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<?rfc tocdepth="4"?>
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<rfc category="std" docName="draft-ietf-cdni-metadata-08" ipr="trust200902">
  <front>
    <title abbrev="CDN Interconnection Metadata">CDN Interconnection
    Metadata</title>
    <author fullname="Ben Niven-Jenkins" initials="B" surname="Niven-Jenkins">
      <organization>Velocix (Alcatel-Lucent)</organization>

      <address>
        <postal>
          <street>3 Ely Road</street>

          <city>Milton</city>

          <region>Cambridge</region>

          <code>CB24 6AA</code>

          <country>UK</country>
        </postal>

        <email>ben@velocix.com</email>
      </address>
    </author>

    <author fullname="Rob Murray" initials="R" surname="Murray">
      <organization>Velocix (Alcatel-Lucent)</organization>

      <address>
        <postal>
          <street>3 Ely Road</street>

          <city>Milton</city>

          <region>Cambridge</region>

          <code>CB24 6AA</code>

          <country>UK</country>
        </postal>

        <email>rmurray@velocix.com</email>
      </address>
    </author>

    <author fullname="Matt Caulfield" initials="M" surname="Caulfield">
      <organization>Cisco Systems</organization>

      <address>
        <postal>
          <street>1414 Massachusetts Avenue</street>

          <city>Boxborough</city>

          <region>MA</region>

          <code>01719</code>

          <country>USA</country>
        </postal>

        <phone>+1 978 936 9307</phone>

        <email>mcaulfie@cisco.com</email>
      </address>
    </author>

    <author fullname="Kevin J. Ma" initials="K.J." surname="Ma">
      <organization>Ericsson</organization>

      <address>
        <postal>
          <street>43 Nagog Park</street>

          <city>Acton</city>

          <region>MA</region>

          <code>01720</code>

          <country>USA</country>
        </postal>

        <phone>+1 978-844-5100</phone>

        <email>kevin.j.ma@ericsson.com</email>
      </address>
    </author>

    <date/>

    <abstract>
      <t>The CDNI Metadata interface enables interconnected CDNs to exchange
      content distribution metadata in order to enable content acquisition and
      delivery. The CDNI metadata associated with a piece of content provides
      a downstream CDN with sufficient information for the downstream CDN to
      service content requests on behalf of an upstream CDN. This document
      describes both a base set of CDNI metadata and the protocol for
      exchanging that metadata.</t>
    </abstract>

    <note title="Requirements Language">
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
      document are to be interpreted as described in <xref
      target="RFC2119">RFC 2119</xref>.</t>
    </note>
  </front>

  <middle>
    <section title="Introduction">
      <t>Content Delivery Networks Interconnection (CDNI) (<xref
      target="RFC6707"/>) enables a downstream CDN to service content requests
      on behalf of an upstream CDN.</t>

      <t>The CDNI Metadata interface is discussed in <xref
      target="I-D.ietf-cdni-framework"/> along with four other interfaces that
      may be used to compose a CDNI solution (CDNI Control interface, CDNI
      Request Routing Redirection interface, CDNI Footprint &amp; Capabilities
      Advertisement interface and CDNI Logging interface). <xref
      target="I-D.ietf-cdni-framework"/> describes each interface, and the
      relationships between them. The requirements for the CDNI metadata
      interface are specified in <xref
      target="I-D.ietf-cdni-requirements"/>.</t>

      <t>The CDNI metadata associated with a piece of content (or with a set
      of content) provides a downstream CDN with sufficient information for
      servicing content requests on behalf of an upstream CDN in accordance
      with the policies defined by the upstream CDN.</t>

      <t>This document focuses on the CDNI Metadata interface which enables a
      downstream CDN to obtain CDNI Metadata from an upstream CDN so that the
      downstream CDN can properly process and respond to:</t>

      <t><list style="symbols">
          <t>Redirection requests received over the CDNI Request Routing
          Redirection interface.</t>

          <t>Content requests received directly from User Agents.</t>
        </list></t>

      <t>Specifically, this document specifies:</t>

      <t><list style="symbols">
          <t>A data structure for mapping content requests and redirection
          requests to CDNI Metadata objects (<xref target="data-model"/> and
          <xref target="structural-objects"/>).</t>

          <t>An initial set of CDNI Generic Metadata objects (<xref
          target="property-objects"/>).</t>

          <t>A RESTful web service for the transfer of CDNI Metadata (<xref
          target="metadata-interface"/>).</t>
        </list></t>

      <section anchor="terminology" title="Terminology">
        <t>This document reuses the terminology defined in <xref
        target="RFC6707"/>.</t>

        <t>Additionally, the following terms are used throughout this document
        and are defined as follows:<list style="symbols">
            <t>Object - a collection of properties</t>

            <t>Property - a key and value pair where the key is a property
            name and the value is the property value or an object.</t>
          </list></t>
      </section>

      <section title="Supported Metadata Capabilities">
        <t>Only the metadata for a small set of initial capabilities is
        specified in this document. This set provides the minimum amount of
        metadata for basic CDN interoperability while still meeting the
        requirements set forth by <xref
        target="I-D.ietf-cdni-requirements"/>.</t>

        <t>The following high-level functionality is configured via the
        metadata described in <xref
        target="abstract-metadata-description"/>:</t>

        <t><list style="symbols">
            <t>Acquisition Source: Metadata for allowing a dCDN to fetch
            content from a uCDN.</t>

            <t>Delivery Access Control: Metadata for restricting (or
            permitting) access to content based on any of the following
            factors:<list style="symbols">
                <t>Location</t>

                <t>Time Window</t>

                <t>Delivery Protocol</t>
              </list></t>
          </list><list style="symbols">
            <t>Delivery Authorization: Metadata for authorizing dCDN user
            agent requests.</t>

            <t>Cache Control: Metadata for controlling cache behavior of the
            dCDN.</t>
          </list></t>

        <t>The metadata encoding described by this document is extensible in
        order to allow for future additions to this list.</t>

        <t>This document supports HTTPv1.1 for delivery and both HTTPv1.1 and
        HTTPv1.1. over TLS for acquisition. All metadata is described in a
        protocol-agnostic manner.</t>

        <t>Supporting unencrypted HTTPv2.0 for delivery (or unencrypted
        HTTPv2.0 or HTTPv2.0 over TLS for acquisition) only requires the
        registration of these protocol names in the CDNI Metadata Protocol
        Sub-Registry.</t>

        <t>Supporting HTTPv1.1 over TLS or HTTPv2.0 over TLS for delivery
        requires specifying additional metadata objects to carry the
        properties required to establish a TLS session, for example metadata
        to describe the certificate to use as part of the TLS
        handshake.</t>
      </section>
    </section>

    <section title="Design Principles">
      <t>The CDNI Metadata interface was designed to achieve the following
      objectives:</t>

      <t><list style="numbers">
          <t>Cacheability of CDNI metadata objects.</t>

          <t>Deterministic mapping from redirection requests and content
          requests to CDNI metadata properties.</t>

          <t>Support for DNS redirection as well as application-specific
          redirection (for example HTTP redirection).</t>

          <t>Minimal duplication of CDNI metadata.</t>

          <t>Leveraging of existing protocols.</t>
        </list></t>

      <t>Cacheability improves the latency of acquiring metadata while
      maintaining its freshness, and therefore improves the latency of serving
      content requests and redirection requests, without sacrificing accuracy.
      The CDNI Metadata interface uses HTTP and its existing caching
      mechanisms to achieve CDNI metadata cacheability.</t>

      <t>Deterministic mappings from content to metadata properties eliminates
      ambiguity and ensures that policies are applied consistently by all
      downstream CDNs.</t>

      <t>Support for both HTTP and DNS redirection ensures that the CDNI
      Metadata interface can be used for HTTP and DNS redirection and also
      meets the same design principles for both HTTP and DNS based redirection
      schemes.</t>

      <t>Minimal duplication of CDNI metadata provides space efficiency on
      storage in the CDNs, on caches in the network, and across the network
      between CDNs.</t>

      <t>Leveraging existing protocols avoids reinventing common mechanisms
      such as data structure encoding (e.g., JSON) and data transport
      (e.g., HTTP).</t>
    </section>

    <section anchor="data-model" title="CDNI Metadata Data Model">
      <t>The CDNI Metadata Model describes a data structure for mapping
      redirection requests and content requests to metadata properties.
      Metadata properties describe how to acquire content from an upstream
      CDN, authorize access to content, and deliver content from a downstream
      CDN. The data model relies on the assumption that these metadata
      properties may be aggregated based on the hostname of the content and
      subsequently on the resource path of the content. The data model
      associates a set of CDNI Metadata properties with a Hostname to form a
      default set of metadata properties for content delivered on behalf of
      that Hostname. That default set of metadata properties can be overridden
      by properties that apply to specific paths within a URI.</t>

      <t>Different Hostnames and URI paths will be associated with different
      sets of CDNI Metadata properties in order to describe the required
      behaviour when a dCDN surrogate is processing User Agent requests for
      content at that Hostname or URI path. As a result of this structure,
      significant commonality may exist between the CDNI Metadata properties
      specified for different Hostnames, different URI paths within a Hostname
      and different URI paths on different Hostnames. For example the
      definition of which User Agent IP addresses should be treated as being
      grouped together into a single network or geographic location is likely
      to be common for a number of different Hostnames. Another example is
      that although a uCDN is likely to have several different policies
      configured to express geo-blocking rules, it is likely that a single
      geo-blocking policy would be applied to multiple Hostnames delivered
      through the CDN.</t>

      <t>In order to enable the CDNI Metadata for a given Hostname or URI Path
      to be decomposed into sets of CDNI Metadata properties that can be
      reused by multiple Hostnames and URI Paths, the CDNI Metadata interface
      specified in this document splits the CDNI Metadata into a number of
      objects. Efficiency is improved by enabling a single CDNI Metadata
      object (that is shared across Hostname and/or URI paths) to be retrieved
      and stored by a dCDN once, even if it is referenced by the CDNI Metadata
      of multiple Hostnames or of multiple URI paths.</t>

