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Versions: (draft-davie-cdni-framework) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 7336

Network Working Group                                   L. Peterson, Ed.
Internet-Draft                                 Akamai Technologies, Inc.
Obsoletes: 3466 (if approved)                                   B. Davie
Intended status: Informational                              VMware, Inc.
Expires: August 22, 2013                               February 18, 2013


                   Framework for CDN Interconnection
                      draft-ietf-cdni-framework-03

Abstract

   This document presents a framework for Content Distribution Network
   Interconnection (CDNI).  The purpose of the framework is to provide
   an overall picture of the problem space of CDNI and to describe the
   relationships among the various components necessary to interconnect
   CDNs.  CDN Interconnection requires the specification of several
   interfaces and mechanisms to address issues such as request routing,
   distribution metadata exchange, and logging information exchange
   across CDNs.  The intent of this document is to outline what each
   interface needs to accomplish, and to describe how these interfaces
   and mechanisms fit together, while leaving their detailed
   specification to other documents.  It obsoletes RFC 3466.

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 August 22, 2013.

Copyright Notice

   Copyright (c) 2013 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
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   described in the Simplified BSD License.












































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Reference Model  . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Structure Of This Document . . . . . . . . . . . . . . . .  9
   2.  Building Blocks  . . . . . . . . . . . . . . . . . . . . . . .  9
     2.1.  Request Redirection  . . . . . . . . . . . . . . . . . . .  9
       2.1.1.  DNS Redirection  . . . . . . . . . . . . . . . . . . .  9
       2.1.2.  HTTP Redirection . . . . . . . . . . . . . . . . . . . 10
   3.  Overview of CDNI Operation . . . . . . . . . . . . . . . . . . 11
     3.1.  Preliminaries  . . . . . . . . . . . . . . . . . . . . . . 13
     3.2.  Iterative HTTP Redirect Example  . . . . . . . . . . . . . 14
     3.3.  Recursive HTTP Redirection Example . . . . . . . . . . . . 19
     3.4.  Iterative DNS-based Redirection Example  . . . . . . . . . 23
     3.5.  Dynamic Footprint Discovery Example  . . . . . . . . . . . 27
     3.6.  Content Removal Example  . . . . . . . . . . . . . . . . . 29
     3.7.  Pre-Positioned Content Acquisition Example . . . . . . . . 29
     3.8.  Asynchronous CDNI Metadata Example . . . . . . . . . . . . 31
     3.9.  Synchronous CDNI Metadata Acquisition Example  . . . . . . 33
     3.10. Content and Metadata Acquisition with Multiple
           Upstream CDNs  . . . . . . . . . . . . . . . . . . . . . . 35
   4.  Main Interfaces  . . . . . . . . . . . . . . . . . . . . . . . 36
     4.1.  In-Band versus Out-of-Band Interfaces  . . . . . . . . . . 37
     4.2.  Cross Interface Concerns . . . . . . . . . . . . . . . . . 37
     4.3.  Request Routing Interface  . . . . . . . . . . . . . . . . 38
     4.4.  Logging Interface  . . . . . . . . . . . . . . . . . . . . 39
     4.5.  Control Interface  . . . . . . . . . . . . . . . . . . . . 41
     4.6.  Metadata Interface . . . . . . . . . . . . . . . . . . . . 41
     4.7.  HTTP Adaptive Streaming Concerns . . . . . . . . . . . . . 42
   5.  Deployment Models  . . . . . . . . . . . . . . . . . . . . . . 43
     5.1.  Meshed CDNs  . . . . . . . . . . . . . . . . . . . . . . . 44
     5.2.  CSP combined with CDN  . . . . . . . . . . . . . . . . . . 45
     5.3.  CSP using CDNI Request Routing Interface . . . . . . . . . 46
     5.4.  CDN Federations and CDN Exchanges  . . . . . . . . . . . . 47
   6.  Trust Model  . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 51
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 51
     8.1.  Security of CDNI Interfaces  . . . . . . . . . . . . . . . 52
     8.2.  Digital Rights Management  . . . . . . . . . . . . . . . . 53
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 53
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 53
   11. Informative References . . . . . . . . . . . . . . . . . . . . 53
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 55







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1.  Introduction

   The interconnection of Content Distribution Networks (CDNs) is
   motivated by several use cases, such as those described in
   [I-D.ietf-cdni-use-cases].  The overall problem space for CDN
   Interconnection is described in RFC 6707.  The purpose of this
   document is to provide an overview of the various components
   necessary to interconnect CDNs.  CDN Interconnection requires the
   specification of several interfaces and mechanisms to address issues
   such as request routing, metadata exchange, and the acquisition of
   content by one CDN from another.  The intent of this document is to
   describe how these interfaces and mechanisms fit together, leaving
   their detailed specification to other documents.  We make extensive
   use of message flow examples to illustrate the operation of
   interconnected CDNs, but these examples should be considered
   illustrative rather than prescriptive.

   RFC 3466 uses different terminology and models for "Content
   Internetworking (CDI)".  It is also less prescriptive in terms of
   interfaces.  To avoid confusion, this document obsoletes RFC 3466.

1.1.  Terminology

   This document draws freely on the core terminology defined in RFC
   6707.  It also introduce the following terms:

   CDN-Domain: a host name (FQDN) at the beginning of a URL,
   representing a set of content that is served by a given CDN.  For
   example, in the URL http://cdn.csp.com/...rest of url..., the CDN
   domain is cdn.csp.com.  A major role of CDN-Domain is to identify a
   region (subset) of the URI space relative to which various CDN
   Interconnection rules and policies are to apply.  For example, a
   record of CDN Metadata might be defined for the set of resources
   corresponding to some CDN-Domain.

   Distinguished CDN-Domain: a CDN-Domain that is allocated by a CDN for
   the purposes of communication with a peer CDN, but which is not found
   in client requests.  Such CDN-Domains may be used for inter-CDN
   acquisition, or as redirection targets, and enable a CDN to
   distinguish a request from a peer CDN from an end-user request.

   Delivering CDN: the CDN that ultimately delivers a piece of content
   to the end-user.  The last in a potential sequence of downstream
   CDNs.

   Recursive CDNI Request Redirection: When an Upstream CDN elects to
   redirect a request towards a Downstream CDN, the Upstream CDN can
   query the Downstream CDN Request Routing system via the CDNI Request



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   Routing Redirection Interface (or use information cached from earlier
   similar queries) to find out how the Downstream CDN wants the request
   to be redirected, which allows the Upstream CDN to factor in the
   Downstream CDN response when redirecting the user agent.  This
   approach is referred to as "Recursive" CDNI Request Redirection.
   Note that the Downstream CDN may elect to have the request redirected
   directly to a Surrogate inside the Downstream CDN, to the Request-
   Routing System of the Downstream CDN, to another CDN, or to any other
   system that the Downstream CDN sees as fit for handling the
   redirected request.

   Iterative CDNI Request Redirection: When an Upstream CDN elects to
   redirect a request towards a Downstream CDN, the Upstream CDN can
   base its redirection purely on a local decision (and without
   attempting to take into account how the Downstream CDN may in turn
   redirect the user agent).  In that case, the Upstream CDN redirects
   the request to the request routing system in the Downstream CDN,
   which in turn will decide how to redirect that request: this approach
   is referred to as "Iterative" CDNI Request Redirection.

   Synchronous CDNI operations: operations between CDNs that happen
   during the process of servicing a user request, i.e. between the time
   that the user agent begins its attempt to obtain content and the time
   at which that request is served.

   Asynchronous CDNI operations: operations between CDNs that happen
   independently of any given user request, such as advertisement of
   footprint information or pre-positioning of content for later
   delivery.

   Trigger Interface: a sub-set of the Control Interface that includes
   operations to pre-position, revalidate, and purge both metadata and
   content.  These operations are typically called in response to some
   action (trigger) by the CSP on the upstream CDN.

1.2.  Reference Model

   This document uses the reference model in Figure 1 as originally
   created in RFC 6707.












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     --------
    /        \
    |   CSP  |
    \        /
     --------
         *
         *
         *                         /\
         *                        /  \
     ----------------------      |CDNI|        ----------------------
    /     Upstream CDN     \     |    |       /    Downstream CDN    \
    |      +-------------+ | Control Interface| +-------------+      |
    |*******   Control   |<======|====|========>|   Control   *******|
    |*     +------*----*-+ |     |    |       | +-*----*------+     *|
    |*            *    *   |     |    |       |   *    *            *|
    |*     +------*------+ | Logging Interface| +------*------+     *|
    |* *****   Logging   |<======|====|========>|   Logging   ***** *|
    |* *   +-*-----------+ |     |    |       | +-----------*-+   * *|
    |* *     *         *   | Request Routing  |   *         *     * *|
  .....*...+-*---------*-+ |    Interface     | +-*---------*-+...*.*...
  . |* * *** Req-Routing |<======|====|========>| Req-Routing *** * *| .
  . |* * * +-------------+.|     |    |       | +-------------+ * * *| .
  . |* * *                 .  CDNI Metadata   |                 * * *| .
  . |* * * +-------------+ |.   Interface     | +-------------+ * * *| .
  . |* * * | Distribution|<==.===|====|========>| Distribution| * * *| .
  . |* * * |             | |  .   \  /        | |             | * * *| .
  . |* * * |+---------+  | |   .   \/         | |  +---------+| * * *| .
  . |* * ***| +---------+| |    ....Request......+---------+ |*** * *| .
  . |* *****+-|Surrogate|************************|Surrogate|-+***** *| .
  . |*******  +---------+| |   Acquisition    | |+----------+ *******| .
  . |      +-------------+ |                  | +-------*-----+      | .
  . \                      /                  \         *            / .
  .  ----------------------                    ---------*------------  .
  .                                                     *              .
  .                                                     * Delivery     .
  .                                                     *              .
  .                                                  +--*---+          .
  ...............Request.............................| User |..Request..
                                                     | Agent|
                                                     +------+

  <==>  interfaces inside the scope of CDNI

  ****  interfaces outside the scope of CDNI
  ....  interfaces outside the scope of CDNI

                 Figure 1: CDNI Model and CDNI Interfaces




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   We note that while some interfaces in the reference model are "out of
   scope" for the CDNI WG (in the sense that there is no need to define
   new protocols for those interfaces) we still need to refer to them in
   this document to explain the overall operation of CDNI.

   We also note that, while we generally show only one uCDN serving a
   given CSP, it is entirely possible that multiple uCDNs can serve a
   single CSP.  In fact, this situation effectively exists today in the
   sense that a single CSP can currently delegate its content delivery
   to more than one CDN.

   The following briefly describes the four CDNI interfaces,
   paraphrasing the definitions given in RFC 6707.  We discuss these
   interfaces in more detail in Section 4.

   o  CDNI Control Interface (CI): Operations to bootstrap and
      parameterize the other CDNI interfaces, as well as operations to
      pre-position, revalidate, and purge both metadata and content.
      The latter sub-set of operations is sometimes collectively called
      the "trigger interface."

   o  CDNI Request Routing Interface: Operations to determine what CDN
      (and optionally what surrogate within a CDN) is to serve end-
      user's requests.  Is actually a logical bundling of two separate
      but related interfaces:

      *  Footprint & Capability Interface (FCI): Asynchronous operations
         to exchange routing information (e.g., the network footprint
         and capabilities served by a given CDN) that enables CDN
         selection for subsequent user requests; and

      *  Request Routing Redirection (RI): Synchronous operations to
         select a delivery CDN (surrogate) for a given user request.

   o  CDNI Metadata Interface (MI): Operations to communicate metadata
      that governs the how content is delivered by interconnected CDNs.
      Examples of CDNI metadata include geo-blocking directives,
      availability windows, access control mechanisms, and purge
      directives.  May include a combination of:

      *  Asynchronous operations to exchange metadata that govern
         subsequent user requests for content; and

      *  Synchronous operations that govern behavior for a given user
         request for content.






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   o  CDNI Logging Interface (LI): Operations that allow interconnected
      CDNs to exchange relevant activity logs.  May include a
      combination of:

      *  Real-time exchanges, suitable for runtime traffic monitoring;
         and

      *  Off-line exchanges, suitable for analytics and billing.

