Internet Engineering Task Force (IETF)                        J. Seedorf
Request for Comments: 9241     HFT Stuttgart - Univ. of Applied Sciences
Category: Standards Track                                        Y. Yang
ISSN: 2070-1721                                          Yale University
                                                                   K. Ma
                                                                Ericsson
                                                             J. Peterson
                                                                 NeuStar
                                                                J. Zhang
                                                       Tongji University
                                                                May 2022

     Content Delivery Network Interconnection (CDNI) Request Routing: CDNI Footprint and
Capabilities Advertisement Using ALTO Application-Layer Traffic Optimization
                                 (ALTO)

Abstract

   The Content Delivery Networks Interconnection (CDNI) framework in RFC
   6707 defines a set of protocols to interconnect CDNs to achieve
   multiple goals, including extending the reach of a given CDN.  A CDNI
   Request Routing Footprint & Capabilities Advertisement interface
   (FCI) is needed to achieve the goals of a CDNI.  RFC 8008 defines the
   FCI semantics and provides guidelines on the FCI protocol, but the
   exact protocol is not specified.  This document defines a new
   Application-Layer Traffic Optimization (ALTO) service, called "CDNI
   Advertisement Service", that provides an implementation of the FCI,
   following the guidelines defined in RFC 8008.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9241.

Copyright Notice

   Copyright (c) 2022 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
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology and Background
     2.1.  Terminology
     2.2.  Semantics of FCI Advertisement
     2.3.  ALTO Background and Benefits
   3.  CDNI Advertisement Service
     3.1.  Media Type
     3.2.  HTTP Method
     3.3.  Accept Input Parameters
     3.4.  Capabilities
     3.5.  Uses
     3.6.  Response
     3.7.  Examples
       3.7.1.  IRD
       3.7.2.  A Basic Example
       3.7.3.  Incremental Updates
   4.  CDNI Advertisement Service Using ALTO Network Map
     4.1.  Network Map Footprint Type: altopid
     4.2.  Examples
       4.2.1.  ALTO Network Map for CDNI Advertisements
       4.2.2.  ALTO PID Footprints in CDNI Advertisements
       4.2.3.  Incremental Updates
   5.  Filtered CDNI Advertisement Using CDNI Capabilities
     5.1.  Media Type
     5.2.  HTTP Method
     5.3.  Accept Input Parameters
     5.4.  Capabilities
     5.5.  Uses
     5.6.  Response
     5.7.  Examples
       5.7.1.  A Basic Example
       5.7.2.  Incremental Updates
   6.  Query Footprint Properties Using ALTO Property Map Service
     6.1.  Representing Footprint Objects as Property Map Entities
       6.1.1.  ASN Domain
       6.1.2.  COUNTRYCODE Domain
     6.2.  Representing CDNI Capabilities as Property Map Entity
           Properties
       6.2.1.  Defining Information Resource Media Type for Property
               Type cdni-capabilities
       6.2.2.  Intended Semantics of Property Type cdni-capabilities
     6.3.  Examples
       6.3.1.  Property Map
       6.3.2.  Filtered Property Map
       6.3.3.  Incremental Updates
   7.  IANA Considerations
     7.1.  application/alto-cdni+json Media Type
     7.2.  application/alto-cdnifilter+json Media Type
     7.3.  CDNI Metadata Footprint Types Registry
     7.4.  ALTO Entity Domain Types Registry
     7.5.  ALTO Entity Property Types Registry
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Contributors
   Authors' Addresses

1.  Introduction

   The ability to interconnect multiple content delivery networks (CDNs)
   has many benefits, including increased coverage, capability, and
   reliability.  The Content Delivery Networks Interconnection (CDNI)
   framework [RFC6707] defines four interfaces to interconnect CDNs: (1)
   the CDNI Request Routing Interface, (2) the CDNI Metadata Interface,
   (3) the CDNI Logging Interface, and (4) the CDNI Control Interface.

   Among these four interfaces, the CDNI Request Routing Interface
   provides key functions, as specified in [RFC6707]:

   |  The CDNI Request Routing interface enables a Request Routing
   |  function in an Upstream CDN to query a Request Routing function in
   |  a Downstream CDN to determine if the Downstream CDN is able (and
   |  willing) to accept the delegated Content Request.  It also allows
   |  the Downstream CDN to control what should be returned to the User
   |  Agent in the redirection message by the upstream Request Routing
   |  function.

   At a high level, therefore, the scope of the CDNI Request Routing
   Interface contains two main tasks: (1) determining if the dCDN
   (downstream CDN) is willing to accept a delegated content request and
   (2) redirecting the content request coming from a uCDN (upstream CDN)
   to the proper entry point or entity in the dCDN.

   Correspondingly, the Request Routing Interface is broadly divided
   into two functionalities: (1) the CDNI Footprint & Capabilities
   Advertisement interface (FCI) defined in [RFC8008] and (2) the CDNI
   Request Routing Redirection interface (RI) defined in [RFC7975].
   This document focuses on the first functionality (CDNI FCI).

   Specifically, CDNI FCI allows both an Advertisement from a dCDN to a
   uCDN (push) and a query from a uCDN to a dCDN (pull) so that the uCDN
   knows whether it can redirect a particular user request to that dCDN.

   A key component in defining the CDNI FCI is defining the objects that
   describe the footprints and capabilities of a dCDN.  Such objects are
   already specified in Section 5 of [RFC8008].  However, no protocol is
   defined to transport and update such objects between a uCDN and a
   dCDN.

   To define such a protocol, this document specifies an extension of
   the Application-Layer Traffic Optimization (ALTO) Protocol [RFC7285]
   by introducing a new ALTO service called "CDNI Advertisement
   Service".

   Section 2.3 discusses the benefits in using ALTO as a transport
   protocol.

2.  Terminology and Background

   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.

   The design of CDNI FCI transport using ALTO assumes an understanding
   of both FCI semantics and ALTO.  Hence, this document starts with a
   non-normative review of both.

2.1.  Terminology

   The document uses the CDNI terms defined in [RFC6707], [RFC8006], and
   [RFC8008].  Also, the document uses the ALTO terms defined in
   [RFC7285] and [RFC9240].  This document uses the following
   abbreviations:

   ALTO:   Application-Layer Traffic Optimization

   ASN:    Autonomous System Number

   CDN:    Content Delivery Network

   CDNI:   CDN Interconnection

   dCDN:   Downstream CDN

   FCI:    CDNI FCI, CDNI Request Routing Footprint & Capabilities
           Advertisement interface

   IRD:    Information Resource Directory in ALTO

   PID:    Provider-defined Identifier in ALTO

   uCDN:   Upstream CDN

2.2.  Semantics of FCI Advertisement

   [RFC8008] defines the semantics of CDNI FCI, provides guidance on
   what footprint and capabilities mean in a CDNI context, and specifies
   the requirements on the CDNI FCI transport protocol.  The definitions
   in [RFC8008] depend on [RFC8006].  Below is a non-normative review of
   key related points of [RFC8008] and [RFC8006].  For detailed
   information and normative specification, the reader should refer to
   these two RFCs.

   *  Multiple types of mandatory-to-implement footprints (i.e.,
      "ipv4cidr", "ipv6cidr", "asn", and "countrycode") are defined in
      [RFC8006].  A "set of IP prefixes" can contain both full IP
      addresses (i.e., a /32 for IPv4 or a /128 for IPv6) and IP
      prefixes with an arbitrary prefix length.  There must also be
      support for multiple IP address versions, i.e., IPv4 and IPv6, in
      such a footprint.

   *  Multiple initial types of capabilities are defined in [RFC8008]
      including (1) Delivery Protocol, (2) Acquisition Protocol, (3)
      Redirection Mode, (4) capabilities related to CDNI Logging, and
      (5) capabilities related to CDNI Metadata.  They are required in
      all cases and, therefore, considered as mandatory-to-implement
      capabilities for all CDNI FCI implementations.

   *  Footprint and capabilities are defined together and cannot be
      interpreted independently from each other.  Specifically,
      [RFC8008] integrates footprint and capabilities with an approach
      of "capabilities with footprint restrictions", by expressing
      capabilities on a per footprint basis.