      <t><xref target="hostindex-intro"/> introduces a high level description
      of the HostIndex, HostMetadata and PathMetadata objects and describes
      the relationships between those objects.</t>

      <t><xref target="other-objects-intro"/> introduces a high level
      description of the CDNI GenericMetadata object which represents the
      level at which CDNI Metadata override occurs between HostMetadata and
      PathMetadata objects.</t>

      <t><xref target="abstract-metadata-description"/> describes in detail
      the specific CDNI Metadata objects and properties which may be contained
      within a CDNI GenericMetadata object.</t>

      <section anchor="hostindex-intro"
               title="HostIndex, HostMetadata and PathMetadata objects">
        <t>A HostIndex object contains (or references) a list of Hostnames
        (and/or IP addresses) for which content requests may be delegated to
        the downstream CDN. The HostIndex is the starting point for accessing
        the uCDN CDNI Metadata data store. It enables the dCDN to
        deterministically discover, on receipt of a User Agent request for
        content, which other CDNI Metadata objects it requires in order to
        deliver the requested content.</t>

        <t>The HostIndex links Hostnames (and/or IP addresses) to HostMetadata
        objects via HostMatch objects. HostMetadata objects contain (or
        reference) the default CDNI Metadata required to serve content for
        that host. When looking up CDNI Metadata, the downstream CDN looks up
        the requested Hostname (or IP address) against the HostMatch entries
        in the HostIndex, from there it can find HostMetadata which describes
        properties for a host and PathMetadata which may override those
        properties for given URI paths within the host.</t>

        <t>HostMetadata and PathMetadata objects may also contain PathMatch
        objects which in turn contain PathMetadata objects. PathMetadata objects
        override the CDNI Metadata in the HostMetadata object or one or more
        preceding PathMetadata objects with more specific CDNI Metadata that
        applies to content requests matching the pattern defined in that
        PathMatch object.</t>

        <t>For the purposes of retrieving CDNI Metadata, all other required
        CDNI Metadata objects and their properties are discoverable from the
        appropriate HostMetadata, PathMatch and PathMetadata objects for the
        requested content.</t>

        <t>The relationships between the HostIndex, HostMatch, HostMetadata,
        PathMatch and PathMetadata objects are described in <xref
        target="metadata-model-figure-top"/>.</t>

        <t><figure anchor="metadata-model-figure-top"
            title="Relationships between CDNI Metadata Objects (Diagram Representation)">
            <artwork><![CDATA[
+---------+      +---------+      +------------+
|HostIndex+-(*)->|HostMatch+-(1)->|HostMetadata+-------(*)------+
+---------+      +---------+      +------+-----+                |
                                         |                      |
                                        (*)                     |
                                         |                      V
--> Contains or References               V         ******************
(1) One and only one                +---------+    *Generic Metadata*
(*) Zero or more               +--->|PathMatch|    *     Objects    *
                               |    +----+---++    ******************
                               |         |   |                  ^
                              (*)       (1) (1) +------------+  |
                               |         |   +->|PatternMatch|  |
                               |         V      +------------+  |
                               |  +------------+                |
                               +--+PathMetadata+-------(*)------+
                                  +------------+
]]></artwork>
          </figure></t>

        <t>The relationships in <xref target="metadata-model-figure-top"/> are
        also represented in tabular format in <xref
        target="metadata-model-table"/> below.</t>

        <texttable anchor="metadata-model-table"
                   title="Relationships between CDNI Metadata Objects (Table Representation)">
          <ttcol>Data Object</ttcol>

          <ttcol>Objects it contains or references</ttcol>

          <c>HostIndex</c>

          <c>0 or more HostMatch objects.</c>

          <c>HostMatch</c>

          <c>1 HostMetadata object.</c>

          <c>HostMetadata</c>

          <c>0 or more PathMatch objects. 0 or more GenericMetadata
          objects.</c>

          <c>PathMatch</c>

          <c>1 PatternMatch object. 1 PathMetadata object.</c>

          <c>PatternMatch</c>

          <c>Does not contain or reference any other objects.</c>

          <c>PathMetadata</c>

          <c>0 or more PathMatch objects. 0 or more GenericMetadata
          objects.</c>
        </texttable>

        <t>The table below describes the HostIndex, HostMetadata and
        PathMetadata objects in more detail.</t>

        <texttable anchor="hostindex-objects-table"
                   title="HostIndex, HostMetadata and PathMetadata CDNI Metadata Objects">
          <ttcol>Data Object</ttcol>

          <ttcol>Description</ttcol>

          <c>HostIndex</c>

          <c>A HostIndex object lists HostMatch objects</c>

          <c>HostMatch</c>

          <c>A HostMatch object defines a hostname (or IP address) to match
          against a requested host, and contains (or references) a
          HostMetadata object which contains (or references) CDNI Metadata
          objects to be applied when a request matches against the hostname.
          For example, if "example.com" is a content provider, a HostMatch
          object may include an entry for "example.com" with the URI of the
          associated HostMetadata object.</c>

          <c>HostMetadata</c>

          <c>A HostMetadata object contains (or references) the default CDNI
          Metadata objects for content served from that host, i.e., the CDNI
          Metadata objects for content requests that do not match any of the
          PathMatch objects contained (or referenced) by that HostMetadata
          object. For example, a HostMetadata object may describe the metadata
          properties which apply to "example.com" and may contain PathMatches
          for "example.com/movies/*" and "example.com/music/*" which reference
          corresponding PathMetadata objects that contain the CDNI Metadata
          objects for those more specific URI paths.</c>

          <c>PathMatch</c>

          <c>A PathMatch object defines a pattern (inside a PatternMatch
          object which PathMatch object contains or references) to match
          against the requested URI path, and contains (or references) a
          PathMetadata object which contains (or references) the CDNI Metadata
          objects to be applied when a content request matches against the
          defined URI path pattern. For example, a PathMatch object may
          include a PatternMatch object containing a pattern for the path
          "/movies/*" and may reference a PathMetadata object which contains
          (or references) the CDNI Metadata for content with that path.</c>

          <c>PatternMatch</c>

          <c>A PatternMatch object contains the pattern string and flags that
          describe the URI path that a PathMatch applies to.</c>

          <c>PathMetadata</c>

          <c>A PathMetadata object contains (or references) the CDNI
          GenericMetadata objects for content served with the associated URI
          path (defined in a PathMatch object). A PathMetadata object may also
          contain (or reference) PathMatch objects in order to recursively
          define more specific URI paths that require different (e.g., more
          specific) CDNI Metadata to this one. For example, the PathMetadata
          object which applies to "example.com/movies/*" may describe CDNI
          Metadata which apply to that resource path and may contain a
          PathMatch object for "example.com/movies/hd/*" which would reference
          the corresponding PathMetadata object for the
          "example.com/movies/hd/" path prefix.</c>

          <c>GenericMetadata</c>

          <c>A GenericMetadata object contains (or references) individual CDNI
          Metadata objects which define the specific policies and attributes
          needed to properly deliver the associated content. For example, a
          GenericMetadata object may describe the source from which a CDN may
          acquire a piece of content. The GenericMetadata object is an atomic
          unit that may be referenced by HostMetadata and/or PathMetadata
          objects, but SHOULD NOT contain references to other CDNI Metadata
          objects. The member objects of a specific CDNI Metadata object MAY
          be referenced by the GenericMetadata object.</c>
        </texttable>

        <t/>
      </section>

      <section anchor="other-objects-intro"
               title="Generic CDNI Metadata Object Properties">
        <t>The HostMetadata and PathMetadata objects contain or can reference
        other CDNI Metadata objects that contain properties which describe how
        User Agent requests for content should be processed, for example where
        to acquire the content, authorization rules that should be applied,
        delivery location restrictions and so on. Each such CDNI Metadata
        object is a specialization of a CDNI GenericMetadata object. The
        GenericMetadata object abstracts the basic information required for
        Metadata override and Metadata distribution, from the specifics of any
        given property (e.g., property semantics, enforcement options,
        etc.).</t>

        <t>The GenericMetadata object defines the type of properties contained
        within it as well as whether or not the properties are
        "mandatory-to-enforce". If the dCDN does not understand or support the
        property type and the property type is "mandatory-to-enforce", the
        dCDN MUST NOT serve the content to the User Agent. If the dCDN does
        not understand or support the property type and the property type is
        not "mandatory-to-enforce", then that GenericMetadata object may be
        safely ignored and the dCDN MUST process the content request in
        accordance with the rest of the CDNI metadata.</t>

        <t>Although a CDN MUST NOT serve content to a User Agent if a
        "mandatory-to-enforce" property cannot be enforced, it may be
        "safe-to-redistribute" that metadata to another CDN without
        modification. For example, in the cascaded CDN case, a transit CDN may
        pass through "mandatory-to-enforce" metadata to a downstream CDN. For
        Metadata which does not require customization or translation (i.e.,
        metadata that is "safe-to-redistribute"), the data representation
        received off the wire MAY be stored and redistributed without being
        natively understood or supported by the transit CDN.  However, for
        Metadata which requires translation, transparent redistribution of the
        uCDN Metadata values may not be appropriate. Certain Metadata may be
        safely, though possibly not optimally, redistributed unmodified. For
        example, source acquisition address may not be optimal if
        transparently redistributed, but may still work.</t>

        <t>Redistribution safety MUST be specified for each GenericMetadata.
        If a CDN does not understand or support a given GenericMetadata
        property type and the property type is not "safe-to-redistribute",
        before redistributing the metadata, the CDN MUST set the
        "incomprehensible" flag for the GenericMetadata property that it did
        not understand and was marked as not "safe-to-redistribute". The
        "incomprehensible" flag signals to a dCDN that the metadata was not
        properly transformed by the transit CDN. A CDN MUST NOT attempt to use
        metadata that has been marked as "incomprehensible" by a uCDN.</t>

        <t>Transit CDNs MUST NOT change the value of "mandatory-to-enforce" or
        "safe-to-redistribute" when propagating metadata to a dCDN. Although a
        transit CDN may set the value of "incomprehensible" to true, a transit
        CDN MUST NOT change the value of "incomprehensible" from true to
        false.</t>