   There is some potential overlap between the set of trigger-based
   operations in the Control Interface and the Metadata Interface.  For
   both cases, the information passed from the upstream CDN to the
   downstream CDN can broadly be viewed as metadata that describes how
   content is to be managed by the downstream CDN.  For example, the
   information conveyed by Control operations to pre-position,
   revalidate or purge metadata is similar to the information conveyed
   by posting updated metadata via the Metadata Interface.  Even the
   Control operation to purge content could be viewed as an metadata
   update for that content: purge simply says that the availability
   window for the named content ends now.  The two interfaces share much
   in common, so minimally, there will need to be a consistent data
   model that spans both.

   The distinction we draw has to do with what the caller knows about
   the successful application of the metadata by the callee.  In the
   case of the Control Interface, the downstream CDN returning a
   successful status message guarantees that the operation has been
   successfully completed; e.g., the content has been purged or pre-
   positioned.  This implies that the downstream CDN accepts
   responsibility for having successfully completed the requested
   operation.  In contrast, metadata passed between CDNs via the
   Metadata Interface carries no such completion guarantee.  Returning
   success implies successful receipt of the metadata, but nothing can
   be inferred about precisely when the metadata will take effect in the
   downstream CDN, only that it will take effect eventually.  This is
   because of the challenge in globally synchronizing updates to
   metadata with end-user requests that are currently in progress (or
   indistinguishable from currently being in progress).  Clearly, a CDN
   will not be viewed as a trusted peer if "eventually" often becomes an
   indefinite period of time, but the acceptance of responsibility
   cannot be as crisply defined for the Metadata Interface.

   Finally, there is a practical issue that impacts all of the CNDI
   interfaces, and that is whether or not to optimize CDNI for HTTP
   Adaptive Streaming (HAS).  We highlight specific issues related to
   delivering HAS content throughout this document, but for a more
   thorough treatment of the topic, see [I-D.brandenburg-cdni-has].




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1.3.  Structure Of This Document

   The remainder of this document is organized as follows:

   o  Section 2 describes some essential building blocks for CDNI,
      notably the various options for redirecting user requests to a
      given CDN.

   o  Section 3 provides a number of illustrative examples of various
      CDNI operations.

   o  Section 4 describes the functionality of the four main CDNI
      interfaces.

   o  Section 5 shows how various deployment models of CDNI may be
      achieved using the defined interfaces.

   o  Section 6 describes the trust model of CDNI and the issues of
      transitive trust in particular that CDNI raises.


2.  Building Blocks

2.1.  Request Redirection

   At its core, CDN Interconnection requires the redirection of requests
   from one CDN to another.  For any given request that is received by
   an upstream CDN, it will either respond to the request directly, or
   somehow redirect the request to a downstream CDN.  Two main
   mechanisms are available for redirecting a request to a downstream
   CDN.  The first leverages the DNS name resolution process and the
   second uses in-protocol redirection mechanisms such as the HTTP 302
   or 307 redirection response.  We discuss these below as background
   before discussing some examples of their use in Section 3.

2.1.1.  DNS Redirection

   DNS redirection is based on returning different IP addresses for the
   same DNS name, for example, to balance server load or to account for
   the client's location in the network.  A DNS server, sometimes called
   the Local DNS (LDNS), resolves DNS names on behalf of an end-user.
   The LDNS server in turn queries other DNS servers until it reaches
   the authoritative DNS server for the CDN-Domain.  The network
   operator typically provides the LDNS server, although the user is
   free to choose other DNS servers (e.g., OpenDNS, Google Public DNS).

   The advantage of DNS redirection is that it is completely transparent
   to the end user--the user sends a DNS name to the LDNS server and



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   gets back an IP address.  On the other hand, DNS redirection is
   problematic because the DNS request comes from the LDNS server, not
   the end-user.  This may affect the accuracy of server selection that
   is based on the user's location.  The transparency of DNS redirection
   is also a problem in that there is no opportunity to take the
   attributes of the user agent or the URI path component into account.
   We consider two main forms of DNS redirection: simple and CNAME-
   based.

   In simple DNS redirection, the authoritative DNS server for the name
   simply returns an IP address from a set of possible IP addresses.
   The answer is chosen from the set based on characteristics of the set
   (e.g., the relative loads on the servers) or characteristics of the
   client (e.g., the location of the client relative to the servers).
   Simple redirection is straightforward.  The only caveats are (1)
   there is a limit to the number alternate IP addresses a single DNS
   server can manage; and (2) DNS responses are cached by downstream
   servers so the TTL on the response must be set to an appropriate
   value so as to preserve the fresheness of the redirection.

   In CNAME-based DNS redirection, the authoritative server returns a
   CNAME response to the DNS request, telling the LDNS server to restart
   the name lookup using a new name.  A CNAME is essentially a symbolic
   link in the DNS namespace, and like a symbolic link, redirection is
   transparent to the client--the LDNS server gets the CNAME response
   and re-executes the lookup.  Only when the name has been resolved to
   an IP address does it return the result to the user.  Note that DNAME
   would be preferable to CNAME if it becomes widely supported.

2.1.2.  HTTP Redirection

   HTTP redirection makes use of the redirection response of the HTTP
   protocol (e.g.,"302" or "307").  This response contains a new URL
   that the application should fetch instead of the original URL.  By
   changing the URL appropriately, the server can cause the user to
   redirect to a different server.  The advantages of HTTP redirection
   are that (1) the server can change the URL fetched by the client to
   include, for example, both the DNS name of the particular server to
   use, as well as the original HTTP server that was being accessed; (2)
   the client sends the HTTP request to the server, so that its IP
   address is known and can be used in selecting the server; and (3)
   other attributes (e.g., content type, user-agent type) are visible to
   the redirection mechanism.

   The disadvantages of HTTP redirection are (1) it is visible to the
   application, so it requires application support and may affect the
   application behavior (e.g., web browsers will not send cookies if the
   URL changes to a different domain); (2) HTTP is a heavy-weight



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   protocol layered on TCP so it has relatively high overhead; and (3)
   the results of HTTP redirection are not cached so that all
   redirections must go through to the server.


3.  Overview of CDNI Operation

   To provide a big-picture overview of the various components of CDN
   Interconnection, we walk through a "day in the life" of a content
   item that is made available via a pair of interconnected CDNs.  This
   will serve to illustrate many of the functions that need to be
   supported in a complete CDNI solution.  We give examples using both
   DNS-based and HTTP-based redirection.  We begin with very simple
   examples and then how additional capabilities, such as recursive
   request redirection and content removal, might be added.

   Before walking through some specific examples, we present a high-
   level view of the operations that may take place.  This high-level
   overview is illustrated in Figure 2.  Note that most operations will
   involve only a subset of all the messages shown below, and that the
   order and number of operations may vary considerably, as more
   detailed examples illustrate below.

   The following shows Operator A as the upstream CDN (uCDN) and
   Operator B as the downstream CDN (dCDN), where the former has a
   relationship with a content provider and the latter being the CDN
   selected by Operator A to deliver content to the end-user.  The
   interconnection relationship may be symmetric between these two CDN
   operators, but each direction can be considered as operating
   independently of the other so for simplicity we show the interaction
   in one direction only.




















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         End-User                  Operator B                Operator A
             |                         |                         |
             |                         |                         |
             |                         |  [Async FCI Push]       | (1)
             |                         |                         |
             |                         |  [MI pre-positioning]   | (2)
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |-------------------------------------------------->| (3)
             |                         |                         |
             |                         |   [Sync RI Pull]        | (4)
             |                         |                         |
             | [RI REPLY]              |                         |
             |<--------------------------------------------------| (5)
             |                         |                         |
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |------------------------>|                         | (6)
             |                         |                         |
             |                         |   [Sync MI Pull]        | (7)
             |                         |                         |
             |                         | ACQUISITION REQUEST     |
             |                         X------------------------>| (8)
             |                         X                         |
             |                         X CONTENT DATA            |
             |                         X<------------------------| (9)
             |                         |                         |
             | CONTENT DATA            |                         |
             |<------------------------|                         | (10)
             |                         |                         |
             :                         :                         :
                 :          [Other content requests]                 :
             :                         :                         :
             |                         |  [CI: Content Purge]    | (11)
             :                         :                         :
             |                         |  [LI: Log exchange]     | (12)
             |                         |                         |



                      Figure 2: Overview of Operation

   The operations shown in the Figure are as follows:

   1.   dCDN uses the FCI to advertise information relevant to its
        delivery footprint and capabilities prior to any content
        requests being redirected.




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   2.   Prior to any content request, the uCDN uses the MI to
        pre=position CDNI metadata to the dCDN, thereby making that
        metadata available in readiness for later content requests.

   3.   A content request from a user agent arrives at uCDN.

   4.   uCDN may use the RI to synchronously request information from
        dCDN regarding its delivery capabilities to decide if dCDN is a
        suitable target for redirection of this request.

   5.   uCDN redirects the request to dCDN by sending some response
        (DNS, HTTP) to the user agent.

   6.   The user agent requests the content from dCDN.

   7.   dCDN may use the MI to synchronously request metadata related to
        this content from uCDN, e.g. to decide whether to serve it.

   8.   If the content is not already in a suitable cache in dCDN, dCDN
        may acquire it from uCDN.

   9.   The content is delivered to dCDN from uCDN.

   10.  The content is delivered to the user agent by dCDN.

   11.  Some time later, perhaps at the request of the CSP (not shown)
        uCDN may use the CI to instruct dCDN to purge the content,
        thereby ensuring it is not delivered again.

   12.  After one or more content delivery actions by dCDN, a log of
        delivery actions may be provided to uCDN using the LI.

   The following sections show some more specific examples of how these
   operations may be combined to perform various delivery, control and
   logging operations across a pair of CDNs.

3.1.  Preliminaries

   Initially, we assume that there is at least one CSP that has
   contracted with an upstream CDN (uCDN) to deliver content on its
   behalf.  We are not particularly concerned with the interface between
   the CSP and uCDN, other than to note that it is expected to be the
   same as in the "traditional" (non-interconnected) CDN case.  Existing
   mechanisms such as DNS CNAMEs or HTTP redirects (Section 2) can be
   used to direct a user request for a piece of content from the CSP
   towards the CSP's chosen upstream CDN.

   We assume Operator A provides an upstream CDN that serves content on



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   behalf of a CSP with CDN-Domain cdn.csp.com.  We assume that Operator
   B provides a downstream CDN.  An end user at some point makes a
   request for URL

   http://cdn.csp.com/...rest of url...

   It may well be the case that cdn.csp.com is just a CNAME for some
   other CDN-Domain (such as csp.op-a.net).  Nevertheless, the HTTP
   request in the examples that follow is assumed to be for the example
   URL above.

   Our goal is to enable content identified by the above URL to be
   served by the CDN of operator B. In the following sections we will
   walk through some scenarios in which content is served, as well as
   other CDNI operations such as the removal of content from a
   downstream CDN.

3.2.  Iterative HTTP Redirect Example

   In this section we walk through a simple, illustrative example using
   HTTP redirection from uCDN to dCDN.  The example also assumes the use
   of HTTP redirection inside uCDN and dCDN; however, this is
   independent of the choice of redirection approach across CDNs, so an
   alternative example could be constructed still showing HTTP
   redirection from uCDN to dCDN but using DNS for handling of request
   inside each CDN.

   We assume for this example that Operators A and B have established an
   agreement to interconnect their CDNs, with A being upstream and B
   being downstream.

   The operators agree that a CDN-Domain peer-a.op-b.net will be used as
   the target of redirections from uCDN to dCDN.  We assume the name of
   this domain is communicated by some means to each CDN.  (This could
   be established out-of-band or via a CDNI interface.)  We refer to
   this domain as a "distinguished" CDN-Domain to convey the fact that
   its use is limited to the interconnection mechanism; such a domain is
   never used directly by a CSP.

   We assume the operators also agree on some distinguished CDN-Domain
   that will be used for inter-CDN acquisition of CSP's content from
   uCDN by dCDN.  In this example, we'll use op-b-acq.op-a.net.

   We assume the operators also exchange information regarding which
   requests dCDN is prepared to serve.  For example, dCDN may be
   prepared to serve requests from clients in a given geographical
   region or a set of IP address prefixes.  This information may again
   be provided out of band or via a defined CDNI interface.