   *  Specifically, for all mandatory-to-implement footprint types,
      footprints can be viewed as constraints for delegating requests to
      a dCDN: a dCDN footprint advertisement tells the uCDN the
      limitations for delegating a request to the dCDN.  For IP prefixes
      or Autonomous System Numbers (ASNs), the footprint signals to the
      uCDN that it should consider the dCDN a candidate only if the IP
      address of the request routing source falls within the prefix set
      or ASN, respectively.  The CDNI specifications do not define how a
      given uCDN determines what address ranges are in a particular ASN.
      Similarly, for country codes, a uCDN should only consider the dCDN
      a candidate if it covers the country of the request routing
      source.  The CDNI specifications do not define how a given uCDN
      determines the country of the request routing source.  Different
      types of footprint constraints can be combined together to narrow
      the dCDN candidacy, i.e., the uCDN should consider the dCDN a
      candidate only if the request routing source satisfies all the
      types of footprint constraints in the advertisement.

   *  Given that a large part of Footprint and Capabilities
      Advertisement may happen in contractual agreements, the semantics
      of CDNI Footprint and Capabilities Advertisement refers to
      answering the following question: what exactly still needs to be
      advertised by the CDNI FCI?  For instance, updates about temporal
      failures of part of a footprint can be useful information to
      convey via the CDNI FCI.  Such information would provide updates
      on information previously agreed to in contracts between the
      participating CDNs.  In other words, the CDNI FCI is a means for a
      dCDN to provide changes and updates regarding a footprint and/or
      capabilities that it has previously agreed to serve in a contract
      with a uCDN.  Hence, server push and incremental encoding will be
      necessary techniques.

2.3.  ALTO Background and Benefits

   Application-Layer Traffic Optimization (ALTO) [RFC7285] defines an
   approach for conveying network-layer (topology) information to
   "guide" the resource provider selection process in distributed
   applications that can choose among several candidate resources
   providers to retrieve a given resource.  Usually, it is assumed that
   an ALTO server conveys information that these applications cannot
   measure or have difficulty measuring themselves [RFC5693].

   Originally, ALTO was motivated by optimizing cross-ISP traffic
   generated by peer-to-peer applications [RFC5693].  However, ALTO can
   also be used for improving the request routing in CDNs.  In
   particular, Section 5 of [RFC7971] explicitly mentions ALTO as a
   candidate protocol to improve the selection of a CDN surrogate or
   origin.

   The following reasons make ALTO a suitable candidate protocol for
   dCDN selection as part of CDNI request routing and, in particular,
   for an FCI protocol:

   *  Application-Layer-oriented: ALTO is a protocol specifically
      designed to improve application-layer traffic (and application-
      layer connections among hosts on the Internet) by providing
      additional information to applications that these applications
      could not easily retrieve themselves.  This matches the need of
      CDNI, where a uCDN wants to improve application-layer CDN request
      routing by using information (provided by a dCDN) that the uCDN
      could not easily obtain otherwise.  Hence, ALTO can help a uCDN to
      select a proper dCDN by first providing dCDNs' capabilities as
      well as footprints (see Section 3) and then providing costs of
      surrogates in a dCDN by ALTO cost maps.

   *  Security: The identification between uCDNs and dCDNs is an
      important requirement (see Section 8).  ALTO maps can be signed
      and hence provide inherent origin protection.  Please see
      Section 15.1.2 of [RFC7285] for detailed protection strategies.

   *  RESTful design: The ALTO Protocol has undergone extensive
      revisions in order to provide a RESTful design regarding the
      client-server interaction specified by the protocol.  It is
      flexible and extensible enough to handle existing and potential
      future data formats defined by CDNI.  It can provide the
      consistent client-server interaction model for other existing CDNI
      interfaces or potential future extensions and therefore reduce the
      learning cost for both users and developers, although they are not
      in the scope of this document.  A CDNI FCI interface based on ALTO
      would inherit this RESTful design.  Please see Section 3.

   *  Error handling: The ALTO Protocol provides extensive error
      handling in the whole request and response process (see
      Section 8.5 of [RFC7285]).  A CDNI FCI interface based on ALTO
      would inherit this extensive error-handling framework.  Please see
      Section 5.

   *  Map Service: The semantics of an ALTO network map is an exact
      match for the needed information to convey a footprint by a dCDN,
      in particular, if such a footprint is being expressed by IP prefix
      ranges.  Please see Section 4.

   *  Filtered Map Service: The ALTO map filtering service would allow a
      uCDN to query only for parts of an ALTO map.  For example, the
      ALTO filtered property map service can enable a uCDN to query
      properties of a part of footprints efficiently.  Please see
      Section 6.

   *  Server-initiated notifications and incremental updates: When the
      footprint or the capabilities of a dCDN change (i.e., unexpectedly
      from the perspective of a uCDN), server-initiated notifications
      would enable a dCDN to inform a uCDN about such changes directly.
      Consider the case where -- due to failure -- part of the footprint
      of the dCDN is not functioning, i.e., the CDN cannot serve content
      to such clients with reasonable QoS.  Without server-initiated
      notifications, the uCDN might still use a recent network and cost
      map from the dCDN and therefore redirect requests to the dCDN that
      it cannot serve.  Similarly, the possibility for incremental
      updates would enable efficient conveyance of the aforementioned
      (or similar) status changes by the dCDN to the uCDN.  The newest
      design of ALTO supports server-pushed incremental updates
      [RFC8895].

   *  Content availability on hosts: A dCDN might want to express CDN
      capabilities in terms of certain content types (e.g., codecs and/
      or formats, or content from certain content providers).  ALTO
      Entity Property Map [RFC9240] would enable a dCDN to make such
      information available to a uCDN.  This would enable a uCDN to
      assess whether a dCDN has the capabilities for a given type of
      content requested.

   *  Resource availability on hosts or links: The capabilities on links
      (e.g., maximum bandwidth) or caches (e.g., average load) might be
      useful information for a uCDN for optimized dCDN selection.  For
      instance, if a uCDN receives a streaming request for content with
      a certain bitrate, it needs to know if it is likely that a dCDN
      can fulfill such stringent application-level requirements (i.e.,
      can be expected to have enough consistent bandwidth) before it
      redirects the request.  In general, if ALTO could convey such
      information via ALTO Entity Property Map [RFC9240], it would
      enable more sophisticated means for dCDN selection with ALTO.  The
      ALTO Path Vector extension [ALTO-PATH-VECTOR] is designed to allow
      ALTO clients to query information such as capacity regions for a
      given set of flows.

3.  CDNI Advertisement Service

   The ALTO Protocol relies upon the ALTO information service framework,
   which consists of multiple services.  All ALTO services are "provided
   through a common transport protocol; messaging structure and
   encoding; and transaction model" [RFC7285].  The ALTO Protocol
   specification defines multiple initial services, e.g., the ALTO
   network map service and cost map service.

   This document defines a new ALTO service, called "CDNI Advertisement
   Service", which conveys JSON [RFC8259] objects of media type
   "application/alto-cdni+json".  These JSON objects are used to
   transport BaseAdvertisementObject objects defined in [RFC8008].  This
   document specifies how to transport such BaseAdvertisementObject
   objects via the ALTO Protocol with the ALTO "CDNI Advertisement
   Service".  Similar to other ALTO services, this document defines the
   ALTO information resource for the "CDNI Advertisement Service" as
   follows.

   Note that the encoding of BaseAdvertisementObject reuses the one
   defined in [RFC8008] and therefore also follows the recommendations
   of I-JSON (Internet JSON) [RFC7493], which is required by [RFC8008].

3.1.  Media Type

   The media type of the CDNI Advertisement resource is "application/
   alto-cdni+json" (see Section 7).

3.2.  HTTP Method

   A CDNI Advertisement resource is requested using the HTTP GET method.

3.3.  Accept Input Parameters

   There are no applicable Accept Input parameters.

3.4.  Capabilities

   There are no applicable capabilities.

3.5.  Uses

   The "uses" field MUST NOT appear unless the CDNI Advertisement
   resource depends on other ALTO information resources.  If the CDNI
   Advertisement resource has dependent resources, the resource IDs of
   its dependent resources MUST be included into the "uses" field.  This
   document only defines one potential dependent resource for the CDNI
   Advertisement resource.  See Section 4 for details of when and how to
   use it.  Future documents may extend the CDNI Advertisement resource
   and allow other dependent resources.

3.6.  Response

   The "meta" field of a CDNI Advertisement response MUST include the
   "vtag" field defined in Section 10.3 of [RFC7285].  This field
   provides the version of the retrieved CDNI FCI resource.