        <t>The following table describes the action to be taken by a transit
        CDN (tCDN) for the different "mandatory-to-enforce" (MtE) and
        "safe-to-redistribute" (StR) cases, when the tCDN either does or does
        not understand the metadata in question:</t>

        <texttable>
          <ttcol>MtE</ttcol>

          <ttcol>StR</ttcol>

          <ttcol>Metadata Understood</ttcol>

          <ttcol>Actions</ttcol>

          <c>False</c>

          <c>True</c>

          <c>True</c>

          <c>Can serve and redistribute.</c>

          <c>False</c>

          <c>True</c>

          <c>False</c>

          <c>Can serve and redistribute.</c>

          <c>False</c>

          <c>False</c>

          <c>False</c>

          <c>Can serve. MUST set "incomprehensible" to True when
          redistributing.</c>

          <c>False</c>

          <c>False</c>

          <c>True</c>

          <c>Can serve. Can redistribute either by transforming not StR
          metadata (if the CDN know how to do so safely), otherwise MUST set
          "incomprehensible" to True when redistributing.</c>

          <c>True</c>

          <c>True</c>

          <c>True</c>

          <c>Can serve and redistribute.</c>

          <c>True</c>

          <c>True</c>

          <c>False</c>

          <c>MUST NOT serve but can redistribute.</c>

          <c>True</c>

          <c>False</c>

          <c>True</c>

          <c>Can serve and redistribute.</c>

          <c>True</c>

          <c>False</c>

          <c>False</c>

          <c>MUST NOT serve. MUST set "incomprehensible" to True when
          redistributing.</c>
        </texttable>

        <t>The following table describes the action to be taken by a dCDN for
        the different "mandatory-to-enforce" (MtE)
        and "incomprehensible" (Incomp) cases, when the dCDN either does
        or does not understand the metadata in question:</t>

        <texttable>
          <ttcol>MtE</ttcol>

          <ttcol>Metadata Understood</ttcol>

          <ttcol>Incomp</ttcol>

          <ttcol>Actions</ttcol>

          <c>False</c>

          <c>True</c>

          <c>False</c>

          <c>Can serve.</c>

          <c>False</c>

          <c>True</c>

          <c>True</c>

          <c>Can serve but MUST NOT interpret/apply any metadata marked
          incomprehensible.</c>

          <c>False</c>

          <c>False</c>

          <c>False</c>

          <c>Can serve.</c>

          <c>False</c>

          <c>False</c>

          <c>True</c>

          <c>Can serve but MUST NOT interpret/apply any metadata marked
          incomprehensible.</c>

          <c>True</c>

          <c>True</c>

          <c>False</c>

          <c>Can serve.</c>

          <c>True</c>

          <c>True</c>

          <c>True</c>

          <c>Can serve but MUST NOT interpret/apply any metadata marked
          incomprehensible.</c>

          <c>True</c>

          <c>False</c>

          <c>False</c>

          <c>MUST NOT serve.</c>

          <c>True</c>

          <c>False</c>

          <c>True</c>

          <c>MUST NOT serve.</c>

        </texttable>

        <t/>
      </section>

      <section anchor="metadata-inheritance"
               title="Metadata Inheritance and Override">
        <t>In the data model, a HostMetadata object may contain (or reference)
        multiple PathMetadata objects (via PathMatch objects). Each
        PathMetadata object may in turn contain (or reference) other
        PathMetadata objects. HostMetadata and PathMetadata objects form an
        inheritance tree where each node in the tree inherits or overrides the
        property values set by its parent.</t>

        <t>GenericMetadata objects of a given type override all
        GenericMetadata objects of the same type previously defined by any
        parent object in the tree. GenericMetadata objects of a given type
        previously defined by a parent object in the tree are inherited when
        no object of the same type is defined by the child object. For
        example, if HostMetadata for the host "example.com" contains
        GenericMetadata objects of type LocationACL and TimeWindowACL, while a
        PathMetadata object which applies to "example.com/movies/*" defines an
        alternate GenericMetadata object of type TimeWindowACL, then: <list
            style="symbols">
            <t>the TimeWindowACL defined in the PathMetadata would override
            the TimeWindowACL defined in the HostMetadata for all User Agent
            requests for content under "example.com/movies", and</t>

            <t>the LocationACL defined in the HostMetadata would be inherited
            for all User Agent requests for content under
            "example.com/movies".</t>

          <t>A single HostMetadata or PathMetadata object SHOULD NOT contain
            multiple GenericMetadata objects of the same type. If a list of
            GenericMetadata contains objects of duplicate types, the receiver
            MUST ignore all but the first object of each type. </t>
        </list></t>

        <t></t>
      </section>
    </section>

    <section anchor="abstract-metadata-description"
             title="Encoding-Independent CDNI Metadata Object Descriptions">
      <t><xref target="structural-objects"/> provides the definitions of each
      object type declared in <xref target="data-model"/>. These objects are
      described as structural objects as they provide the structure for the
      inheritance tree and identify which specific properties apply to a
      given User Agent content request.</t>

      <t><xref target="property-objects"/> provides the definitions for a base
      set of core metadata objects which may be contained within a
      GenericMetadata object. These objects are described as property objects,
      as they define the structure, semantics, and enforcement options for
      specific properties of the metadata being described. Property objects
      govern how User Agent requests for content are handled. Property objects
      may be composed of, or contain references to, other property sub-objects
      (i.e., property objects contained within or referenced by the property
      object that refers to that property sub-object). In those cases the
      value of the property sub-objects can be either a complete serialized
      representation of the sub-object, or a Link object that contains a URI
      and relationship that can be dereferenced to retrieve the complete
      serialized representation of the property sub-object.</t>

      <t><xref target="extensibility"/> discusses the ability to extend the
      base set of metadata objects specified in this document with additional
      standards based or vendor specific property objects that may be defined
      in the future in separate documents.</t>

      <t>Downstream CDNs MUST support parsing of all CDNI metadata objects
      specified in this document. A dCDN does not have to implement the
      underlying functionality represented by the metadata object,
      though that may
      restrict the content that a given dCDN can serve. uCDNs as generators of
      CDNI Metadata only need to support generating the CDNI metadata that
      they need in order to express the policies and treatment
      required by the content they are describing.</t>

      <t>Note: In the following sections, the term "mandatory-to-specify" is
      used to convey which property sub-objects MUST be specified for a given
      structural or property object. When mandatory-to-specify is set to true
      on a sub-object, it implies that if the property object containing that
      property sub-object is specified, then the mandatory-to-specify property
      sub-object MUST also be specified, e.g., a HostMatch property object
      without a host to match against does not make sense, therefore, the host
      is mandatory-to-specify inside a HostMatch property object.</t>

      <section anchor="structural-objects"
               title="Descriptions of the CDNI Structural Metadata Objects">
        <t>Each of the sub-sections below describe the structural objects
        defined in <xref target="hostindex-objects-table"/>.</t>

        <section anchor="HostIndex" title="HostIndex">
          <t>The HostIndex object is the entry point into the CDNI Metadata
          hierarchy. It contains (or references) a list of HostMatch objects.
          An incoming content request is checked against the hostname (or
          IP address) specified by
          each of the listed HostMatch objects to find the HostMatch object
          which applies to the request.</t>

          <t><list style="empty">
              <t>Property: hosts<list style="empty">
                  <t>Description: List of HostMatch objects, in priority
                  order.</t>

                  <t>Type: List of HostMatch objects</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="HostMatch" title="HostMatch">
          <t>The HostMatch object contains a hostname or IP address to match
          against content requests. The HostMatch object also contains or
          references a HostMetadata object to apply if a match is found.</t>

          <t><list style="empty">
              <t>Property: host<list style="empty">
                  <t>Description: String (hostname or IP address) to match
                  against the requested host.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: host-metadata<list style="empty">
                  <t>Description: CDNI Metadata to apply when delivering
                  content that matches this host.</t>

                  <t>Type: HostMetadata</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="HostMetadata" title="HostMetadata">
          <t>A HostMetadata object contains (or references) the CDNI Metadata
          properties for content served for a particular host (defined
          in the HostMatch object) and possibly child PathMatch objects.</t>

          <t><list style="empty">
              <t>Property: metadata<list style="empty">
                  <t>Description: List of host related metadata.</t>

                  <t>Type: List of GenericMetadata objects</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: paths<list style="empty">
                  <t>Description: Path specific rules. Path patterns
                  (PathMatch objects) MUST be evaluated in the order they
                  appear and the first PathMatch object that matches the
                  content request being process is applied.</t>

                  <t>Type: List of PathMatch objects</t>

                  <t>Mandatory-to-Specify: No.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="PathMatch" title="PathMatch">
          <t>The PathMatch object contains (or references) an expression given
          as a PatternMatch object to match against a resource URI path and
          contains or references a PathMetadata object to apply if a
          match is found.</t>

          <t><list style="empty">
              <t>Property: path-pattern<list style="empty">
                  <t>Description: Pattern to match against the requested path,
                  i.e., against the <xref target="RFC3986"/> path-absolute.</t>

                  <t>Type: PatternMatch</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: path-metadata<list style="empty">
                  <t>Description: CDNI Metadata to apply when delivering
                  content that matches this path.</t>

                  <t>Type: PathMetadata</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="PathMetadata" title="PathMetadata">
          <t>A PathMetadata object contains (or references) the CDNI Metadata
          properties for content served with the associated URI path (defined
          in a PathMatch object) and possibly child PathMatch objects.</t>

          <t>Note that if DNS-based redirection is employed, then any metadata
          at the PathMetadata level or below will be inaccessible at request
          routing time because only the content request hostname is available
          at request routing time.</t>

          <t><list style="empty">
              <t>Property: metadata<list style="empty">
                  <t>Description: List of path related metadata.</t>

                  <t>Type: List of GenericMetadata objects</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: paths<list style="empty">
                  <t>Description: Path specific rules. First match
                  applies.</t>

                  <t>Type: List of PathMatch objects</t>

                  <t>Mandatory-to-Specify: No.</t>
                </list></t>
            </list></t>
        </section>

