





Internet Engineering Task Force (IETF)             B. Niven-Jenkins, Ed.
Request for Comments: 7975                                         Nokia
Category: Standards Track                        R. van Brandenburg, Ed.
ISSN: 2070-1721                                                      TNO
                                                            October 2016


               Request Routing Redirection Interface for
             Content Delivery Network (CDN) Interconnection

Abstract

   The Request Routing interface comprises (1) the asynchronous
   advertisement of footprint and capabilities by a downstream Content
   Delivery Network (CDN) that allows an 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 is an Internet Standards Track document.

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

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7975.
















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Copyright Notice

   Copyright (c) 2016 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Interface Function and Operation Overview . . . . . . . . . .   4
   4.  HTTP-Based Interface for the Redirection Interface  . . . . .   6
     4.1.  Information Passed in RI Requests and Responses . . . . .   8
     4.2.  JSON Encoding of RI Requests and Responses  . . . . . . .   9
     4.3.  MIME Media Types Used by the RI Interface . . . . . . . .  11
     4.4.  DNS Redirection . . . . . . . . . . . . . . . . . . . . .  12
       4.4.1.  DNS Redirection Requests  . . . . . . . . . . . . . .  12
       4.4.2.  DNS Redirection Responses . . . . . . . . . . . . . .  14
     4.5.  HTTP Redirection  . . . . . . . . . . . . . . . . . . . .  17
       4.5.1.  HTTP Redirection Requests . . . . . . . . . . . . . .  17
       4.5.2.  HTTP Redirection Responses  . . . . . . . . . . . . .  19
     4.6.  Cacheability and Scope of Responses . . . . . . . . . . .  22
     4.7.  Error Responses . . . . . . . . . . . . . . . . . . . . .  24
     4.8.  Loop Detection and Prevention . . . . . . . . . . . . . .  28
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
     5.1.  Authentication, Authorization, Confidentiality, and
           Integrity Protection  . . . . . . . . . . . . . . . . . .  29
     5.2.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . .  30
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  31
     6.1.  CDNI Payload Type Parameter Registrations . . . . . . . .  31
       6.1.1.  CDNI RI Redirection Request Payload Type  . . . . . .  31
       6.1.2.  CDNI RI Redirection Response Payload Type . . . . . .  31
     6.2.  RI Error Response Registry  . . . . . . . . . . . . . . .  31
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  32
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  34
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  34
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  35
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  35



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1.  Introduction

   A Content Delivery Network (CDN) is a system built on an existing IP
   network that 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.

   The CDNI Request Routing interface outlined in [RFC7336] is comprised
   of:

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

   2.  The synchronous operation of a uCDN requesting whether a dCDN is
       prepared to accept a user request and of a dCDN 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 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 a CDN's
      routing decision 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 Real
      Time Messaging Protocol (RTMP) [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 (UA) 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.




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   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.

   Redirection Target (RT):  The endpoint to which the User Agent is
      redirected.  In CDNI, an 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 dCDN, or a surrogate in
      a dCDN.

3.  Interface Function and Operation Overview

   The main function of the CDNI Redirection interface (RI) 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 [RFC7337].

   The User Agent will make a request to a request router in the uCDN
   using one of either DNS or HTTP.  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
   the User Agent and uCDN request router.  The dCDN has control over
   the Redirection Target it provides.  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 that returned the RI
      response to the uCDN or another CDN (if the dCDN delegates the
      delivery to another CDN); or

   o  A request router (in the dCDN or another CDN), which may use a
      different redirection protocol (DNS or HTTP) than the one included
      in the RI request.

   The Redirection interface operates between the request routing
   systems of a pair of interconnected CDNs.  To enable communication
   over the Redirection interface, the uCDN needs to know the URI
   (endpoint) in the dCDN to send CDNI request routing queries.

   The Redirection interface URI may be statically preconfigured,
   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.



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   The Redirection interface is only relevant in the case of Recursive
   Request Redirection, as Iterative Request Redirection does not invoke
   any interaction over the Redirection interface between interconnected
   CDNs.  Therefore, the scope of this document is limited to Recursive
   Request Redirection.