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   We assume DNS is configured in the following way:

   o  The content provider is configured to make operator A the
      authoritative DNS server for cdn.csp.com (or to return a CNAME for
      cdn.csp.com for which operator A is the authoritative DNS server).

   o  Operator A is configured so that a DNS request for op-b-acq.op-
      a.net returns a request router in Operator A.

   o  Operator B is configured so that a DNS request for peer-a.op-
      b.net/cdn.csp.com returns a request router in Operator B.

   Figure 3 illustrates how a client request for

   http://cdn.csp.com/...rest of url...

   is handled.

         End-User                 Operator B                Operator A
             |DNS cdn.csp.com          |                         |
             |-------------------------------------------------->|
             |                         |                         |(1)
             |IPaddr of A's Request Router                       |
             |<--------------------------------------------------|
             |HTTP cdn.csp.com         |                         |
             |-------------------------------------------------->|
             |                         |                         |(2)
             |302 peer-a.op-b.net/cdn.csp.com                    |
             |<--------------------------------------------------|
             |DNS peer-a.op-b.net      |                         |
             |------------------------>|                         |
             |                         |(3)                      |
             |IPaddr of B's Request Router                       |
             |<------------------------|                         |
             |                         |                         |
             |HTTP peer-a.op-b.net/cdn.csp.com                   |
             |------------------------>|                         |
             |                         |(4)                      |
             |302 node1.peer-a.op-b.net/cdn.csp.com              |
             |<------------------------|                         |
             |DNS node1.peer-a.op-b.net|                         |
             |------------------------>|                         |
             |                         |(5)                      |
             |IPaddr of B's Delivery Node                        |
             |<------------------------|                         |
             |                         |                         |
             |HTTP node1.peer-a.op-b.net/cdn.csp.com             |
             |------------------------>|                         |



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             |                         |(6)                      |
             |                         |DNS op-b-acq.op-a.net    |
             |                         |------------------------>|
             |                         |                         |(7)
             |                         |IPaddr of A's Request Router
             |                         |<------------------------|
             |                         |HTTP op-b-acq.op-a.net   |
             |                         |------------------------>|
             |                         |                         |(8)
             |                         |302 node2.op-b.acq.op-A.net
             |                         |<------------------------|
             |                         |DNS node2.op-b-acq.op-a.net
             |                         |------------------------>|
             |                         |                         |(9)
             |                         |IPaddr of A's Delivery Node
             |                         |<------------------------|
             |                         |                         |
             |                         |HTTP node2.op-b-acq.op-a.net
             |                         |------------------------>|
             |                         |                         |(10)
             |                         |Data                     |
             |                         |<------------------------|
             |Data                     |                         |
             |<------------------------|                         |

           Figure 3: Message Flow for Iterative HTTP Redirection

   The steps illustrated in the figure are as follows:

   1.   A DNS resolver for Operator A processes the DNS request for its
        customer based on CDN-Domain cdn.csp.com.  It returns the IP
        address of a request router in Operator A.

   2.   A Request Router for Operator A processes the HTTP request and
        recognizes that the end-user is best served by another CDN--
        specifically one provided by Operator B--and so it returns a 302
        redirect message for a new URL constructed by "stacking"
        Operator B's distinguished CDN-Domain (peer-a.op-b.net) on the
        front of the original URL.  (Note that more complex URL
        manipulations are possible, such as replacing the initial CDN-
        Domain by some opaque handle.)

   3.   The end-user does a DNS lookup using Operator B's distinguished
        CDN-Domain (peer-a.op-b.net).  B's DNS resolver returns the IP
        address of a request router for Operator B. Note that if request
        routing within dCDN was performed using DNS instead of HTTP
        redirection, B's DNS resolver would also behave as the request
        router and directly return the IP address of a delivery node.



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   4.   The request router for Operator B processes the HTTP request and
        selects a suitable delivery node to serve the end-user request,
        and returns a 302 redirect message for a new URL constructed by
        replacing the hostname by a subdomain of the Operator B's
        distinguished CDN-Domain that points to the selected delivery
        node.

   5.   The end-user does a DNS lookup using Operator B's delivery node
        subdomain (node1.peer-a.op-b.net).  B's DNS resolver returns the
        IP address of the delivery node.

   6.   The end-user requests the content from B's delivery node.  In
        the case of a cache hit, steps 6, 7, 8, 9 and 10 below do not
        happen, and the content data is directly returned by the
        delivery node to the end-user.  In the case of a cache miss, the
        content needs to be acquired by dCDN from uCDN (not the CSP).
        The distinguished CDN-Domain peer-a.op-b.net indicates to dCDN
        that this content is to be acquired from uCDN; stripping the
        CDN-Domain reveals the original CDN-Domain cdn.csp.com and dCDN
        may verify that this CDN-Domain belongs to a known peer (so as
        to avoid being tricked into serving as an open proxy).  It then
        does a DNS request for an inter-CDN acquisition CDN-Domain as
        agreed above (in this case, op-b-acq.op-a.net).

   7.   Operator A's DNS resolver processes the DNS request and returns
        the IP address of a request router in operator A.

   8.   The request router for Operator A processes the HTTP request
        from Operator B delivery node.  Operator A request router
        recognizes that the request is from a peer CDN rather than an
        end-user because of the dedicated inter-CDN acquisition domain
        (op-b-acq.op-a.net).  (Note that without this specially defined
        inter-CDN acquisition domain, operator A would be at risk of
        redirecting the request back to operator B, resulting in an
        infinite loop).  The request router for Operator A selects a
        suitable delivery node in uCDN to serve the inter-CDN
        acquisition request and returns a 302 redirect message for a new
        URL constructed by replacing the hostname by a subdomain of the
        Operator A's distinguished inter-CDN acquisition domain that
        points to the selected delivery node.

   9.   Operator A DNS resolver processes the DNS request and returns
        the IP address of the delivery node in operator A.

   10.  Operator B requests (acquires) the content from Operator A.
        Although not shown, Operator A processes the rest of the URL: it
        extracts information identifying the origin server, validates
        that this server has been registered, and determines the content



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        provider that owns the origin server.  It may also perform its
        own content acquisition steps if needed before returning the
        content to dCDN.

   The main advantage of this design is that it is simple: each CDN need
   only know the distinguished CDN-Domain for each peer, with the
   upstream CDN "pushing" the downstream CDN-Domain onto the URL as part
   of its redirect (step 2) and the downstream CDN "popping" its CDN-
   Domain off the URL to expose a CDN-Domain that the upstream CDN can
   correctly process.  Neither CDN needs to be aware of the internal
   structure of the other's URLs.  Moreover, the inter-CDN redirection
   is entirely supported by a single HTTP redirect; neither CDN needs to
   be aware of the other's internal redirection mechanism (i.e., whether
   it is DNS or HTTP based).

   One disadvantage is that the end-user's browser is redirected to a
   new URL that is not in the same domain of the original URL.  This has
   implications on a number of security or validation mechanisms
   sometimes used on endpoints.  For example, it is important that any
   redirected URL be in the same domain (e.g., csp.com) if the browser
   is expected to send any cookies associated with that domain.  As
   another example, some video players enforce validation of a cross
   domain policy that needs to allow for the domains involved in the CDN
   redirection.  These problems are generally soluble, but the solutions
   complicate the example, so we do not discuss them further in this
   version of the draft.

   We note that this example begins to illustrate some of the interfaces
   that may be required for CDNI, but does not require all of them.  For
   example, obtaining information from dCDN regarding the set of client
   IP addresses or geographic regions it might be able to serve is an
   aspect of the CDNI request routing interface (specifically of the
   CDNI Footprint and Capabilities Interface).  Important configuration
   information such as the distinguished names used for redirection and
   inter-CDN acquisition could also be conveyed via a CDNI interface
   (e.g., perhaps the Control Interface).  The example also shows how
   existing HTTP-based methods suffice for the acquisition interface.
   Arguably, the absolute minimum metadata required for CDNI is the
   information required to acquire the content, and this information was
   provided "in-band" in this example by means of the URI handed to the
   client in the HTTP 302 response.  The example also assumes that the
   CSP does not require any distribution policy (e.g. time window, geo-
   blocking) or delivery processing to be applied by the interconnected
   CDNs.  Hence, there is no explicit Metadata Interface invoked in this
   example.  There is also no explicit Logging Interface discussed in
   this example.

   We also note that the step of deciding when a request should be



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   redirected to dCDN rather than served by uCDN has been somewhat
   glossed over.  It may be as simple as checking the client IP address
   against a list of prefixes, or it may be considerably more complex,
   involving a wide range of factors, such as the geographic location of
   the client (perhaps determined from a third party service), CDN load,
   or specific business rules.

   This example uses the "iterative" CDNI request redirection approach.
   That is, uCDN performs part of the request redirection function by
   redirecting the client to a request router in the dCDN, which then
   performs the rest of the redirection function by redirecting to a
   suitable surrogate.  If request routing is performed in the dCDN
   using HTTP redirection, this translates in the end-user experiencing
   two successive HTTP redirections.  By contrast, the alternative
   approach of "recursive" CDNI request redirection effectively
   coalesces these two successive HTTP redirections into a single one,
   sending the end-user directly to the right delivery node in the dCDN.
   This "recursive" CDNI request routing approach is discussed in the
   next section.

3.3.  Recursive HTTP Redirection Example

   The following example builds on the previous one to illustrate the
   use of the Request Routing Interface (specifically the CDNI Request
   Routing Redirection Interface) to enable "recursive" CDNI request
   routing.  We build on the HTTP-based redirection approach because it
   illustrates the principles and benefits clearly, but it is equally
   possible to perform recursive redirection when DNS-based redirection
   is employed.

   In contrast to the prior example, the operators need not agree in
   advance on a CDN-Domain to serve as the target of redirections from
   uCDN to dCDN.  We assume that the operators agree on some
   distinguished CDN-Domain that will be used for inter-CDN acquisition
   of CSP's content by dCDN.  In this example, we'll use op-b-acq.op-
   a.net.

   We assume the operators also exchange information regarding which
   requests dCDN is prepared to serve.  For example, dCDN may be
   prepared to serve requests from clients in a given geographical
   region or a set of IP address prefixes.  This information may again
   be provided out of band or via a defined protocol.

   We assume DNS is configured in the following way:

   o  The content provider is configured to make operator A the
      authoritative DNS server for cdn.csp.com (or to return a CNAME for
      cdn.csp.com for which operator A is the authoritative DNS server).



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   o  Operator A is configured so that a DNS request for op-b-acq.op-
      a.net returns a request router in Operator A.

   o  Operator B is configured so that a request for node1.op-b.net/
      cdn.csp.com returns the IP address of a delivery node.  Note that
      there might be a number of such delivery nodes.

   Figure 3 illustrates how a client request for

   http://cdn.csp.com/...rest of url...

   is handled.







































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         End-User                 Operator B                Operator A
             |DNS cdn.csp.com          |                         |
             |-------------------------------------------------->|
             |                         |                         |(1)
             |IPaddr of A's Request Router                       |
             |<--------------------------------------------------|
             |HTTP cdn.csp.com         |                         |
             |-------------------------------------------------->|
             |                         |                         |(2)
             |                         |RR/RI REQ cdn.csp.com    |
             |                         |<------------------------|
             |                         |                         |
             |                         |RR/RI RESP node1.op-b.net|
             |                         |------------------------>|
             |                         |                         |(3)
             |302 node1.op-b.net/cdn.csp.com                     |
             |<--------------------------------------------------|
             |DNS node1.op-b.net       |                         |
             |------------------------>|                         |
             |                         |(4)                      |
             |IPaddr of B's Delivery Node                        |
             |<------------------------|                         |
             |HTTP node1.op-b.net/cdn.csp.com                    |
             |------------------------>|                         |
             |                         |(5)                      |
             |                         |DNS op-b-acq.op-a.net    |
             |                         |------------------------>|
             |                         |                         |(6)
             |                         |IPaddr of A's Request Router
             |                         |<------------------------|
             |                         |HTTP op-b-acq.op-a.net   |
             |                         |------------------------>|
             |                         |                         |(7)
             |                         |302 node2.op-b.acq.op-A.net
             |                         |<------------------------|
             |                         |DNS node2.op-b-acq.op-a.net
             |                         |------------------------>|
             |                         |                         |(8)
             |                         |IPaddr of A's Delivery Node
             |                         |<------------------------|
             |                         |                         |
             |                         |HTTP node2.op-b-acq.op-a.net
             |                         |------------------------>|
             |                         |                         |(9)
             |                         |Data                     |
             |                         |<------------------------|
             |Data                     |                         |
             |<------------------------|                         |



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           Figure 4: Message Flow for Recursive HTTP Redirection

   The steps illustrated in the figure are as follows:

   1.  A DNS resolver for Operator A processes the DNS request for its
       customer based on CDN-Domain cdn.csp.com.  It returns the IP
       address of a Request Router in Operator A.

