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Network Working Group                                  Danhua. Wang, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                   B. Niven-Jenkins, Ed.
Expires: April 24, 2014                         Velocix (Alcatel-Lucent)
                                                             Xiaoyan. He
                                                                  Huawei
                                                                Chen. Ge
                                                           China Telecom
                                                                 Wei. Ni
                                                            China Mobile
                                                        October 21, 2013


     Request Routing Redirection Interface for CDN Interconnection
                     draft-ietf-cdni-redirection-01

Abstract

   The Request Routing Interface comprises of (1) the asynchronous
   advertisement of footprint and capabilities by a downstream CDN that
   allows a upstream CDN to decide whether to redirect particular user
   requests to that downstream CDN; and (2) the synchronous operation of
   an upstream CDN requesting whether a downstream CDN is prepared to
   accept a user request and of a downstream CDN responding with how to
   actually redirect the user request.  This document describes an
   interface for the latter part, i.e. the CDNI request routing/
   Redirection Interface.

Status of This Memo

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

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

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

   This Internet-Draft will expire on April 24, 2014.

Copyright Notice





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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Interface function and operation overview . . . . . . . . . .   4
   4.  HTTP based RESTful interface for the Redirection Interface  .   5
     4.1.  Information passed in RI requests & responses . . . . . .   7
     4.2.  JSON encoding of RI requests & responses  . . . . . . . .   9
     4.3.  MIME Media Types used by the RI interface . . . . . . . .  10
     4.4.  DNS redirection . . . . . . . . . . . . . . . . . . . . .  10
       4.4.1.  DNS Redirection requests  . . . . . . . . . . . . . .  10
       4.4.2.  DNS Redirection responses . . . . . . . . . . . . . .  12
     4.5.  HTTP Redirection  . . . . . . . . . . . . . . . . . . . .  13
       4.5.1.  HTTP Redirection requests . . . . . . . . . . . . . .  13
       4.5.2.  HTTP Redirection responses  . . . . . . . . . . . . .  15
     4.6.  Indicating the cacheability and scope of responses  . . .  16
     4.7.  Error responses . . . . . . . . . . . . . . . . . . . . .  18
     4.8.  Loop detection & prevention . . . . . . . . . . . . . . .  20
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   8.  Outstanding considerations  . . . . . . . . . . . . . . . . .  22
   9.  Contributing Authors  . . . . . . . . . . . . . . . . . . . .  22
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     10.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   A Content Delivery Network (CDN) is a system built on an existing IP
   network which is used for large scale content delivery, via
   prefetching or dynamically caching content on its distributed
   surrogates (caching servers).  [RFC6707] describes the problem area
   of interconnecting CDNs.



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   The CDNI request routing interface outlined in
   [I-D.ietf-cdni-framework] comprises of:

   1.  The asynchronous advertisement of footprint and capabilities by a
       downstream CDN that allows a upstream CDN to decide whether to
       redirect particular user requests to that downstream CDN.

   2.  The synchronous operation of an upstream CDN requesting whether a
       downstream CDN is prepared to accept a user request and of a
       downstream CDN responding with how to actually redirect the user
       request.

   This document describes an interface for the latter part, i.e. the
   CDNI request routing/Redirection Interface (RI).

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This document reuses the terminology defined in [RFC6707].  The term
   "Distinguished CDN Domain" defined in [I-D.ietf-cdni-framework] is
   also reused in this document.

   The following additional terms are introduced by this document:

   Application Level Redirection: The act of using an application
   specific redirection mechanism for the request routing process of a
   CDN.  The Redirection Target (RT) is the result of the routing
   decision of a CDN at the time it receives a content request via an
   application specific protocol response.  Examples of an application
   level redirection are HTTP 302 Redirection and RTMP 302 Redirection.

   DNS Redirection: The act of using DNS name resolution for the request
   routing process of a CDN.  In DNS Redirection, the DNS name server of
   the CDN makes the routing decision based on a local policy and
   selects one or more Redirection Targets (RTs) and redirects the user
   agent to the RT(s) by returning the details of the RT(s) in response
   to the DNS query request from the user agent's DNS resolver.

   HTTP Redirection: The act of using an HTTP redirection response for
   the request routing process of a CDN.  The Redirection Target (RT) is
   the result of the routing decision of a CDN at the time it receives a
   content request via HTTP.  HTTP Redirection is a particular case of
   Application Level Redirection.





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   Redirection Target (RT): A Redirection Target is the endpoint to
   which the user agent is redirected.  In CDNI, a RT may point to a
   number of different components, some examples include a surrogate in
   the same CDN as the request router, a request router in a downstream
   CDN or a surrogate in a downstream CDN, etc.

