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Versions: (draft-ma-cdni-metadata) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 RFC 8006

Network Working Group                                   B. Niven-Jenkins
Internet-Draft                                                 R. Murray
Intended status: Standards Track                               G. Watson
Expires: April 5, 2013                          Velocix (Alcatel-Lucent)
                                                            M. Caulfield
                                                                K. Leung
                                                           Cisco Systems
                                                                   K. Ma
                                                     Azuki Systems, Inc.
                                                         October 2, 2012


                       CDN Interconnect Metadata
                      draft-ietf-cdni-metadata-00

Abstract

   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 the core set of CDNI metadata and
   the protocol for exchanging that metadata.

Requirements Language

   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 RFC 2119 [RFC2119].

Status of this Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 5, 2013.




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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Design Principles  . . . . . . . . . . . . . . . . . . . . . .  5
   3.  CDNI Metadata Data Model . . . . . . . . . . . . . . . . . . .  5
     3.1.  HostIndex, HostMetadata & PathMetadata objects . . . . . .  6
     3.2.  Generic CDNI Metadata Object Properties  . . . . . . . . .  9
     3.3.  Metadata Inheritance . . . . . . . . . . . . . . . . . . . 10
     3.4.  Metadata Naming  . . . . . . . . . . . . . . . . . . . . . 10
   4.  Encoding-Independent CDNI Metadata Object Descriptions . . . . 11
     4.1.  CDNI Metadata Structural Object Descriptions . . . . . . . 11
       4.1.1.  HostIndex  . . . . . . . . . . . . . . . . . . . . . . 11
       4.1.2.  HostMatch  . . . . . . . . . . . . . . . . . . . . . . 12
       4.1.3.  HostMetadata . . . . . . . . . . . . . . . . . . . . . 12
       4.1.4.  PathMatch  . . . . . . . . . . . . . . . . . . . . . . 12
       4.1.5.  PathMetadata . . . . . . . . . . . . . . . . . . . . . 13
       4.1.6.  PatternMatch . . . . . . . . . . . . . . . . . . . . . 13
       4.1.7.  GenericMetadata  . . . . . . . . . . . . . . . . . . . 14
     4.2.  CDNI Metadata Property Object Descriptions . . . . . . . . 14
       4.2.1.  Source Metadata  . . . . . . . . . . . . . . . . . . . 14
         4.2.1.1.  Source . . . . . . . . . . . . . . . . . . . . . . 14
       4.2.2.  LocationACL Metadata . . . . . . . . . . . . . . . . . 15
         4.2.2.1.  LocationRule . . . . . . . . . . . . . . . . . . . 15
         4.2.2.2.  Location . . . . . . . . . . . . . . . . . . . . . 15
       4.2.3.  TimeWindowACL Metadata . . . . . . . . . . . . . . . . 16
         4.2.3.1.  TimeWindowRule . . . . . . . . . . . . . . . . . . 16
         4.2.3.2.  TimeWindow . . . . . . . . . . . . . . . . . . . . 16
       4.2.4.  ProtocolACL Metadata . . . . . . . . . . . . . . . . . 17
         4.2.4.1.  ProtocolRule . . . . . . . . . . . . . . . . . . . 17
       4.2.5.  Authorization Metadata . . . . . . . . . . . . . . . . 17
       4.2.6.  Auth . . . . . . . . . . . . . . . . . . . . . . . . . 17



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     4.3.  CDNI Metadata Simple Data Type Descriptions  . . . . . . . 18
       4.3.1.  Link . . . . . . . . . . . . . . . . . . . . . . . . . 18
       4.3.2.  Protocol . . . . . . . . . . . . . . . . . . . . . . . 18
       4.3.3.  Endpoint . . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.4.  IPRange  . . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.5.  URI  . . . . . . . . . . . . . . . . . . . . . . . . . 19
       4.3.6.  Time . . . . . . . . . . . . . . . . . . . . . . . . . 19
   5.  CDNI Metadata interface  . . . . . . . . . . . . . . . . . . . 20
     5.1.  Transport  . . . . . . . . . . . . . . . . . . . . . . . . 20
     5.2.  Retrieval of CDNI Metadata resources . . . . . . . . . . . 21
     5.3.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 22
     5.4.  Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 22
       5.4.1.  MIME Media Types . . . . . . . . . . . . . . . . . . . 22
       5.4.2.  JSON Encoding of Objects . . . . . . . . . . . . . . . 23
         5.4.2.1.  JSON Example . . . . . . . . . . . . . . . . . . . 24
       5.4.3.  XML Encoding of Objects  . . . . . . . . . . . . . . . 27
         5.4.3.1.  XML Example  . . . . . . . . . . . . . . . . . . . 27
     5.5.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . 30
       5.5.1.  Metadata Enforcement . . . . . . . . . . . . . . . . . 30
       5.5.2.  Metadata Override  . . . . . . . . . . . . . . . . . . 31
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 31
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 32
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 32
   Appendix A.  Relationship to the CDNI Requirements . . . . . . . . 33
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34























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1.  Introduction

   CDNI enables a downstream CDN to service content requests on behalf
   of an upstream CDN.  The CDNI metadata associated with a piece of
   content (or with a set of contents) 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.