   2.  A Request Router for Operator A processes the HTTP request and
       recognizes that the end-user is best served by another CDN--
       specifically one provided by Operator B--and so it queries the
       CDNI Request Routing Redirection Interface of Operator B,
       providing a set of information about the request including the
       URL requested.  Operator B replies with the DNS name of a
       delivery node.

   3.  Operator A returns a 302 redirect message for a new URL obtained
       from the Request Routing Interface.

   4.  The end-user does a DNS lookup using the host name of the URL
       just provided (node1.op-b.net).  B's DNS resolver returns the IP
       address of the corresponding delivery node.  Note that, since the
       name of the delivery node was already obtained from B using the
       CDNI Request Routing Interface, there should not be any further
       redirection here (in contrast to the iterative method described
       above.)

   5.  The end-user requests the content from B's delivery node,
       potentially resulting in a cache miss.  In the case of a cache
       miss, the content needs to be acquired from uCDN (not the CSP.)
       The distinguished CDN-Domain op-b.net indicates to dCDN that this
       content is to be acquired from another CDN; stripping the CDN-
       Domain reveals the original CDN-Domain cdn.csp.com, dCDN may
       verify that this CDN-Domain belongs to a known peer (so as to
       avoid being tricked into serving as an open proxy).  It then does
       a DNS request for the inter-CDN Acquisition "distinguished" CDN-
       Domain as agreed above (in this case, op-b-acq.op-a.net).

   6.  Operator A DNS resolver processes the DNS request and returns the
       IP address of a request router in operator A.

   7.  The request router for Operator A processes the HTTP request from
       Operator B delivery node.  Operator A request router recognizes
       that the request is from a peer CDN rather than an end-user
       because of the dedicated inter-CDN acquisition domain (op-b-
       acq.op-a.net).  (Note that without this specially defined inter-
       CDN acquisition domain, operator A would be at risk of
       redirecting the request back to operator B, resulting in an



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       infinite loop).  The request router for Operator A selects a
       suitable delivery node in uCDN to serve the inter-CDN acquisition
       request and returns a 302 redirect message for a new URL
       constructed by replacing the hostname by a subdomain of the
       Operator A's distinguished inter-CDN acquisition domain that
       points to the selected delivery node.

   8.  Operator A recognizes that the DNS request is from a peer CDN
       rather than an end-user (due to the internal CDN-Domain) and so
       returns the address of a delivery node.  (Note that without this
       specially defined internal domain, Operator A would be at risk of
       redirecting the request back to Operator B, resulting in an
       infinite loop.)

   9.  Operator B requests (acquires) the content from Operator A.
       Operator A serves content for the requested CDN-Domain to dCDN.
       Although not shown, it is at this point that Operator A processes
       the rest of the URL: it extracts information identifying the
       origin server, validates that this server has been registered,
       and determines the content provider that owns the origin server.
       It may also perform its own content acquisition steps if needed
       before returning the content to dCDN.

   Recursive redirection has the advantage over iterative of being more
   transparent from the end-user's perspective, but the disadvantage of
   each CDN exposing more of its internal structure (in particular, the
   addresses of edge caches) to peer CDNs.  By contrast, iterative
   redirection does not require dCDN to expose the addresses of its edge
   caches to uCDN.

   This example happens to use HTTP-based redirection in both CDN A and
   CDN B, but a similar example could be constructed using DNS-based
   redirection in either CDN.  Hence, the key point to take away here is
   simply that the end user only sees a single redirection of some type,
   as opposed to the pair of redirections in the prior (iterative)
   example.

   The use of the Request Routing Interface requires that interface to
   be appropriately configured and bootstrapped, which is not shown
   here.  More discussion on the bootstrapping of interfaces is provided
   in Section 4

3.4.  Iterative DNS-based Redirection Example

   In this section we walk through a simple example using DNS-based
   redirection for request redirection from uCDN to dCDN (as well as for
   request routing inside dCDN and uCDN).  As noted in Section 2.1, DNS-
   based redirection has certain advantages over HTTP-based redirection



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   (notably, it is transparent to the end-user) as well as some
   drawbacks (notably the client IP address is not visible to the
   request router).

   As before, Operator A has to learn the set of requests that dCDN is
   willing or able to serve (e.g. which client IP address prefixes or
   geographic regions are part of the dCDN footprint).  We assume
   Operator has and makes known to operator A some unique identifier
   that can be used for the construction of a distinguished CDN-Domain,
   as shown in more detail below.  (This identifier strictly needs only
   to be unique within the scope of Operator A, but a globally unique
   identifier, such as an AS number assigned to B, is one easy way to
   achieve that.)  Also, Operator A obtains the NS records for Operator
   B's externally visible redirection servers.  Also, as before, a
   distinguished CDN-Domain, such as op-b-acq.op-a.net, must be assigned
   for inter-CDN acquisition.

   We assume DNS is configured in the following way:

   o  The CSP is configured to make Operator A the authoritative DNS
      server for cdn.csp.com (or to return a CNAME for cdn.csp.com for
      which operator A is the authoritative DNS server).

   o  When uCDN sees a request best served by dCDN, it returns CNAME and
      NS records for "b.cdn.csp.com", where "b" is the unique identifier
      assigned to Operator B. (It may, for example, be an AS number
      assigned to Operator B.)

   o  dCDN is configured so that a request for "b.cdn.csp.com" returns a
      delivery node in dCDN.

   o  uCDN is configured so that a request for "op-b-acq.op-a.net"
      returns a delivery node in uCDN.

   Figure 5 depicts the exchange of DNS and HTTP requests.  The main
   differences from Figure 3 are the lack of HTTP redirection and
   transparency to the end-user.














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         End-User                 Operator B                Operator A
             |DNS cdn.csp.com          |                         |
             |-------------------------------------------------->|
             |                         |                         |(1)
             |CNAME b.cdn.csp.com      |                         |
             |NS records for b.cdn.csp.com                       |
             |<--------------------------------------------------|
             |DNS b.cdn.csp.com        |                         |
             |------------------------>|                         |
             |                         |(2)                      |
             |IPaddr of B's Delivery Node                        |
             |<------------------------|                         |
             |HTTP cdn.csp.com         |                         |
             |------------------------>|                         |
             |                         |(3)                      |
             |                         |DNS op-b-acq.op-a.net    |
             |                         |------------------------>|
             |                         |                         |(4)
             |                         |IPaddr of A's Delivery Node
             |                         |<------------------------|
             |                         |HTTP op-b-acq.op-a.net   |
             |                         |------------------------>|
             |                         |                         |(5)
             |                         |Data                     |
             |                         |<------------------------|
             |Data                     |                         |
             |<------------------------|                         |

             Figure 5: Message Flow for DNS-based Redirection

   The steps illustrated in the figure are as follows:

   1.  Request Router for Operator A processes the DNS request for CDN-
       Domain cdn.csp.com and recognizes that the end-user is best
       served by another CDN.  (This may depend on the IP address of the
       user's local DNS resolver, or other information discussed below.)
       The Request Router returns a DNS CNAME response by "stacking" the
       distinguished identifier for Operator B onto the original CDN-
       Domain (e.g., b.cdn.csp.com), plus an NS record that maps
       b.cdn.csp.com to B's Request Router.

   2.  The end-user does a DNS lookup using the modified CDN-Domain
       (i.e., b.cdn.csp.com).  This causes B's Request Router to respond
       with a suitable delivery node.

   3.  The end-user requests the content from B's delivery node.  The
       requested URL contains the name cdn.csp.com.  (Note that the
       returned CNAME does not affect the URL.)  At this point the



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       delivery node has the correct IP address of the end-user and can
       do an HTTP 302 redirect if the redirections in steps 2 and 3 were
       incorrect.  Otherwise B verifies that this CDN-Domain belongs to
       a known peer (so as to avoid being tricked into serving as an
       open proxy).  It then does a DNS request for an "internal" CDN-
       Domain as agreed above (op-b-acq.op-a.net).

   4.  Operator A recognizes that the DNS request is from a peer CDN
       rather than an end-user (due to the internal CDN-Domain) and so
       returns the address of a delivery node in uCDN.

   5.  Operator A serves content to dCDN.  Although not shown, it is at
       this point that Operator A processes the rest of the URL: it
       extracts information identifying the origin server, validates
       that this server has been registered, and determines the content
       provider that owns the origin server.

   The advantages of this approach are that it is more transparent to
   the end-user and requires fewer round trips than HTTP-based
   redirection (in its worst case, i.e., when none of the needed DNS
   information is cached).  A potential problem is that the upstream CDN
   depends on being able to learn the correct downstream CDN that serves
   the end-user from the client address in the DNS request.  In standard
   DNS operation, uCDN will only obtain the address of the client's
   local DNS resolver (LDNS), which is not guaranteed to be in the same
   network (or geographic region) as the client.  If not--e.g., the end-
   user uses a global DNS service--then the upstream CDN cannot
   determine the appropriate downstream CDN to serve the end-user.  In
   this case, and assuming the uCDN is capable of detecting that
   situation, one option is for the upstream CDN to treat the end-user
   as it would any user not connected to a peer CDN.  Another option is
   for the upstream CDN to "fall back" to a pure HTTP-based redirection
   strategy in this case (i.e., use the first method).  Note that this
   problem affects existing CDNs that rely on DNS to determine where to
   redirect client requests, but the consequences are arguably less
   serious for CDNI since the LDNS is likely in the same network as the
   dCDN serves.  One approach to ensuring that the client's IP address
   prefix is correctly determined in such situations is described in
   [I-D.vandergaast-edns-client-subnet].

   As with the prior example, this example partially illustrates the
   various interfaces involved in CDNI.  Operator A could learn
   dynamically from Operator B the set of prefixes or regions that B is
   willing and able to serve via the Footprint & Capabilities Interface.
   The distinguished name used for acquisition and the identifier for
   Operator B that is prepended to the CDN-Domain on redirection are
   examples of information elements that might also be conveyed by CDNI
   interfaces (or, alternatively, statically configured).  As before,



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   minimal metadata sufficient to obtain the content is carried "in-
   band" as part of the redirection process, and standard HTTP is used
   for inter-CDN acquisition.  There is no explicit Logging Interface
   discussed in this example.

3.5.  Dynamic Footprint Discovery Example

   There could be situations where being able to dynamically discover
   the set of requests that a given dCDN is willing and able to serve is
   beneficial.  For example, a CDN might at one time be able to serve a
   certain set of client IP prefixes, but that set might change over
   time due to changes in the topology and routing policies of the IP
   network.  The following example illustrates this capability.  We have
   chosen the example of DNS-based redirection, but HTTP-based
   redirection could equally well use this approach.




































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         End-User                 Operator B                Operator A
             |DNS cdn.csp.com          |                         |
             |-------------------------------------------------->|
             |                         |                         |(1)
             |                         |   RI REQ op-b.net       |
             |                         |<------------------------|
             |                         |                         |(2)
             |                         |    RI REPLY             |
             |                         |------------------------>|
             |                         |                         |(3)
             |CNAME b.cdn.csp.com      |                         |
             |NS records for b.cdn.csp.com                       |
             |<--------------------------------------------------|
             |DNS b.cdn.csp.com        |                         |
             |------------------------>|                         |
             |                         |(2)                      |
             |IPaddr of B's Delivery Node                        |
             |<------------------------|                         |
             |HTTP cdn.csp.com         |                         |
             |------------------------>|                         |
             |                         |(3)                      |
             |                         |DNS op-b-acq.op-a.net    |
             |                         |------------------------>|
             |                         |                         |(4)
             |                         |IPaddr of A's Delivery Node
             |                         |<------------------------|
             |                         |HTTP op-b-acq.op-a.net   |
             |                         |------------------------>|
             |                         |                         |(5)
             |                         |Data                     |
             |                         |<------------------------|
             |Data                     |                         |
             |<------------------------|                         |

          Figure 6: Message Flow for Dynamic Footprint Discovery

   This example differs from the one in Figure 5 only in the addition of
   a CDNI Request Routing Interface Footprint request (step 2) and
   corresponding response (step 3).  The RI REQ could be a message such
   as "Can you serve clients from this IP Prefix?" or it could be
   "Provide the list of client IP prefixes you can currently serve".  In
   either case the response might be cached by operator A to avoid
   repeatedly asking the same question.  Alternatively, or in addition,
   Operator B may spontaneously advertise to Operator A information (or
   changes) on the set of requests it is willing and able to serve on
   behalf of operator A; in that case, Operator B may spontaneously
   issue RR/RI REPLY messages that are not in direct response to a
   corresponding RR/RI REQ message.  (Note that the issues of



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   determining the client's subnet from DNS requests, as described
   above, are exactly the same here as in Section 3.4.)