   If a CDNI Advertisement response depends on other ALTO information
   resources, it MUST include the "dependent-vtags" field, whose value
   is an array to indicate the version tags of the resources used, where
   each resource is specified in "uses" of its Information Resource
   Directory (IRD) entry.

   The data component of an ALTO CDNI Advertisement response is named
   "cdni-advertisement", which is a JSON object of type
   CDNIAdvertisementData:

       object {
         CDNIAdvertisementData cdni-advertisement;
       } InfoResourceCDNIAdvertisement : ResponseEntityBase;

       object {
         BaseAdvertisementObject capabilities-with-footprints<0..*>;
       } CDNIAdvertisementData;

   Specifically, a CDNIAdvertisementData object is a JSON object that
   includes only one property named "capabilities-with-footprints",
   whose value is an array of BaseAdvertisementObject objects.  It
   provides capabilities with footprint restrictions for the uCDN to
   decide the dCDN selection.  If the value of this property is an empty
   array, it means the corresponding dCDN cannot provide any mandatory-
   to-implement CDNI capabilities for any footprints.

   The syntax and semantics of BaseAdvertisementObject are well defined
   in Section 5.1 of [RFC8008].  A BaseAdvertisementObject object
   includes multiple properties, including capability-type, capability-
   value, and footprints, where footprints are defined in
   Section 4.2.2.2 of [RFC8006].

   To be self-contained, below is an equivalent specification of
   BaseAdvertisementObject described in the ALTO-style notation (see
   Section 8.2 of [RFC7285]).  As mentioned above, the normative
   specification of BaseAdvertisementObject is in [RFC8008].

       object {
         JSONString capability-type;
         JSONValue capability-value;
         Footprint footprints<0..*>;
       } BaseAdvertisementObject;

       object {
         JSONString footprint-type;
         JSONString footprint-value<1..*>;
       } Footprint;

   For each BaseAdvertisementObject, the ALTO client MUST interpret
   footprints appearing multiple times as if they appeared only once.
   If footprints in a BaseAdvertisementObject is null or empty or does
   not appear, the ALTO client MUST understand that the capabilities in
   this BaseAdvertisementObject have the "global" coverage, i.e., the
   corresponding dCDN can provide them for any request routing source.

   Note: Further optimization of BaseAdvertisementObjects to effectively
   provide the advertisement of capabilities with footprint restrictions
   is certainly possible.  For example, these two examples below both
   describe that the dCDN can provide capabilities ["http/1.1",
   "https/1.1"] for the same footprints.  However, the latter one is
   smaller in its size.

   EXAMPLE 1
       {
         "meta": {...},
         "cdni-advertisement": {
           "capabilities-with-footprints": [
             {
               "capability-type": "FCI.DeliveryProtocol",
               "capability-value": {
                 "delivery-protocols": [
                   "http/1.1"
                 ]
               },
               "footprints": [
                 <Footprint objects>
               ]
             },
             {

               "capability-type": "FCI.DeliveryProtocol",
               "capability-value": {
                 "delivery-protocols": [
                   "https/1.1"
                 ]
               },
               "footprints": [
                 <Footprint objects>
               ]
             }
           ]
         }
       }

   EXAMPLE 2
       {
         "meta": {...},
         "cdni-advertisement": {
           "capabilities-with-footprints": [
             {
               "capability-type": "FCI.DeliveryProtocol",
               "capability-value": {
                 "delivery-protocols": [
                   "https/1.1",
                   "http/1.1"
                 ]
               },
               "footprints": [
                 <Footprint objects>
               ]
             }
           ]
         }
       }

   Since such optimizations are not required for the basic
   interconnection of CDNs, the specifics of such mechanisms are outside
   the scope of this document.

   This document only requires the ALTO server to provide the initial
   FCI-specific CDNI Payload Types defined in [RFC8008] as the
   mandatory-to-implement CDNI capabilities.

3.7.  Examples

3.7.1.  IRD

   Below is the IRD of a simple, example ALTO server.  The server
   provides both base ALTO information resources (e.g., network maps)
   and CDNI FCI-related information resources (e.g., CDNI Advertisement
   resources), demonstrating a single, integrated environment.

   Specifically, the IRD announces nine information resources as
   follows:

   *  two network maps,

   *  one CDNI Advertisement resource without dependency,

   *  one CDNI Advertisement resource depending on a network map,

   *  one filtered CDNI Advertisement resource to be defined in
      Section 5,

   *  one property map including "cdni-capabilities" as its entity
      property,

   *  one filtered property map including "cdni-capabilities" and "pid"
      as its entity properties, and

   *  two update stream services:

      -  one for updating CDNI Advertisement resources,

      -  one for updating property maps

    GET /directory HTTP/1.1
    Host: alto.example.com
    Accept: application/alto-directory+json,application/alto-error+json

    HTTP/1.1 200 OK
    Content-Length: 3531
    Content-Type: application/alto-directory+json

    {
      "meta": {
        "default-alto-network-map": "my-default-network-map"
      },
      "resources": {
        "my-default-network-map": {
          "uri": "https://alto.example.com/networkmap",
          "media-type": "application/alto-networkmap+json"
        },
        "my-eu-netmap": {
          "uri": "https://alto.example.com/myeunetmap",
          "media-type": "application/alto-networkmap+json"
        },
        "my-default-cdnifci": {
          "uri": "https://alto.example.com/cdnifci",
          "media-type": "application/alto-cdni+json"
        },
        "my-cdnifci-with-pid-footprints": {
          "uri": "https://alto.example.com/networkcdnifci",
          "media-type": "application/alto-cdni+json",
          "uses": [ "my-eu-netmap" ]
        },
        "my-filtered-cdnifci": {
          "uri": "https://alto.example.com/cdnifci/filtered",
          "media-type": "application/alto-cdni+json",
          "accepts": "application/alto-cdnifilter+json"
        },
        "cdnifci-property-map": {
          "uri": "https://alto.example.com/propmap/full/cdnifci",
          "media-type": "application/alto-propmap+json",
          "uses": [ "my-default-cdni" ],
          "capabilities": {
            "mappings": {
              "ipv4": [ "my-default-cdni.cdni-capabilities" ],
              "ipv6": [ "my-default-cdni.cdni-capabilities" ],
              "countrycode": [
                "my-default-cdni.cdni-capabilities" ],
              "asn": [ "my-default-cdni.cdni-capabilities" ]
            }
          }
        },
        "filtered-cdnifci-property-map": {
          "uri": "https://alto.example.com/propmap/lookup/cdnifci-pid",
          "media-type": "application/alto-propmap+json",
          "accepts": "application/alto-propmapparams+json",
          "uses": [ "my-default-cdni", "my-default-network-map" ],
          "capabilities": {
            "mappings": {
              "ipv4": [ "my-default-cdni.cdni-capabilities",
                        "my-default-network-map.pid" ],
              "ipv6": [ "my-default-cdni.cdni-capabilities",
                        "my-default-network-map.pid" ],
              "countrycode": [
                "my-default-cdni.cdni-capabilities" ],
              "asn": [ "my-default-cdni.cdni-capabilities" ]
            }
          }
        },
        "update-my-cdni-fci": {
          "uri": "https://alto.example.com/updates/cdnifci",
          "media-type": "text/event-stream",
          "accepts": "application/alto-updatestreamparams+json",
          "uses": [
            "my-default-network-map",
            "my-eu-netmap",
            "my-default-cdnifci",
            "my-filtered-cdnifci",
            "my-cdnifci-with-pid-footprints"
          ],
          "capabilities": {
            "incremental-change-media-types": {
             "my-default-network-map": "application/json-patch+json",
             "my-eu-netmap": "application/json-patch+json",
             "my-default-cdnifci":
             "application/merge-patch+json,application/json-patch+json",
             "my-filtered-cdnifci":
             "application/merge-patch+json,application/json-patch+json",
             "my-cdnifci-with-pid-footprints":
             "application/merge-patch+json,application/json-patch+json"
            }
          }
        },
        "update-my-props": {
          "uri": "https://alto.example.com/updates/properties",
          "media-type": "text/event-stream",
          "uses": [
            "cdnifci-property-map",
            "filtered-cdnifci-property-map"
          ],
          "capabilities": {
            "incremental-change-media-types": {
             "cdnifci-property-map":
             "application/merge-patch+json,application/json-patch+json",
             "filtered-cdnifci-property-map":
             "application/merge-patch+json,application/json-patch+json"
            }
          }
        }
      }
    }

3.7.2.  A Basic Example

   This basic example demonstrates a simple CDNI Advertisement resource,
   which does not depend on other resources.  There are three
   BaseAdvertisementObjects in this resource and these objects'
   capabilities are http/1.1 delivery protocol, [http/1.1, https/1.1]
   delivery protocol, and https/1.1 acquisition protocol, respectively.