3.  Interface function and operation overview

   [[Editor's note: Need to factor token authorisation into a future
   draft when that work is more stable/mature within the WG.]]

   The CDNI request routing/Redirection Interface (RI) is one of the
   main building blocks required in order to interconnect CDNs.  The
   main function of the Redirection Interface is to allow the Request
   Routing systems in interconnected CDNs to communicate to facilitate
   the redirection of User Agent requests between interconnected CDNs.

   The detailed requirements for the Redirection Interface and their
   relative priorities are described in section 5 of
   [I-D.ietf-cdni-requirements].

   The User Agent will make a request to a request router in the uCDN
   using one of either DNS or HTTP.  If the RI is used between the uCDN
   and one or more dCDNs.  The dCDN's RI response may contain a
   Redirection Target with a type that is compatible with the protocol
   used between User Agent and uCDN request router.  The dCDN has
   control over the Redirection Target it provides and depending on the
   returned Redirection Target, the User Agent's request may be
   redirected to:

   o  The final Surrogate, which may be in the dCDN or another dCDN (if
      dCDN delegates the delivery to another CDN).

   o  A request router (in dCDN or another CDN) that will be using a
      redirection protocol (DNS or HTTP) which may or may not be the
      same as original redirection protocol.

   The Redirection Interface operates between the Request Routing
   systems of a pair of interconnected CDNs.  To enable communication
   over the Redirection Interface, the two interconnected CDNs need to
   know the end point (URI) in the other CDN to query.  For example, an
   Upstream CDN needs to know the URI (end point) in a Downstream CDN to
   send its CDNI request routing queries to.








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   The Redirection Interface URI may be statically pre-configured,
   dynamically discovered via the CDNI control interface, or discovered
   via other means.  However, such discovery mechanisms are not
   specified in this document, as they are considered out of the scope
   of the Redirection Interface specification.

   CDNI solutions must support both of the request routing mechanisms
   illustrated in section 2.1 of [I-D.ietf-cdni-framework], namely
   Iterative Request Redirection and Recursive Request Redirection.
   However, the Iterative Request Redirection method does not invoke any
   interaction over the Redirection Interface between interconnected
   CDNs.  Therefore, the Redirection Interface is only relevant in the
   case of Recursive Request Redirection and so this document will not
   discuss Iterative Request Redirection further.

   In the case of Recursive Request Redirection, in order to perform
   redirection of a request received from a User Agent, the Upstream CDN
   queries the Downstream CDN so that the Downstream CDN can select and
   provide a Redirection Target.  In cases where a uCDN has a choice of
   dCDNs it is down to the uCDN to decide (for example via configured
   policies) which dCDN(s) to query and in which order to query them.  A
   number of strategies are possible including selecting a preferred
   dCDN based on local policy, possibly falling back to querying an
   alternative dCDN(s) if the first dCDN does not return a Redirection
   Target or otherwise reject the uCDN's RI request.  A more complex
   strategy could be to query multiple dCDNs in parallel before
   selecting one and using the Redirection Target provided by that dCDN.

   The Upstream CDN->User Agent redirection protocols addressed in this
   draft are: DNS redirection and HTTP redirection.  Other types of
   application level redirection will not be discussed further in this
   draft.  However the Redirection Interface is designed to be
   extensible and could be extended to support additional application
   level redirection protocols.

   Also, according to the CDNI generic and request routing interface
   requirements, the CDNI solution shall support mechanisms to prevent
   and detect RI request loops.  To meet such requirements, this
   document defines a loop prevention and detection mechanism as part of
   the Redirection Interface.

4.  HTTP based RESTful interface for the Redirection Interface

   This document defines a simple RESTful interface for the Redirection
   Interface based on HTTP [RFC2616], where the attributes of a User
   Agent's requests are encapsulated along with any other data that can
   aid the downstream CDN in processing the requests.  The RI response
   encapsulates the attributes of the RT(s) that the upstream CDN should



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   return to the User Agent (if it decides to utilize the Downstream CDN
   for delivery) along with the policy for how the response can be
   reused.

   The same RESTful interface is used for both DNS and HTTP redirection
   of User Agent's requests, although the contents of the RI requests/
   responses contain data specific to either DNS or HTTP redirection.

   This approach has been chosen because it enables CDN operators to
   only have to deploy a single (RESTful) interface for the RI between
   their CDNs, regardless of the User Agent redirection method.  In this
   way, from an operational point of view there is only one interface to
   monitor, manage, develop troubleshooting tools for, etc.

   In addition, having a single RI where the attributes of the User
   Agent's DNS or HTTP request are encapsulated along with the other
   data required for the downstream CDN to make a request routing
   decision, avoids having to try and encapsulate or proxy DNS/HTTP/RTMP
   /etc requests and find ways to somehow embed the additional CDNI
   request routing/Redirection Interface properties/data within those
   End User DNS/HTTP/RTMP/etc requests.