   Once Operator A obtains the RI response, it is now able to determine
   that Operator B's CDN is an appropriate dCDN for this request and
   therefore a valid candidate dCDN to consider in its Redirection
   decision.  If that dCDN is selected, the redirection and serving of
   the request proceeds as before (i.e. in the absence of dynamic
   footprint discovery).

3.6.  Content Removal Example

   The following example illustrates how the Control Interface may be
   used to achieve pre-positioning of an item of content in the dCDN.
   In this example, user requests for a particular content, and
   corresponding redirection of such requests from Operator A to
   Operator B CDN, may (or may not) have taken place earlier.  Then, at
   some point in time, the uCDN (for example, in response to a
   corresponding trigger from the Content Provider) uses the Control
   Interface to request that content identified by a particular URL be
   removed from dCDN.  The following diagram illustrates the operation.
         End-User                 Operator B                Operator A
             |                         |CI purge cdn.csp.com/... |
             |                         |<------------------------|
             |                         |                         |
             |                         |CI OK                    |
             |                         |------------------------>|
             |                         |                         |


                Figure 7: Message Flow for Content Removal

   The Control Interface is used to convey the request from uCDN to dCDN
   that some previously acquired content should be deleted.  The URL in
   the request specifies which content to remove.  This example
   corresponds to a DNS-based redirection scenario such as Section 3.4.
   If HTTP-based redirection had been used, the URL for removal would be
   of the form peer-a.op-b.net/cdn.csp.com/...

   The dCDN is expected to confirm to the uCDN, as illustrated by the CI
   OK message, the completion of the removal of the targeted content
   from all the caches in dCDN.

3.7.  Pre-Positioned Content Acquisition Example

   The following example illustrates how the Control Interface may be
   used to pre-position an item of content in the dCDN.  In this
   example, Operator A uses the Metadata Interface to request that



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   content identified by a particular URL be pre-positioned into
   Operator B CDN.

         End-User                 Operator B                Operator A

             |                         |CI pre-position cdn.csp.com/...
             |                         |<------------------------|
             |                         |                         |(1)
             |                         |CI OK                    |
             |                         |------------------------>|
             |                         |                         |
             |                         |DNS op-b-acq.op-a.net    |
             |                         |------------------------>|
             |                         |                         |(2)
             |                         |IPaddr of A's Delivery Node
             |                         |<------------------------|
             |                         |HTTP op-b-acq.op-a.net   |
             |                         |------------------------>|
             |                         |                         |(3)
             |                         |Data                     |
             |                         |<------------------------|
             |DNS cdn.csp.com          |                         |
             |-------------------------------------------------->|
             |                         |                         |(4)
             |IPaddr of A's Request Router                       |
             |<--------------------------------------------------|
             |HTTP cdn.csp.com         |                         |
             |-------------------------------------------------->|
             |                         |                         |(5)
             |302 peer-a.op-b.net/cdn.csp.com                    |
             |<--------------------------------------------------|
             |DNS peer-a.op-b.net      |                         |
             |------------------------>|                         |
             |                         |(6)                      |
             |IPaddr of B's Delivery Node                        |
             |<------------------------|                         |
             |HTTP peer-a.op-b.net/cdn.csp.com                   |
             |------------------------>|                         |
             |                         |(7)                      |
             |Data                     |                         |
             |<------------------------|                         |

            Figure 8: Message Flow for Content Pre-Positioning

   The steps illustrated in the figure are as follows:

   1.  Operator A uses the Control Interface to request that Operator B
       pre-positions a particular content item identified by its URL.



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       Operator B responds by confirming that it is willing to perform
       this operation.

   Steps 2 and 3 are exactly the same as steps 5 and 6 of Figure 3, only
   this time those steps happen as the result of the Pre-positioning
   request instead of as the result of a cache miss.

   Steps 4, 5, 6, 7 are exactly the same as steps 1, 2, 3, 4 of
   Figure 3, only this time Operator B CDN can serve the end-user
   request without triggering dynamic content acquisition, since the
   content has been pre-positioned in dCDN.  Note that, depending on
   dCDN operations and policies, the content pre-positioned in the dCDN
   may be pre-positioned to all, or a subset of, dCDN caches.  In the
   latter case, intra-CDN dynamic content acquisition may take place
   inside the dCDN serving requests from caches on which the content has
   not been pre-positioning; however, such intra-CDN dynamic acquisition
   would not involve the uCDN.

3.8.  Asynchronous CDNI Metadata Example

   In this section we walk through a simple example illustrating a
   scenario of asynchronously exchanging CDNI metadata, where the
   downstream CDN obtains CDNI metadata for content ahead of a
   corresponding content request.  The example that follows assumes that
   HTTP-based inter-CDN redirection and recursive CDNI request-routing
   are used, as in Section 3.3.  However, asynchronous exchange of CDNI
   Metadata is similarly applicable to DNS-based inter-CDN redirection
   and iterative request routing (in which cases the CDNI metadata may
   be used at slightly different processing stages of the message
   flows).





















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         End-User                 Operator B                Operator A
             |                         |                         |
             |                         |CI pre-position (trigger)|
             |                         |<------------------------|(1)
             |                         |                         |
             |                         |CI OK                    |
             |                         |------------------------>|(2)
             |                         |                         |
             |                         |MI pull REQ              |
             |                         |------------------------>|(3)
             |                         |                         |
             |                         |MI metadata REP          |(4)
             |                         |                         |
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |-------------------------------------------------->|(5)
             |                         |                         |
             |                         |   RI REQ                |
             |                         |<------------------------|(6)
             |                         |                         |
             |                         |   RI RESP               |
             |                         |------------------------>|(7)
             |                         |                         |
             | CONTENT REDIRECTION     |                         |
             |<--------------------------------------------------| (8)
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |------------------------>|(9)                      |
             |                         |                         |
             :                         :                         :
             | CONTENT DATA            |                         |
             |<------------------------|                         |(10)


           Figure 9: Message Flow for Asynchronous CDNI Metadata

   The steps illustrated in the figure are as follows:

   1.   Operator A uses the Control Interface to trigger to signal the
        availability of CDNI metadata to Operator B.

   2.   Operator B acknowledges the receipt of this trigger.

   3.   Operator B requests the latest metadata from Operator A using
        the Metadata Interface.

   4.   Operator A replies with the requested metadata.  This document
        does not constrain how the CDNI metadata information is actually



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        represented.  For the purposes of this example, we assume that
        Operator A provides CDNI metadata to Operator B indicating that:

        *  this CDNI Metadata is applicable to any content referenced by
           some CDN-Domain.

        *  this CDNI metadata consists of a distribution policy
           requiring enforcement by the delivery node of a specific per-
           request authorization mechanism (e.g.  URI signature or token
           validation).

   5.   A Content Request occurs as usual.

   6.   A CDNI Request Routing Redirection request (RI REQ) is issued by
        operator A CDN, as discussed in Section 3.3.  Operator B's
        request router can access the CDNI Metadata that are relevant to
        the requested content and that have been pre-positioned as per
        Steps 1-4, which may or may not affect the response.

   7.   Operator B's request router issues a CDNI Request Routing
        Redirection response (RI RESP) as in Section 3.3.

   8.   Operator B performs content redirection as discussed in
        Section 3.3.

   9.   On receipt of the Content Request by the end user, the delivery
        node detects that previously acquired CDNI metadata is
        applicable to the requested content.  In accordance with the
        specific CDNI metadata of this example, the delivery node will
        invoke the appropriate per-request authorization mechanism,
        before serving the content.  (Details of this authorization are
        not shown.)

   10.  Assuming successful per-request authorization, serving of
        Content Data (possibly preceded by inter-CDN acquisition)
        proceeds as in Section 3.3.

3.9.  Synchronous CDNI Metadata Acquisition Example

   In this section we walk through a simple example illustrating a
   scenario of synchronous CDNI metadata acquisition, in which the
   downstream CDN obtains CDNI metadata for content at the time of
   handling a first request for the corresponding content.  As in the
   preceding section, this example assumes that HTTP-based inter-CDN
   redirection and recursive CDNI request-routing are used (as in
   Section 3.3), but dynamic CDNI metadata acquisition is applicable to
   other variations of request routing.




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       End-User                 Operator B                Operator A
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |-------------------------------------------------->|(1)
             |                         |                         |
             |                         |   RI REQ                |
             |                      (2)|<------------------------|
             |                         |                         |
             |                         |   MI REQ                |
             |                      (3)|------------------------>|
             |                         |   MI RESP               |
             |                         |<------------------------|(4)
             |                         |                         |
             |                         |   RI RESP               |
             |                         |------------------------>|(5)
             |                         |                         |
             |                         |                         |
             | CONTENT REDIRECTION     |                         |
             |<--------------------------------------------------|(6)
             |                         |                         |
             | CONTENT REQUEST         |                         |
             |------------------------>| (7)                     |
             |                         |                         |
             |                         |   MI REQ                |
             |                      (8)|------------------------>|
             |                         |   MI RESP               |
             |                         |<------------------------|(9)
             |                         |                         |
             :                         :                         :
             | CONTENT DATA            |                         |
             |<------------------------|                         | (10)


     Figure 10: Message Flow for Synchronous CDNI Metadata Acquisition

   The steps illustrated in the figure are as follows:

   1.   A Content Request arrives as normal.

   2.   A Request Routing Interface request occurs as in the prior
        example.

   3.   On receipt of the CDNI Request Routing Request, Operator B's CDN
        initiates synchronous acquisition of CDNI Metadata that are
        needed for routing of the end-user request.  We assume the URI
        for the a Metadata server is known ahead of time through some
        out-of-band means.




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   4.   On receipt of a CDNI Metadata Request, Operator A's CDN
        responds, making the corresponding CDNI metadata information
        available to Operator B's CDN.  This metadata is considered by
        operator B's CDN before responding to the Request Routing
        request.  (In a simple case, the metadata could simply be an
        allow or deny response for this particular request.)

   5.   Response to the RI request as normal.

   6.   Redirection message is sent to the end user.

   7.   A delivery node of Operator B receives the end user request.

   8.   The delivery node triggers dynamic acquisition of additional
        CDNI metadata that are needed to process the end-user content
        request.  Note that there may exist cases where this step need
        not happen, for example because the metadata were already
        acquired previously.

   9.   Operator A's CDN responds to the CDNI Metadata Request and makes
        the corresponding CDNI metadata available to Operator B. This
        metadata influence how Operator B's CDN processes the end-user
        request.

   10.  Content is served (possibly preceded by inter-CDN acquisition)
        as in Section 3.3.

3.10.  Content and Metadata Acquisition with Multiple Upstream CDNs

   A single dCDN may receive end-user requests from multiple uCDNs.
   When a dCDN receives an end-user request, it must determine the
   identity of the uCDN from which it should acquire the requested
   content.

   Ideally, the acquisition path of an end-user request will follow the
   redirection path of the request.  The dCDN should acquire the content
   from the same uCDN which redirected the request.

   Determining the acquisition path requires the dCDN to reconstruct the
   redirection path based on information in the end-user request.  The
   method for reconstructing the redirection path differs based on the
   redirection approach: HTTP or DNS.

   With HTTP-redirection, the rewritten URI should include sufficient
   information for the dCDN to directly or indirectly determine the uCDN
   when the end-user request is received.  The HTTP-redirection approach
   can be further broken-down based on the how the URL is rewritten
   during redirection: HTTP-redirection with or without Site



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   Aggregation.  HTTP-redirection with Site Aggregation hides the
   identity of the original CSP.  HTTP-redirection without Site
   Aggregation does not attempt to hide the identity of the original
   CSP.  With both approaches, the rewritten URI includes enough
   information to identify the immediate neighbor uCDN.