     GET /cdnifci HTTP/1.1
     Host: alto.example.com
     Accept: application/alto-cdni+json,application/alto-error+json

     HTTP/1.1 200 OK
     Content-Length: 1411
     Content-Type: application/alto-cdni+json

     {
       "meta": {
         "vtag": {
           "resource-id": "my-default-cdnifci",
           "tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
         }
       },
       "cdni-advertisement": {
         "capabilities-with-footprints": [
           {
             "capability-type": "FCI.DeliveryProtocol",
             "capability-value": {
               "delivery-protocols": [
                 "http/1.1"
               ]
             },
             "footprints": [
               {
                 "footprint-type": "ipv4cidr",
                 "footprint-value": [ "192.0.2.0/24" ]
               },
               {
                 "footprint-type": "ipv6cidr",
                 "footprint-value": [ "2001:db8::/32" ]
               }
             ]
           },
           {
             "capability-type": "FCI.DeliveryProtocol",
             "capability-value": {
               "delivery-protocols": [
                 "https/1.1",
                 "http/1.1"
               ]
             },
             "footprints": [
               {
                 "footprint-type": "ipv4cidr",
                 "footprint-value": [ "198.51.100.0/24" ]
               }
             ]
           },
           {
             "capability-type": "FCI.AcquisitionProtocol",
             "capability-value": {
               "acquisition-protocols": [
                 "https/1.1"
               ]
             },
             "footprints": [
               {
                 "footprint-type": "ipv4cidr",
                 "footprint-value": [ "203.0.113.0/24" ]
               }
             ]
           }
         ]
       }
     }

3.7.3.  Incremental Updates

   A benefit of using ALTO to provide CDNI Advertisement resources is
   that such resources can be updated using ALTO incremental updates
   [RFC8895].  Below is an example that also shows the benefit of having
   both JSON merge patch and JSON patch to encode updates.

   At first, an ALTO client requests updates for "my-default-cdnifci",
   and the ALTO server returns the "control-uri" followed by the full
   CDNI Advertisement response.  Then when there is a change in the
   delivery-protocols in that http/1.1 is removed (from [http/1.1,
   https/1.1] to only https/1.1) due to maintenance of the http/1.1
   clusters, the ALTO server regenerates the new CDNI Advertisement
   resource and pushes the full replacement to the ALTO client.  Later
   on, the ALTO server notifies the ALTO client that "192.0.2.0/24" is
   added into the "ipv4" footprint object for delivery-protocol
   https/1.1 by sending the change encoded by JSON patch to the ALTO
   client.

    POST /updates/cdnifci HTTP/1.1
    Host: alto.example.com
    Accept: text/event-stream,application/alto-error+json
    Content-Type: application/alto-updatestreamparams+json
    Content-Length: 94

    {
      "add": {
        "my-cdnifci-stream": {
          "resource-id": "my-default-cdnifci"
        }
      }
    }

    HTTP/1.1 200 OK
    Connection: keep-alive
    Content-Type: text/event-stream

    event: application/alto-updatestreamcontrol+json
    data: {"control-uri":
    data: "https://alto.example.com/updates/streams/3141592653589"}

    event: application/alto-cdni+json,my-cdnifci-stream
    data: { ... full CDNI Advertisement resource ... }

    event: application/alto-cdni+json,my-cdnifci-stream
    data: {
    data:   "meta": {
    data:     "vtag": {
    data:       "tag": "dasdfa10ce8b059740bddsfasd8eb1d47853716"
    data:     }
    data:   },
    data:   "cdni-advertisement": {
    data:     "capabilities-with-footprints": [
    data:       {
    data:         "capability-type": "FCI.DeliveryProtocol",
    data:         "capability-value": {
    data:           "delivery-protocols": [
    data:             "https/1.1"
    data:           ]
    data:         },
    data:         "footprints": [
    data:           { "footprint-type": "ipv4cidr",
    data:             "footprint-value": [ "203.0.113.0/24" ]
    data:           }
    data:         ]
    data:       },
    data:       { ... other CDNI advertisement object ... }
    data:     ]
    data:   }
    data: }

    event: application/json-patch+json,my-cdnifci-stream
    data: [
    data:   { "op": "replace",
    data:     "path": "/meta/vtag/tag",
    data:     "value": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
    data:   },
    data:   { "op": "add",
    data:     "path": "/cdni-advertisement/capabilities-with-footprints
    /0/footprints/0/footprint-value/-",
    data:     "value": "192.0.2.0/24"
    data:   }
    data: ]

4.  CDNI Advertisement Service Using ALTO Network Map

4.1.  Network Map Footprint Type: altopid

   The ALTO Protocol defines a concept called Provider-defined
   Identifier (PID) to represent a group of IPv4 or IPv6 addresses to
   which can be applied the same management policy.  The PID is an
   alternative to the predefined CDNI footprint types (i.e., "ipv4cidr",
   "ipv6cidr", "asn", and "countrycode").

   To leverage this concept, this document defines a new CDNI Footprint
   Type called "altopid".  A CDNI Advertisement resource can depend on
   an ALTO network map resource and use "altopid" footprints to compress
   its CDNI Footprint Payload.

   Specifically, the "altopid" footprint type indicates that the
   corresponding footprint value is a list of PIDNames as defined in
   [RFC7285].  These PIDNames are references of PIDs in a network map
   resource.  Hence a CDNI Advertisement resource using "altopid"
   footprints depends on a network map.  For such a CDNI Advertisement
   resource, the resource ID of its dependent network map MUST be
   included in the "uses" field of its IRD entry, and the "dependent-
   vtags" field with a reference to this network map MUST be included in
   its response (see the example in Section 4.2.2).

4.2.  Examples

   The following examples use the same IRD given in Section 3.7.1.

4.2.1.  ALTO Network Map for CDNI Advertisements

   Below provides a sample network map whose resource ID is "my-eu-
   netmap".  This map is referenced by the CDNI Advertisement example in
   Section 4.2.2.

    GET /myeunetmap HTTP/1.1
    Host: alto.example.com
    Accept: application/alto-networkmap+json,application/alto-error+json

    HTTP/1.1 200 OK
    Content-Length: 344
    Content-Type: application/alto-networkmap+json

    {
      "meta": {
        "vtag": [
          { "resource-id": "my-eu-netmap",
            "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
          }
        ]
      },
      "network-map": {
        "south-france" : {
          "ipv4": [ "192.0.2.0/24", "198.51.100.0/25" ],
          "ipv6": [ "2001:db8::/32" ]
        },
        "germany": {
          "ipv4": [ "203.0.113.0/24" ]
        }
      }
    }

4.2.2.  ALTO PID Footprints in CDNI Advertisements

   This example shows a CDNI Advertisement resource that depends on a
   network map described in Section 4.2.1.

    GET /networkcdnifci HTTP/1.1
    Host: alto.example.com
    Accept: application/alto-cdni+json,application/alto-error+json

    HTTP/1.1 200 OK
    Content-Length: 736
    Content-Type: application/alto-cdni+json

    {
      "meta": {
        "dependent-vtags": [
          {
            "resource-id": "my-eu-netmap",
            "tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"
          }
        ]
      },
      "cdni-advertisement": {
        "capabilities-with-footprints": [
          { "capability-type": "FCI.DeliveryProtocol",
            "capability-value": [ "https/1.1" ],
            "footprints": [
              { "footprint-type": "altopid",
                "footprint-value": [ "south-france" ]
              }
            ]
          },
          { "capability-type": "FCI.AcquisitionProtocol",
            "capability-value": [ "https/1.1" ],
            "footprints": [
              { "footprint-type": "altopid",
                "footprint-value": [ "germany", "south-france" ]
              }
            ]
          }
        ]
      }
    }

4.2.3.  Incremental Updates

   In this example, the ALTO client is interested in changes of "my-
   cdnifci-with-pid-footprints" and its dependent network map "my-eu-
   netmap".  Considering two changes, the first one is to change
   footprints of the https/1.1 delivery protocol capability, and the
   second one is to remove the "south-france" PID from the footprints of
   the https/1.1 acquisition protocol capability.