   Finally, the RI is easily extendable to support other User Agent
   request redirection methods (e.g. RTMP 302 redirection).

   The generic Recursive Request Redirection message flow between
   Request Routing systems in a pair of interconnected CDNs is as
   follows:























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   User Agent                CDN B RR                  CDN A RR
       |UA Request (DNS or HTTP) |                         |
       |-------------------------------------------------->| (1)
       |                         |                         |
       |                         |HTTP POST to CDN B's RI  |
       |                         |URI encapsulating UA     |
       |                         |request attributes       |
       |                         |<------------------------| (2)
       |                         |                         |
       |                         |HTTP Response with body  |
       |                         |containing attributes of |
       |                         |protocol specific        |
       |                         |response to return to UA |
       |                         |------------------------>| (3)
       |                         |                         |
       |           Protocol specific response (redirection)|
       |<--------------------------------------------------| (4)
       |                         |                         |

       Figure 1: Generic Recursive Request Redirection message flow

   1.  The User Agent sends its request, either DNS request or HTTP
       request, to CDN A. The Request Routing System of CDN A processes
       the request and, through local policy, it recognizes that the
       request is best served by another CDN, specifically CDN B (or
       that CDN B is one of a number of candidate dCDNs it could use).

   2.  The Request Routing System of CDN A sends an HTTP POST to CDN B's
       RI URI containing the attributes of the User Agent's request.

   3.  The Request Routing System of CDN B processes the request and
       assuming the request is well formed, etc. responds with an HTTP
       "200" response with a message body containing the RT(s) to return
       to the User Agent as well as parameters that indicate the
       properties of the response (cacheability and scope).

   4.  The Request Routing System of CDN A sends a protocol specific
       response (containing the returned attributes) to the User Agent,
       so that the User Agent's request will be redirected to the RT(s)
       returned by CDN B.

4.1.  Information passed in RI requests & responses

   The information passed in RI requests splits into two basic
   categories:

   1.  The attributes of the User Agent's request to the upstream CDN.




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   2.  Properties/parameters that the uCDN can use to control the dCDN's
       response or that can help the dCDN make its decision.

   To assist the routing decision of a Downstream CDN, the Upstream CDN
   shall convey as much information as possible to the Downstream CDN,
   for example the URI of the requested content and the User Agent's
   location information, when those are known by the uCDN Request
   Routing system.

   In order for the Downstream CDN to determine whether it is capable of
   delivering any requested content, it requires CDNI metadata related
   to the content the User Agent is requesting.  That metadata will
   describe the content and any policies associated with it.  It is
   expected that the RI request contains sufficient information for the
   Request Router in the Downstream CDN to be able to retrieve the
   require CDNI Metadata via the CDNI Metadata interface.

   The information passed in RI responses splits into two basic
   categories:

   1.  The attributes of the RT to return to the User Agent in the DNS
       response or HTTP response.

   2.  Parameters/policies that indicate the properties of the response,
       such as, whether it is cacheable, the scope of the response, etc.

   In addition to details of how to redirect the User Agent, the
   Downstream CDN may wish to return additional policy to the Upstream
   CDN to help the Upstream CDN with future RI requests.  For example
   the Downstream CDN may wish to return a policy that expresses "this
   response can be reused without requiring a RI request for 60 seconds
   provided the User Agent's IP address is in the range 192.0.2.0 -
   192.0.2.255".

   These additional policies split into two basic categories:

   o  An indication of the cacheability of the response carried in the
      HTTP response headers (to reduce the number of subsequent RI
      requests the uCDN needs to make).

   o  The scope of the response (if it is cacheable) carried within the
      body of the HTTP response.  For example whether the response
      applies to a wider range of IP addresses than what was included in
      the RI request.

   The cacheability of the response is indicated using the standard HTTP
   Cache-Control mechanisms.




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4.2.  JSON encoding of RI requests & responses

   The body of RI requests and responses is a JSON object containing a
   dictionary of keys.  Keys MUST always be encoded in lowercase.
   Unknown keys MUST be ignored but the response MUST NOT be considered
   invalid unless the syntax of the request is invalid.