   The CDNI Metadata Interface is introduced by
   [I-D.ietf-cdni-problem-statement] along with three other interfaces
   that may be used to compose a CDNI solution (Control, Request Routing
   and Logging).  [I-D.davie-cdni-framework] expands on the information
   provided in [I-D.ietf-cdni-problem-statement] and describes each
   interface, and the relationships between them, in more detail.  The
   requirements for the CDNI metadata interface are specified in
   [I-D.ietf-cdni-requirements]

   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:

   o  Redirection Requests received over the CDNI Request Routing
      protocol.
   o  Content Requests received directly from User Agents.

   Specifically this document proposes:

   o  A data structure for mapping content requests to CDNI Metadata
      properties (Section 3).
   o  An initial set of CDNI Metadata properties (Section 4.2).
   o  A RESTful web service for the transfer of CDNI Metadata
      (Section 5).

1.1.  Terminology

   This document reuses the terminology defined in
   [I-D.ietf-cdni-problem-statement].

   Additionally, the following terms are used throughout this document
   and are defined as follows:
   o  Object - a collection of properties
   o  Property - a key and value pair where the key is a property name
      and the value is the property value or an object.







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2.  Design Principles

   The proposed CDNI Metadata Interface aims to achieve the following
   design principles:

   1.  Cacheability of CDNI metadata objects
   2.  Deterministic mapping from content requests to CDNI metadata
       properties
   3.  Support for DNS redirection as well as application-specific
       redirection (for example HTTP redirection)
   4.  Minimal duplication of CDNI metadata
   5.  Leverage existing protocols

   Cacheability improves the latency of acquiring metadata and therefore
   improves the latency of serving content requests.  The CDNI Metadata
   Interface uses HTTP to achieve cacheability.

   Deterministic mappings from content requests to metadata properties
   eliminates ambiguity and ensures that the same policies are applied
   consistently by all downstream CDNs.

   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.

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

   Leveraging existing protocols avoids reinventing common mechanisms
   such as data structure encoding (e.g.  XML, JSON) and data transport
   (e.g.  HTTP).


3.  CDNI Metadata Data Model

   The CDNI Metadata Model describes a data structure for mapping
   content requests to metadata properties.  Metadata properties
   describe how to acquire, authorize, 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 for that Hostname.  That default set of metadata properties
   can be overridden by properties that apply to specific paths within a
   URI.



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   Different Hostnames and URI paths will contain 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.

   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 by a dCDN once, even if it is referenced by the CDNI
   Metadata of multiple Hostnames.

   Section 3.1 introduces a high level description of the HostIndex,
   HostMetadata and PathMetadata objects and describes the relationships
   between those objects.

   Section 3.2 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.

   Section 4 describes in detail the specific CDNI Metadata objects and
   properties which may be contained within a CDNI GenericMetadata
   object.

3.1.  HostIndex, HostMetadata & PathMetadata objects

   A HostIndex object contains a list of Hostnames (and/or IP addresses)
   that may be delegated to the downstream CDN.  The HostIndex is the
   starting point for accessing the uCDN's CDNI Metadata data store.  It
   enables surrogates in 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.

   The HostIndex links Hostnames (and/or IP addresses) to HostMetadata



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   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) in the HostIndex, from
   there it can find HostMetadata which describes delivery rules for a
   host and PathMetadata which may override those rules for given URI
   paths within the host.

   As well as containing the default CDNI Metadata for the specified
   Hostname, HostMetadata and PathMetadata objects may also contain
   PathMatch objects which in turn contain PathMetadata objects.
   PathMatch 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.

   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.

   The relationships between the HostIndex, HostMatch, HostMetadata,
   PathMatch and PathMetadata objects are described in Figure 1.


+---------+     +---------+     +------------+
|HostIndex+---->|HostMatch|---->|HostMetadata+----------------+
+---------+     +---------+     +------+-----+                |
                                       |                      |
                                       V                      V
                                  +---------+    **************************
                             +--->|PathMatch|    *Generic Metadata Objects*
                             |    +---------+    **************************
                             |         |                      ^
                             |         V                      |
                             |  +------------+                |
                             +--|PathMetadata+----------------+
                                +------------+

   Key: ----> = References

       Figure 1: Relationships between the HostIndex, HostMetadata &
                    PathMetadata CDNI Metadata Objects

   The relationships in Figure 1 are summarised in Table 1 below.






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   +--------------+----------------------------------------------------+
   | Data Object  | Objects it References                              |
   +--------------+----------------------------------------------------+
   | HostIndex    | 0 or more HostMatch objects.                       |
   | HostMatch    | 1 HostMetadata object.                             |
   | HostMetadata | 0 or more PathMatch objects. 0 or more             |
   |              | GenericMetadata objects.                           |
   | PathMatch    | 1 PathMetadata object.                             |
   | PathMetadata | 0 or more PathMatch objects. 0 or more             |
   |              | GenericMetadata objects.                           |
   +--------------+----------------------------------------------------+

           Table 1: Relationships between CDNI Metadata Objects

   The table below describes the HostIndex, HostMetadata and
   PathMetadata objects in more detail.

