CDNI Request Routing Extensions
draft-ietf-cdni-request-routing-extensions-08

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Details
Network Working Group                                       O. Finkelman
Internet-Draft                                                     Qwilt
Intended status: Standards Track                               S. Mishra
Expires: May 23, 2020                                            Verizon
                                                       November 20, 2019

                    CDNI Request Routing Extensions
             draft-ietf-cdni-request-routing-extensions-08

Abstract

   Open Caching architecture is a use case of Content Delivery Networks
   Interconnection (CDNI) in which the commercial Content Delivery
   Network (CDN) is the upstream CDN (uCDN) and the ISP caching layer
   serves as the downstream CDN (dCDN).  The extensions specified in
   this document to the CDNI Metadata Interface (MI) and the Footprint
   and Capabilities Interface (FCI) are derived from requirements raised
   by Open Caching but are also applicable to CDNI use cases in general.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 23, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Redirect Target Capability  . . . . . . . . . . . . . . . . .   4
     2.1.  DNS Redirect Target . . . . . . . . . . . . . . . . . . .   5
     2.2.  HTTP Redirect Target  . . . . . . . . . . . . . . . . . .   5
     2.3.  Properties of Redirect Target Capability Object . . . . .   5
     2.4.  DnsTarget Object  . . . . . . . . . . . . . . . . . . . .   7
       2.4.1.  DNS Target Example  . . . . . . . . . . . . . . . . .   7
     2.5.  HttpTarget Object . . . . . . . . . . . . . . . . . . . .   8
       2.5.1.  HTTP Target Example . . . . . . . . . . . . . . . . .   9
     2.6.  Usage Example . . . . . . . . . . . . . . . . . . . . . .  10
   3.  Fallback Target Address Metadata  . . . . . . . . . . . . . .  11
     3.1.  Properties of Fallback Target Address Metadata Object . .  12
     3.2.  Usage Example . . . . . . . . . . . . . . . . . . . . . .  13
     3.3.  uCDN addressing considerations  . . . . . . . . . . . . .  15
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     4.1.  CDNI Payload Types  . . . . . . . . . . . . . . . . . . .  16
       4.1.1.  CDNI FCI RedirectTarget Payload Type  . . . . . . . .  16
       4.1.2.  CDNI MI FallbackTarget Payload Type . . . . . . . . .  16
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     5.1.  Confidentiality and Privacy . . . . . . . . . . . . . . .  17
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  17
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The Streaming Video Alliance [SVA] is a global association that works
   to solve streaming video challenges in an effort to improve end-user
   experience and adoption.  The Open Caching Working Group [OCWG] of
   the Streaming Video Alliance [SVA] is focused on the delegation of
   video delivery requests from commercial CDNs to a caching layer at
   the Internet Service Provider's (ISP) network.  Open Caching
   architecture is a specific use case of CDNI where the commercial CDN
   is the upstream CDN (uCDN) and the ISP caching layer is the
   downstream CDN (dCDN).  The Open Caching Request Routing
   Specification [OC-RR] defines the Request Routing process and the
   interfaces that are required for its provisioning.  This document
   defines and registers CDNI metadata object [RFC8006] and CDNI

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   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 commercial CDN and
   ISP caching layer respectively.

   This document also registers CDNI Payload Types [RFC7736] for the
   defined objects:

   o  Redirect Target Capability (for dCDN advertising redirect target
      address)

   o  Fallback Target Metadata (for uCDN configuring fallback target
      address)

1.1.  Terminology

   The following terms are used throughout this document:

   o  FQDN - Fully Qualified Domain Name

   o  CDN - Content Delivery Network

   Additionally, this document reuses the terminology defined in
   [RFC6707], [RFC7336], [RFC8006], [RFC8007], and [RFC8008].
   Specifically, we use the following CDNI acronyms:

   o  FCI - Footprint and Capability Interface (see [RFC8008])

   o  MI - Metadata Interface (see [RFC8006])

   o  uCDN, dCDN - Upstream CDN and Downstream CDN respectively (see
      [RFC7336])

   o  RT - Redirection Target.  Endpoint for redirection from uCDN to
      dCDN.

   o  RR - Request Router.  An element responsible for routing user
      requests, typically using HTTP redirect or DNS CNAME, depending on
      the use case.