   The following keys are defined:

   +------------+------------------+-----------------------------------+
   | Key        | Request/Response | Description                       |
   +------------+------------------+-----------------------------------+
   | dns        | Both             | The attributes of the UA's DNS    |
   |            |                  | request or the attributes of the  |
   |            |                  | RT(s) to return in a DNS          |
   |            |                  | response.                         |
   | http       | Both             | The attributes of the UA's HTTP   |
   |            |                  | request or the attributes of the  |
   |            |                  | RT to return in a HTTP response.  |
   | scope      | Response         | The scope of the response (if it  |
   |            |                  | is cacheable). For example        |
   |            |                  | whether the response applies to a |
   |            |                  | wider range of IP addresses than  |
   |            |                  | what was included in the RI       |
   |            |                  | request.                          |
   | error      | Response         | Additional details if the         |
   |            |                  | response is an error response.    |
   | cdn-path   | Both             | A List of Strings. Contains the   |
   |            |                  | CDN Provider IDs of previous CDNs |
   |            |                  | this RI request has passed        |
   |            |                  | through. When cascading a RI      |
   |            |                  | request the transit CDN appends   |
   |            |                  | its own CDN Provider ID to the    |
   |            |                  | list in cdn-path so that          |
   |            |                  | downstream CDNs can detect loops  |
   |            |                  | in the RI request chain. Transit  |
   |            |                  | CDNs should check the cdn-path    |
   |            |                  | and not cascade the RI request to |
   |            |                  | downstream CDNs that are already  |
   |            |                  | listed in cdn-path. The cdn-path  |
   |            |                  | MUST be reflected back in RI      |
   |            |                  | responses.                        |
   | max-hops   | Request          | Integer specifying the Maximum    |
   |            |                  | Number of hops (CDN Provider IDs) |
   |            |                  | this request is allowed to be     |
   |            |                  | propagated along. This allows the |
   |            |                  | uCDN to crudely constrain the     |
   |            |                  | latency of the request routing    |



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   |            |                  | chain.                            |
   +------------+------------------+-----------------------------------+

                  Top-Level keys in RI requests/responses

   A single request or response MUST contain only one of the dns or http
   keys.  Requests MUST contain a cdn-path key.

   [[Editor's note: Need some text on minimum attributes to be able to
   (at least parse) - e.g. A/AAAA/CNAME, etc)]]

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

4.3.  MIME Media Types used by the RI interface

   RI requests SHOULD use a MIME Media Type of application/
   cdni.redirectionrequest

   RI responses SHOULD use a MIME Media Type of application/
   cdni.redirectionresponse.

4.4.  DNS redirection

   The following sections provide more detailed descriptions of the
   information that should be passed in RI requests and responses for
   DNS redirection.

4.4.1.  DNS Redirection requests

   For DNS based redirection the uCDN needs to pass the following
   information to the dCDN in the RI request:

   o  The IP address of the DNS resolver that made the DNS request to
      the Upstream CDN.

   o  The type of DNS query made (A, AAAA, RCODEs, etc.).

   o  The class of DNS query made (usually IN).  [[Editor's Note: Do we
      need to include class or can we always assume it is IN?]]

   o  The fully qualified domain name for which DNS redirection is being
      requested.





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   o  The IP address or prefix of the User Agent (if known to the
      Upstream CDN, e.g. through draft-vandergaast-edns-client-subnet).

   The information above is encoded as a set of key:value pairs within
   the dns dictionary as follows:

   +---------------+---------+-----------+-----------------------------+
   | Key           | Value   | Mandatory | Description                 |
   +---------------+---------+-----------+-----------------------------+
   | resolver-ip   | String  | Yes       | The IP address of the UA's  |
   |               |         |           | DNS resolver.               |
   | qtype         | String  | Yes       | The type of DNS query made  |
   |               |         |           | by the UA's DNS resolvers   |
   |               |         |           | in uppercase (A, AAAA,      |
   |               |         |           | etc.).                      |
   | qclass        | String  | Yes       | The class of DNS query made |
   |               |         |           | in uppercase (IN, etc.).    |
   | qname         | String  | Yes       | The fully qualified domain  |
   |               |         |           | name being queried.         |
   | c-subnet      | String  | No        | The IP address of the UA in |
   |               |         |           | CIDR format.                |
   | dns-only      | Boolean | No        | If True then dCDN MUST only |
   |               |         |           | use DNS redirection to a    |
   |               |         |           | surrogate and MUST include  |
   |               |         |           | the dns-only property set   |
   |               |         |           | to True on any cascaded RI  |
   |               |         |           | requests. Defaults to       |
   |               |         |           | False.                      |
   +---------------+---------+-----------+-----------------------------+


   The dns dictionary of a RI request for DNS based redirection MUST
   contain the following keys: resolver-ip, qtype, qclass, qname and the
   value of each MUST be the value of the appropriate part of the User
   Agent's DNS query/request.