     POST /updates/cdnifci HTTP/1.1
     Host: alto.example.com
     Accept: text/event-stream,application/alto-error+json
     Content-Type: application/alto-updatestreamparams+json
     Content-Length: 185

     {
       "add": {
         "my-eu-netmap-stream": {
           "resource-id": "my-eu-netmap"
         },
         "my-netmap-cdnifci-stream": {
           "resource-id": "my-cdnifci-with-pid-footprints"
         }
       }
     }

     HTTP/1.1 200 OK
     Connection: keep-alive
     Content-Type: text/event-stream

     event: application/alto-updatestreamcontrol+json
     data: {"control-uri":
     data: "https://alto.example.com/updates/streams/3141592653590"}

     event: application/alto-networkmap+json,my-eu-netmap-stream
     data: { ... full Network Map of my-eu-netmap ... }

     event: application/alto-cdnifci+json,my-netmap-cdnifci-stream
     data: { ... full CDNI Advertisement resource ... }

     event: application/json-patch+json,my-netmap-cdnifci-stream
     data: [
     data:   { "op": "replace",
     data:     "path": "/meta/vtag/tag",
     data:     "value": "dasdfa10ce8b059740bddsfasd8eb1d47853716"
     data:   },
     data:   { "op": "add",
     data:     "path":
     data:     "/cdni-advertisement/capabilities-with-footprints
     /0/footprints/0/footprint-value/-",
     data:     "value": "germany"
     data:   }
     data: ]

     event: application/json-patch+json,my-netmap-cdnifci-stream
     data: [
     data:   { "op": "replace",
     data:     "path": "/meta/vtag/tag",
     data:     "value": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
     data:   },
     data:   { "op": "remove",
     data:     "path":
     data:     "/cdni-advertisement/capabilities-with-footprints
     /1/footprints/0/footprint-value/1"
     data:   }
     data: ]

5.  Filtered CDNI Advertisement Using CDNI Capabilities

   Sections 3 and 4 describe the CDNI Advertisement Service that can be
   used to enable a uCDN to get capabilities with footprint restrictions
   from dCDNs.  However, since always getting full CDNI Advertisement
   resources from dCDNs is inefficient, this document introduces a new
   service named "Filtered CDNI Advertisement Service" to allow a client
   to filter a CDNI Advertisement resource using a client-given set of
   CDNI capabilities.  For each entry of the CDNI Advertisement
   response, an entry will only be returned to the client if it contains
   at least one of the client-given CDNI capabilities.  The relationship
   between a filtered CDNI Advertisement resource and a CDNI
   Advertisement resource is similar to the relationship between a
   filtered network/cost map and a network/cost map.

5.1.  Media Type

   A filtered CDNI Advertisement resource uses the same media type
   defined for the CDNI Advertisement resource in Section 3.1:
   "application/alto-cdni+json".

5.2.  HTTP Method

   A filtered CDNI Advertisement resource is requested using the HTTP
   POST method.

5.3.  Accept Input Parameters

   The input parameters for a filtered CDNI Advertisement resource are
   supplied in the entity body of the POST request.  This document
   specifies the input parameters with a data format indicated by the
   media type "application/alto-cdnifilter+json", which is a JSON object
   of type ReqFilteredCDNIAdvertisement where:

      object {
          JSONString capability-type;
          JSONValue capability-value;
      } CDNICapability;

      object {
          CDNICapability cdni-capabilities<0..*>;
      } ReqFilteredCDNIAdvertisement;

   with fields:

   capability-type:  The same as Base Advertisement Object's capability-
      type defined in Section 5.1 of [RFC8008].

   capability-value:  The same as Base Advertisement Object's
      capability-value defined in Section 5.1 of [RFC8008].

   cdni-capabilities:  A list of CDNI capabilities defined in
      Section 5.1 of [RFC8008] for which footprints are to be returned.
      If this list is empty, the ALTO server MUST interpret it as a
      request for the full CDNI Advertisement resource.  The ALTO server
      MUST interpret entries appearing in this list multiple times as if
      they appeared only once.  If the ALTO server does not define any
      footprints for a CDNI capability, it MUST omit this capability
      from the response.

5.4.  Capabilities

   There are no applicable capabilities.

5.5.  Uses

   Same to the "uses" field of the CDNI Advertisement resource (see
   Section 3.5).

5.6.  Response

   If the request is invalid, the response MUST indicate an error using
   ALTO Protocol error handling specified in Section 8.5 of [RFC7285].

   Specifically, a filtered CDNI Advertisement request is invalid if:

   *  the value of "capability-type" is null;

   *  the value of "capability-value" is null; or

   *  the value of "capability-value" is inconsistent with "capability-
      type".

   When a request is invalid, the ALTO server MUST return an
   "E_INVALID_FIELD_VALUE" error defined in Section 8.5.2 of [RFC7285],
   and the "value" field of the error message SHOULD indicate this CDNI
   capability.

   The ALTO server returns a filtered CDNI Advertisement resource for a
   valid request.  The format of a filtered CDNI Advertisement resource
   is the same as a full CDNI Advertisement resource (see Section 3.6).

   The returned filtered CDNI Advertisement resource MUST contain all
   the BaseAdvertisementObject objects satisfying the following
   condition: the CDNI capability object of each included
   BaseAdvertisementObject object MUST follow two constraints:

   *  The "cdni-capabilities" field of the input includes a CDNI
      capability object X having the same capability type as it.

   *  All the mandatory properties in its capability value is a superset
      of mandatory properties in capability value of X semantically.

   See Section 5.7.1 for a concrete example.

   The version tag included in the "vtag" field of the response MUST
   correspond to the full CDNI Advertisement resource from which the
   filtered CDNI Advertisement resource is provided.  This ensures that
   a single, canonical version tag is used independently of any
   filtering that is requested by an ALTO client.

5.7.  Examples

   The following examples use the same IRD example as in Section 3.7.1.

5.7.1.  A Basic Example

   This example filters the full CDNI Advertisement resource in
   Section 3.7.2 by selecting only the http/1.1 delivery protocol
   capability.  Only the second BaseAdvertisementObject in the full
   resource will be returned because the second object's capability is
   http/1.1 and https/1.1 delivery protocols, which is the superset of
   https/1.1 delivery protocol.

     POST /cdnifci/filtered HTTP/1.1
     Host: alto.example.com
     Accept: application/alto-cdni+json
     Content-Type: application/cdnifilter+json
     Content-Length: 176

     {
       "cdni-capabilities": [
         {
           "capability-type": "FCI.DeliveryProtocol",
           "capability-value": {
             "delivery-protocols": [ "https/1.1" ]
           }
         }
       ]
     }

     HTTP/1.1 200 OK
     Content-Length: 570
     Content-Type: application/alto-cdni+json

     {
       "meta": {
         "vtag": {
           "resource-id": "my-filtered-cdnifci",
           "tag": "da65eca2eb7a10ce8b059740b0b2e3f8eb1d4785"
         }
       },
       "cdni-advertisement": {
         "capabilities-with-footprints": [
           {
             "capability-type": "FCI.DeliveryProtocol",
             "capability-value": {
               "delivery-protocols": [
                 "https/1.1",
                 "http/1.1"
               ]
             },
             "footprints": [
               {
                 "footprint-type": "ipv4cidr",
                 "footprint-value": [ "198.51.100.0/24" ]
               }
             ]
           }
         ]
       }
     }

5.7.2.  Incremental Updates

   In this example, the ALTO client only cares about the updates of one
   advertisement object for delivery protocol capability whose value
   includes "https/1.1".  Thus, it adds its limitation of capabilities
   in "input" field of the POST request.