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "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.

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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 definition 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

   o  Footprint: The dCDN may want to have a different target per
      footprint.  Note that a dCDN may spread across multiple
      geographies.  This makes it easier to route client requests to a
      nearby request router.  Though this can be achieved using a single
      canonical name and "Geo DNS", such that in different geographies
      the same hostname is resolved to different IP address, that
      approach has limitations; for example a client may be using a
      third party DNS resolver, making it impossible for the redirector
      to detect where the client is located, or Geo DNS granularity may
      be too rough for the requirement of the application.

   o  Scaling: The dCDN may choose to scale its request routing service
      by deploying more request routers in new locations and advertise
      them via an updatable interface like the FCI.

   The Redirect Target capability object is used to indicate the target
   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
   uCDN hosts, or used globally for all the hosts of the uCDN.

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   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
   Redirect Target capability object as "redirecting-hosts".  In this
   case, the uCDN can redirect to that dCDN address, only if the User
   Agent request was to one of these uCDN hosts.

   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 interpret it as an update that deletes the previous
   redirect target.

2.1.  DNS Redirect Target

   A redirect target for DNS redirection is a FQDN used as an alias in a
   CNAME record response (see [RFC1034]) of the uCDN DNS router.  Note
   that DNS routers make routing decisions based on either the DNS
   resolver's IP address or the client IP subnet when EDNS0 client-
   subnet (ECS) is used (see [RFC7871]).  The dCDN may choose to
   advertise redirect targets and footprints to cover both cases, such
   that the uCDN resolution would route the DNS query to a different
   dCDN CNAMEs according client subnet or dCDN resolver IP address.
   This method further allows the dCDN DNS to optimize the resolution by
   localizing the target CNAMEs.  A uCDN implementation SHOULD prefer
   routing based on client IP subnet when ECS option is present.  A dCDN
   implementation using the ECS option MUST be aware of the privacy
   drawbacks listed in Section 2 of [RFC7871] and SHOULD follow the
   guidelines provided in Section 11.1 of [RFC7871].

2.2.  HTTP Redirect Target

   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,
   typically a 302 (Found) (see Section 7.1.2 of [RFC7231] and section
   6.4 of [RFC7231]).

2.3.  Properties of Redirect Target Capability Object

   The Redirect Target capability object consists of the following
   properties:

      Property: redirecting-hosts

         Description: One or more uCDN hosts to which this redirect
         target is attached.  A redirecting host SHOULD be a host that
         was published in a HostMatch object by the uCDN as defined in
         Section 4.1.2 of [RFC8006].

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         Type: A list of Endpoint objects (see Section 4.3.3 of
         [RFC8006])

         Mandatory-to-Specify: No.  If not present, or empty, the
         redirect target applies to all hosts of the redirecting uCDN.

      Property: dns-target

         Description: Target CNAME record for DNS redirection.

         Type: DnsTarget object (see Section 2.4)

         Mandatory-to-Specify: No.  If the dns-target is not present or
         empty the uCDN MUST interpret it as "no dns-target available".

      Property: http-target

         Description: Target URI for a HTTP redirect.

         Type: HttpTarget object (see Section 2.5)

         Mandatory-to-Specify: No.  If the http-target is not present or
         empty the uCDN MUST interpret it as "no http-target available".

   The following is an example of a Redirect Target capability object
   serialization that advertises a dCDN target address that is attached
   to a specific list of uCDN "redirecting-hosts".  A uCDN host that is
   included in that list can redirect to the advertised dCDN redirect
   target.  The capabilities object is serialized as a JSON object as
   defined in Section 5.1 of [RFC8008]

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   {
     "capabilities": [
       {
         "capability-type": "FCI.RedirectTarget",
         "capability-value": {
             "redirecting-hosts": [
                "a.service123.ucdn.example.com",
                "b.service123.ucdn.example.com"
             ],
             "dns-target": {
                "host": "service123.ucdn.dcdn.example.com"
             },
             "http-target": {
                 "host": "us-east1.dcdn.example.com",
                 "path-prefix": "/cache/1/",
                 "include-redirecting-host": true
             }
         },
         "footprints": [
             <Footprint objects>
         ]
       }
     ]
   }

2.4.  DnsTarget Object

   The DnsTarget object gives the target address for the DNS response to
   delegate from the uCDN to the dCDN.