   +-----------------+-------------------------------------------------+
   | Data Object     | Description                                     |
   +-----------------+-------------------------------------------------+
   | HostIndex       | A HostIndex object lists the Hostnames (and/or  |
   |                 | IP addresses) that an upstream CDN can provide  |
   |                 | CDNI Metadata for and the URIs to use for       |
   |                 | retrieving that CDNI Metadata.  For example, if |
   |                 | "example.com" is a content provider, the        |
   |                 | HostIndex object may include an entry for       |
   |                 | "example.com" with the URI of the associated    |
   |                 | HostMetadata object.  These hostnames are       |
   |                 | contained inside a list of HostMatch objects.   |
   | HostMatch       | A HostMatch object defines a hostname to match  |
   |                 | against a requested host, and contains or       |
   |                 | references a HostMetadata object which contains |
   |                 | CDNI Metadata objects to be applied when a      |
   |                 | content request matches against the hostname.   |
   | HostMetadata    | 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.                             |



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   | PathMatch       | A PathMatch object defines a pattern to match   |
   |                 | against the requested 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.                   |
   | PathMetadata    | A PathMetadata object contains the CDNI         |
   |                 | GenericMetadata objects for content served with |
   |                 | the associated URI path (defined in a PathMatch |
   |                 | object).  A PathMetadata object may also        |
   |                 | contain 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.           |
   | GenericMetadata | A GenericMetadata object contains individual    |
   |                 | CDNI Metadata property objects which define the |
   |                 | specific policies and attributes needed to      |
   |                 | properly deliver the associated content.        |
   +-----------------+-------------------------------------------------+

      Table 2: HostIndex, HostMetadata and PathMetadata CDNI Metadata
                                  Objects

3.2.  Generic CDNI Metadata Object Properties

   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 opaque Metadata distribution, from the
   specifics of any given property (e.g., property semantics,
   enforcement options, serialization rules, etc.).

   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



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   or support the property type it is also not going to be able to
   properly deserialize and reserialize the Metadata for cascaded
   distribution.

   For Metadata which does not require customization, 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 require for translations, transparent
   redistribution of the uCDN Metadata values may not be appropriate.
   Certain Metadata may be safely, though possibly not optimially,
   redistributed unmodified, e.g., source acquisition address may not be
   optimal if transparently redistributed, but may still work.
   Redistribution safety MUST be specified for each GenericMetadata.

3.3.  Metadata Inheritance

   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.

   GenericMetadata objects of a given type override all GenericMetadata
   objects of the same type previously defined by any parent object in
   the tree.  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, The PathMetadata defined TimeWindowACL would
   override the TimeWindowACL defined in the HostMetadata for all User
   Agent requests for movies.

3.4.  Metadata Naming

   GenericMetadata objects are identified by their type.  The type
   SHOULD be descriptive, and MAY be hierarchical to support aggregating
   groups of properties for the purpose of readability and for avoiding
   name conflicts between vendor extensions.  A dotted alpha-numeric
   notation is suggested for human readability.  For example:

      ext.vendor1.featurex
      ext.vendor1.featurey
      ext.vendor2.featurex

   Metadata types defined by this document are not hierarchical.

   [Ed.  It is intended that Metadata capability advertisements will



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   allow either individual Metadata names or Metadata bundle identifiers
   to be used.  Need to have a procedure for defining and distributing
   bundle information to be used in Metadata capability advertisement.]


4.  Encoding-Independent CDNI Metadata Object Descriptions

   Section 4.1 provides the definitions of each object type declared in
   Section 3.  These objects are described as structural objects as they
   provide the structure for the inheritance tree and identifying which
   specific properties apply to a given User Agent content request.

   Section 4.2 provides the definitions for the set of core metadata
   objects which may be contained within a GenericMetadata object.
   These objects are described as property objects as they define the
   semantics, enforcement options, and serialization rules for specific
   properties.  These properties govern how User Agent requests for
   content are handled.  Property objects may be composed of or contain
   references to other objects.  In those cases the value of the
   property can be either an object of that type (the object is
   embedded) or a Link object that contains a URI and relationship that
   can be dereferenced to retrieve the CDNI Metadata object that
   represents the value of that property.

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

4.1.  CDNI Metadata Structural Object Descriptions

   Each of the sub-sections below describe the structural objects
   defined in Table 2.

4.1.1.  HostIndex

   The HostIndex object is the entry point into the CDNI Metadata
   hierarchy.  An incoming content request is matched against the list
   of hosts to find the HostMatch object which applies to the request.

      Property: hosts
         Description: List of HostMatch objects.





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         Type: List of HostMatch
         Mandatory-to-Specify: Yes.

4.1.2.  HostMatch

   The HostMatch object contains a hostname or IP address to match
   against content requests.  The HostMatch object references Metadata
   objects to apply if a match is found.

      Property: host
         Description: String (hostname or IP address) to match against
         the requested host.
         Type: String
         Mandatory-to-Specify: Yes.
      Property: host-metadata
         Description: CDNI Metadata to apply when delivering content
         that matches this host.
         Type: HostMetadata
         Mandatory-to-Specify: Yes.

4.1.3.  HostMetadata

   The HostMetadata object contains both Metadata that applies to
   content requests for a particular host and a list of pattern matches
   for finding more specific Metadata based on the resource path in a
   content request.

      Property: metadata
         Description: List of host related metadata.
         Type: List of GenericMetadata
         Mandatory-to-Specify: Yes.
      Property: paths
         Description: Path specific rules.  First match applies.
         Type: List of PathMatch
         Mandatory-to-Specify: No.

4.1.4.  PathMatch

   The PathMatch object contains an expression given as a PatternMatch
   object to match against a resource URI path and Metadata objects to
   apply if a match is found.

      Property: path-pattern
         Description: Pattern to match against the requested path, i.e.
         against the [RFC3986] path-absolute.
         Type: PatternMatch





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         Mandatory-to-Specify: Yes.
      Property: path-metadata
         Description: CDNI Metadata to apply when delivering content
         that matches this pattern.
         Type: PathMetadata
         Mandatory-to-Specify: Yes.