        <section title="PatternMatch">
          <t>A PatternMatch object contains the pattern string and flags that
          describe the PathMatch expression.</t>

          <t><list style="empty">
              <t>Property: pattern<list style="empty">
                  <t>Description: A pattern for string matching. The pattern
                  may contain the wildcards * and ?, where * matches any
                  sequence of characters (including the empty string) and ?
                  matches exactly one character. The three literals \ , * and
                  ? should be escaped as \\, \* and \?. All other characters
                  are treated as literals.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: case-sensitive<list style="empty">
                  <t>Description: Flag indicating whether or not
                  case-sensitive matching should be used.</t>

                  <t>Type: Boolean</t>

                  <t>Mandatory-to-Specify: No. Default is case-insensitive
                  match.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: ignore-query-string<list style="empty">
                  <t>Description: List of query parameters which should be
                  ignored when searching for a pattern match. If all query
                  parameters should be ignored then the list MUST be
                  empty.</t>

                  <t>Type: List of String</t>

                  <t>Mandatory-to-Specify: No. Default is to include query
                  strings when matching.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="generic-metadata" title="GenericMetadata">
          <t>A GenericMetadata object is an abstraction for managing
          individual CDNI Metadata properties in an opaque manner.</t>

          <t><list style="empty">
              <t>Property: generic-metadata-type<list style="empty">
                  <t>Description: CDNI Metadata property object type.</t>

                  <t>Type: MIME Type String (from <xref
                      target="metadata-registry"></xref>)</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: generic-metadata-value<list style="empty">
                  <t>Description: CDNI Metadata property object.</t>

                  <t>Type: Format/Type is defined by the value of
                  generic-metadata-type property above.</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: mandatory-to-enforce<list style="empty">
                  <t>Description: Flag identifying whether or not the
                  enforcement of the property Metadata is required.</t>

                  <t>Type: Boolean</t>

                  <t>Mandatory-to-Specify: No. Default is to treat metadata as
                  mandatory to enforce (i.e., true).</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: safe-to-redistribute<list style="empty">
                  <t>Description: Flag identifying whether or not the property
                  Metadata may be safely redistributed without
                  modification.</t>

                  <t>Type: Boolean</t>

                  <t>Mandatory-to-Specify: No. Default is allow transparent
                  redistribution (i.e., true).</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: incomprehensible<list style="empty">
                  <t>Description: Flag identifying whether or not any
                  CDN in the chain of delegation has failed to
                  understand and/or failed to properly transform the
                  Metadata.</t>

                  <t>Type: Boolean</t>

                  <t>Mandatory-to-Specify: No. Default is
                  comprehensible (i.e., false).</t>
                </list></t>
            </list></t>
        </section>
      </section>

      <section anchor="property-objects"
               title="Description of the CDNI Generic Metadata Objects">
        <t>The property objects defined below are intended to be used in the
        GenericMetadata object generic-metadata-value field as defined in
        <xref target="generic-metadata"/> and their generic-metadata-type
        property MUST be set to the appropriate Media Type as defined in
        <xref target="metadata-registry"></xref>.</t>

        <section anchor="SourceMetadata" title="Source Metadata">
          <t>Source Metadata provides the dCDN information about content
          acquisition, i.e., how to contact an uCDN Surrogate or an Origin
          Server to obtain the content to be served. The sources are not
          necessarily the actual Origin Servers operated by the CSP but might
          be a set of Surrogates in the uCDN.</t>

          <t/>

          <t>Endpoints within a source should be treated as equivalent/equal
          so one can specify a list of sources in preference order and for
          each source/preference rank one can specify a list of endpoints that
          are equivalent, e.g., a pool of servers that are not behind a load
          balancer.</t>

          <t><list style="empty">
              <t>Property: sources<list style="empty">
                  <t>Description: Sources from which the dCDN can acquire
                  content, listed in order of preference.</t>

                  <t>Type: List of Source objects</t>

                  <t>Mandatory-to-Specify: No. Default is to use static
                  configuration, out-of-band from the metadata interface.</t>
                </list></t>
            </list></t>

          <section anchor="Source" title="Source">
            <t>A Source object describes the Source which should be used by
            the dCDN for content acquisition, e.g., a Surrogate within the uCDN
            or an alternate Origin Server, the protocol to be used and any
            authentication method.</t>

            <t><list style="empty">
                <t>Property: acquisition-auth<list style="empty">
                    <t>Description: Authentication method to use when
                    requesting content from this source.</t>

                    <t>Type: Auth</t>

                    <t>Mandatory-to-Specify: No. Default is no authentication
                    required.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: endpoints<list style="empty">
                    <t>Description: Origins from which the dCDN can acquire
                    content. If multiple endpoints are specified they are all
                    equal, i.e., the list is not in preference order, for
                    example a pool of servers behind a load balancer.</t>

                    <t>Type: List of EndPoint objects</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: protocol<list style="empty">
                    <t>Description: Network retrieval protocol to use when
                    requesting content from this source.</t>

                    <t>Type: Protocol</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list></t>
          </section>
        </section>

        <section anchor="LocationACL" title="LocationACL Metadata">
          <t>LocationACL Metadata defines location-based restrictions.</t>

          <t>A LocationACL which does not include a locations property results
          in an action of allow, meaning that delivery can be performed
          regardless of the User Agent's location. The action from the first
          footprint to match against the User Agent's location is the action a
          CDN MUST take. If two or more footprints overlap, the first
          footprint that matches against the User Agent's location determines
          the action a CDN MUST take. If the locations property is included
          but is empty, or if none of the listed footprints matches the User
          Agent's location, then the result is an action of deny.</t>

          <t>Although the LocationACL, TimeWindowACL, and ProtocolACL are
            independent GenericMetadata objects, they may provide conflicting
            information to a dCDN, e.g., a content request which is
            simultaneously allowed based on the LocationACL and denied based on
            the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs
            (where 'allow' is true and 'deny' is false) to determine whether or
            not a request should be allowed. Thus, in the example given, the
            request should be denied.</t>

          <t><list style="empty">
              <t>Property: locations<list style="empty">
                  <t>Description: Access control list which
                  allows or blocks delivery based on client location.</t>

                  <t>Type: List of LocationRule objects</t>

                  <t>Mandatory-to-Specify: No. Default is allow all
                  locations.</t>
                </list></t>
            </list></t>

          <section anchor="LocationRule" title="LocationRule">
            <t>A LocationRule contains or references a list of Footprint
            objects and the corresponding action.</t>

            <t><list style="empty">
                <t>Property: footprints<list style="empty">
                    <t>Description: List of footprints to which the rule
                    applies.</t>

                    <t>Type: List of Footprint objects</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: action<list style="empty">
                    <t>Description: Defines whether the rule specifies
                    locations to allow or deny.</t>

                    <t>Type: Enumeration [allow|deny]</t>

                    <t>Mandatory-to-Specify: No. Default is deny.</t>
                  </list></t>
              </list></t>
          </section>

          <section anchor="Footprint" title="Footprint">
            <t>A Footprint object describes the footprint to which a
            LocationRule may be applied by, e.g., an IPv4 address range or a
            geographic location.</t>

            <t><list style="empty">
                <t>Property: footprint-type<list style="empty">
                    <t>Description: Registered footprint type (see <xref
                    target="FootprintReg"/>).</t>

                    <t>Type: String</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: footprint-value<list style="empty">
                    <t>Description: Footprint object conforming to the
                    specification associated with the registered footprint
                    type.</t>

                    <t>Type: String</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list></t>
          </section>
        </section>

        <section anchor="TimeWindowACL" title="TimeWindowACL Metadata">
          <t>TimeWindowACL Metadata defines time-based restrictions. </t>

          <t>A TimeWindowACL which does not include a times property results
          in an action of allow, meaning that delivery can be performed
          regardless of the time of the User Agent's request. The
          action from the first window to match against the current
          time is the action a CDN MUST take. If two or more windows
          overlap, the first window that matches against the current
          time determines the action a CDN MUST take. If the times
          property is included but is empty, or if none of the listed
          windows matches the current time, then the result is an
          action of deny.</t>

          <t>Although the LocationACL, TimeWindowACL, and ProtocolACL are
            independent GenericMetadata objects, they may provide conflicting
            information to a dCDN, e.g., a content request which is
            simultaneously allowed based on the LocationACL and denied based on
            the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs
            (where 'allow' is true and 'deny' is false) to determine whether or
            not a request should be allowed. Thus, in the example given, the
            request should be denied.</t>

          <t><list style="empty">
              <t>Property: times<list style="empty">
                  <t>Description: Description: Access control list which
                  allows or blocks delivery based on request time.</t>

                  <t>Type: List of TimeWindowRule objects</t>

                  <t>Mandatory-to-Specify: No. Default is allow all time
                  windows.</t>
                </list></t>
            </list></t>

          <section anchor="TimeWindowRule" title="TimeWindowRule">
            <t>A TimeWindowRule contains or references a list of TimeWindow
            objects and the corresponding action.</t>

            <t><list style="empty">
                <t>Property: windows<list style="empty">
                    <t>Description: List of time windows to which the rule
                    applies.</t>

                    <t>Type: List of TimeWindow objects</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: action<list style="empty">
                    <t>Description: Defines whether the rule specifies time
                    windows to allow or deny.</t>

                    <t>Type: Enumeration [allow|deny]</t>

                    <t>Mandatory-to-Specify: No. Default is deny.</t>
                  </list></t>
              </list></t>
          </section>

          <section anchor="TimeWindow" title="TimeWindow">
            <t>A TimeWindow object describes a time range which may be applied
            by an TimeWindowACL, e.g., start 946717200 (i.e., 09:00AM
            01/01/2000 UTC), end: 946746000 (i.e., 17:00AM 01/01/2000
            UTC).</t>

            <t><list style="empty">
                <t>Property: start<list style="empty">
                    <t>Description: The start time of the window.</t>

                    <t>Type: Time</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: end<list style="empty">
                    <t>Description: The end time of the window.</t>

                    <t>Type: Time</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list></t>
          </section>
        </section>