      Property: host

         Description: The host property is a hostname or an IP address,
         without a port number.

         Type: Endpoint object as defined in Section 4.3.3 of [RFC8006]
         with the limitation that it SHOULD NOT include a port number
         and, in case a port number is present, the uCDN MUST ignore it.

         Mandatory-to-Specify: Yes.

2.4.1.  DNS Target Example

   The following is an example of DnsTarget object:

    {
       "host": "service123.ucdn.dcdn.example.com"
    }

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   The following is an example of a DNS query for uCDN address
   "a.service123.ucdn.example.com" and the corresponding CNAME
   redirection response:

    Query:
    a.service123.ucdn.example.com:
    type A, class IN

    Response:
    NAME: a.service123.ucdn.example.com, TYPE: CNAME, CLASS: IN,
    TTL: 120, RDATA: service123.ucdn.dcdn.example.com

2.5.  HttpTarget Object

   The HttpTarget object gives the necessary information to construct
   the target Location URI for HTTP redirection.

      Property: host

         Description: Hostname or IP address and an optional port, i.e.,
         the host and port of the authority component of the URI as
         described in Section 3.2 of [RFC3986].

         Type: Endpoint object as defined in Section 4.3.3 of [RFC8006].

         Mandatory-to-Specify: Yes.

      Property: scheme

         Description: A URI scheme to be used in the redirect response
         location construction.  When present, the uCDN MUST use the
         provided scheme in for HTTP redirection to the dCDN.

         Type: A URI scheme as defined in Section 3.1 of [RFC3986]
         represented as a JSON string.  The scheme MUST be either "http"
         or "https".

         Mandatory-to-Specify: No.  If this property is absent or empty
         the uCDN request router MUST use the same scheme as was used in
         the original request before redirection.

      Property: path-prefix

         Description: A path prefix for the HTTP redirect Location
         header.  The original path is appended after this prefix.

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         Type: A prefix of a path-absolute as defined in Section 3.3 of
         [RFC3986].  The prefix MUST end with a trailing slash, to
         indicate the end of the last path segment in the prefix.

         Mandatory-to-Specify: No.  If this property is absent or empty,
         the uCDN MUST NOT prepend a path prefix to the original content
         path, i.e., the original path MUST appear in the location URI
         right after the authority component.

      Property: include-redirecting-host

         Description: A flag indicating whether or not to include the
         redirecting host as the first path segment after the path-
         prefix.  If set to true and a "path-prefix" is used, the uCDN
         redirecting host MUST be added as a separate path segment after
         the path-prefix and before the original URL path.  If set to
         true and there is no path-prefix, the uCDN redirecting host
         MUST be prepended as the first path segment in the redirect
         URL.

         Type: Boolean.

         Mandatory-to-Specify: No.  Default value is False.

2.5.1.  HTTP Target Example

   Example of HttpTarget object with a "scheme", a "path-prefix", and
   "include-redirecting-host" properties:

   {
      "host": "us-east1.dcdn.example.com",
      "scheme": "https",
      "path-prefix": "/cache/1/",
      "include-redirecting-host": true
   }

   Example of a HTTP request for content at uCDN host
   "a.service123.ucdn.example.com" and the corresponding HTTP response
   with a Location header, used for redirecting the client to the dCDN,
   constructed according to the HttpTarget object from the above
   example:

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    Request:
    GET /vod/1/movie.mp4 HTTP/1.1
    Host: a.service123.ucdn.example.com

    Response:
    HTTP/1.1 302 Found
    Location: https://us-east1.dcdn.example.com/cache/1/
    a.service123.ucdn.example.com/vod/1/movie.mp4