   An example RI request (uCDN->dCDN) for DNS based redirection:

   POST /dcdn/ri HTTP/1.1
   Host: rr1.dcdn.example.net
   Accept: application/vnd.cdni.ri.response+json

   {
     "dns" : {
       "resolver-ip" : "192.0.2.1",
       "c-subnet" : "198.51.100.0/24",
       "qtype" : "A",
       "qclass" : "IN",



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       "qname" : "www.example.com"
     },
     "cdn-path": ["AS65551:0"],
     "max-hops": 3
   }


4.4.2.  DNS Redirection responses

   For DNS based redirection the dCDN needs to return one of the
   following to the uCDN in the RI response:

   o  The IP address of (or a CNAME to) the RT (if the dCDN is
      performing DNS based redirection); or

   o  The IP address of (or a CNAME to) a RT which is a Request Router
      (if the dCDN is performing HTTP based redirection).

   The information above is encoded as a set of key:value pairs within
   the dns dictionary as follows:

   +---------+-------------+-------------+-----------------------------+
   | Key     | Value       | Mandatory   | Description                 |
   +---------+-------------+-------------+-----------------------------+
   | rcode   | Integer     | Yes         | DNS response code.          |
   | name    | String      | Yes         | The fully qualified domain  |
   |         |             |             | name the response relates   |
   |         |             |             | to.                         |
   | a       | List of     | No          | Set of IPv4 Addresses of    |
   |         | String      |             | RT(s).                      |
   | aaaa    | List of     | No          | Set of IPv6 Addresses of    |
   |         | String      |             | RT(s).                      |
   | cname   | List of     | No          | Set of fully qualified      |
   |         | String      |             | domain names of RT(s).      |
   | ttl     | Integer     | No          | TTL of DNS response.        |
   |         |             |             | Default is 0.               |
   +---------+-------------+-------------+-----------------------------+


   Response must contain at least one of a, aaaa, cname.

   An example of a successful RI response (dCDN->uCDN) for DNS based
   redirection:

   [[Editor's note: Currently shows both A/AAAA & CNAME in single
   response, need to split to show the different use cases]]





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   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.ri.response+json

   {
     "dns" : {
       "rcode" : 0,
       "name" : "www.example.com",
       "a" : ["192.0.2.200", "192.0.2.201"],
       "aaaa" : ["2001:DB8::C8", "2001:DB8::C9"],
       "cname" : ["rr1.dcdn.example",
                  "rr2.dcdn.example"],
       "ttl" : 60
     }
   }


4.5.  HTTP Redirection

   The following sections provide more detailed descriptions of the
   information that should be passed in RI requests and responses for
   HTTP redirection.

4.5.1.  HTTP Redirection requests

   For HTTP based redirection the uCDN MUST pass the following
   information to the dCDN in the RI request:

   o  The IP address of the User Agent.

   o  The URL requested by the User Agent.

   The uCDN MAY also pass additional information to the dCDN in the RI
   request, such as:

   o  The HTTP method or version number of the User Agent's request.

   o  Additional HTTP header included in the User Agent request.

   The information above is encoded as a set of key:value pairs within
   the http dictionary as follows:

   +--------------------+---------+-----------+------------------------+
   | Key                | Value   | Mandatory | Description            |
   +--------------------+---------+-----------+------------------------+
   | c-ip               | String  | Yes       | The IP address of the  |
   |                    |         |           | UA.                    |
   | cs-uri             | String  | Yes       | The URI requested by   |



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   |                    |         |           | the UA.                |
   | cs-method          | String  | Yes       | The Method part of the |
   |                    |         |           | Request-Line as        |
   |                    |         |           | defined in Section 5.1 |
   |                    |         |           | of [RFC2616].          |
   | cs-version         | String  | Yes       | The HTTP-Version part  |
   |                    |         |           | of the Request-Line as |
   |                    |         |           | defined in Section 5.1 |
   |                    |         |           | of [RFC2616].          |
   | cs(<HeaderName>)   | String  | No        | The contents of the    |
   |                    |         |           | HTTP header named      |
   |                    |         |           | <HeaderName> as a      |
   |                    |         |           | string, for example    |
   |                    |         |           | cs(Cookie) would       |
   |                    |         |           | contain the content of |
   |                    |         |           | the HTTP Cookie:       |
   |                    |         |           | header.                |
   +--------------------+---------+-----------+------------------------+


   The http dictionary of a RI request for HTTP based redirection MUST
   contain the following keys: c-ip, cs-method, cs-version and cs-uri
   and the value of each MUST be the value of the appropriate part of
   the User Agent's DNS query/request.