        <section anchor="ProtocolACL" title="ProtocolACL Metadata">
          <t>ProtocolACL Metadata defines delivery protocol restrictions.</t>

          <t>A ProtocolACL which does not include a protocol-acl
          property results in an action of allow, meaning that
          delivery can be performed regardless of the protocol of the
          User Agent's request. The action from the first protocol to
          match against the request protocol is the action a CDN MUST
          take. If two or more request protocols overlap, the first
          protocol that matches thre request protocol determines the
          action a CDN MUST take. If the protocol-acl property is
          included but is empty, or if none of the listed protocol
          matches the request protocol, then the result is an
          action of deny.</t>

          <t>Although the LocationACL, TimeWindowACL, and ProtocolACL are
            independent GenericMetadata objects, they may provide conflicting
            information to a dCDN, e.g., a content request which is
            simultaneously allowed based on the LocationACL and denied based on
            the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs
            (where 'allow' is true and 'deny' is false) to determine whether or
            not a request should be allowed. Thus, in the example given, the
            request should be denied.</t>

          <t><list style="empty">
              <t>Property: protocol-acl<list style="empty">
                  <t>Description: Description: Access control list which
                  allows or blocks delivery based on delivery protocol.</t>

                  <t>Type: List of ProtocolRule objects</t>

                  <t>Mandatory-to-Specify: No. Default is allow all
                  protocols.</t>
                </list></t>
            </list></t>

          <section anchor="ProtocolRule" title="ProtocolRule">
            <t>A ProtocolRule contains or references a list of Protocol
            objects. ProtocolRule objects are used to construct a ProtocolACL
            to apply restrictions to content acquisition or delivery.</t>

            <t><list style="empty">
                <t>Property: protocols<list style="empty">
                    <t>Description: List of protocols to which the rule
                    applies.</t>

                    <t>Type: List of protocol objects</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list> <list style="empty">
                <t>Property: action<list style="empty">
                    <t>Description: Defines whether the rule specifies
                    protocols to allow or deny.</t>

                    <t>Type: Enumeration [allow|deny]</t>

                    <t>Mandatory-to-Specify: No. Default is deny.</t>
                  </list></t>
              </list></t>
          </section>
        </section>

        <section anchor="DeliveryAuthorization" title="DeliveryAuthorization Metadata">
          <t>Delivery Authorization defines authorization
          methods for the delivery of content to User Agents.</t>

          <t><list style="empty">
              <t>Property: delivery-auth-methods<list style="empty">
                  <t>Description: Options for authorizing content requests.
                  Delivery for a content request is authorized if any
                  of the authorization method in the list is satisfied
                  for that request.</t>

                  <t>Type: List of Auth objects</t>

                  <t>Mandatory-to-Specify: No. Default is no authorization
                  required.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="Cache" title="Cache">
          <t>A Cache object describes the cache control parameters to be
          applied to the content by intermediate caches.</t>

          <t><list style="empty">
              <t>Property: ignore-query-string<list style="empty">
                  <t>Description: Allows a cache to ignore URI query string
                  parameters while comparing URIs for equivalence. Each query
                  parameter to ignore is specified in the list. If all query
                  parameters should be ignored, then the list MUST be
                  specified and MUST be empty.</t>

                  <t>Type: List of String</t>

                  <t>Mandatory-to-Specify: No. Default is to consider query
                  string parameters when comparing URIs.</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="Grouping" title="Grouping">
          <t>A Grouping object identifies a large group of content to which
          a given asset belongs.</t>

          <t><list style="empty">
              <t>Property: ccid<list style="empty">
                  <t>Description: Content Collection identifier for an
                  application-specific purpose such as logging.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: No. Default is an empty string.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: sid<list style="empty">
                  <t>Description: Session identifier for an
                  application-specific purpose such as logging.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: No. Default is an empty string.</t>
                </list></t>
            </list></t>
        </section>
      </section>

      <section anchor="simple-data-types"
               title="CDNI Metadata Simple Data Type Descriptions">
        <t>This section describes the simple data types that are used for
        properties of CDNI Metadata objects.</t>

        <section anchor="Link" title="Link">
          <t>A link object may be used in place of any of the objects or
          properties described above. Links can be used to avoid duplication
          if the same metadata information is repeated within the metadata
          tree. When a link replaces an object, its href property is set to
          the URI of the resource and its type property is set to the type of
          the object it is replacing.</t>

          <t><list style="empty">
              <t>Property: href<list style="empty">
                  <t>Description: The URI of the addressable object
                  being referenced.</t>

                  <t>Type: URI</t>

                  <t>Mandatory-to-Specify: Yes</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: type<list style="empty">
                  <t>Description: The type of the object being referenced.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: No</t>
                </list></t>
            </list></t>
        </section>

        <section anchor="Protocol" title="Protocol">
          <t>Protocol objects are used to specify registered protocols for
          content acquisition or delivery (see <xref
          target="ProtocolReg"/>).</t>

          <t>Type: String</t>
        </section>

        <section title="Endpoint">
          <t>A hostname (with optional port) or an IP address (with optional
          port).</t>

          <t>Note: All implementations MUST support IPv4 addresses encoded as
          specified by the 'IPv4address' rule in Section 3.2.2 of <xref
          target="RFC3986"/> and MUST support all IPv6 address formats
          specified in <xref target="RFC4291"/>. Server implementations SHOULD
          use IPv6 address formats specified in <xref target="RFC5952"/>.</t>

          <t>Type: String</t>
        </section>

        <section title="URI">
          <t>A URI as specified in <xref target="RFC3986"/>.</t>

          <t>Type: String</t>
        </section>

        <section title="Time">
          <t>A time value expressed in seconds since Unix epoch in the UTC
          timezone.</t>

          <t>Type: Integer</t>
        </section>
      </section>

        <section anchor="Auth" title="Auth">
          <t>An Auth object defines authentication and authorization methods
          to be used during content acquisition and content delivery,
          respectively.</t>

          <t><list style="empty">
              <t>Property: auth-type<list style="empty">
                  <t>Description: Registered Auth type (see <xref
                  target="AuthReg"/>).</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list> <list style="empty">
              <t>Property: auth-value<list style="empty">
                  <t>Description: An object conforming to the specification
                  associated with the Registered Auth type.</t>

                  <t>Type: String</t>

                  <t>Mandatory-to-Specify: Yes.</t>
                </list></t>
            </list></t>

          <section anchor="CredentialAuth" title="CredentialAuth Type">
            <t>CredentialAuth is a Registered Auth type defining an
            object for encapsulating user credentials (i.e., username
            and password) (see <xref target="AuthReg"/>). The 
            CredentialAuth object contains the following properties:</t>

            <t><list style="empty">
                <t>Property: username<list style="empty">
                    <t>Description: Identification of user.</t>

                    <t>Type: String</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>

                <t>Property: password<list style="empty">
                    <t>Description: Password for user identified by username
                    property.</t>

                    <t>Type: String</t>

                    <t>Mandatory-to-Specify: Yes.</t>
                  </list></t>
              </list></t>
          </section>
        </section>

    </section>

    <section anchor="metadata-capabilities" title="CDNI Metadata Capabilities">
      <t>CDNI Metadata is used to convey information pertaining to content
      delivery from uCDN to dCDN. For optional metadata, it may be useful for
      the uCDN to know if the dCDN supports the metadata, prior to delegating
      any content requests to the dCDN. If optional-to-implement metadata is
      "mandatory-to-enforce", and the dCDN does not support it, any delegated
      requests for that content will fail. The uCDN will likely want to
      avoid delegating those requests to that dCDN. Likewise, for any metadata
      which may be assigned optional values, it may be useful for the uCDN to
      know which values a dCDN supports, prior to delegating any content
      requests to that dCDN. If the optional value assigned to a given piece of
      content's metadata is not supported by the dCDN, any delegated requests
      for that content may fail, so again the uCDN is likely to want to avoid
      delegating those requests to that dCDN.</t>

      <t>The CDNI Footprint and Capabilities Interface (FCI) <xref
      target="I-D.ietf-cdni-framework"/> provides a means of advertising
      capabilities from dCDN to uCDN. Support for optional metadata and
      support for optional metadata values may be advertised using the
      FCI.</t>

    </section>

    <section anchor="metadata-interface" title="CDNI Metadata interface">
      <t>This section specifies an interface to enable a Downstream CDN to
      retrieve CDNI Metadata objects from an Upstream CDN.</t>

      <t>The interface can be used by a Downstream CDN to retrieve CDNI
      Metadata objects either</t>

      <t><list style="symbols">
          <t>Dynamically as required by the Downstream CDN to process received
          requests. For example in response to a query from an Upstream CDN
          over the CDNI Request Routing Redirection interface (RI) <xref
          target="I-D.ietf-cdni-redirection"/> or in response to receiving a
          request for content from a User Agent. Or;</t>

          <t>In advance of being required. For example in the case of
          Pre-positioned CDNI Metadata acquisition.</t>
        </list></t>

      <t>The CDNI Metadata interface is built on the principles of RESTful web
      services. In particular, this means that requests and responses over the
      interface are built around the transfer of representations of
      hyperlinked resources. A resource in the context of the CDNI Metadata
      interface is any object in the Data Model (as described in <xref
      target="data-model"/> through <xref
      target="abstract-metadata-description"/>).</t>

      <t>To retrieve CDNI metadata, a CDNI Metadata client (i.e., a client in
      the dCDN) first makes a HTTP GET request for the URI of the HostIndex
      which provides the CDNI Metadata client with a list of Hostnames for
      which the upstream CDN may delegate content delivery to the downstream
      CDN. The CDNI Metadata client can then obtain any other CDNI Metadata
      objects by making a HTTP GET requests for any linked Metadata objects it
      requires.</t>

      <t>CDNI Metadata servers (i.e., servers in the uCDN) are free to assign
      whatever structure they desire to the URIs for CDNI Metadata objects and
      CDNI Metadata clients MUST NOT make any assumptions regarding the
      structure of CDNI Metadata URIs or the mapping between CDNI Metadata
      objects and their associated URIs. Therefore any URIs present in the
      examples below are purely illustrative and are not intended to impose a
      definitive structure on CDNI Metadata interface implementations.</t>