   With DNS-redirection, the dCDN receives the published URI (instead of
   a rewritten URI) and does not have sufficient information for the
   dCDN to identify the appropriate uCDN.  The dCDN may narrow the set
   of viable uCDNs by examining the CDNI metadata from each to determine
   which uCDNs are hosting metadata for the requested content.  If there
   is a single uCDN hosting metadata for the requested content, the dCDN
   can assume that the request redirection is coming from this uCDN and
   can acquire content from that uCDN.  If there are multiple uCDNs
   hosting metadata for the requested content, the dCDN may be ready to
   trust any of these uCDNs to acquire the content (provided the uCDN is
   in a position to serve it).  If the dCDN is not ready to trust any of
   these uCDNs, it needs to ensure via out of band arrangements that,
   for a given content, only a single uCDN will ever redirect requests
   to the dCDN.

   Content acquisition may be preceded by content metadata acquisition.
   If possible, the acquisition path for metadata should also follow the
   redirection path.  Additionally, we assume metadata is indexed based
   on rewritten URIs in the case of HTTP-redirection and is indexed
   based on published URIs in the case of DNS-redirection.  Thus, the
   Request Routing Interface and the Metadata Interface are tightly
   coupled in that the result of request routing (a rewritten URI
   pointing to the dCDN) serves as an input to metadata lookup.  If the
   content metadata includes information for acquiring the content, then
   the Metadata Interface is also tightly coupled with the acquisition
   interface in that the result of the metadata lookup (an acquisition
   URL likely hosted by the uCDN) should serve as input to the content
   acquisition.


4.  Main Interfaces

   Figure 1 illustrates the four main interfaces that are in scope for
   the CDNI WG, along with several others.  The detailed specifications
   of these interfaces are left to other documents, but see RFC 6707 and
   [I-D.ietf-cdni-requirements] for some discussion of the interfaces.

   One interface that is not shown in Figure 1 is the interface between
   the user and the CSP.  While for the purposes of CDNI that interface
   is out of scope, it is worth noting that it does exist and can
   provide useful functions, such as end-to-end performance monitoring
   and some forms of authentication and authorization.



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   There is also an important interface between the user and the Request
   Routing function of both uCDN and dCDN (shown as the "Request"
   Interface in Figure 1).  As we saw in some of the preceding examples,
   that interface can be used as a way of passing information a subset
   of metadata such as the minimum information that is required for dCDN
   to obtain the content from uCDN.

   In this section we will provide an overview of the functions
   performed by each of the CDNI interfaces and discuss how they fit
   into the overall solution.  We also examine some of the design
   tradeoffs.  We begin with an examination of one such tradeoff that
   affects all the interfaces - the use of in-band or out-of-band
   communication.

4.1.  In-Band versus Out-of-Band Interfaces

   Before getting to the individual interfaces, we observe that there is
   a high-level design choice for each, involving the use of existing
   in-band communication channels versus defining new out-of-band
   interfaces.

   It is possible that the information needed to carry out various
   interconnection functions can be communicated between peer CDNs using
   existing in-band protocols.  The use of HTTP 302 redirect is an
   example of how certain aspects of request routing can be implemented
   in-band (embedded in URIs).  Note that using existing in-band
   protocols does not imply that the CDNI interfaces are null; it is
   still necessary to establish the rules (conventions) by which such
   protocols are used to implement the various interface functions.

   There are other opportunities for in-band communication beyond HTTP
   redirects.  For example, many of the HTTP directives used by proxy
   servers can also be used by peer CDNs to inform each other of caching
   activity.  Of these, one that is particularly relevant is the If-
   Modified-Since directive, which is used with the GET method to make
   it conditional: if the requested object has not been modified since
   the time specified in this field, a copy of the object will not be
   returned, and instead, a 304 (not modified) response will be
   returned.

4.2.  Cross Interface Concerns

   Although the CDNI interfaces are largely independent, there are a set
   of conventions practiced consistently across all interfaces.  Most
   important among these is how resources are named, for exampmle, how
   the Metadata and Control Interfaces identify the set of resources to
   which a given directive applies, or the Logging Interface identifies
   the set of resources for which a summary record applies.



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   While in the limit the CDNI interfaces could explicitly identify
   every individual resource, in practice, they name resource aggregates
   (sets of URIs) that are to be treated in a similar way.  For example,
   URI aggregates can be identified by a CDN-Domain (i.e., the FQDN at
   the beginning of a URI) or by a URI-Filter (i.e., a regular
   expression that matches a subset of URIs contained in some CDN-
   Doman).  In other words, CDN-Domains and URI-Filters provide a
   uniform means to aggregate sets (and subsets) of URIs for the purpose
   of defining the scope for some operation in one of the CDNI
   interfaces.

4.3.  Request Routing Interface

   The Request Routing Interface comprises two parts: the asynchronous
   interface used by a dCDN to advertize footprint and capabilities
   (denoted FCI) to a uCDN, allowing the uCDN to decide whether to
   redirect particular user requests to that dCDN; and the synchronous
   interface used by the uCDN to redirect a user request to the dCDN
   (denoted RI).  (These are somewhat analogous to the operations of
   routing and forwarding in IP.)

   As illustrated in Section 3, the RI part of request routing may be
   implemented in part by DNS and HTTP.  Naming conventions may be
   established by which CDN peers communicate whether a request should
   be routed or content served.

   We also note that RI plays a key role in enabling recursive
   redirection, as illustrated in Section 3.3.  It enables the user to
   be redirected to the correct delivery node in dCDN with only a single
   redirection step (as seen by the user).  This may be particularly
   valuable as the chain of interconnected CDNs increases beyond two
   CDNs.

   In support of these redirection requests, it is necessary for CDN
   peers to exchange additional information with each other, and this is
   the role of the FCI part of request routing.  Depending on the
   method(s) supported, this might includes

   o  The operator's unique id (operator-id) or distinguished CDN-Domain
      (operator-domain);

   o  NS records for the operator's set of externally visible request
      routers;

   o  The set of requests the dCDN operator is prepared to serve (e.g. a
      set of client IP prefixes or geographic regions that may be served
      by dCDN).




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   o  Additional capabilities of the dCDN, such as its ability to
      support different CDNI Metadata requests.

   Note that the set of requests that dCDN is willing to serve could in
   some cases be relatively static (e.g., a set of IP prefixes) which
   could be exchanged off-line, or might even be negotiated as part of a
   peering agreement.  However, it may also be more dynamic, in which
   case the exchange supported by FCI would be be helpful.  A further
   discussion of the Footprint & Capability Advertisement Interface can
   be found in [I-D.spp-cdni-rr-foot-cap-semantics].

4.4.  Logging Interface

   It is necessary for the upstream CDN to have visibility into the
   delivery of content that it redirected to a downstream CDN.  This
   allows the upstream CDN to properly bill its customers for multiple
   deliveries of content cached by the downstream CDN, as well as to
   report accurate traffic statistics to those content providers.  This
   is one role of the Logging Interface.

   Other operational data that may be relevant to CDNI can also be
   exchanged by the Logging Interface.  For example, dCDN may report the
   amount of content it has acquired from uCDN, and how much cache
   storage has been consumed by content cached on behalf of uCDN.

   Traffic logs are easily exchanged off-line.  For example, the
   following traffic log is a small deviation from the Apache log file
   format, where entries include the following fields:

   o  Domain - the full domain name of the origin server

   o  IP address - the IP address of the client making the request

   o  End time - the ending time of the transfer

   o  Time zone - any time zone modifier for the end time

   o  Method - the transfer command itself (e.g., GET, POST, HEAD)

   o  URL - the requested URL

   o  Version - the protocol version, such as HTTP/1.0

   o  Response - a numeric response code indicating transfer result

   o  Bytes Sent - the number of bytes in the body sent to the client





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   o  Request ID - a unique identifier for this transfer

   o  User agent - the user agent, if supplied

   o  Duration - the duration of the transfer in milliseconds

   o  Cached Bytes - the number of body bytes served from the cache

   o  Referrer - the referrer string from the client, if supplied

   Of these, only the Domain field is indirect in the downstream CDN--it
   is set to the CDN-Domain used by the upstream CDN rather than the
   actual origin server.  This field could then used to filter traffic
   log entries so only those entries matching the upstream CDN are
   reported to the corresponding operator.  Further discussion of the
   Logging Interface can be found in [I-D.bertrand-cdni-logging].

   One open question is who does the filtering.  One option is that the
   downstream CDN filters its own logs, and passes the relevant records
   directly to each upstream peer.  This requires that the downstream
   CDN knows the set of CDN-Domains that belong to each upstream peer.
   If this information is already exchanged between peers as part of
   another interface, then direct peer-to-peer reporting is
   straightforward.  If it is not available, and operators do not wish
   to advertise the set of CDN-Domains they serve to their peers, then
   the second option is for each CDN to send both its non-local traffic
   records and the set of CDN-Domains it serves to an independent third-
   party (i.e., a CDN Exchange), which subsequently filters, merges, and
   distributes traffic records on behalf of each participating CDN
   operator.

   A second open question is how timely traffic information should be.
   For example, in addition to off-line traffic logs, accurate real-time
   traffic monitoring might also be useful, but such information
   requires that the downstream CDN inform the upstream CDN each time it
   serves upstream content from its cache.  The downstream CDN can do
   this, for example, by sending a conditional HTTP GET request (If-
   Modified-Since) to the upstream CDN each time it receives an HTTP GET
   request from one of its end-users.  This allows the upstream CDN to
   record that a request has been issued for the purpose of real-time
   traffic monitoring.  The upstream CDN can also use this information
   to validate the traffic logs received later from the downstream CDN.

   There is obviously a tradeoff between accuracy of such monitoring and
   the overhead of the downstream CDN having to go back to the upstream
   CDN for every request.

   Another design tradeoff in the Logging Interface is the degree of



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   aggregation or summarization of data.  One situation that lends
   itself to summarization is the delivery of HTTP adaptive streaming
   (HAS), since the large number of individual chunk requests
   potentially results in large volumes of logging information.  This
   case is discussed below, but other forms of aggregation may also be
   useful.  For example, there may be situations where bulk metrics such
   as bytes delivered per hour may suffice rather than the detailed per-
   request logs outlined above.  It seems likely that a range of
   granularities of logging will be needed along with ways to specify
   the type and degree of aggregation required.

4.5.  Control Interface

   The Control Interface is initially used to bootstrap the other
   interfaces.  As a simple example, it could be used to provide the
   address of the logging server in dCDN to uCDN in order to bootstrap
   the Logging Interface.  It may also be used, for example, to
   establish security associations for the other interfaces.

   The other role the Control Interface plays is to allow the uCDN to
   pre-position, revalidate, or purge metadata and content on a dCDN.
   These operations, sometimes collectively called the trigger
   interface, are discussed further in [I-D.murray-cdni-triggers].

4.6.  Metadata Interface

   The role of the CDNI Metadata Interface is to enable CDNI
   distribution metadata to be conveyed to the downstream CDN by the
   upstream CDN.  For example, see [I-D.ietf-cdni-metadata].  Such
   metadata includes geo-blocking restrictions, availability windows,
   access control policies, and so on.  It may also include information
   to facilitate acquisition of content by dCDN (e.g., alternate sources
   for the content, authorization information needed to acquire the
   content from the source).

   Some distribution metadata may be partially emulated using in-band
   mechanisms.  For example, in case of any geo-blocking restrictions or
   availability windows, the upstream CDN can elect to redirect a
   request to the downstream CDN only if that CDN's advertised delivery
   footprint is acceptable for the requested URL.  Similarly, the
   request could be forwarded only if the current time is within the
   availability window.  However, such approaches typically come with
   shortcomings such as inability to prevent from replay outside the
   time window or inability to make use of a downstream CDN that covers
   a broader footprint than the geo-blocking restrictions.

   Similarly, some forms of access control may also be performed on a
   per-request basis using HTTP directives.  For example, being able to



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   respond to a conditional GET request gives the upstream CDN an
   opportunity to influence how the downstream CDN delivers its content.
   Minimally, the upstream CDN can invalidate (purge) content previously
   cached by the downstream CDN.

