redirecting-hosts: us-east1.dcdn.example.com |
			| target host: s123.ucdn.example.com |
			+------------------------------------------------------->
			| |
			| |
			+ +
			Figure 1: Redirect target address advertisement
			1. The uCDN advertises a host (s123.ucdn.example.com) with the host
			metadata.
			2. The dCDN adveritses its FCI objects to the uCDN including a
			FCI.RedirectTarget object that contains the redirect target
			address (us-east1.dcdn.example.com) specified for that uCDN host.
			Once the redirect target has been set, the uCDN can start redirecting
			user requests to the dCDN. The following is a generic sequence of
			redirection using the host and redirect target that were advertised
			in Figure 1 above.
			End User dCDN uCDN RR
			+ + +
			| | |
			(1) | Request sent s123.ucdn.example.com |
			+-----------------------+----------------------->
			| | |
			(2) | Redirect to us-east1.dcdn.example.com |
			<-----------------------+-----------------------+
			| | |
			(3) | Request us-east1.dcdn.example.com |
			+-----------------------> |
			| | |
			(4) | Response | |
			<-----------------------+ |
			| | |
			+ + +
			Figure 2: Generic requests redirection sequence
			1. The End User sends a request (DNS or HTTP) to the uCDN Request
			Router (RR).
			2. Using the previously advertised Redirect Target, the uCDN
			redirects the request to the dCDN.
			3. The End User sends a request to the dCDN.
			4. The dCDN either sends a response or reroutes it, for example, to
			a dCDN surrogate.
	3. Fallback Target Address Metadata		3. Fallback Target Address Metadata
	Open Caching requires that the uCDN provide a fallback target server		Open Caching requires that the uCDN provides a fallback target server
	to the dCDN, to be used in cases where the dCDN cannot properly		to the dCDN, to be used in cases where the dCDN cannot properly
	handle the request. To avoid redirect loops, the fallback target		handle the request. To avoid redirect loops, the fallback target
	server's address at the uCDN MUST be differnet from the original uCDN		server's address at the uCDN MUST be different from the original uCDN
	address from which the client was redirected to the dCDN. The uCDN		address from which the client was redirected to the dCDN. The uCDN
	MUST avoid further redirection when receiving the client request at		MUST avoid further redirection when receiving the client request at
	the fallback target. The fallback target is defined as a generic		the fallback target. The fallback target is defined as a generic
	metadata object (see section 3.2 of [RFC8006])		metadata object (see Section 3.2 of [RFC8006])
	Use cases		Use cases
	o Failover: A dCDN request router receives a request but has no		o Failover: A dCDN request router receives a request but has no
	caches to which it can route the request. This can happen in the		caches to which it can route the request. This can happen in the
	case of failures or temporary network overload.		case of failures or temporary network overload.
	o No coverage: A dCDN request router receives a request from a		o No coverage: A dCDN request router receives a request from a
	client located in an area inside the footprint but not covered by		client located in an area inside the footprint but not covered by
	the dCDN caches or outside the dCDN footprint coverage. In such		the dCDN caches or outside the dCDN footprint coverage. In such
	skipping to change at page 8, line 47 ¶		skipping to change at page 11, line 21 ¶
	o Error: A cache may receive a request that it cannot properly		o Error: A cache may receive a request that it cannot properly
	serve, for example, some of the metadata objects for that service		serve, for example, some of the metadata objects for that service
	were not properly acquired. In this case, the cache may resolve		were not properly acquired. In this case, the cache may resolve
	to redirect back to uCDN.		to redirect back to uCDN.
	The Fallback target metadata object is used to indicate the target		The Fallback target metadata object is used to indicate the target
	address the dCDN should use in order to redirect a client back to the		address the dCDN should use in order to redirect a client back to the
	uCDN. Fallback target is represented as endpoint objects as defined		uCDN. Fallback target is represented as endpoint objects as defined
	in section 4.3.3 of [RFC8006].		in section 4.3.3 of [RFC8006].
	The uCDN fallback target address may be used as a DNS A record or		The uCDN fallback target address may be used as a DNS A record, AAAA
	CNAME record in case of DNS redirection or a hostname for HTTP		record or CNAME record in case of DNS redirection or a hostname for
	redirect.		HTTP redirect.
	When using HTTP redirect to route a client request back to the uCDN,		When using HTTP redirect to route a client request back to the uCDN,
	it is the dCDN's responsibility to use the original URL path as the		it is the dCDN's responsibility to use the original URL path as the
	client would have used for the original uCDN request, stripping, if		client would have used for the original uCDN request, stripping, if
	needed, the dCDN path-prefix and/or the uCDN hostname from the		needed, the dCDN path-prefix and/or the uCDN hostname from the
	redirect URL that may have been used to request the content from the		redirect URL that may have been used to request the content from the
	dCDN.		dCDN.