      <section title="Transport">
        <t>The CDNI Metadata interface uses HTTP as the underlying protocol
        transport.</t>

        <t>The HTTP Method in the request defines the operation the request
        would like to perform. A server implementation of the CDNI Metadata
        interface MUST support the HTTP GET and HEAD methods.</t>

        <t>The corresponding HTTP Response returns the status of the operation
        in the HTTP Status Code and returns the current representation of the
        resource (if appropriate) in the Response Body. HTTP Responses from
        servers implementing the CDNI Metadata interface that contain a
        response body SHOULD include an ETag to enable validation of cached
        versions of returned resources.</t>

        <t>The CDNI Metadata interface specified in this document is a
        read-only interface. Therefore support for other HTTP methods such as
        PUT, POST and DELETE etc. is not specified. A server implementation
        of the CDNI Metadata interface SHOULD reject all methods other than
        GET and HEAD.</t>

        <t>As the CDNI Metadata interface builds on top of HTTP, CDNI Metadata
        server implementations MAY make use of any HTTP feature when
        implementing the CDNI Metadata interface, for example a CDNI Metadata
        server MAY make use of HTTP's caching mechanisms to indicate that the
        returned response/representation can be reused without re-contacting
        the CDNI Metadata server.</t>
      </section>

      <section title="Retrieval of CDNI Metadata resources">
        <t>In the general case a CDNI Metadata server makes each instance of
        an addressable CDNI Metadata object available via a unique URI and
        therefore in order to retrieve CDNI Metadata, a CDNI Metadata client
        first makes a HTTP GET request for the URI of the HostIndex which
        provides the CDNI Metadata client with a list of Hostnames for which
        the upstream CDN may delegate content delivery to the downstream
        CDN.</t>

        <t>In order to retrieve the CDNI Metadata for a particular request the
        CDNI Metadata client processes the received HostIndex object and finds
        the corresponding HostMetadata entry (by matching the hostname in the
        request against the hostnames in the HostMatch). If the HostMetadata
        is linked (rather than embedded), the CDNI metadata client then makes
        a GET request for the URI specified in the href property of the Link
        object which points to the HostMetadata object itself.</t>

        <t>In order to retrieve the most specific metadata for a particular
        request, the CDNI metadata client inspects the HostMetadata for
        references to more specific PathMetadata objects. If any PathMetadata
        match the request (and are linked rather than embedded), the CDNI
        metadata client makes another GET request for the PathMetadata. Each
        PathMetadata object may also include references to yet more specific
        metadata. If this is the case, the CDNI metadata client continues
        requesting PathMetadata recursively.</t>

        <t>Where a downstream CDN is interconnected with multiple upstream
        CDNs, the downstream CDN needs to determine which upstream CDN's CDNI
        metadata should be used to handle a particular User Agent request.</t>

        <t>When application level redirection (e.g., HTTP 302 redirects) is
        being used between CDNs, it is expected that the downstream CDN will
        be able to determine the upstream CDN that redirected a particular
        request from information contained in the received request (e.g., via
        the URI). With knowledge of which upstream CDN routed the request, the
        downstream CDN can choose the correct metadata server from which to
        obtain the HostIndex. Note that the HostIndex served by each uCDN may
        be unique.</t>

        <t>In the case of DNS redirection there is not always sufficient
        information carried in the DNS request from User Agents to determine
        the upstream CDN that redirected a particular request (e.g., when
        content from a given host is redirected to a given downstream CDN by
        more than one upstream CDN) and therefore downstream CDNs may have to
        apply local policy when deciding which upstream CDN's metadata to
        apply.</t>
      </section>

      <section title="Bootstrapping">
        <t>The URI for the HostIndex object of a given upstream CDN needs to
        be either configured in, or discovered by, the downstream CDN. All
        other objects/resources are then discoverable from the HostIndex
        object by following the links in the HostIndex object and the
        referenced HostMetadata and PathMetadata objects.</t>

        <t>If the URI for the HostIndex object is not manually configured in
        the downstream CDN then the HostIndex URI could be discovered. A
        mechanism allowing the downstream CDN to discover the URI of the
        HostIndex is outside the scope of this document.</t>
      </section>

      <section title="Encoding">
        <t>Objects are resources that may be:</t>

        <t><list style="symbols">
            <t>Addressable, where the object is a resource that may be
            retrieved or referenced via its own URI.</t>

            <t>Embedded, where the object is contained within a property of an
            addressable object.</t>
          </list></t>

        <t>The descriptions of objects use the phrase "X contains Y" to
        mean that Y is either directly embedded in X or is linked to by X. It
        is generally a deployment choice for the uCDN implementation to decide
        when and which CDNI Metadata objects to embed and which are made
        separately addressable.</t>

        <section anchor="media-types" title="MIME Media Types">
          <t>All MIME types for CDNI Metadata objects are prefixed with
          "application/cdni.". The MIME type for each object then contains the
          object name of that object as defined by this document. The object
          type name is followed by ".v" and the version number of the object
          type (e.g., &ldquo;.v1&rdquo;). Finally, the encoding type "+json" is
          appended. <xref target="metadata-media-types-table"/> 3 lists a few
          examples of the MIME Media Type for some object (resource) that are
          retrievable through the CDNI Metadata interface.</t>

          <texttable anchor="metadata-media-types-table"
                     title="Example MIME Media Types for CDNI Metadata objects">
            <ttcol>Data Object</ttcol>

            <ttcol>MIME Media Type</ttcol>

            <c>HostIndex</c>

            <c>application/cdni.HostIndex.v1+json</c>

            <c>HostMatch</c>

            <c>application/cdni.HostMatch.v1+json</c>

            <c>HostMetadata</c>

            <c>application/cdni.HostMetadata.v1+json</c>

            <c>PathMatch</c>

            <c>application/cdni.PathMatch.v1+json</c>

            <c>PathMetadata</c>

            <c>application/cdni.PathMetadata.v1+json</c>

            <c>Source</c>

            <c>application/cdni.Source.v1+json</c>

            <c>LocationACL</c>

            <c>application/cdni.LocationACL.v1+json</c>

            <c>LocationRule</c>

            <c>application/cdni.LocationRule.v1+json</c>
          </texttable>

          <t/>
        </section>

        <section title="JSON Encoding of Objects">
          <t>A CDNI Metadata object is encoded as a JSON object containing a
          dictionary of (key,value) pairs where the keys are the property
          names and the values are the associated property values.</t>

          <t>The keys of the dictionary are the names of the properties
          associated with the object and are therefore dependent on the
          specific object being encoded (i.e., dependent on the MIME Media Type
          of the returned resource). Likewise, the values associated with each
          key are dependent on the specific object being encoded (i.e.,
          dependent on the MIME Media Type of the returned resource).</t>

          <t>Dictionary keys in JSON are case sensitive. By convention any
          dictionary key defined by this document (for example the names of
          CDNI Metadata object properties) MUST be represented in
          lowercase.</t>

          <t>In addition to the properties specified for each object type, the
          keys defined below may be present in any object.</t>

          <t><list style="empty">
              <t>Key: base<list style="empty">
                  <t>Description: Provides a prefix for any relative URLs in
                  the object. This is similar to the XML base tag <xref
                  target="XML-BASE"/>. If absent, all URLs in the remainder of
                  the response MUST be absolute URLs.</t>

                  <t>Type: URI</t>

                  <t>Mandatory: No</t>
                </list></t>
            </list></t>

          <t><list style="empty">
              <t>Key: _links<list style="empty">
                  <t>Description: The links from this object to other
                  addressable objects. Any property whose value is an object
                  may be replaced by a link to an object with the same type as
                  the property it replaces. The keys of the _links dictionary
                  are the names of the properties being replaced. The values
                  of the dictionary are Link objects with href set to the URI
                  of the object and type set to the MIME type of the object
                  being replaced.</t>

                  <t>Type: Dictionary object of Link objects</t>

                  <t>Mandatory: Yes</t>
                </list></t>
            </list></t>

          <section title="Encoded CDNI Metadata Example">
            <t>A downstream CDN may request the HostIndex and receive the
            following object of type "application/cdni.HostIndex.v1+json":</t>

            <t><figure>
                <artwork><![CDATA[{
  "hosts": [
    {
      "host": "video.example.com",
      "_links": {
        "host-metadata" : {
          "type": "application/cdni.HostMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234"
        }
      }
    },
    {
      "host": "images.example.com",
      "_links": {
        "host-metadata" : {
          "type": "application/cdni.HostMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host5678"
        }
      }
    }
  ]
}]]></artwork>
              </figure></t>

            <t>If the incoming request has a Host header with
            "video.example.com" then the downstream CDN would fetch the next
            metadata object from "http://metadata.ucdn.example/host1234"
            expecting a MIME type of
            "application/cdni.HostMetadata.v1+json":</t>

            <t><figure>
                <artwork><![CDATA[{
  "metadata": [
    {
      "generic-metadata-type": "application/cdni.SourceMetadata.v1+json",
      "generic-metadata-value": {
        "sources": [
          {
            "_links": {
              "acquisition-auth": {
                "auth-type": "application/cdni.Auth.v1+json",
                "href": "http://metadata.ucdn.example/auth1234"
              }
            },
            "endpoint": "acq1.ucdn.example",
            "protocol": "ftp"
          },
          {
            "_links": {
              "acquisition-auth": {
                "auth-type": "application/cdni.Auth.v1+json",
                "href": "http://metadata.ucdn.example/auth1234"
              }
            },
            "endpoint": "acq2.ucdn.example",
            "protocol": "http"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "application/cdni.LocationACL.v1+json",
      "generic-metadata-value": {
        "locations": [
          {
            "footprints": [
              {
                "footprint-type": "IPv4CIDR",
                "footprint-value": "192.168.0.0/16"
              }
            ],
            "action": "deny"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "application/cdni.ProtocolACL.v1+json",
      "generic-metadata-value": {
        "protocol-acl": [
          {
            "protocols": [
              "ftp"
            ],
            "action": "deny"
          }
        ]
      }
    }
  ],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/video/trailers/*"
      },
      "_links": {
        "path-metadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234/pathABC"
        }
      }
    },
    {
      "path-pattern": {
        "pattern": "/video/movies/*"
      },
      "_links": {
        "path-metadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234/pathDCE"
        }
      }
    }
  ]
}]]></artwork>
              </figure></t>