4.1.5.  PathMetadata

   A PathMetadata object contains the CDNI Metadata properties for
   content served with the associated URI path (defined in a PathMatch
   object).  Note that if CDNI metadata is used as an input to CDNI
   request routing and DNS-based redirection is employed, then any
   metadata at the PathMetadata level or below will be inaccessible at
   request routing time.

      Property: metadata
         Description: List of path related metadata.
         Type: List of GenericMetadata
         Mandatory-to-Specify: Yes.
      Property: paths
         Description: Path specific rules.  First match applies.
         Type: List of PathMatch
         Mandatory-to-Specify: No.

4.1.6.  PatternMatch

   A PatternMatch object contains the pattern string and flags that
   describe the PathMatch expression.

      Property: pattern
         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 \?
         Type: String
         Mandatory-to-Specify: Yes.
      Property: case-sensitive
         Description: Flag indicating whether or not case-sensitive
         matching should be used.
         Type: Boolean
         Mandatory-to-Specify: No.  Default is case-insensitive match.
      Property: match-query-string
         Description: Flag indicating whether or not the query string
         should be included in the pattern match.





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         Type: Boolean
         Mandatory-to-Specify: No.  Default is not to include query
         strings when matching.

4.1.7.  GenericMetadata

   A GenericMetadata object is a abstraction for managing individual
   CDNI Metadata properties in an opaque manner.

      Property: type
         Description: CDNI Metadata property object type.
         Type: String
         Mandatory-to-Specify: Yes.
      Property: value
         Description: CDNI Metadata property object.
         Type: matches the type property above
         Mandatory-to-Specify: Yes.
      Property: mandatory-to-enforce
         Description: Flag identifying whether or not the enforcement of
         the property Metadata is required.
         Type: Boolean
         Mandatory-to-Specify: Yes.
      Property: safe-to-redistribute
         Description: Flag identifying whether or not the the property
         Metadata may be safely redistributed without modification.
         Type: Boolean
         Mandatory-to-Specify: No.  Default is allow transparent
         redistribution.

4.2.  CDNI Metadata Property Object Descriptions

4.2.1.  Source Metadata

   Source Metadata provides the dCDN information about content
   acquisition e.g. how to contact an uCDN Surrogate or an Origin
   Server.  The sources are not necessarily the actual Origin Servers
   operated by the CSP but might be a set of Surrogates in the uCDN.

      Property: sources
         Description: Sources from which the dCDN can acquire content.
         Type: List of Source
         Mandatory-to-Specify: No.

4.2.1.1.  Source

   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



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   authentication method.

      Property: auth
         Description: Authentication method to use when requesting
         content from this source.
         Type: Auth
         Mandatory-to-Specify: No.  Default is no authentication is
         required.
      Property: endpoints
         Description: Origins from which the dCDN can acquire content.
         Type: List of EndPoint
         Mandatory-to-Specify: Yes.
      Property: protocol
         Description: Protocol to use for content acquisition.
         Type: Protocol
         Mandatory-to-Specify: Yes.

4.2.2.  LocationACL Metadata

   LocationACL Metadata defines location-based restrictions.

      Property: locations
         Description: Access control list which applies restrictions to
         delivery based on client location.
         Type: List of LocationRule
         Mandatory-to-Specify: No.  Default is allow all locations.

4.2.2.1.  LocationRule

   A LocationRule contains or references a list of Location objects.
   LocationRule objects are used to construct a LocationACL to apply
   restrictions to content delivery.

      Property: locations
         Description: List of locations to which the rule applies.
         Type: List of Location
         Mandatory-to-Specify: Yes.
      Property: action
         Description: Defines whether the rule specifies locations to
         allow or deny.
         Type: Enumeration [allow|deny]
         Mandatory-to-Specify: Yes.

4.2.2.2.  Location

   A Location object describes a Location which may be applied by an
   ACLRule, e.g. a Location may be an IPv4 address range or a geographic
   location.



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      Property: iprange
         Description: A set of IP Addresses.
         Type: List of IPRange.
         Mandatory-to-Specify: Yes.

   [Ed: Location as specified above only supports the Class 1a names
   described in [I-D.jenkins-cdni-names].  Need to add support for Class
   1b names to a later version.]

4.2.3.  TimeWindowACL Metadata

   TimeWindowACL Metadata defines time-based restrictions.

      Property: times
         Description: Access control list which applies restrictions to
         delivery based on request time.
         Type: List of TimeWindowRule
         Mandatory-to-Specify: No.  Default is allow all time windows.

4.2.3.1.  TimeWindowRule

   A TimeWindowRule contains or references a list of TimeWindow objects.
   TimeWindowRule objects are used to construct a TimeWindowACL to apply
   restrictions to content delivery.

      Property: times
         Description: List of time windows to which the rule applies.
         Type: List of TimeWindow
         Mandatory-to-Specify: Yes.
      Property: action
         Description: Defines whether the rule specifies time windows to
         allow or deny.
         Type: Enumeration [allow|deny]
         Mandatory-to-Specify: Yes.

4.2.3.2.  TimeWindow

   A TimeWindow object describes a time range which may be applied by an
   ACLRule, e.g.  Start 09:00AM 01/01/2000 UTC End 17:00PM 01/01/2000
   UTC.

      Property: start
         Description: The start time of the window.
         Type: Time
         Mandatory-to-Specify: Yes.
      Property: end





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         Description: The end time of the window.
         Type: Time
         Mandatory-to-Specify: Yes.