	3.1. Properties Fallback Target Address Metadata Object		3.1. Properties of Fallback Target Address Metadata Object
	The MI.FallbackTarget Metadata object consists of the following		The MI.FallbackTarget Metadata object consists of the following
	single property:		single property:
	Property: host		Property: host
	Description: Target address to which the dCDN can redirect the		Description: Target address to which the dCDN can redirect the
	client.		client.
	Type: Endpoint object as defined in section 4.3.3 of [RFC8006]		Type: Endpoint object as defined in Section 4.3.3 of [RFC8006]
	with the limitation that in case of DNS delegation it SHOULD		with the limitation that in case of DNS delegation it SHOULD
	NOT include a port number and, in case a port number is		NOT include a port number and, in case a port number is
	present, the dCDN MUST ignore it.		present, the dCDN MUST ignore it.
	Mandatory-to-Specify: Yes.		Mandatory-to-Specify: Yes.
	Example of a MI.FallbackTarget Metadata object that designates the		Example of a MI.FallbackTarget Metadata object that designates the
	host address the dCDN should use as fallback address to redirect back		host address the dCDN should use as fallback address to redirect back
	to the uCDN.		to the uCDN.
	{		{
	"generic-metadata-type": "MI.FallbackTarget",		"generic-metadata-type": "MI.FallbackTarget",
	"generic-metadata-value":		"generic-metadata-value":
	{		{
	"host": "fallback-a.service123.ucdn.example"		"host": "fallback-a.service123.ucdn.example"
	}		}
	}		}
			3.2. Usage Example
			The uCDN advertises out-of-band the fallback target address to the
			dCDN, so that the dCDN may redirect a request back to the uCDN in
			case the dCDN cannot serve it. Using the MI the uCDN advertises its
			hosts to the dCDN, along with their specific host metadata (see
			Section 4.1.2 of [RFC8006]. The Fallback Target generic metadata
			object is encapsulated within the "host-metadata" property of each
			host. The following is an example of a message flow between an
			upstream CDN and a downstream dCDN. For simplicity, we focus on the
			sequence of messages between the uCDN and dCDN, not on how they are
			passed.
			dCDN uCDN
			+ +
			| |
			(1) | MI: host: s123.ucdn.example.com |
			| host-metadata: |
			| < metadata objects > |
			| < MI.FallbackTarget |
			| host: fallback-a.service123.ucdn.example > |
			| < metadata objects > |
			<-------------------------------------------------------+
			| |
			(2) | FCI: capability-type: FCI.RedirectTarget |
			| redirecting-hosts: us-east1.dcdn.example.com |
			| target host: s123.ucdn.example.com |
			+------------------------------------------------------->
			| |
			| |
			+ +
			Figure 3: Advertisement of host metadata with Fallback Target
			1. The uCDN advertises a host (s123.ucdn.example.com) with the host
			metadata. The host-metadata property contains a
			MI.FallbackTarget object.
			2. The dCDN adveritses its FCI objects to the uCDN including a
			FCI.RedirectTarget object that contains the redirect target
			address (us-east1.dcdn.example.com) specified for that uCDN host.
			The following is a generic sequence of redirection using the
			configurations that were advertised in Figure 3 above. In this case
			the dCDN redirects back to the uCDN fallback target address.
			End User dCDN uCDN fallback uCDN RR
			+ + + +
			| | | |
			(1) | Request sent s123.ucdn.example.com | |
			+-------------------+-------------------+------------------->
			| | | |
			(2) | Redirect to us-east1.dcdn.example.com | |
			<-------------------+-------------------+-------------------+
			| | | |
			(3) | Request us-east1.dcdn.example.com | |
			+-------------------> | |
			| | | |
			(4) | Redirect back to fallback-a.service123.ucdn.example |
			<-------------------+ | |
			| | | |
			(5) | Request fallback-a.service123.ucdn.example |
			+---------------------------------------> |
			| | | |
			(6) | Response | | |
			<-------------------+-------------------+ |
			| | | |
			+ + + +
			Figure 4: Redirection to Fallback Target
			1. The End User sends a request (DNS or HTTP) to the uCDN Request
			Router (RR).
			2. Using the previously advertised Redirect Target, the uCDN
			redirects the request to the dCDN.
			3. The End User sends a request to the dCDN.
			4. The dCDN cannot handled the request and, therefore, redirects it
			back to the uCDN fallback target address.