   Fine-grain control over how the downstream CDN delivers content on
   behalf of the upstream CDN is also possible.  For example, by
   including the X-Forwarded-For HTTP header with the conditional GET
   request, the downstream CDN can report the end-user's IP address to
   the upstream CDN, giving it an opportunity to control whether the
   downstream CDN should serve the content to this particular end-user.
   The upstream CDN would communicate its directive through its response
   to the conditional GET.  The downstream CDN can cache information for
   a period of time specified by the upstream CDN, thereby reducing
   control overhead.

   All of these in-band techniques serve to illustrate that uCDNs have
   the option of enforcing some of their access control policies
   themselves (at the expense of increased inter-CDN signaling load),
   rather than delegating enforcement to dCDNs using the Metadata
   Interface.  As a consequence, the Metadata Interface should provide a
   means for the uCDN to express its desire to retain enforcement for
   itself.  For example, this might be done by including a "check with
   me" flag in the metadata associated with certain content.

4.7.  HTTP Adaptive Streaming Concerns

   We consider HTTP Adaptive Streaming (HAS) and the impact it has on
   the CDNI interfaces because large objects (e.g., videos) are broken
   into a sequence of small, independent chunks.  For each of the
   following, a more thorough discussion, including an overview of the
   tradeoffs involved in alternative designs, can be found in
   [I-D.brandenburg-cdni-has].

   First, with respect to Content Acquisition and File Management, which
   are out-of-scope for the CDNI interfaces but nontheless relevant to
   the overall operation, we assume no additional measures are required
   to deal with large numbers of chunks.  This means that the dCDN is
   not explicitly made aware of any relationship between different
   chunks and the dCDN handles each chunk as if it were an individual
   and independent content item.  The result is that content acquisition
   between uCDN and dCDN also happens on a per-chunk basis.  This
   approach is in line with the recommendations made in
   [I-D.brandenburg-cdni-has], which also identifies potential
   improvements in this area that might be considered in the future.

   Second, with respect to Request Routing, we note that HAS manifest
   files have the potential to interfere with request routing since



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   manifest files contain URLs pointing to the location of content
   chunks.  To make sure that a manifest file does not hinder CDNI
   request routing and does not place excessive load on CDNI resources,
   the use of manifest files could either be limited to those containing
   relative URLs or the uCDN could modify the URLs in the manifest.  Our
   approach for dealing with these issues is twofold.  As a mandatory
   requirement, CDNs should be able to handle unmodified manifest files
   containing either relative or absolute URLs.  To limit the number of
   redirects, and thus the load placed on the CDNI Interfaces, as an
   optional feature uCDNs can use the information obtained through the
   CNDI Request Routing Redirection Interface to modify the URLs in the
   manifest file.  Since the modification of the manifest file is an
   optional uCDN-internal process, this does not require any
   standardization effort beyond being able to communicate chunk
   locations in the CDNI Request Routing Redirection Interface.

   Third, with respect to the Logging Interface, there are several
   potential issues, including the large number of individual chunk
   requests potentially resulting in large volumes of logging
   information, and the desire to correlate logging information for
   chunk requests that correspond to the same HAS session.  For the
   initial CDNI specification, our approach is to expect participating
   CDNs to support per-chunk logging (e.g. logging each chunk request as
   if it were an independent content request) over the CDNI Logging
   Interface.  Optionally, the Logging Interface may include a Content
   Collection IDentifier (CCID) and/or a Session IDentifier (SID) as
   part of the logging fields, thereby facilitating correlation of per-
   chunk logs into per-session logs for applications benefiting from
   such session level information (e.g. session-based analytics).  This
   approach is in line with the recommendations made in
   [I-D.brandenburg-cdni-has], which also identifies potential
   improvements in this area that might be considered in the future.

   Fourth, with respect to the Control Interface, and in particular
   purging HAS chunks from a given CDN, our approach is to expect each
   CDN supports per-chunk content purge (e.g. purging of chunks as if
   they were individual content items).  Optionally, a CDN may support
   content purge on the basis of a "Purge IDentifier (Purge-ID)"
   allowing the removal of all chunks related to a given Content
   Collection with a single reference.  It is possible that this
   Purge-ID could be merged with the CCID discussed above for HAS
   Logging, or alternatively, they may remain distinct.


5.  Deployment Models

   In this section we describe a number of possible deployment models
   that may be achieved using the CDNI interfaces described above.  We



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   note that these models are by no means exhaustive, and that many
   other models may be possible.

   Although the reference model of Figure 1 shows all CDN functions on
   each side of the CDNI interface, deployments can rely on entities
   that are involved in any subset of these functions, and therefore
   only support the relevant subset of CDNI interfaces.  As already
   noted in Section 3, effective CDNI deployments can be built without
   necessarily implementing all four interfaces.  Some examples of such
   deployments are shown below.

   Note that, while we refer to upstream and downstream CDNs, this
   distinction applies to specific content items and transactions.  That
   is, a given CDN may be upstream for some transactions and downstream
   for others, depending on many factors such as location of the
   requesting client and the particular piece of content requested.

5.1.  Meshed CDNs

   Although the reference model illustrated in Figure 1 shows a
   unidirectional CDN interconnection with a single uCDN and a single
   dCDN, any arbitrary CDNI meshing can be built from this, such as the
   example meshing illustrated in Figure 11.  (Support for arbitrary
   meshing may or may not be in the initial scope for the working group,
   but the model allows for it.)


























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         -------------             -----------
        /    CDN A    \<==CDNI===>/   CDN B   \
        \             /           \           /
         -------------             -----------
              /\      \\                 /\
              ||       \\                ||
             CDNI       \==CDNI===\\    CDNI
              ||                   \\    ||
              \/                   \/    \/
         -------------             -----------
        /    CDN C    \===CDNI===>/   CDN D   \
        \             /           \           /
         -------------             -----------
              /\
              ||
             CDNI
              ||
              \/
         -------------
        /    CDN E    \
        \             /
         -------------

      ===>  CDNI interfaces, with right-hand side CDN acting as dCDN
            to left-hand side CDN
      <==>  CDNI interfaces, with right-hand side CDN acting as dCDN
            to left-hand side CDN and with left-hand side CDN acting
            as dCDN to right-hand side CDN

           Figure 11: CDNI Deployment Model: CDN Meshing Example

5.2.  CSP combined with CDN

   Note that our terminology refers to functional roles and not economic
   or business roles.  That is, a given organization may be operating as
   both a CSP and a fully-fledged uCDN when we consider the functions
   performed, as illustrated in Figure 12.














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   #####################################       ##################
   #                                   #       #                #
   #       Organization A              #       # Organization B #
   #                                   #       #                #
   #     --------       -------------  #       #  -----------   #
   #    /   CSP  \     /   uCDN      \ #       # /   dCDN    \  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  | C  |     | #       # |  | C  |   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  | L  |     | #       # |  | L  |   |  #
   #    |        |*****|  +----+     |===CDNI===>|  +----+   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  | RR |     | #       # |  | RR |   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |     |  | D  |     | #       # |  | D  |   |  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    \        /     \             / #       # \           /  #
   #     --------       -------------  #       #  -----------   #
   #                                   #       #                #
   #####################################       ##################

   ===>  CDNI interfaces, with right-hand side CDN acting as dCDN
         to left-hand side CDN
   ****  interfaces outside the scope of CDNI
   C     Control component of the CDN
   L     Logging component of the CDN
   RR    Request Routing component of the CDN
   D     Distribution component of the CDN

    Figure 12: CDNI Deployment Model: Organization combining CSP & uCDN

5.3.  CSP using CDNI Request Routing Interface

   As another example, a content provider organization may choose to run
   its own request routing function as a way to select among multiple
   candidate CDN providers; In this case the content provider may be
   modeled as the combination of a CSP and of a special, restricted case
   of a CDN.  In that case, as illustrated in Figure 13, the CDNI
   Request Routing Interfaces can be used between the restricted CDN
   operated by the content provider Organization and the CDN operated by
   the full-CDN organization acting as a dCDN in the request routing
   control plane.  Interfaces outside the scope of the CDNI work can be
   used between the CSP functional entities of the content provider
   organization and the CDN operated by the full-CDN organization acting
   as a uCDN) in the CDNI control planes other than the request routing
   plane (i.e.  Control, Distribution, Logging).



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   #####################################       ##################
   #                                   #       #                #
   #       Organization A              #       # Organization B #
   #                                   #       #                #
   #     --------       -------------  #       #  -----------   #
   #    /   CSP  \     /  uCDN(RR)   \ #       # /  dCDN(RR) \  #
   #    |        |     |  +----+     | #       # |  +----+   |  #
   #    |        |*****|  | RR |==========CDNI=====>| RR |   |  #
   #    |        |     |  +----+     | #   RR  # |  +----+   |  #
   #    |        |     \             / #       # |           |  #
   #    |        |      -------------  #       # |uCDN(C,L,D)|  #
   #    |        |                     #       # |  +----+   |  #
   #    |        |                     #       # |  | C  |   |  #
   #    |        |*******************************|  +----+   |  #
   #    |        |                     #       # |  +----+   |  #
   #    |        |                     #       # |  | L  |   |  #
   #    |        |                     #       # |  +----+   |  #
   #    |        |                     #       # |  +----+   |  #
   #    |        |                     #       # |  | D  |   |  #
   #    |        |                     #       # |  +----+   |  #
   #    \        /                     #       # \           /  #
   #     --------                      #       #  -----------   #
   #                                   #       #                #
   #####################################       ##################

   ===>  CDNI Request Routing Interface
   ****  interfaces outside the scope of CDNI

     Figure 13: CDNI Deployment Model: Organization combining CSP and
                                partial CDN

5.4.  CDN Federations and CDN Exchanges

   There are two additional concepts related to, but distinct from CDN
   Interconnection.  The first is CDN Federation.  Our view is that CDNI
   is the more general concept, involving two or more CDNs serving
   content to each other's users, while federation implies a multi-
   lateral interconnection arrangement, but other CDN interconnection
   agreements are also possible (e.g., symmetric bilateral, asymmetric
   bilateral).  An important conclusion is that CDNI technology should
   not presume (or bake in) a particular interconnection agreement, but
   should instead be general enough to permit alternative
   interconnection arrangements to evolve.

   The second concept often used in the context of CDN Federation is CDN
   Exchange--a third party broker or exchange that is used to facilitate
   a CDN federation.  Our view is that a CDN exchange offers valuable
   machinery to scale the number of CDN operators involved in a multi-



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   lateral (federated) agreement, but that this machinery is built on
   top of the core CDNI interconnection mechanisms.  For example, as
   illustrated in Figure 14, the exchange might aggregate and
   redistribute information about each CDN footprint and capacity, as
   well as collect, filter, and re-distribute traffic logs that each
   participant needs for interconnection settlement, but inter-CDN
   request routing, inter-CDN content distribution (including inter-CDN
   acquisition) and inter-CDN control which fundamentally involve a
   direct interaction between an upstream CDN and a downstream CDN--
   operate exactly as in a pair-wise peering arrangement.  Turning to
   Figure 14, we observe that in this example:

   o  each CDN supports a direct CDNI Control Interface to every other
      CDN

   o  each CDN supports a direct CDNI Metadata Interface to every other
      CDN

   o  each CDN supports a CDNI Logging Interface with the CDN Exchange

   o  each CDN supports both a CDNI Request Routing Interface with the
      CDN Exchange (for aggregation and redistribution of dynamic CDN
      footprint discovery information) and a direct CDNI Request Routing
      Interface to every other CDN (for actual request redirection).



