2.6.  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 hostname 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 2.3 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: s123.ucdn.example.com        |
       |       target host: us-east1.dcdn.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 advertises 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

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   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

   Open Caching requires that the uCDN provides a fallback target server
   to the dCDN, to be used in cases where the dCDN cannot properly
   handle the request.  To avoid redirect loops, the fallback target
   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
   MUST avoid further redirection when receiving the client request at
   the fallback target.  The fallback target is defined as a generic
   metadata object (see Section 3.2 of [RFC8006])

   Use cases

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   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
      case of failures or temporary network overload.

   o  No coverage: A dCDN request router receives a request from a
      client located in an area inside the footprint but not covered by
      the dCDN caches or outside the dCDN footprint coverage.  In such
      cases, the router may choose to redirect the request back to the
      uCDN fallback address.

   o  Error: A cache may receive a request that it cannot properly
      serve, for example, some of the metadata objects for that service
      were not properly acquired.  In this case, the cache's "default
      action" may be to "redirect back to uCDN".

   The Fallback target metadata object is used to indicate the target
   address the dCDN should redirect a client to when falling back to the
   uCDN.  Fallback target address is represented as an endpoint object
   as defined in Section 4.3.3 of [RFC8006].

   In DNS redirection a CNAME record is used as the fallback target
   address.

   In HTTP redirection a hostname is used as the fallback target
   address.

   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
   client would have used for the original uCDN request, stripping, if
   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
   dCDN.

3.1.  Properties of Fallback Target Address Metadata Object

   The MI.FallbackTarget Metadata object consists of the following
   single property:

      Property: host

         Description: Target address to which the dCDN can redirect the
         client.

         Type: Endpoint object as defined in Section 4.3.3 of [RFC8006]
         with the limitation that in case of DNS delegation it SHOULD
         NOT include a port number and, in case a port number is
         present, the dCDN MUST ignore it.

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         Mandatory-to-Specify: Yes.

      Property: scheme

         Description: A URI scheme to be used in the redirect response
         location construction.  When present, the dCDN MUST use this
         scheme in case of HTTP redirection to the uCDN fallback
         address.

         Type: A URI scheme as defined in Section 3.1 of [RFC3986]
         represented as a JSON string.  The scheme MUST be either "http"
         or "https".

         Mandatory-to-Specify: No.  In case of HTTP redirection to
         fallback, if this property is absent or empty, the dCDN
         redirecting entity MUST use the same scheme as in the request
         received by the dCDN.

   Example of a MI.FallbackTarget Metadata object that designates the
   host address the dCDN should use as fallback address to redirect back
   to the uCDN.

   {
       "generic-metadata-type": "MI.FallbackTarget",
       "generic-metadata-value":
       {
           "host": "fallback-a.service123.ucdn.example",
           "scheme": "https"
       }
   }

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.

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     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: s123.ucdn.example.com        |
       |       target host: us-east1.dcdn.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 advertises 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.

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   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.

3.3.  uCDN addressing considerations

   When advertising fallback addresses to the dCDN the uCDN SHOULD
   consider the failure use cases that may lead the dCDN to route
   requests to uCDN fallback.  In extreme dCDN network failures or under
   denial-of-service (DoS) attacks, requests coming from a large segment

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   or multiple segments of the dCDN may be routed back to the uCDN.  The
   uCDN SHOULD therefore design its fallback addressing scheme and its
   available resources accordingly.  A favorable approach would be for
   the uCDN to use different fallback target address for each uCDN host,
   enabling it to load balance the requests using the same methods as it
   would for its original hosts.  See Sections 4.1.2 and 4.1.3 of
   [RFC8006] for a detailed description of how to use GenericMetadata
   objects within the HostMatch object advertised in the HostIndex of
   the uCDN.

4.  IANA Considerations

4.1.  CDNI Payload Types

   This document requests the registration of the following CDNI Payload
   Types under the IANA "CDNI Payload Types" registry defined in
   [RFC7736]:

                  +--------------------+---------------+
                  | Payload Type       | Specification |
                  +--------------------+---------------+
                  | FCI.RedirectTarget | RFCthis       |
                  | MI.FallbackTarget  | RFCthis       |
                  +--------------------+---------------+

   [RFC Editor: Please replace RFCthis with the published RFC number for
   this document.]