     POST /updates/cdnifci HTTP/1.1
     Host: fcialtoupdate.example.com
     Accept: text/event-stream,application/alto-error+json
     Content-Type: application/alto-updatestreamparams+json
     Content-Length: 346

     {
       "add": {
         "my-filtered-fci-stream": {
           "resource-id": "my-filtered-cdnifci",
           "input": {
             "cdni-capabilities": [
               {
                 "capability-type": "FCI.DeliveryProtocol",
                 "capability-value": {
                   "delivery-protocols": [ "https/1.1" ]
                 }
               }
             ]
           }
         }
       }
     }

     HTTP/1.1 200 OK
     Connection: keep-alive
     Content-Type: text/event-stream

     event: application/alto-updatestreamcontrol+json
     data: {"control-uri":
     data: "https://alto.example.com/updates/streams/3141592653590"}

     event: application/alto-cdni+json,my-filtered-fci-stream
     data: { ... filtered CDNI Advertisement resource ... }

     event: application/json-patch+json,my-filtered-fci-stream
     data: [
     data:   {
     data:     "op": "replace",
     data:     "path": "/meta/vtag/tag",
     data:     "value": "a10ce8b059740b0b2e3f8eb1d4785acd42231bfe"
     data:   },
     data:   { "op": "add",
     data:     "path":
     data:     "/cdni-advertisement/capabilities-with-footprints
     /0/footprints/0/footprint-value/-",
     data:     "value": "192.0.2.0/24"
     data:   }
     data: ]

6.  Query Footprint Properties Using ALTO Property Map Service

   Besides the requirement of retrieving footprints of given
   capabilities, another common requirement for uCDN is to query CDNI
   capabilities of given footprints.

   Considering each footprint as an entity with properties including
   CDNI capabilities, a natural way to satisfy this requirement is to
   use the ALTO property map as defined in [RFC9240].  This section
   describes how ALTO clients look up properties for individual
   footprints.  First, it describes how to represent footprint objects
   as entities in the ALTO property map.  Then it describes how to
   represent footprint capabilities as entity properties in the ALTO
   property map.  Finally, it provides examples of the full property map
   and the filtered property map supporting CDNI capabilities, and their
   incremental updates.

6.1.  Representing Footprint Objects as Property Map Entities

   A footprint object has two properties: footprint-type and footprint-
   value.  A footprint-value is an array of footprint values conforming
   to the specification associated with the registered footprint type
   ("ipv4cidr", "ipv6cidr", "asn", "countrycode", and "altopid").
   Considering each ALTO entity defined in [RFC9240] also has two
   properties: entity domain type and domain-specific identifier, a
   straightforward approach to represent a footprint as an ALTO entity
   is to represent its footprint-type as an entity domain type, and its
   footprint value as a domain-specific identifier.

   Each existing footprint type can be represented as an entity domain
   type as follows:

   *  According to [RFC9240], "ipv4" and "ipv6" are two predefined
      entity domain types, which can be used to represent "ipv4cidr" and
      "ipv6cidr" footprints respectively.  Note that both "ipv4" and
      "ipv6" domains can include not only hierarchical addresses but
      also individual addresses.  Therefore, a "ipv4cidr" or "ipv6cidr"
      footprint with the longest prefix can also be represented by an
      individual address entity.  When the uCDN receives a property map
      with individual addresses in an "ipv4" or "ipv6" domain, it can
      translate them as corresponding "ipv4cidr" or "ipv6cidr"
      footprints with the longest prefix.

   *  "pid" is also a predefined entity domain type, which can be used
      to represent "altopid" footprints.  Note that "pid" is a resource-
      specific entity domain.  To represent an "altopid" footprint, the
      specifying information resource of the corresponding "pid" entity
      domain MUST be the dependent network map used by the CDNI
      Advertisement resource providing this "altopid" footprint.

   *  However, no existing entity domain type can represent "asn" and
      "countrycode" footprints.  To represent footprint-type "asn" and
      "countrycode", this document registers two new entity domains in
      Section 7 in addition to the ones in [RFC9240].

   Here is an example of representing a footprint object of "ipv4cidr"
   type as a set of "ipv4" entities in the ALTO property map.  The
   representation of the footprint object of "ipv6cidr" type is similar.

   { "footprint-type": "ipv4cidr",
     "footprint-value": ["192.0.2.0/24", "198.51.100.0/24"]
   } --> "ipv4:192.0.2.0/24", "ipv4:198.51.100.0/24"

   And here is an example of the corresponding footprint object of
   "ipv4cidr" type represented by an individual address in an "ipv4"
   domain in the ALTO property map.  The translation of the entities in
   an "ipv6" domain is similar.

   "ipv4:203.0.113.100" --> {
     "footprint-type": "ipv4cidr",
     "footprint-value": ["203.0.113.100/32"]
   }

6.1.1.  ASN Domain

   The ASN domain associates property values with Autonomous Systems in
   the Internet.

6.1.1.1.  Entity Domain Type

   The entity domain type of the ASN domain is "asn" (in lowercase).

6.1.1.2.  Domain-Specific Entity Identifiers

   The entity identifier of an entity in an ASN domain MUST be encoded
   as a string consisting of the characters "as" (in lowercase) followed
   by the ASN [RFC6793] as a decimal number without leading zeros.

6.1.1.3.  Hierarchy and Inheritance

   There is no hierarchy or inheritance for properties associated with
   ASN.

6.1.2.  COUNTRYCODE Domain

   The COUNTRYCODE domain associates property values with countries.

6.1.2.1.  Entity Domain Type

   The entity domain type of the COUNTRYCODE domain is "countrycode" (in
   lowercase).

6.1.2.2.  Domain-Specific Entity Identifiers

   The entity identifier of an entity in a COUNTRYCODE domain is encoded
   as an ISO 3166-1 alpha-2 code [ISO3166-1] in lowercase.

6.1.2.3.  Hierarchy and Inheritance

   There is no hierarchy or inheritance for properties associated with
   country codes.

6.2.  Representing CDNI Capabilities as Property Map Entity Properties

   This document defines a new entity property type called "cdni-
   capabilities".  An ALTO server can provide a property map resource
   mapping the "cdni-capabilities" entity property type for a CDNI
   Advertisement resource that it provides to an "ipv4", "ipv6", "asn",
   or "countrycode" entity domain.

6.2.1.  Defining Information Resource Media Type for Property Type cdni-
        capabilities

   The entity property type "cdni-capabilities" allows defining
   resource-specific entity properties.  When resource-specific entity
   properties are defined with entity property type "cdni-capabilities",
   the defining information resource for a "cdni-capabilities" property
   MUST be a CDNI Advertisement resource provided by the ALTO server.
   The media type of the defining information resource for a "cdni-
   capabilities" property is therefore:

   application/alto-cdni+json

6.2.2.  Intended Semantics of Property Type cdni-capabilities

   The purpose of a "cdni-capabilities" property for an entity is to
   indicate all the CDNI capabilities that a corresponding CDNI
   Advertisement resource provides for the footprint represented by this
   entity.  Thus, the value of a "cdni-capabilities" property MUST be a
   JSON array.  Each element in a "cdni-capabilities" property MUST be a
   JSON object as format of CDNICapability (see Section 5.3).  The value
   of a "cdni-capabilities" property for an "ipv4", "ipv6", "asn",
   "countrycode", or "altopid" entity MUST include all the
   CDNICapability objects satisfying the following conditions: (1) they
   are provided by the defining CDNI Advertisement resource, and (2) the
   represented footprint object of this entity is in their footprint
   restrictions.

6.3.  Examples

   The following examples use the same IRD example given by
   Section 3.7.1.

6.3.1.  Property Map

   This example shows a full property map in which entities are
   footprints and entities' property is "cdni-capabilities".

    GET /propmap/full/cdnifci HTTP/1.1
    Host: alto.example.com
    Accept: application/alto-propmap+json,application/alto-error+json

    HTTP/1.1 200 OK
    Content-Length: 1522
    Content-Type: application/alto-propmap+json

    {
      "property-map": {
        "meta": {
          "dependent-vtags": [
            { "resource-id": "my-default-cdnifci",
              "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf62"}
          ]
        },
        "countrycode:us": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": ["http/1.1"]}}]
        },
        "ipv4:192.0.2.0/24": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": ["http/1.1"]}}]
        },
        "ipv4:198.51.100.0/24": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": ["https/1.1", "http/1.1"]}}]
        },
        "ipv4:203.0.113.0/24": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.AcquisitionProtocol",
              "capability-value": {
                "acquisition-protocols": ["http/1.1"]}}]
        },
        "ipv6:2001:db8::/32": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": ["http/1.1"]}}]
        },
        "asn:as64496": {
          "my-default-cdnifci.cdni-capabilities": [
            { "capability-type": "FCI.DeliveryProtocol",
              "capability-value": {
                "delivery-protocols": ["https/1.1", "http/1.1"]}}]
        }
      }
    }

6.3.2.  Filtered Property Map

   This example uses the filtered property map service to get "pid" and
   "cdni-capabilities" properties for two footprints "ipv4:192.0.2.0/24"
   and "ipv6:2001:db8::/32".