            <t>Suppose the path of the requested resource matches the
            "/video/movies/*" pattern, the next metadata requested would be
            for "http://metadata.ucdn.example/host1234/pathDCE" with an
            expected type of "application/cdni.PathMetadata.v1+json":</t>

            <t><figure>
                <artwork><![CDATA[{
  "metadata": [],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/videos/movies/hd/*"
      },
      "_links": {
        "pathmetadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": 
            "http://metadata.ucdn.example/host1234/pathABC/path123"
        }
      }
    }
  ]
}]]></artwork>
              </figure></t>

            <t>Finally, if the path of the requested resource also matches the
            "/videos/movies/hd/*" pattern, the downstream CDN would also fetch
            the following object from
            "http://metadata.ucdn.example/host1234/movies/hd" with MIME type
            "application/cdni.PathMetadata.v1+json":</t>

            <t><figure>
                <artwork><![CDATA[{
  "metadata": [
    {
      "generic-metadata-type": "application/cdni.TimeWindowACL.v1+json",
      "generic-metadata-value": {
        "times": [
          "windows": [
            {
              "start": "1213948800",
              "end": "1327393200"
            }
          ],
          "action": "allow"
        ]
      }
    }
  ]
}]]></artwork>
              </figure></t>
          </section>
        </section>
      </section>

      <section anchor="extensibility" title="Extensibility">
        <t>The set of property Metadata may be extended with additional
        (standards based or vendor specific) property Metadata. The
        GenericMetadata object defined in <xref target="generic-metadata"/>
        allows any Metadata property to be included in either the HostMetadata
        or PathMetadata lists. It is expected that additional property
        Metadata will be defined in the future and that the documents defining
        those property Metadata will be registered in the CDNI GenericMetadata
        Types registry <xref target="metadata-registry"/>.</t>

        <t>Note: Identification, within the type name defined for a property
        Metadata object, of the organization that defined the extension
        property Metadata decreases the possibility of property Metadata type
        collisions.</t>

        <section title="Metadata Enforcement">
          <t>At any given time, the set of GenericMetadata types supported by
          the uCDN may not match the set of GenericMetadata types supported by
          the dCDN.</t>

          <t>In the cases where a uCDN sends Metadata containing a
          GenericMetadata type that a dCDN does not support, the dCDN MUST
          enforce the semantics of the "mandatory-to-enforce&rdquo; property.
          If a dCDN does not understand or is unable to perform the functions
          associated with any "mandatory-to-enforce&rdquo; Metadata, the dCDN
          MUST NOT service any requests for the corresponding content.</t>

          <t>Note: Ideally, uCDNs would not delegate content requests to a
          dCDN which does not support the "mandatory-to-enforce" Metadata
          associated with the content being requested. However, even if the
          uCDN has a priori knowledge of the Metadata supported by the dCDN
          (e.g., via the CDNI capabilities interface or through out-of-band
          negotiation between CDN operators) Metadata support may fluctuate or
          be inconsistent (e.g., due to mis-communication, mis-configuration,
          or temporary outage). Thus, the dCDN MUST always evaluate all
          Metadata associated with content requests and reject any requests
          where "mandatory-to-enforce" Metadata associated with the content
          cannot be enforced.</t>
        </section>

        <section title="Metadata Conflicts">
          <t>It is possible that new Metadata definitions may obsolete or
            conflict with existing property Metadata (e.g., a future revision of
            the CDNI Metadata interface may redefine the Auth Metadata or a
            custom vendor extension may implement an alternate Auth Metadata
            option).  If multiple Metadata (e.g., cdni.Auth.v2, vendor1.Auth,
            and vendor2.Auth) all conflict with an existing Metadata (e.g.,
            cdni.Auth) and all are marked as "mandatory-to-enforce", it may be
            ambiguous which Metadata should be applied, especially if the
            functionality of the Metadata overlap.</t>

          <t>As described in <xref target="metadata-inheritance"/>, Metadata
            override only applies to Metadata objects of the same exact type,
            found in HostMetadata and nested PathMetadata structures. The CDNI
            Metadata interface does not support enforcement of dependencies
            between different Metadata types. It is the responsibility of the
            CSP and the CDN operators to ensure that Metadata assigned to a
            given content do not conflict.</t>

          <t>Note: Because Metadata is inherently ordered in GenericMetadata
            lists, as well as in the PathMetadata hierarchy and PathMatch lists,
            multiple conflicting Metadata types MAY be used, however, Metadata
            hierarchies MUST ensure that independent PathMatch root objects are
            used to prevent ambiguous or conflicting Metadata definitions.</t>
        </section>
      </section>

      <section title="Versioning">
        <t>The version of CDNI Metadata Structural objects is conveyed inside
        the MIME-Type that is included in the HTTP Content-Type header. Upon
        responding to a request for an object, a metadata server MUST include
        a Content-Type header with the MIME-type containing the version number
        of the object. HTTP requests sent to a metadata server SHOULD include
        an Accept header with the MIME-type (which includes the version) of
        the expected object. Metadata clients can specify multiple MIME-types
        in the Accept header, for example if a metadata client is capable of
        processing two different versions of the same type of object (defined
        by different MIME-types) it may decide to include both in the Accept
        header. The version of each object defined by this document is version
        1. For example: "Content-Type:
        application/cdni.HostIndex.v1+json".</t>

        <t>GenericMetadata objects include a "type" property which specifies
        the MIME-type of the GenericMetadata value. This MIME-type should also
        include a version. Any document which defines a new type of
        GenericMetadata MUST specify the version number which it describes.
        For example: "application/cdni.Location.v1+json".</t>
      </section>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <t>This document requests the registration of the following MIME Media
        Type under the IANA MIME Media Type registry
        (http://www.iana.org/assignments/media-types/index.html).<list>
        <t>application/cdni.HostIndex.v1</t>
        <t>application/cdni.HostMetadata.v1</t>
        <t>application/cdni.PathMatch.v1</t>
        <t>application/cdni.PathMetadata.v1</t>
        <t>application/cdni.PatternMatch.v1</t>
        <t>application/cdni.GenericMetadata.v1</t>
        <t>application/cdni.SourceMetadata.v1</t>
        <t>application/cdni.Source.v1</t>
        <t>application/cdni.LocationACL.v1</t>
        <t>application/cdni.LocationRule.v1</t>
        <t>application/cdni.Footprint.v1</t>
        <t>application/cdni.TimeWindowACL.v1</t>
        <t>application/cdni.TimeWindowRule.v1</t>
        <t>application/cdni.TimeWindow.v1</t>
        <t>application/cdni.ProtocolACL.v1</t>
        <t>application/cdni.ProtocolRule.v1</t>
        <t>application/cdni.Authorization.v1</t>
        <t>application/cdni.Auth.v1</t>
        <t>application/cdni.CredentialsAuth.v1</t>
        <t>application/cdni.Cache.v1</t>
        <t>application/cdni.Grouping.v1</t>
      </list></t>

      <section anchor="metadata-registry"
               title="GenericMetadata Type Registry">
        <t>CDNI Metadata is distributed as a list of GenericMetadata objects
        which specify a type field and a type-specific value field, as
        described in <xref target="generic-metadata"/>. In order to prevent
        namespace collisions for GenericMetadata object types a new IANA
        registry is requested for the "CDNI GenericMetadata Types" namespace.
        The namespace shall be split into two partitions: standard and
        optional.</t>

        <t>The standard namespace partition is intended to contain
        mandatory-to-implement capabilities and conforms to the "IETF
        Review" policy as
        defined in <xref target="RFC5226"/>. The registry contains the generic
        metadata type name, the RFC number of the specification defining the
        metadata type, the version number of the GenericMetadata set to which
        the standard capability applies, and boolean values indicating whether
        or not the new type is considered "mandatory-to-enforce" or
        "safe-to-redistribute" (as defined in <xref
        target="generic-metadata"/>).</t>

        <t>The following table defines the initial values for the standard
        partition:</t>

        <texttable>
          <ttcol align="left">Type name</ttcol>

          <ttcol align="left">Specification</ttcol>

          <ttcol align="left">Version</ttcol>

          <ttcol align="left">MTE</ttcol>

          <ttcol align="left">STR</ttcol>

          <c>application/cdni.SourceMetadata.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.LocationACL.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.TimeWindowACL.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.ProtocolACL.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.Auth.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.Cache.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>

          <c>application/cdni.Grouping.v1</c>

          <c>RFCthis</c>

          <c>1</c>

          <c>true</c>

          <c>true</c>
        </texttable>

        <t>The initial MI version number is set to 1. All of the initial
        GenericMetadata types are considered mandatory-to-implement for
        version 1. The version field should be incremented when new
        GenericMetadata type sets are added to the registry.</t>

        <t>The "optional" namespace partition conforms to the "Expert Review"
        policy as defined in <xref target="RFC5226"/>. The expert review is
        intended to prevent namespace hoarding and to prevent the definition
        of redundant GenericMetadata types. Vendors defining new
        GenericMetadata types which conflict with existing GenericMetadata
        types follow the guidelines for the "Specification Required" policy as
        defined in <xref target="RFC5226"/>. The Version field in the registry
        is set to "-1" (negative one) for non-standard GenericMetadata
        types.</t>

        <t>As with the initial GenericMetadata types defined in <xref
        target="property-objects"/>, future GenericMetadata type registrations
        will specify the information necessary for constructing and decoding
        the GenericMetadata object. This information includes the list of
        properties contained within the GenericMetadata object, and for each
        property, the specification should include a description, a type, and
        whether or not the given property is mandatory-to-specify.</t>