4.1.1.  CDNI FCI RedirectTarget Payload Type

   Purpose: The purpose of this payload type is to distinguish
   RedirectTarget FCI objects

   Interface: FCI

   Encoding: see Section 2.3

4.1.2.  CDNI MI FallbackTarget Payload Type

   Purpose: The purpose of this payload type is to distinguish
   FallbackTarget MI objects (and any associated capability
   advertisement)

   Interface: MI/FCI

   Encoding: see Section 3.1

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5.  Security Considerations

   This specification is in accordance with the CDNI Metadata Interface
   and the CDNI Request Routing: Footprint and Capabilities Semantics.
   As such, it is subject to the security and privacy considerations as
   defined in Section 8 of [RFC8006] and in Section 7 of [RFC8008]
   respectively.

5.1.  Confidentiality and Privacy

   The Redirect Target FCI object potentially reveals information about
   the internal structure of the dCDN network.  A third party could
   intercept the FCI transactions and use the information to attack the
   dCDN.  The same is also true for the Fallback Target Metadata object
   as it may reveal information about the internal structure of the
   uCDN, exposing it to external exploits.  Implementations of the FCI
   and MI MUST therefore use strong authentication and encryption and
   strictly follow the directions for securing the interface as defined
   for the Metadata Interface in Section 8.3 of [RFC8006].

6.  Acknowledgements

   The authors thank Nir B. Sopher for reality checks against production
   use cases, his contribution is significant to this document.  The
   authors also thank Ben Niven-Jenkins for his review and feedback and
   Kevin J. Ma for his guidance throughout the development of this
   document including his regular reviews.

7.  References

7.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

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   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, DOI 10.17487/RFC6707, September
              2012, <https://www.rfc-editor.org/info/rfc6707>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7336]  Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
              "Framework for Content Distribution Network
              Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
              August 2014, <https://www.rfc-editor.org/info/rfc7336>.

   [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,
              "Content Delivery Network Interconnection (CDNI)
              Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,
              <https://www.rfc-editor.org/info/rfc8006>.

   [RFC8007]  Murray, R. and B. Niven-Jenkins, "Content Delivery Network
              Interconnection (CDNI) Control Interface / Triggers",
              RFC 8007, DOI 10.17487/RFC8007, December 2016,
              <https://www.rfc-editor.org/info/rfc8007>.

   [RFC8008]  Seedorf, J., Peterson, J., Previdi, S., van Brandenburg,
              R., and K. Ma, "Content Delivery Network Interconnection
              (CDNI) Request Routing: Footprint and Capabilities
              Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016,
              <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

   [OC-RR]    Finkelman, O., Ed., Hofmann, J., Klein, E., Mishra, S.,
              Ma, K., Sahar, D., and B. Zurat, "Open Caching - Request
              Routing Functional Specification", Version 1.1, October
              2019, <https://www.streamingvideoalliance.org/books/open-
              cache-request-routing-functional-specification/>.

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   [OCWG]     "Open Caching Home Page",
              <https://www.streamingvideoalliance.org/technical-groups/
              open-caching/>.

   [RFC7736]  Ma, K., "Content Delivery Network Interconnection (CDNI)
              Media Type Registration", RFC 7736, DOI 10.17487/RFC7736,
              December 2015, <https://www.rfc-editor.org/info/rfc7736>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <https://www.rfc-editor.org/info/rfc7871>.

   [SVA]      "Streaming Video Alliance Home Page",
              <https://www.streamingvideoalliance.org>.

Authors' Addresses

   Ori Finkelman
   Qwilt
   6, Ha'harash
   Hod HaSharon  4524079
   Israel

   Email: ori.finkelman.ietf@gmail.com

   Sanjay Mishra
   Verizon
   13100 Columbia Pike
   Silver Spring, MD  20904
   USA

   Email: sanjay.mishra@verizon.com

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