   An example RI request (uCDN->dCDN) for HTTP based redirection:

   POST/dcdn/rrri HTTP/1.1
   Host: rr1.dcdn.example.net
   Accept: application/vnd.cdni.rrri.response+json

   {
     "http": {
       "c-ip": "198.51.100.1",
       "cs-uri": "http://www.example.com",
       "cs-version": "HTTP/1.1",
       "cs-method": "GET"
     },
     "cdn-path": ["AS65551:0"],
     "max-hops": 3
   }










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4.5.2.  HTTP Redirection responses

   For HTTP based redirection the dCDN needs to return one of the
   following to the uCDN in the RI response:

   o  A URL pointing to the selected RT (if the dCDN is redirecting the
      User Agent directly to a surrogate); or

   o  A URL pointing to a RT which is a Request Router (if the dCDN is
      not redirecting the User Agent directly to a surrogate).

   The information above is encoded as a set of key:value pairs within
   the http dictionary as follows:

   +--------------------+----------+-----------+-----------------------+
   | Key                | Value    | Mandatory | Description           |
   +--------------------+----------+-----------+-----------------------+
   | sc-status          | Integer  | Yes       | The status code of    |
   |                    |          |           | the HTTP response to  |
   |                    |          |           | return to the UA      |
   |                    |          |           | (usually 302).        |
   | cs-uri             | String   | Yes       | The URI requested by  |
   |                    |          |           | the UA/client.        |
   | sc-location        | String   | Yes       | The contents of the   |
   |                    |          |           | Location header to    |
   |                    |          |           | return to the UA      |
   |                    |          |           | (i.e. a URI pointing  |
   |                    |          |           | to the RT(s)).        |
   | sc-cache-control   | String   | No        | The contents of the   |
   |                    |          |           | Cache-Control header  |
   |                    |          |           | to return to the UA.  |
   +--------------------+----------+-----------+-----------------------+


   [[Editor's Note: Should we change the format above to align with the
   cs() format for headers on the RI request and allow the dCDN to
   signal back any headers it wants in the response as sc(<HeaderName>)?
   How to handle sc-status in that case - as a "special" header or
   separate key?  Probably need to give some advice on HTTP headers the
   uCDN may want to override/not pass through, e.g. Server:?]]

   An example of a successful RI response (dCDN->uCDN) for HTTP based
   redirection:

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.ri.response+json




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   {
     "http": {
       "sc-status": 302,
       "cs-uri": "http://www.example.com"
       "sc-location":
         "http://sur1.dcdn.example/ucdn/example.com",
       "sc-cache-control" : "public, max-age=30"
     }
   }


4.6.  Indicating the cacheability and scope of responses

   RI responses may be cacheable and may be reused by the uCDN in
   response to User Agent requests without the uCDN issuing another RI
   request to the dCDN if the RI response is considered cacheable & not
   stale according to the standard HTTP Cache-Control, etc mechanisms.
   Additionally, an RI response MUST NOT be reused unless the request
   from the User Agent would generate an identical RI request to the
   dCDN as the one that resulted in the cached RI response.

   Additionally, although RI requests only encode a single User Agent
   request to be redirected there may be cases where a dCDN wishes to
   indicate to the uCDN that the RI response can be reused for other
   User Agent requests without the uCDN having to make another request
   via the RI.  For example a dCDN may know that it will always select
   the same Surrogates for a given set of User Agent IP addresses and in
   order to reduce request volume across the RI or to remove the
   additional latency associated with an RI request, the dCDN may wish
   to indicate that set of User Agent IP addresses to the uCDN in the
   initial RI response.  This is achieved by including an optional scope
   dictionary in the RI response.

   Scope is encoded as a set of key:value pairs within the scope
   dictionary as follows:

   +-----------+----------+------------+-------------------------------+
   | Key       | Value    | Mandatory  | Description                   |
   +-----------+----------+------------+-------------------------------+
   | iprange   | List of  | No         | A List of IP subnets in CIDR  |
   |           | String   |            | notation that this RI         |
   |           |          |            | response can be reused for,   |
   |           |          |            | provided the RI response is   |
   |           |          |            | still considered fresh.       |
   +-----------+----------+------------+-------------------------------+






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   If a uCDN has multiple cached responses with overlapping scopes,
   longest prefix matching of the User Agent's IP against the IP subnets
   in the scope of each response SHOULD be used to select the most
   appropriate RI response to use.  [[Editor's note: is this always
   true?  What about the most recent response, should that override
   older ones for the overlappign scope?]]

   Example of DNS redirection response from Section 4.4.2 that is
   cacheable by the uCDN for 60 seconds and can be returned to any User
   Agent with an IPv4 address in 198.51.100.0/16.

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.ri.response+json
   Cache-Control: public, max-age=60

   {
     "dns" : {
       "rcode" : 0,
       "name" : "www.example.com",
       "a" : ["192.0.2.200", "192.0.2.201"],
       "aaaa" : ["2001:DB8::C8", "2001:DB8::C9"],
       "cname" : ["rr1.dcdn.example",
                  "rr2.dcdn.example"],
       "ttl" : 60
     }
     "scope" : {
       "iprange" : ["198.51.100.0/16"]
     }
   }


   Example of HTTP redirection response from Section 4.5.2 that is
   cacheable by the uCDN for 60 seconds and can be returned to any User
   Agent with an IPv4 address in 198.51.100.0/16.