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             ----------                            ---------
            /    CDN A \                          /   CDN B  \
            | +----+   |                         |  +----+   |
   //========>| C  |<==============CDNI============>| C  |<==========\\
   ||       | +----+   |            C            |  +----+   |       ||
   ||       | +----+   |                         |  +----+   |       ||
   || //=====>| D  |<==============CDNI============>| D  |<=======\\ ||
   || ||    | +----+   |            M            |  +----+   |    || ||
   || ||    |          |     /------------\      |           |    || ||
   || ||    | +----+   |     | +--+ CDN Ex|      |  +----+   |    || ||
   || || //==>| RR |<===CDNI==>|RR|<=======CDNI====>| RR |<====\\ || ||
   || || || | +----+   | RR  | +--+       | RR   |  +----+   | || || ||
   || || || |          |     |  /\        |      |           | || || ||
   || || || | +----+   |     |  ||  +---+ |      |  +----+   | || || ||
   || || || | | L  |<===CDNI=======>| L |<=CDNI====>| L  |   | || || ||
   || || || | +----+   |  L  |  ||  +---+ |  L   |  +----+   | || || ||
   || || || \          /     \  ||    /\  /      \           / || || ||
   || || || -----------       --||----||--        -----------  || || ||
   || || ||                     ||    ||                       || || ||
   || || ||                  CDNI RR  ||                       || || ||
   || || ||                     ||   CDNI L                    || || ||
   || || ||                     ||    ||                       || || ||
   || || ||                  ---||----||----                   || || ||
   || || ||                 /   \/    ||    \                  || || ||
   || || ||                 |  +----+ ||    |                  || || ||
   || || \\=====CDNI==========>| RR |<=============CDNI========// || ||
   || ||         RR         |  +----+ \/    |       RR            || ||
   || ||                    |        +----+ |                     || ||
   || ||                    |        | L  | |                     || ||
   || ||                    |        +----+ |                     || ||
   || ||                    |  +----+       |                     || ||
   || \\=======CDNI===========>| D  |<=============CDNI===========// ||
   ||           M           |  +----+       |       M                ||
   ||                       |  +----+       |                        ||
   \\==========CDNI===========>| C  |<=============CDNI==============//
                C           |  +----+       |       C
                            \        CDN C  /
                             --------------

   <=CDNI RR=>     CDNI Request Routing Interface
   <=CDNI M==>     CDNI Metadata Interface
   <=CDNI C==>     CDNI Control Interface
   <=CDNI L==>     CDNI Logging Interface

              Figure 14: CDNI Deployment Model: CDN Exchange

   Note that a CDN exchange may alternatively support a different set of
   functionality (e.g.  Logging only, or Logging and full request



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   routing, or all the functionality of a CDN including content
   distribution).  All these options are expected to be allowed by the
   IETF CDNI specifications.


6.  Trust Model

   There are a number of trust issues that need to be addressed by a
   CDNI solution.  Many of them are in fact similar or identical to
   those in a simple CDN without interconnection.  In a standard CDN
   environment (without CDNI), the CSP places a degree of trust in a
   single CDN operator to perform many functions.  The CDN is trusted to
   deliver content with appropriate quality of experience for the end
   user.  The CSP trusts the CDN operator not to corrupt or modify the
   content.  The CSP often relies on the CDN operator to provide
   reliable accounting information regarding the volume of delivered
   content.  The CSP may also trust the CDN operator to perform actions
   such as timely invalidation of content and restriction of access to
   content based on certain criteria such as location of the user and
   time of day, and to enforce per-request authorization performed by
   the CSP using techniques such as URI signing.

   A CSP also places trust in the CDN not to distribute any information
   that is confidential to the CSP (e.g., how popular a given piece of
   content is) or confidential to the end user (e.g., which content has
   been watched by which user).

   A CSP does not necessarily have to place complete trust in a CDN.  A
   CSP will in some cases take steps to protect its content from
   improper distribution by a CDN, e.g. by encrypting it and
   distributing keys in some out of band way.  A CSP also depends on
   monitoring (possibly by third parties) and reporting to verify that
   the CDN has performed adequately.  A CSP may use techniques such as
   client-based metering to verify that accounting information provided
   by the CDN is reliable.  HTTP conditional requests may be used to
   provide the CSP with some checks on CDN operation.  In other words,
   while a CSP may trust a CDN to perform some functions in the short
   term, the CSP is able in most cases to verify whether these actions
   have been performed correctly and to take action (such as moving the
   content to a different CDN) if the CDN does not live up to
   expectations.

   The main trust issue raised by CDNI is that it introduces transitive
   trust.  A CDN that has a direct relationship with a CSP can now
   "outsource" the delivery of content to another (downstream) CDN.
   That CDN may in term outsource delivery to yet another downstream
   CDN, and so on.




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   The top level CDN in such a chain of delegation is responsible for
   ensuring that the requirements of the CSP are met.  Failure to do so
   is presumably just as serious as in the traditional single CDN case.
   Hence, an upstream CDN is essentially trusting a downstream CDN to
   perform functions on its behalf in just the same way as a CSP trusts
   a single CDN.  Monitoring and reporting can similarly be used to
   verify that the downstream CDN has performed appropriately.  However,
   the introduction of multiple CDNs in the path between CSP and end
   user complicates the picture.  For example, third party monitoring of
   CDN performance (or other aspects of operation, such as timely
   invalidation) might be able to identify the fact that a problem
   occurred somewhere in the chain but not point to the particular CDN
   at fault.

   In summary, we assume that an upstream CDN will invest a certain
   amount of trust in a downstream CDN, but that it will verify that the
   downstream CDN is performing correctly, and take corrective action
   (including potentially breaking off its relationship with that CDN)
   if behavior is not correct.  We do not expect that the trust
   relationship between a CSP and its "top level" CDN will differ
   significantly from that found today in single CDN situations.
   However, it does appear that more sophisticated tools and techniques
   for monitoring CDN performance and behavior will be required to
   enable the identification of the CDN at fault in a particular
   delivery chain.

   We expect that the detailed designs for the specific interfaces for
   CDNI will need to take the transitive trust issues into account.  For
   example, explicit confirmation that some action (such as content
   removal) has taken place in a downstream CDN may help to mitigate
   some issues of transitive trust.


7.  IANA Considerations

   This memo includes no request to IANA.


8.  Security Considerations

   While there is a variety of security issues introduced by a single
   CDN, we are concerned here specifically with the additional issues
   that arise when CDNs are interconnected.  For example, when a single
   CDN has the ability to distribute content on behalf of a CSP, there
   may be concerns that such content could be distributed to parties who
   are not authorized to receive it, and there are mechanisms to deal
   with such concerns.  Our focus in this section is on how CDN
   interconnection introduces new security issues not found in the



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   single CDN case.

   Many of the security issues that arise in CDNI are related to the
   transitivity of trust (or lack thereof) described in Section 6.  As
   noted above, the design of the various interfaces for CDNI must take
   account of the additional risks posed by the fact that a CDN with
   whom a CSP has no direct relationship is now potentially distributing
   content for that CSP.  The mechanisms used to mitigate these risks
   may be similar to those used in the single CDN case, but their
   suitability in this more complex environment must be validated.

   Another concern that arises in any CDN is that information about the
   behavior of users (what content they access, how much content they
   consume, etc.) may be gathered by the CDN.  This risk certainly
   exists in inter-connected CDNs, but it should be possible to apply
   the same techniques to mitigate it as in the single CDN case.

   CDNs today offer a variety of means to control access to content,
   such as time-of-day restrictions, geo-blocking, and URI signing.
   These mechanisms must continue to function in CDNI environments, and
   this consideration is likely to affect the design of certain CDNI
   interfaces (e.g. metadata, request routing.)

   Just as with a single CDN, each peer CDN must ensure that it is not
   used as an "open proxy" to deliver content on behalf of a malicious
   CSP.  Whereas a single CDN typically addresses this problem by having
   CSPs explicitly register content (or origin servers) that is to be
   served, simply propagating this information to peer downstream CDNs
   may be problematic because it reveals more information than the
   upstream CDN is willing to specify.  (To this end, the content
   acquisition step in the earlier examples force the dCDN to retrieve
   content from the uCDN rather than go directly to the origin server.)

   There are several approaches to this problem.  One is for the uCDN to
   encoded a signed token generated from a shared secret in each URL
   routed to a dCDN, and for the dCDN to validate the request based on
   this token.  Another one is to have each upstream CDN advertise the
   set of CDN-Domains they serve, where the downstream CDN checks each
   request against this set before caching and delivering the associated
   object.  Although straightforward, this approach requires operators
   to reveal additional information, which may or may not be an issue.

8.1.  Security of CDNI Interfaces

   It is noted in [I-D.ietf-cdni-requirements] that all CDNI interfaces
   must be able to operate securely over insecure IP networks.  Since it
   is expected that the CDNI interfaces will be implemented using
   existing application protocols such as HTTP or XMPP, we also expect



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   that the security mechanisms available to those protocols may be used
   by the CDNI interfaces.  Details of how these interfaces are secured
   will be specified in the relevant interface documents.

8.2.  Digital Rights Management

   Issues of digital rights management (DRM, also sometimes called
   digital restrictions management) is often employed for content
   distributed via CDNs.  In general, DRM relies on the CDN to
   distribute encrypted content, with decryption keys distributed to
   users by some other means (e.g. directly from the CSP to the end
   user.)  For this reason, DRM is considered out of scope for the CDNI
   WG RFC 6707 and does not introduce additional security issues for
   CDNI.


9.  Contributors

   The following individuals contributed to this document:

   o  Ray Brandenburg

   o  Matt Caulfield

   o  Francois le Faucheur

   o  Aaron Falk

   o  David Ferguson

   o  John Hartman

   o  Ben Niven-Jenkins

   o  Kent Leung


10.  Acknowledgements

   We thank Huw Jones for helpful input to the draft.


11.  Informative References

   [I-D.bertrand-cdni-logging]
              Bertrand, G., Emile, S., Peterkofsky, R., Faucheur, F.,
              and P. Grochocki, "CDNI Logging Interface",
              draft-bertrand-cdni-logging-02 (work in progress),



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              October 2012.

   [I-D.brandenburg-cdni-has]
              Brandenburg, R., Deventer, O., Faucheur, F., and K. Leung,
              "Models for adaptive-streaming-aware CDN Interconnection",
              draft-brandenburg-cdni-has-04 (work in progress),
              January 2013.

   [I-D.ietf-cdni-metadata]
              Niven-Jenkins, B., Murray, R., Watson, G., Caulfield, M.,
              Leung, K., and K. Ma, "CDN Interconnect Metadata",
              draft-ietf-cdni-metadata-00 (work in progress),
              October 2012.

   [I-D.ietf-cdni-requirements]
              Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements",
              draft-ietf-cdni-requirements-04 (work in progress),
              December 2012.

   [I-D.ietf-cdni-use-cases]
              Bertrand, G., Emile, S., Burbridge, T., Eardley, P., Ma,
              K., and G. Watson, "Use Cases for Content Delivery Network
              Interconnection", draft-ietf-cdni-use-cases-10 (work in
              progress), August 2012.

   [I-D.lefaucheur-cdni-logging-delivery]
              Faucheur, F., Viveganandhan, M., and K. Leung, "CDNI
              Logging Formats for HTTP and HTTP Adaptive Streaming
              Deliveries", draft-lefaucheur-cdni-logging-delivery-01
              (work in progress), July 2012.

   [I-D.murray-cdni-triggers]
              Murray, R. and B. Niven-Jenkins, "CDN Interconnect
              Triggers", draft-murray-cdni-triggers-01 (work in
              progress), August 2012.

   [I-D.seedorf-alto-for-cdni]
              Seedorf, J., "ALTO for CDNi Request Routing",
              draft-seedorf-alto-for-cdni-00 (work in progress),
              October 2011.

   [I-D.spp-cdni-rr-foot-cap-semantics]
              Seedorf, J., Peterson, J., and S. Previdi, "CDNI Request
              Routing: Footprint and Capabilities Semantics",
              draft-spp-cdni-rr-foot-cap-semantics-02 (work in
              progress), October 2012.




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   [I-D.vandergaast-edns-client-subnet]
              Contavalli, C., Gaast, W., Leach, S., and E. Lewis,
              "Client subnet in DNS requests",
              draft-vandergaast-edns-client-subnet-01 (work in
              progress), April 2012.

   [RFC3466]  Day, M., Cain, B., Tomlinson, G., and P. Rzewski, "A Model
              for Content Internetworking (CDI)", RFC 3466,
              February 2003.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, September 2012.


Authors' Addresses

   Larry Peterson (editor)
   Akamai Technologies, Inc.
   8 Cambridge Center
   Cambridge, MA  02142
   USA

   Email: lapeters@akamai.com


   Bruce Davie
   VMware, Inc.
   3401 Hillview Ave.
   Palo Alto, CA  94304
   USA

   Email: bdavie@vmware.com














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