4.2.4.  ProtocolACL Metadata

   ProtocolACL Metadata defines delivery protocol restrictions.

      Property: protocols
         Description: Access control list which applies restrictions to
         delivery based on delivery protocol.
         Type: List of ProtocolRule
         Mandatory-to-Specify: No.  Default is allow all protocols.

4.2.4.1.  ProtocolRule

   A ProtocolRule contains or references a list of Protocol objects.
   ProtocolRule objects are used to construct a ProtocolACL to apply
   restrictions to content delivery.

      Property: protocols
         Description: List of protocols to which the rule applies.
         Type: List of protocol
         Mandatory-to-Specify: Yes.
      Property: action
         Description: Defines whether the rule specifies protocols to
         allow or deny.
         Type: Enumeration [allow|deny]
         Mandatory-to-Specify: Yes.

4.2.5.  Authorization Metadata

   Authorization Metadata define content authorization methods.

      Property: methods
         Description: Options for authenticating content requests.  All
         options in the list are equally valid.
         Type: List of Auth
         Mandatory-to-Specify: No.  Default is no authorization
         required.

4.2.6.  Auth

   An Auth object defines authentication and authorization methods to be
   used during content delivery and content acquisition, e.g. methods
   such as tokenization and URL Signing.

   [Ed.  Need to synchronize authentication configuration with CDNI URL



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   signing draft definitions.]

   [Ed.  Need to consider how to separate protocol specific method
   configuration (e.g., HTTP basic/digest authentication), which must
   match the HostMatch protocol, from protocol agnostic method
   configurations (e.g., URL signing/tokenization).]

4.3.  CDNI Metadata Simple Data Type Descriptions

   This section describes the simpler data types that are used for
   properties of CDNI Metadata objects.

4.3.1.  Link

   A link object may be used in place of any of the objects 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, its rel property is set to the name of the property it is
   replacing, and its type property is set to the type of the object it
   is replacing.

      Property: href
         Description: The URI of the of the addressable object being
         referenced.
         Type: URI
         Mandatory: Yes
      Property: rel
         Description: The Relationship between the referring object and
         the object it is referencing.
         Type: String
         Mandatory: Yes
      Property: type
         Description: The type of the object being referenced.
         Type: String
         Mandatory: Yes

4.3.2.  Protocol

   This type only appears in Links.  Links with this type are not
   machine readable but rather represent particular feature sets of a
   protocol defined in a specification and implemented in code.  The URI
   contained in the link needs to be defined for each delivery protocol
   with an associated interoperable feature set.

   The following examples are illustrative:





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   o  http://url.cdni.ietf.example/protocol/delivery/http/rfcABCD
   o  http://url.cdni.ietf.example/protocol/delivery/rtmp/rfcEFGH
   o  http://url.vendorY.ietf.example/protocol/delivery/rtmp/releaseP.Q

   [Editor's Note: It may be more appropriate to use the 'tag' URI
   scheme [RFC4151] for these URIs.]

4.3.3.  Endpoint

   A hostname (with optional port) or an IP address (with optional
   port).

   Note: All implementations MUST support IPv4 addresses encoded as
   specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] and
   MUST support all IPv6 address formats specified in [RFC4291].  Server
   implementations SHOULD use IPv6 address formats specified in
   [RFC5952].

4.3.4.  IPRange

   One of:

   o  A range of consecutive IP addresses (IPv4 or IPv6) expressed as
      Address1-Address2 which does not have to be to power of two
      aligned, for example the range 192.0.2.1-192.0.2.10 is valid.  The
      first Address in the range MUST be 'lower' than the final address
      in the range.
   o  A valid IP subnet (IPv4 or IPv6) expressed using CIDR notation.
   o  A single IP address (IPv4 or IPv6).

   Note: Client implementations MUST support IPv4 addresses encoded as
   specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] and
   MUST support all IPv6 address formats specified in [RFC4291].  Server
   implementations SHOULD use IPv6 address formats specified in
   [RFC5952].

4.3.5.  URI

   A URI as specified in [RFC3986].

4.3.6.  Time

   A time value expressed in seconds since Unix epoch in the UTC
   timezone.







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5.  CDNI Metadata interface

   This section specifies an interface to enable a Downstream CDN to
   retrieve CDNI Metadata objects from an Upstream CDN.

   The interface can be used by a Downstream CDN to retrieve CDNI
   Metadata objects either dynamically as required by the Downstream CDN
   to process received requests (for example in response to receiving a
   CDNI Request Routing request from an Upstream CDN or in response to
   receiving a request for content from a User Agent) or in advance of
   being required.

   The CDNI Metadata interface is built on the principles of RESTful web
   services.  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 Section 3 through
   Section 4).

   In the general case a CDNI Metadata server makes each instance of an
   addressable CDNI Metadata object available via a unique URI that
   returns a representation of that instance of that CDNI Metadata
   object.  When an object needs to reference another addressable CDNI
   Metadata object (for example a HostIndex object referencing a
   HostMetadata object) it does so by including a link to the referenced
   object.

   CDNI Metadata servers 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 impose a definitive
   structure on CDNI Metadata interface implementations.

5.1.  Transport

   The CDNI Metadata interface uses HTTP as the underlying protocol
   transport.

   The HTTP Method in the request defines the operation the request
   would like to perform.  Servers implementing the CDNI Metadata
   interface MUST support the HTTP GET and HEAD methods.