			5. The End User sends the request to the uCDN fallback target
			address.
			6. The uCDN either sends a response or reroutes it, for example, to
			a uCDN surrogate.
	4. IANA Considerations		4. IANA Considerations
	4.1. CDNI Payload Types		4.1. CDNI Payload Types
	This document requests the registration of the following CDNI Payload		This document requests the registration of the following CDNI Payload
	Types under the IANA "CDNI Payload Types" registry defined in		Types under the IANA "CDNI Payload Types" registry defined in
	[RFC7736]:		[RFC7736]:
	+--------------------+---------------+		+--------------------+---------------+
	| Payload Type | Specification |		| Payload Type | Specification |
	skipping to change at page 10, line 47 ¶		skipping to change at page 15, line 17 ¶
	The redirect Target FCI object potentially exposes information about		The redirect Target FCI object potentially exposes information about
	the internal strcture of the dCDN network. A third party could		the internal strcture of the dCDN network. A third party could
	intercept the FCI transactions and use the information to attack the		intercept the FCI transactions and use the information to attack the
	dCDN. An implemenation of the FCI MUST therefore use strong		dCDN. An implemenation of the FCI MUST therefore use strong
	authentication and encryption and strictly follow the directions for		authentication and encryption and strictly follow the directions for
	securing the interface as defined for the Metadata Interface in		securing the interface as defined for the Metadata Interface in
	Section 8.3 of [RFC8006].		Section 8.3 of [RFC8006].
	6. Acknowledgements		6. Acknowledgements
	The authors thank Nir B. Sopher for reality checks against		The authors thank Nir B. Sopher for reality checks against production
	production use cases, his contribution is significant to this		use cases, his contribution is significant to this document. The
	document. The authors also thank Ben Niven-Jenkins for his review		authors also thank Ben Niven-Jenkins for his review and feedback and
	and feedback and Kevin J. Ma for his guidance throughout the		Kevin J. Ma for his guidance throughout the development of this
	development of this document including his regular reviews.		document including his regular reviews.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",		[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
	STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,		STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
	<https://www.rfc-editor.org/info/rfc1034>.		<https://www.rfc-editor.org/info/rfc1034>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	skipping to change at page 11, line 28 ¶		skipping to change at page 15, line 46 ¶
	[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, DOI 10.17487/RFC3986, January 2005,		RFC 3986, DOI 10.17487/RFC3986, January 2005,
	<https://www.rfc-editor.org/info/rfc3986>.		<https://www.rfc-editor.org/info/rfc3986>.
	[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>.
			[RFC7975] Niven-Jenkins, B., Ed. and R. van Brandenburg, Ed.,
			"Request Routing Redirection Interface for Content
			Delivery Network (CDN) Interconnection", RFC 7975,
			DOI 10.17487/RFC7975, October 2016,
			<https://www.rfc-editor.org/info/rfc7975>.
	[RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,		[RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
	"Content Delivery Network Interconnection (CDNI)		"Content Delivery Network Interconnection (CDNI)
	Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,		Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,
	<https://www.rfc-editor.org/info/rfc8006>.		<https://www.rfc-editor.org/info/rfc8006>.
	[RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network		[RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network
	Interconnection (CDNI) Control Interface / Triggers",		Interconnection (CDNI) Control Interface / Triggers",
	RFC 8007, DOI 10.17487/RFC8007, December 2016,		RFC 8007, DOI 10.17487/RFC8007, December 2016,
	<https://www.rfc-editor.org/info/rfc8007>.		<https://www.rfc-editor.org/info/rfc8007>.
	[RFC8008] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg,		[RFC8008] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg,
	R., and K. Ma, "Content Delivery Network Interconnection		R., and K. Ma, "Content Delivery Network Interconnection
	(CDNI) Request Routing: Footprint and Capabilities		(CDNI) Request Routing: Footprint and Capabilities
	Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016,		Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016,
	<https://www.rfc-editor.org/info/rfc8008>.		<https://www.rfc-editor.org/info/rfc8008>.
			[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
			2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
			May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	7.2. Informative References		7.2. Informative References
	[RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content		[RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
	Distribution Network Interconnection (CDNI) Problem		Distribution Network Interconnection (CDNI) Problem
	Statement", RFC 6707, DOI 10.17487/RFC6707, September		Statement", RFC 6707, DOI 10.17487/RFC6707, September
	2012, <https://www.rfc-editor.org/info/rfc6707>.		2012, <https://www.rfc-editor.org/info/rfc6707>.
	[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed.,		[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
	"Framework for Content Distribution Network		"Framework for Content Distribution Network
	Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,		Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
End of changes. 40 change blocks.
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