      POST /propmap/lookup/cdnifci-pid HTTP/1.1
      Host: alto.example.com
      Content-Type: application/alto-propmapparams+json
      Accept: application/alto-propmap+json,application/alto-error+json
      Content-Length: 181

      {
        "entities": [
          "ipv4:192.0.2.0/24",
          "ipv6:2001:db8::/32"
        ],
        "properties": [ "my-default-cdnifci.cdni-capabilities",
                        "my-default-networkmap.pid" ]
      }

    HTTP/1.1 200 OK
    Content-Length: 796
    Content-Type: application/alto-propmap+json

    {
      "property-map": {
        "meta": {
          "dependent-vtags": [
             {"resource-id": "my-default-cdnifci",
               "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf62"},
             {"resource-id": "my-default-networkmap",
               "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf63"}
          ]
        },
        "ipv4:192.0.2.0/24": {
          "my-default-cdnifci.cdni-capabilities": [
            {"capability-type": "FCI.DeliveryProtocol",
             "capability-value": {"delivery-protocols": ["http/1.1"]}}],
          "my-default-networkmap.pid": "pid1"
        },
        "ipv6:2001:db8::/32": {
          "my-default-cdnifci.cdni-capabilities": [
            {"capability-type": "FCI.DeliveryProtocol",
             "capability-value": {"delivery-protocols": ["http/1.1"]}}],
          "my-default-networkmap.pid": "pid3"
        }
      }
    }

6.3.3.  Incremental Updates

   In this example, the ALTO client is interested in updates for the
   properties "cdni-capabilities" and "pid" of two footprints
   "ipv4:192.0.2.0/24" and "countrycode:fr".

    POST /updates/properties HTTP/1.1
    Host: alto.example.com
    Accept: text/event-stream,application/alto-error+json
    Content-Type: application/alto-updatestreamparams+json
    Content-Length: 339

    {
      "add": {
        "fci-propmap-stream": {
          "resource-id": "filtered-cdnifci-property-map",
          "input": {
            "properties": [ "my-default-cdnifci.cdni-capabilities",
                            "my-default-networkmap.pid" ],
            "entities": [ "ipv4:192.0.2.0/24",
                          "ipv6:2001:db8::/32" ]
          }
        }
      }
    }

    HTTP/1.1 200 OK
    Connection: keep-alive
    Content-Type: text/event-stream

    event: application/alto-updatestreamcontrol+json
    data: {"control-uri":
    data: "https://alto.example.com/updates/streams/1414213562373"}

    event: application/alto-cdni+json,fci-propmap-stream
    data: { ... filtered property map ... }

    event: application/merge-patch+json,fci-propmap-stream
    data: {
    data:   "property-map": {
    data:     "meta": {
    data:       "dependent-vtags": [
    data:         { "resource-id": "my-default-cdnifci",
    data:           "tag": "2beeac8ee23c3dd1e98a73fd30df80ece9fa5627"},
    data:         { "resource-id": "my-default-networkmap",
    data:           "tag": "7915dc0290c2705481c491a2b4ffbec482b3cf63"}
    data:       ]
    data:     },
    data:     "ipv4:192.0.2.0/24": {
    data:       "my-default-cdnifci.cdni-capabilities": [
    data:         { "capability-type": "FCI.DeliveryProtocol",
    data:           "capability-value": {
    data:             "delivery-protocols": ["http/1.1", "https/1.1"]}}]
    data:     }
    data:   }
    data: }

    event: application/json-patch+json,fci-propmap-stream
    data: [
    data:   { "op": "replace",
    data:     "path": "/meta/dependent-vtags/0/tag",
    data:     "value": "61b23185a50dc7b334577507e8f00ff8c3b409e4"
    data:   },
    data:   { "op": "replace",
    data:     "path":
    data:     "/property-map/countrycode:fr/my-default-networkmap.pid",
    data:     "value": "pid5"
    data:   }
    data: ]

7.  IANA Considerations

   This document defines two new media types: "application/alto-
   cdni+json", as described in Section 7.1, and "application/
   cdnifilter+json", as described in Section 7.2.  It also defines a new
   CDNI metadata footprint type (Section 7.3), two new ALTO entity
   domain types (Section 7.4), and a new ALTO entity property type
   (Section 7.5).

7.1.  application/alto-cdni+json Media Type

   Type name:
      application

   Subtype name:
      alto-cdni+json

   Required parameters:
      N/A

   Optional parameters:
      N/A

   Encoding considerations:
      Encoding considerations are identical to those specified for the
      "application/json" media type.  See [RFC8259].

   Security considerations:
      Security considerations related to the generation and consumption
      of ALTO Protocol messages are discussed in Section 15 of
      [RFC7285].

   Interoperability considerations:
      N/A

   Published specification:
      Section 3 of RFC 9241

   Applications that use this media type:
      ALTO servers and ALTO clients [RFC7285] either stand alone or are
      embedded within other applications that provide CDNI interfaces
      for uCDNs or dCDNs.

   Fragment identifier considerations:
      N/A

   Additional information:
      Magic number(s):  N/A

      File extension(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      See Authors' Addresses section.

   Intended usage:
      COMMON

   Restrictions on usage:
      N/A

   Author:
      See Authors' Addresses section.

   Change controller:
      Internet Engineering Task Force (iesg@ietf.org)

7.2.  application/alto-cdnifilter+json Media Type

   Type name:
      application

   Subtype name:
      alto-cdnifilter+json

   Required parameters:
      N/A

   Optional parameters:
      N/A

   Encoding considerations:
      Encoding considerations are identical to those specified for the
      "application/json" media type.  See [RFC8259].

   Security considerations:
      Security considerations related to the generation and consumption
      of ALTO Protocol messages are discussed in Section 15 of
      [RFC7285].

   Interoperability considerations:
      N/A

   Published specification:
      Section 5 of RFC 9241

   Applications that use this media type:
      ALTO servers and ALTO clients [RFC7285] either stand alone or are
      embedded within other applications that provide CDNI interfaces
      for uCDNs or dCDNs and supports CDNI capability-based filtering.

   Fragment identifier considerations:
      N/A

   Additional information:
      Magic number(s):  N/A

      File extension(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      See Authors' Addresses section.

   Intended usage:
      COMMON

   Restrictions on usage:
      N/A

   Author:
      See Authors' Addresses section.

   Change controller:
      Internet Engineering Task Force (iesg@ietf.org)

7.3.  CDNI Metadata Footprint Types Registry

   This document updates the "CDNI Metadata Footprint Types" registry
   created by Section 7.2 of [RFC8006].  A new footprint type, which is
   listed in Table 1, has been registered.

      +================+=====================+=====================+
      | Footprint Type | Description         | Reference           |
      +================+=====================+=====================+
      | altopid        | A list of PID names | RFC 9241, Section 4 |
      +----------------+---------------------+---------------------+

                  Table 1: CDNI Metadata Footprint Type

7.4.  ALTO Entity Domain Types Registry

   This document updates the "ALTO Entity Domain Types" registry created
   by Section 11.2 of [RFC9240].  Two new entity domain types, which are
   listed in Table 2, have been registered.

    +=============+============+=============+=============+=========+
    | Identifier  | Entity     | Hierarchy   | Media Type  | Mapping |
    |             | Identifier | and         | of Defining | to ALTO |
    |             | Encoding   | Inheritance | Resource    | Address |
    |             |            |             |             | Type    |
    +=============+============+=============+=============+=========+
    | asn         | See RFC    | None        | None        | false   |
    |             | 9241,      |             |             |         |
    |             | Section    |             |             |         |
    |             | 6.1.1.2    |             |             |         |
    +-------------+------------+-------------+-------------+---------+
    | countrycode | See RFC    | None        | None        | false   |
    |             | 9241,      |             |             |         |
    |             | Section    |             |             |         |
    |             | 6.1.2.2    |             |             |         |
    +-------------+------------+-------------+-------------+---------+

               Table 2: Additional ALTO Entity Domain Types

7.5.  ALTO Entity Property Types Registry

   This document updates the "ALTO Entity Property Types" registry
   created by Section 11.3 of [RFC9240].  A new entity property type,
   which is listed in Table 3, has been registered.