   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



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   response body SHOULD include an ETag to enable validation of cached
   versions of returned resources.

   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.  Server implementations of
   this interface SHOULD reject all methods other than GET and HEAD.

   As the CDNI Metadata interface builds on top of HTTP, CDNI Metadata
   servers 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.

5.2.  Retrieval of CDNI Metadata resources

   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 that the
   upstream CDN may delegate to the downstream CDN.

   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 HostIndex).  The CDNI
   metadata client then makes a GET request for the URI specified in the
   href key of that Host's entry in the HostIndex.

   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, 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.

   Where a downstream CDN is interconnected with multiple upstream CDNs,
   the downstream CDN must decide which upstream CDN's CDNI metadata
   should be used to handle a particular User Agent request.

   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



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   the URI in case of HTTP redirection across CDNs).  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.

   In the case of DNS redirection there is not sufficient information
   carried in the DNS request from User Agents to determine the upstream
   CDN that redirected a particular request and therefore downstream
   CDNs may have to apply local policy when deciding which upstream
   CDN's metadata to apply.

5.3.  Bootstrapping

   The URI for the HostIndex object of a given upstream CDN needs to be
   either discovered by or configured in 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.

   If the URI for the HostIndex object is not manually configured in the
   downstream CDN then the HostIndex URI could be discovered via the
   CDNI Control interface.  An upstream CDN would provide the URI of the
   HostIndex object to the downstream CDN via the CDNI Control
   Interface.

5.4.  Encoding

   Object are resources that may be:

   o  Addressable, where the object is a resource that may be retrieved
      or referenced via its own URI.
   o  Embedded, where the object is contained (or inlined) within a
      property of an addressable object.

   In the descriptions of objects we use the term "X contains Y" to mean
   either Y is directly embedded in X or that Y 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
   separately addressable.

5.4.1.  MIME Media Types

   All MIME types are prefixed with "application/cdni."  The MIME type
   for each object matches the type name of that object as defined by
   this document.Table 3 lists a few examples of the MIME Media Type for
   each object (resource) that is retrievable through the CDNI Metadata
   interface.  The MIME type suffix depends on the metadata encoding,
   either "+xml" or "+json".



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             +--------------+-------------------------------+
             | Data Object  | MIME Media Type               |
             +--------------+-------------------------------+
             | HostIndex    | application/cdni.HostIndex    |
             | HostMatch    | application/cdni.HostMatch    |
             | HostMetadata | application/cdni.HostMetadata |
             | PathMatch    | application/cdni.PathMatch    |
             | PathMetadata | application/cdni.PathMetadata |
             +--------------+-------------------------------+

           Table 3: MIME Media Types for CDNI Metadata resources

   See http://www.iana.org/assignments/media-types/index.html for
   reference.

5.4.2.  JSON Encoding of Objects

   One possible encoding for a CDNI Metadata object is 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.

   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).

   Dictionary keys in JSON are case sensitive and therefore any
   dictionary key defined by this document (for example the names of
   CDNI Metadata object properties) MUST always be represented in
   lowercase.

   In addition to the properties specific to each object type, the keys
   defined below may be present in any object.

      Key: base
         Description: Provides a prefix for any relative URLs in the
         object.  This is similar to the XML base tag [XML-BASE].  If
         absent, all URLs in the remainder of the document must be
         absolute URLs.
         Type: URI
         Mandatory: No

      Key: links
         Description: The links of this object to other addressable
         objects.  Any property may be replaced by a link to an object
         with the same type as the property it replaces.



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         Type: List of Link
         Mandatory: Yes

5.4.2.1.  JSON Example

   A downstream CDN may request the HostIndex and receive the following
   object of type "application/cdni.HostIndex+json":

   {
     "hosts": [
       {
         "host": "video.example.com",
         "links": [
           {
             "rel": "host-metadata",
             "type": "application/cdni.HostMetadata",
             "href": "http://metadata.example.ucdn.com/video"
           }
         ]
       },
       {
         "host": "images.example.com",
         "links": [
           {
             "rel": "host-metadata",
             "type": "application/cdni.HostMetadata",
             "href": "http://metadata.ucdn.example.com/images"
           }
         ]
       }
     ]
   }

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

   {
     "metadata": [
       {
         "type": "application/cdni.SourceMetadata",
         "value": {
           "sources": [
             {
               "links": [{
                 "rel": "auth",
                 "type": "application/cdni.Auth",



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                 "href": "http://metadata.ucdn.example.com/auth1234"
               }],
               "endpoint": "acq1.ucdn.example.com",
               "protocol": "ftp"
             },
             {
               "links": [{
                 "rel": "auth",
                 "type": "application/cdni.Auth",
                 "href": "http://metadata.ucdn.example.com/auth1234"
               }],
               "endpoint": "acq2.ucdn.example.com",
               "protocol": "http"
             }
           ]
         }
       },
       {
         "type": "application/cdni.LocationACL",
         "value": {
           "locations": [
             {
               "locations": [
                 { "iprange": "192.168.0.0/16" }
               ],
               "action": "deny"
             }
           ]
         }
       },
       {
         "type": "application/cdni.ProtocolACL",
         "value": {
           "protocols": [
             {
               "protocols": [
                 "ftp"
               ],
               "action": "deny"
             }
           ]
         }
       }
     ],
     "paths": [
       {
         "path-pattern": {
           "pattern": "/videos/trailers/*"