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.ri.response+json
   Cache-Control: public, max-age=60

   {
     "http": {
       "sc-status": 302,
       "cs-uri": "http://www.example.com"
       "sc-location":
         "http://sur1.dcdn.example/ucdn/example.com",
       "sc-cache-control" : "public, max-age=30"



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     }
     "scope" : {
       "iprange" : ["198.51.100.0/16"]
     }
   }


4.7.  Error responses

   [[Editor's note: Probably examples of errors that shouldn't be
   propagated to the User Agent?]]

   Errors are indicated via an appropriate HTTP response code.

   There will be many reasons that a server is not able to return a
   successful RI response to the client.  To aid with diagnosing the
   cause of errors, RI responses may include an optional error
   dictionary to provide additional information to the client as to the
   reason/cause of the error.  The intention behind the error dictionary
   is to aid with manual diagnostics of issues and not to provide an
   exhaustive, pre-specified, set of error conditions and associated RI
   specific error codes, etc.

   [[Editor's note: We've tried to keep error specification light weight
   & provide the hooks needed to help with debugging without trying to
   be overly prescriptive over how it gets used as we'd like to avoid
   the rat hole of specifying every possible error condition and
   consequent actions.  This is because it is hard to think of scenarios
   where having a set of pre-defined error codes/etc helps much because
   the relevant consequent action cannot be performed automatically by
   the client.]]

   Additional error information (if present) is encoded as a set of
   key:value pairs within the error dictionary as follows:

   +---------------+-----------+------------+--------------------------+
   | Key           | Value     | Mandatory  | Description              |
   +---------------+-----------+------------+--------------------------+
   | code          | Integer   | No         | A numeric code defined   |
   |               |           |            | by the server to         |
   |               |           |            | indicate the error(s)    |
   |               |           |            | that occurred.           |
   | description   | String    | No         | A string providing       |
   |               |           |            | further (probably human  |
   |               |           |            | readable) information    |
   |               |           |            | related to the error.    |
   +---------------+-----------+------------+--------------------------+




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   RI error response examples.

   RI error response (dCDN->uCDN) for DNS based User Agent requests:

   HTTP/1.1 500 Server Error
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.rrri.error+json
   Cache-Control: private, no-cache

   {
     "dns" : {
       "rcode" : 4                           # DNS response code (e.g.
                                             # doesn't support AAAA)
       "name" : "www.example.com",           # domain name response
                                             # relates to
     },
     "error" : {
       "code" : TBD,                         # Give each error type its
                                             # own numeric code
       "description" :                       # Give more informative
       "IPv6/AAAA queries are not supported" # description than just
     }                                       # protocol specific error
                                             # codes
   }


   RI error response (dCDN->uCDN) for HTTP based User Agent requests:

   HTTP/1.1 500 Server Error
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/vnd.cdni.rrri.error+json
   Cache-Control: private, no-cache

   {
      "http": {
         "sc-status": 400,                       # HTTP response code
         "url": "http://www.example.com",    # URL response
                                             # relates to
         }
       "error" : {
       "code" : TBD,                         # Give each error type its
                                             # own numeric code
       "description" : TBD                   # Give more informative
                                             # description than just
     }                                       # protocol specific error
                                             # codes
   }




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4.8.  Loop detection & prevention

   In order to prevent and detect RI request loops, each CDN MUST insert
   its CDN Provider ID into the cdn-path key of every RI request it
   originates or cascades.  When receiving RI requests a dCDN should
   check the cdn-path and reject any RI requests which already contain
   the downstream CDN's Provider ID in the cdn-path.  Transit CDNs
   should check the cdn-path and not cascade the RI request to
   downstream CDNs that are already listed in cdn-path.  CDNs MUST NOT
   propagate to any downstream CDNs if the number of CDN Provider IDs in
   cdn-path (including the CDN's own Provider ID) is equal to or greater
   than max-hops.

   The CDN Provider ID uniquely identifies each CDN provider during the
   course of request routing redirection.  It consists of the the
   characters AS followed by the CDN Provider's AS number, then a colon
   (':') and an additional qualifier that is used to guarantee
   uniqueness in case a particular AS has multiple independent CDNs
   deployed.  For example "AS65551:0".

   If a downstream CDN receives a RI request whose cdn-path already
   contains that downstream CDN's Provider ID the downstream CDN MUST
   send a RI response with an error code of [[TBD]].