      +===================+====================+===================+
      | Identifier        | Intended Semantics | Media Type of     |
      |                   |                    | Defining Resource |
      +===================+====================+===================+
      | cdni-capabilities | See RFC 9241,      | application/alto- |
      |                   | Section 6.2        | cdni+json         |
      +-------------------+--------------------+-------------------+

              Table 3: Additional ALTO Entity Property Type

8.  Security Considerations

   As an extension of the base ALTO Protocol [RFC7285], this document
   fits into the architecture of the base protocol, and hence Security
   Considerations of the base protocol (Section 15 of [RFC7285]) fully
   apply when this extension is provided by an ALTO server.

   In the context of CDNI Advertisement, the following security risk
   scenarios should be considered:

   *  Authenticity and integrity of ALTO information: an attacker may
      disguise itself as an ALTO server for a dCDN (e.g., by starting a
      man-in-the-middle attack) and provide false capabilities and
      footprints to a uCDN using the CDNI Advertisement Service.  Such
      false information may lead a uCDN to (1) select an incorrect dCDN
      to serve user requests or (2) skip uCDNs in good conditions.  To
      address this risk, protection strategies in Section 15.1.2 of
      [RFC7285] can be applied.

   *  Potential undesirable guidance from authenticated ALTO
      information: a dCDN can provide a uCDN with limited capabilities
      and smaller footprint coverage so that the dCDN can avoid
      transferring traffic for a uCDN that they should have to transfer.
      To reduce this risk, the protection strategies in Section 15.2.2
      of [RFC7285] can be considered.

   *  Confidentiality and privacy of ALTO information: footprint
      properties integrated with ALTO property maps may expose network
      location identifiers (e.g., IP addresses or fine-grained PIDs).
      To address this risk, the protection strategy for risk types (1)
      and (3) as described in Section 15.3 of [RFC7285] can be
      considered.

   *  For availability of ALTO services, an attacker may conduct
      service-degradation attacks using services defined in this
      document to disable ALTO services of a network.  It may request
      potentially large, full CDNI Advertisement resources from an ALTO
      server in a dCDN continuously in order to consume the bandwidth
      resources of that ALTO server.  It may also query filtered
      property map services with many smaller individual footprints in
      order to consume the computation resources of the ALTO server.  To
      mitigate these risks, the protection strategies in Section 15.5.2
      of [RFC7285] can be applied.

   Although protection strategies as described in Section 15 of
   [RFC7285] should be applied to address aforementioned security and
   privacy considerations, two special cases need to be included as
   follows:

   *  As required by Section 7 of [RFC8008],

      |  All protocols that implement these capabilities and footprint
      |  advertisement objects are REQUIRED to provide integrity and
      |  authentication services.

      Therefore, the uCDN (ALTO Client) MUST be authenticated to the
      dCDN (ALTO Server).  And the dCDN (ALTO Server) MUST support HTTP
      Digest Authentication and MAY also support TLS mutual
      authentication.  The authentication method will need to be
      negotiated out of band and is out of scope for this document, as
      is the approach for provisioning and managing these credentials.

   *  One specific information leakage risk introduced by this document
      cannot be addressed by these strategies.  In particular, if a dCDN
      signs agreements with multiple uCDNs without any isolation, this
      dCDN may disclose extra information of one uCDN to another one.
      In that case, one uCDN may redirect requests which should not have
      to be served by this dCDN to it.

      To reduce the risk, a dCDN SHOULD isolate full/filtered CDNI
      Advertisement resources for different uCDNs.  It could consider
      generating URIs of different full/filtered CDNI Advertisement
      resources by hashing its company ID, a uCDN's company ID as well
      as their agreements.  A dCDN SHOULD avoid exposing all full/
      filtered CDNI Advertisement resources in one of its IRDs.

9.  References

9.1.  Normative References

   [ISO3166-1]
              International Organization for Standardization, "Codes for
              the representation of names of countries and their
              subdivisions -- Part 1: Country codes", ISO 3166-1:2020,
              August 2020.

   [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>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <https://www.rfc-editor.org/info/rfc6793>.

   [RFC7285]  Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
              Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
              "Application-Layer Traffic Optimization (ALTO) Protocol",
              RFC 7285, DOI 10.17487/RFC7285, September 2014,
              <https://www.rfc-editor.org/info/rfc7285>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [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>.

   [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>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8895]  Roome, W. and Y. Yang, "Application-Layer Traffic
              Optimization (ALTO) Incremental Updates Using Server-Sent
              Events (SSE)", RFC 8895, DOI 10.17487/RFC8895, November
              2020, <https://www.rfc-editor.org/info/rfc8895>.

   [RFC9240]  Roome, W., Randriamasy, S., Yang, Y., Zhang, J., and K.
              Gao, "ALTO Extension: Entity Property Maps", RFC 9240,
              DOI 10.17487/RFC9240, May 2022,
              <https://www.rfc-editor.org/info/rfc9240>.

9.2.  Informative References

   [ALTO-PATH-VECTOR]
              Gao, K., Lee, Y., Randriamasy, S., Yang, Y. R., and J. J.
              Zhang, "An ALTO Extension: Path Vector", Work in Progress,
              Internet-Draft, draft-ietf-alto-path-vector-25, 20 March
              2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
              alto-path-vector-25>.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              DOI 10.17487/RFC5693, October 2009,
              <https://www.rfc-editor.org/info/rfc5693>.

   [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>.

   [RFC7971]  Stiemerling, M., Kiesel, S., Scharf, M., Seidel, H., and
              S. Previdi, "Application-Layer Traffic Optimization (ALTO)
              Deployment Considerations", RFC 7971,
              DOI 10.17487/RFC7971, October 2016,
              <https://www.rfc-editor.org/info/rfc7971>.

   [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>.

Acknowledgments

   The authors thank Matt Caulfield, Danny Alex Lachos Perez, Daryl
   Malas, and Sanjay Mishra for their timely reviews and invaluable
   comments.  Big thanks also to the ALTO WG Chairs (Qin Wu and Vijay
   Gurbani), all the directorate reviewers, and the IESG reviewers
   (Martin Duke, Erik Kline, Martin Vigoureux, Murray Kucherawy, Roman
   Danyliw, Zaheduzzaman Sarker, Éric Vyncke, and Francesca Palombini),
   for their thorough reviews, discussions, guidance, and shepherding,
   which further improve this document.

   Jan Seedorf has been partially supported by the GreenICN project
   (GreenICN: Architecture and Applications of Green Information Centric
   Networking), a research project supported jointly by the European
   Commission under its 7th Framework Program (contract no. 608518) and
   the National Institute of Information and Communications Technology
   (NICT) in Japan (contract no. 167).  The views and conclusions
   contained herein are those of the authors and should not be
   interpreted as necessarily representing the official policies or
   endorsements, either expressed or implied, of the GreenICN project,
   the European Commission, or NICT.

   This document has also been supported by the Coordination Support
   Action entitled 'Supporting European Experts Presence in
   International Standardisation Activities in ICT' (StandICT.eu
   <https://www.standict.eu/>) funded by the European Commission under
   the Horizon 2020 Programme with Grant Agreement no. 780439.  The
   views and conclusions contained herein are those of the authors and
   should not be interpreted as necessarily representing the official
   policies or endorsements, either expressed or implied, of the
   European Commission.

Contributors

   Xiao Shawn Lin
   Huawei
   2222 Newjinqiao Rd
   Shanghai
   200125
   China
   Phone: +86-15316812351
   Email: x.shawn.lin@gmail.com

Authors' Addresses

   Jan Seedorf
   HFT Stuttgart - Univ. of Applied Sciences
   Schellingstrasse 24
   70174 Stuttgart
   Germany
   Phone: +49-0711-8926-2801
   Email: jan.seedorf@hft-stuttgart.de

   Y. Richard Yang
   Yale University
   51 Prospect Street
   New Haven, CT 06511
   United States of America
   Phone: +1-203-432-6400
   Email: yry@cs.yale.edu
   URI:   http://www.cs.yale.edu/~yry/

   Kevin J. Ma
   Ericsson
   43 Nagog Park
   Acton, MA 01720
   United States of America
   Phone: +1-978-844-5100
   Email: kevin.j.ma.ietf@gmail.com

   Jon Peterson
   NeuStar
   1800 Sutter St., Suite 570
   Concord, CA 94520
   United States of America
   Email: jon.peterson@neustar.biz

   Jingxuan Jensen Zhang
   Tongji University
   4800 Cao'an Hwy
   Shanghai
   201804
   China
   Email: jingxuan.zhang@tongji.edu.cn