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         },
         "links": [{
           "rel": "path-metadata",
           "type": "application/cdni.PathMetadata",
           "href": "http://metadata.ucdn.example.com/videos/trailers"
         }]
       },
       {
         "path-pattern": {
           "pattern": "/videos/movies/*"
         },
         "links": [{
           "rel": "pathmetadata",
           "type": "application/cdni.PathMetadata",
           "href": "http://metadata.ucdn.example.com/videos/movies"
         }]
       }
     ]
   }

   Suppose the path of the requested resource matches the "/video/
   movies/*" pattern, the next metadata requested would be for
   "http://metadata.ucdn.example.com/video/movies" with an expected type
   of "application/cdni.PathMetadata":

   {
     "metadata": [],
     "paths": [
       {
         "path-pattern": {
           "pattern": "/videos/movies/hd/*"
         },
         "links": [{
           "rel": "pathmetadata",
           "type": "application/cdni.PathMetadata",
           "href": "http://metadata.ucdn.example.com/videos/movies/hd"
         }]
       }
     ]
   }

   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.com/videos/movies/hd" with MIME type
   "application/cdni.PathMetadata":





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   {
     "metadata": [
       {
         "type": "application/cdni.TimeWindowACL",
         "value": {
           "times": [
             "times": [
               {
                 "start": "1213948800",
                 "end": "1327393200"
               }
             ],
             "type": "allow"
           ]
         }
       }
     ]
   }

5.4.3.  XML Encoding of Objects

   Another possible encoding for a CDNI Metadata object is an XML
   document containing elements with tag names which match property
   names and values which match the associated property values.

   Tag names of elements 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 element are
   dependent on the specific object being encoded (i.e. dependent on the
   MIME Media Type of the returned resource).

   Lists are encoded by repeating the singular form of a property name.
   For example the "hosts" property is a list of "HostMatch" objects.
   This list would be encoded as multiple "host" elements.

   Link objects are a special case.  If a Link object replaces a
   property then a "link" element replaces the expected element.  The
   properties of the Link object are encoded as XML attributes.  The
   type attribute is set to the MIME type of the target object.  The
   href attribute is set to the URI of the target object.  The rel
   attribute is set to the name of the element being replaced.

5.4.3.1.  XML Example

   A downstream CDN may request the HostIndex and receive the following
   object of type "application/cdni.HostIndex+xml":




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   <HostIndex>
     <host>
       <host>video.example.com</host>
       <link rel="host-metadata" type="application/cdni.HostMetadata"
         href="http://metadata.ucdn.example.com/video"/>
     </host>
     <host>
       <host>images.example.com</host>
       <link rel="host-metadata" type="application/cdni.HostMetadata"
         href="http://metadata.ucdn.example.com/images"/>
     </host>
   </HostIndex>

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

   <HostMetadata>
     <metadata>
       <type>application/cdni.SourceMetadata</type>
       <value>
         <sources>
           <link rel="auth" type="application/cdni.Auth"
             href="http://metadata.ucdn.example.com/auth1234"/>
           <endpoint>acq1.ucdn.example.com</endpoint>
           <protocol>ftp</protocol>
         </source>
         <source>
           <link rel="auth" type="application/cdni.Auth"
             href="http://metadata.ucdn.example.com/auth1234"/>
           <endpoint>acq2.ucdn.example.com</endpoint>
           <protocol>http</protocol>
         </source>
       </value>
     </metadata>
     <metadata>
       <type>application/cdni.LocationACL</type>
       <value>
         <location>
           <location>
             <iprange>192.168.0.0/16</iprange>
           </location>
           <action>deny</type>
         </location>
       </value>
     </metadata>
     <metadata>



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       <type>application/cdni.ProtocolACL</type>
       <value>
         <protocol>
           <protocol>ftp</protocol>
           <action>deny</action>
         </protocol>
       </value>
     </metadata>
     <path>
       <path-pattern>
         <pattern>/videos/trailers/*"</pattern>
       </path-pattern>
       <link rel="path-metadata" type="application/cdni.PathMetadata"
         href="http://metadata.ucdn.example.com/videos/trailers"/>
     </path>
     <path>
       <path-pattern>
         <pattern>/videos/movies/*"</pattern>
       </path-pattern>
       <link rel="path-metadata" type="application/cdni.PathMetadata"
         href="http://metadata.ucdn.example.com/videos/movies"/>
     </path>
   </HostMetadata>

   Suppose the path of the requested resource matches the "/video/
   movies/*" pattern, the next metadata requested would be for
   "http://metadata.ucdn.example.com/video/movies" with an expected type
   of "application/cdni.PathMetadata":

   <PathMetadata>
     <path>
       <path-pattern>
         <pattern>/videos/movies/hd/*</pattern>
       </path-pattern>
       <link rel="path-metadata" type="application/cdni.PathMetadata"
         href="http://metadata.ucdn.example.com/videos/movies/hd"/>
     </path>
   </PathMetadata>

   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.com/videos/movies/hd" with MIME type
   "application/cdni.PathMetadata":







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   <PathMetadata>
     <metadata>
       <type>application/cdni.TimeWindowACL</type>
       <value>
         <time>
           <time>
             <start>1213948800</start>
             <end>1327393200</end>
           </time>
           <type>allow</type>
         </time>
     </metadata>
   </PathMetadata>

5.5.  Extensibility

   The set of property Metadata may be extended with proprietary and/or
   custom property Metadata.  The GenericMetadata object defined in
   Section 4.1.7 allows any Metadata property to be included in either
   the HostMetadata or PathMetadata lists.  As described in Section 3.4,
   it is suggested that proprietary and/or custom property Metadata be
   identified by the "ext." prefix in an appropriately descriptive type
   which conveys the organization defining the property Metadata and the
   function of the property Metadata.