   It should be noted that the loop detection & prevention mechanisms
   described above only cover preventing and detecting loops within the
   RI itself.  As well as loops with the RI itself, there is also the
   possibility of loops in the data plane, for example if the IP
   address(es) or URI(s) returned in RI responses do not resolve
   directly to a surrogate in the final dCDN there is the possibility
   that a User Agent may be continuosly redirected through a loop of
   CDNs.  The specification of solutions to address data plane request
   redirection loops between CDNs is out of the scope of this document.

5.  Security Considerations

   Information passed over the RI could be considered personal or
   sensitive, for example RI requests contain parts of a User Agent's
   original request and RI responses reveal information about the dCDN's
   policy for which surrogates should serve which content/user
   locations.

   The RI interface also provides a mechanism whereby a uCDN could probe
   a dCDN and infer the dCDN's edge topology by making repeated RI
   requests for different content and/or UA IP addresses and correlating
   the responses from the dCDN.  Additionally the ability for a dCDN to
   indicate that a RI response applies more widely that the original
   request (via the scope dictionary) may significantly reduce the



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   number of RI requests required to probe and infer the dCDN's edge
   topology.

   The same information could be obtained in the absence of the RI
   interface, but it could be more difficult to gather as it would
   require a distributed set of machines with a range of different IP
   addresses each making requests directly to the dCDN.  However, the RI
   facilitates easier collection of such information as it enables a
   single client to query the dCDN for a redirection/surrogate selection
   on behalf of any UA IP address.

   In order to prevent passive interception of RI messages the RI
   communications channel should be suitably secured (e.g. use of TLS).

   In order to reduce the risk of information leakage to unauthorized
   parties, RI clients and servers SHOULD use suitable authentication
   prior to trusting the contents of RI messages.

   [[Editor's note: Not sure if the text below is really security
   considerations or whether it is better placed elsewhere in the
   document.]]

   In HTTP based Recursive Request Redirection, the end user's web
   browsers will not send cookies if the content request is redirected
   to a URL in a different domain rather than the original CP's domain,
   e.g. the Downstream CDN's domain.  If the browser is expected to send
   any cookies associated with the original CP's domain, this will cause
   problem that the CP's policy is not enforced by the CDN.

   The section 5.2 of draft [I-D.peterson-cdni-strawman] has discussed a
   similar question and given a solution.

6.  IANA Considerations

   [[Editors' Note: Need to insert some text to register the Media Types
   we use with IANA?]]

7.  Acknowledgements

   The authors would like to thank Ray Brandenburg, Taesang Choi,
   Francois le Faucheur and Scott Wainner for their valuable comments
   and input to this document.









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8.  Outstanding considerations

   Along with the various Editor's notes in the document, the following
   items still need to be addressed:

   o  Additional examples of RI requests/responses (including error
      responses) illustrating different use cases.

   o  Description/specification for how to extend the protocol with
      additional optimonal parameters/attributes.

9.  Contributing Authors

   [RFC Editor Note: Please move the contents of this section to the
   Authors' Addresses section prior to publication as an RFC.]

   Spencer Dawkins
   Huawei

   Email: spencer@wonderhamster.org


   Yunfei Zhang

   Email: hishigh@gmail.com


10.  References

10.1.  Normative References

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

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

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

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.




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10.2.  Informative References

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

   [I-D.ietf-cdni-framework]
              Peterson, L. and B. Davie, "Framework for CDN
              Interconnection", draft-ietf-cdni-framework-03 (work in
              progress), February 2013.

   [I-D.ietf-cdni-requirements]
              Leung, K. and Y. Lee, "Content Distribution Network
              Interconnection (CDNI) Requirements", draft-ietf-cdni-
              requirements-06 (work in progress), April 2013.

   [I-D.peterson-cdni-strawman]
              Peterson, L. and J. Hartman, "A Simple Approach to CDN
              Interconnection", draft-peterson-cdni-strawman-01 (work in
              progress), May 2011.

Authors' Addresses

   Wang Danhua (editor)
   Huawei Technologies
   No. 101 Software Avenue
   Nanjing, Jiangsu Province  210001
   P.R.China

   Phone: +86-25-56624734
   Fax:   +86-25-56624702
   Email: wangdanhua@huawei.com


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

   Email: ben@velocix.com










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   He Xiaoyan
   Huawei
   B2, Huawei Industrial Base
   518129
   P.R.China

   Email: hexiaoyan@huawei.com


   Ge Chen
   China Telecom
   109 West Zhongshan Ave,Tianhe District
   Guangzhou
   P.R. China

   Email: cheng@gsta.com


   Ni Wei
   China Mobile
   No.32 Xuanwumen West Street Xicheng District
   Beijing  100053
   P.R. China

   Email: niwei@chinamobile.com


























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