        <t>Any document which defines a new GenericMetadata has to:<list
            style="numbers">
            <t>Allocate a new type in the <xref target="IANA">GenericMetadata
            Type Registry</xref>. Generic Metadata types should be descriptive
            and may be hierarchnical to support aggregating groups of
            properties for the purpose of readability and for avoiding
            conflicts between vendor defined extensions. A dotted
            alpha-numeric notation is suggested for human readability.</t>

            <t>Define the set of properties associated with the new type.</t>

            <t>For each property, define a name, description, type, and
            whether or not the property is mandatory-to-specify.</t>

            <t>Specify whether or not the new type is "mandatory-to-enforce"
            (vs optional-to-enforce).</t>

            <t>Describe the semantics of the new type including its purpose
            and example of a use case to which it applies.</t>
          </list></t>

        <section title="GenericMetadata Sub-Registries">
          <t>Some of the initial standard GenericMetadata objects contain
          enumerated types which require registration (i.e., LocationACL
          footprint types, ProtocolACL protocols, and Auth protocols). The
          following sections define the initial values for these
          GenericMetadata type sub-registries.</t>

          <section anchor="FootprintReg" title="Footprint Sub-Registry">
            <t>The IANA is requested to create a new "CDNI Metadata
            Footprint Types" sub-registry under the "CDNI
            GenericMetadata Types" registry.
            The "CDNI Metadata Footprint Types" namespace defines the valid
            Footprint object type values used by the Footprint object in <xref
            target="Footprint"/>. Additions to the Footprint type namespace
            conform to the "Expert Review" policy as defined in <xref
            target="RFC5226"/>. The expert review should verify that new type
            definitions do not duplicate existing type definitions and prevent
            gratuitous additions to the namespace.</t>

            <t>The following table defines the initial Footprint type
            values:</t>

            <texttable>
              <ttcol align="left">Type name</ttcol>

              <ttcol align="left">Description</ttcol>

              <ttcol align="left">Specification</ttcol>

              <c>IPv4CIDR</c>

              <c>IPv4 address block using slash prefix length notation (e.g.,
              192.168.0.16/28). Single IP addresses can be expressed as
              /32.</c>

              <c>RFCthis</c>

              <c>IPv6CIDR</c>

              <c>IPv6 address block using slash prefix length notation (e.g.,
              fc80::0010/124). Single IP addresses can be expressed as
              /128.</c>

              <c>RFCthis</c>

              <c>ASN</c>

              <c>Autonomous System (AS) Number</c>

              <c>RFCthis</c>

              <c>CountryCode</c>

              <c>ISO 3166-1 alpha-2 code</c>

              <c>RFCthis</c>
            </texttable>
          </section>

          <section anchor="ProtocolReg" title="Protocol Sub-Registry">
            <t>The IANA is requested to create a new "CDNI Metadata
            Protocols" sub-registry under the "CDNI
            GenericMetadata Types" registry.
            The "CDNI Metadata Protocols" namespace defines the valid
            Protocol object values in <xref target="Protocol"/>, used by the
            SourceMetadata and ProtocolACL objects. Additions to the Protocol
            namespace conform to the "Expert Review" policy as defined in
            <xref target="RFC5226"/>. The expert review should verify that new
            protocol definitions do not duplicate existing protocol
            definitions and prevent gratuitous additions to the namespace.</t>

            <t>The following table defines the initial Protocol values:</t>

            <texttable>
              <ttcol align="left">Protocol</ttcol>

              <ttcol align="left">Description</ttcol>

              <ttcol align="left">Specification</ttcol>

              <c>HTTP</c>

              <c>Hypertext Transfer Protocol -- HTTP/1.1</c>

              <c>RFC2616</c>

              <c>HTTPS</c>

              <c>HTTP Over TLS</c>

              <c>RFC2818</c>

              <c>RTSP</c>

              <c>Real Time Streaming Protocol</c>

              <c>RFC2326</c>

              <c>RTMP</c>

              <c>Real-Time Messaging Protocol</c>

              <c>http://www.adobe.com/devnet/rtmp.html</c>

              <c>FTP</c>

              <c>FILE TRANSFER PROTOCOL</c>

              <c>RFC959</c>

              <c>SFTP</c>

              <c>SSH File Transfer Protocol</c>

              <c>N/A</c>

              <c>SCP</c>

              <c>Secure Copy</c>

              <c>N/A</c>

              <c>fasp</c>

              <c>Aspera fast, adaptive, secure protocol</c>

              <c>N/A</c>
            </texttable>
          </section>

          <section anchor="AuthReg" title="Authentication Type Sub-Registry">
            <t>The IANA is requested to create a new "CDNI Metadata
            Auth Types" sub-registry under the "CDNI
            GenericMetadata Types" registry.
            The "CDNI Metadata Auth Type" namespace defines the valid Auth
            object types used by the Auth object in <xref target="Auth"/>.
            Additions to the Auth Type namespace conform to the "Expert Review"
            policy as defined in <xref target="RFC5226"/>. The expert review
            should verify that new type definitions do not duplicate existing
            type definitions and prevent gratuitous additions to the
            namespace.</t>

            <t>The following table defines the initial Auth type values:</t>

            <texttable>
              <ttcol align="left">Type</ttcol>

              <ttcol align="left">Description</ttcol>

              <ttcol align="left">Specification</ttcol>

              <c>CredentialAuth</c>

              <c>Simple username and password authentication as defined by
              <xref target="CredentialAuth"/>.</c>

              <c>RFCthis</c>
            </texttable>
          </section>
        </section>
      </section>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>An implementation of the CDNI Metadata interface MUST support
      TLS transport as per <xref target="RFC2818"/> for message
      confidentiality and mutual authentication.  An implementation of
      the CDNI Metadata interface MUST support the
      TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 cipher suite
      (<xref target="RFC2818"/>).  An implementation of the CDNI
      Metadata interface SHOULD prefer cipher suites which suppport
      perfect forward secrecy over cipher suites that do not.</t>

      <section anchor="SecurityAuthentication" title="Authentication">
        <t>Unauthorized access to metadata could result in denial of
        service.  A malicious metadata server could provide metadata
        to a dCDN that denies service for one or more pieces of content
        to one or more user agents.  A malicious metadata server could
        also provide metadata directing dCDNs to malicious origin
        servers instead of the actual origin servers.  A malicious
        client could continuously issue large metadata requests to
        overload the uCDN metadata server.</t>

        <t>Unauthorized access to metadata could result in leakage of
        private information.  A malicious metadata client could
        request metadata in order to gain access to origin servers, as
        well as information pertaining to content restrictions.</t>

        <t>An implementation of the CDNI Metadata interface SHOULD use
        mutual authentication to prevent unauthorized access to metadata.</t>
      </section>

      <section anchor="SecurityConfidentiality" title="Confidentiality">
        <t>Unauthorized viewing of metadata could result in leakage of
        private information.  A third party could intercept metadata
        transactions in order to gain access to origin servers, as
        well as information pertaining to content restrictions.</t>

        <t>An implementation of the CDNI Metadata interface SHOULD use
        strong encryption to prevent unauthorized viewing of metadata.</t>
      </section>

      <section anchor="SecurityIntegrity" title="Integrity">
        <t>Unauthorized modification of metadata could result in denial of
        service.  A malicious proxy server could modify metadata destined
        to a dCDN in order to deny service for one or more pieces of content
        to one or more user agents.  A malicious proxy server could
        also modify metadata directing dCDNs to malicious origin
        servers instead of the actual origin servers.</t>

        <t>An implementation of the CDNI Metadata interface SHOULD use
        strong encryption and mutual authentication to prevent
        unauthorized modification of metadata.</t> 
      </section>

      <section anchor="SecurityPrivacy" title="Privacy">
        <t>Content provider origin and policy information is conveyed
        through the CDNI Metadata interface.  The distribution of
        this information to another CDN introduces potential content
        provider privacy protection concerns.</t>

        <t>The use of TLS for transport of the CDNI Metadata as
        discussed above protects the confidentiality of content
        metadata by preventing any party other than the authorized
        dCDN from gaining access to content metadata.</t>
      </section>
    </section>

    <section anchor="Acknowledgements" title="Acknowledgements">
      <t>The authors would like to thank David Ferguson and Francois Le
      Faucheur for their valuable comments and input to this document.</t>
    </section>

    <section title="Contributing Authors">
      <t>[RFC Editor Note: Please move the contents of this section to the
      Authors' Addresses section prior to publication as an RFC.]</t>

      <t><figure>
          <artwork><![CDATA[Grant Watson
Velocix (Alcatel-Lucent)
3 Ely Road
Milton, Cambridge  CB24 6AA
UK

Email: gwatson@velocix.com

Kent Leung
Cisco Systems
3625 Cisco Way
San Jose, 95134
USA

Email: kleung@cisco.com
]]></artwork>
        </figure></t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.2119" ?>

      <?rfc include="reference.RFC.2617" ?>

      <?rfc include="reference.RFC.5226" ?>

      <?rfc include="reference.RFC.4291" ?>

      <?rfc include="reference.RFC.2818" ?>

      <?rfc include="reference.RFC.5952" ?>
    </references>

    <references title="Informative References">
      <?rfc include="reference.I-D.ietf-cdni-requirements"?>

      <?rfc include="reference.I-D.ietf-cdni-framework"?>

      <?rfc include="reference.RFC.6707" ?>

      <?rfc include="reference.RFC.3986" ?>

      <?rfc include="reference.I-D.ietf-cdni-redirection"?>

      <reference anchor="XML-BASE">
        <front>
          <title>XML Base (Second Edition) -
          http://www.w3.org/TR/xmlbase/</title>

          <author fullname="Jonathan" initials="J" role="editor"
                  surname="Marsh">
            <organization/>
          </author>

          <author fullname="Richard" initials="R" role="editor"
                  surname="Tobin">
            <organization/>

            <address>
              <postal>
                <street/>

                <city/>

                <region/>

                <code/>

                <country/>
              </postal>

              <phone/>

              <facsimile/>

              <email/>

              <uri/>
            </address>
          </author>

          <date day="28" month="January" year="2009"/>
        </front>
      </reference>
    </references>
  </back>
</rfc>