   Note: Identification of the property Metadata defining organization
   in the property Metadata type decreases the possibility of property
   Metadata type collision.

5.5.1.  Metadata Enforcement

   At any given time, the set of property Metadata supported by the uCDN
   may not match the set of property Metadata supported by the dCDN.
   The uCDN may or may not know which property Metadata the dCDN
   supports.  In cases where the uCDN supports Metadata that the dCDN
   does not, the dCDN MUST be aware of any Metadata marked as
   "mandatory-to-enforce".  If a CDN does not understand or is unable to
   perform the functions associated with any "mandatory-to-enforce"
   Metadata, the CDN MUST NOT service any requests for the corresponding
   content.

   Note: Ideally, uCDNs would not delegate content requests to a dCDN
   which does not support the 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).  The dCDN



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   MUST evaluate all Metadata associated with content requests and
   reject any requests where "mandatory-to-enforce" Metadata associated
   with the content cannot be enforced.

5.5.2.  Metadata Override

   It is possible that new Metadata definitions may obsolete or override
   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.v2.Auth, ext.vendor1.Auth, and
   ext.vendor2.Auth) all override 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 conflict.

   As described in Section 3.3, 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 asset do not conflict.

   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.


6.  IANA Considerations

   This document requests the registration of the "application/cdni"
   MIME type.

   [Ed.  Need to consider a registry for Metadata type identifiers.]


7.  Security Considerations

   The CDNI Metadata Interface is expected to be secured as a function
   of the transport protocol (e.g.  HTTP authentication, HTTPS, or
   inter-domain IPSec).

   If a malicious metadata server is contacted by a downstream CDN, the
   malicious server may provide metadata to the downstream CDN which
   denies service for any piece of content to any user agent.  The
   malicious server may also provide metadata which directs a downstream



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   CDN to a malicious origin server instead of the actual origin server.

   A malicious metadata client could request metadata for a piece of
   content from an upstream CDN.  The metadata information may then be
   used to glean information regarding the uCDN or to contact an
   upstream origin server.  The uCDN is expected to authenticate client
   requests to prevent this situation.


8.  Acknowledgements

   The authors would like to thank David Ferguson and Francois le
   Faucheur for their valuable comments and input to this document.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

9.2.  Informative References

   [I-D.davie-cdni-framework]
              Davie, B. and L. Peterson, "Framework for CDN
              Interconnection", draft-davie-cdni-framework-00 (work in
              progress), July 2011.

   [I-D.ietf-cdni-problem-statement]
              Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", draft-ietf-cdni-problem-statement-03 (work in
              progress), January 2012.

   [I-D.ietf-cdni-requirements]
              Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements",
              draft-ietf-cdni-requirements-02 (work in progress),
              December 2011.

   [I-D.zyp-json-schema]



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              Zyp, K. and G. Court, "A JSON Media Type for Describing
              the Structure and Meaning of JSON Documents",
              draft-zyp-json-schema-03 (work in progress),
              November 2010.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4151]  Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
              RFC 4151, October 2005.

   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
              Syndication Format", RFC 4287, December 2005.

   [XML-BASE]
              Marsh, J., Ed. and R. Tobin, Ed., "XML Base (Second
              Edition) - http://www.w3.org/TR/xmlbase/", January 2009.


Appendix A.  Relationship to the CDNI Requirements

   Section 6 of [I-D.ietf-cdni-requirements] lists the requirements for
   the CDNI Metadata Distribution interface.  This section outlines
   which of those requirements are met by the CDNI Metadata interface
   specified in this document.

   All metadata requirements are met either directly or indirectly by
   the CDNI Metadata Interface described in this document.  The
   following paragraphs describe notable exceptions.

   Requirements related to pre-positioning of metadata are not met
   directly by this document.  Triggering metadata pre-positioning is
   beyond the scope of the CDNI Metadata interface.  However, the
   interface as described by this document supports pulling metadata on-
   demand for the purpose of pre-positioning.

   Requirement META-13 relating to feedback from the downstream CDN to
   the upstream CDN with respect to metadata is not directly supported
   by the pull-based interface described in this document.  As an
   alternative, the downstream CDN may use the CDNI Logging interface to
   convey error conditions related to metadata.

   Requirement META-18 relating to surrogate cache behavior parameters
   is supported via extensibility.  However, the example parameters in
   META-18 are not described in this document.





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Authors' Addresses

   Ben Niven-Jenkins
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: ben@velocix.com


   Rob Murray
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: rmurray@velocix.com


   Grant Watson
   Velocix (Alcatel-Lucent)
   3 Ely Road
   Milton, Cambridge  CB24 6AA
   UK

   Email: gwatson@velocix.com


   Matt Caulfield
   Cisco Systems
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Phone: +1 978 936 9307
   Email: mcaulfie@cisco.com


   Kent Leung
   Cisco Systems
   3625 Cisco Way
   San Jose  95134
   USA

   Phone: +1 408 526 5030
   Email: kleung@cisco.com




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   Kevin J. Ma
   Azuki Systems, Inc.
   43 Nagog Park
   Acton, MA  01720
   USA

   Phone: +1 978-844-5100
   Email: kevin.ma@azukisystems.com











































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