   In the case of Recursive Request Redirection, in order to perform
   redirection of a request received from a User Agent, the uCDN queries
   the dCDN so that the dCDN can select and provide a Redirection
   Target.  In cases where a uCDN has a choice of dCDNs, it is up 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
   rejects 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 uCDN->User Agent redirection protocols addressed in this document
   are: DNS redirection and HTTP redirection.  Other types of
   application-level redirection will not be discussed further in this
   document.  However, the Redirection interface is designed to be
   extensible and could be extended to support additional application-
   level redirection protocols.

   For both DNS and HTTP redirection, either HTTP or HTTPS could be used
   to connect to the Redirection Target.  When HTTPS is used to connect
   to the uCDN, if the uCDN uses DNS redirection to identify the RT to
   the User Agent, then the new target domain name may not match the
   domain in the URL dereferenced to reach the uCDN; without operational
   precautions, and in the absence of DNSSEC, this can make a legitimate
   redirection look like a DNS-based attack to a User Agent and trigger
   security warnings.  When DNS-based redirection with HTTPS is used,
   this specification assumes that any RT can complete the necessary
   Transport Layer Security (TLS) handshake with the User Agent.  Any
   operational mechanisms this requires, e.g., private key distribution
   to surrogates and request routers in dCDNs, are outside the scope of
   this document.

   This document also defines an RI loop prevention and detection
   mechanism as part of the Redirection interface.









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4.  HTTP-Based Interface for the Redirection Interface

   This document defines a simple interface for the Redirection
   interface based on HTTP [RFC7230], where the attributes of a User
   Agent's requests are encapsulated along with any other data that can
   aid the dCDN in processing the requests.  The RI response
   encapsulates the attributes of the RT(s) that the uCDN should return
   to the User Agent (if it decides to utilize the dCDN for delivery)
   along with the policy for how the response can be reused.  The
   examples of RI requests and responses below do not contain a complete
   set of HTTP headers for brevity; only the pertinent HTTP headers are
   shown.

   The RI between the uCDN and dCDN uses the same HTTP interface to
   encapsulate the attributes of both DNS and HTTP requests received
   from User Agents, 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 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 dCDN to make a request routing decision, avoids
   having to both 1) try to encapsulate or proxy DNS/HTTP/RTMP/
   etc. requests and 2) 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) by defining
   additional protocol-specific keys for RI requests and responses along
   with a specification about how to process them.















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

   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 RT attributes |
       |                         |of the 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 (DNS or HTTP) request to CDN A.  The
       Request Routing System of CDN A processes the request and,
       through local policy, recognizes that the request is best served
       by another CDN, specifically CDN B (or that CDN B may be 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 RI request and,
       assuming the request is well-formed, 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.







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4.1.  Information Passed in RI Requests and Responses

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

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

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

   Generally, dCDNs can provide better routing decisions given
   additional information about the content request, e.g., the URI of
   the requested content or the User Agent's IP address or subnet.  The
   information required to base a routing decision on can be highly
   dependent on the type of content delivered.  A uCDN SHOULD only
   include information that is absolutely necessary for delivering that
   type of content.  Cookies in particular are especially sensitive from
   a security/privacy point of view and in general SHOULD NOT be
   conveyed in the RI Requests to the dCDN.  The information necessary
   to be conveyed for a particular type of request is expected to be
   conveyed out of band between the uCDN and dCDN.  See Section 5.2 for
   more detail on the privacy aspects of using RI Requests to convey
   information about UA requests.

   In order for the dCDN 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 dCDN to be able to retrieve the required 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 about how to redirect the User Agent, the dCDN
   may wish to return additional policy information to the uCDN.  For
   example, the dCDN may wish to return a policy that expresses "this
   response can be reused without requiring an RI request for 60 seconds
   provided the User Agent's IP address is in the range 198.51.100.0 --
   198.51.100.255".




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   These additional policies split into two basic categories:

   o  Cacheability information signaled via the HTTP response headers of
      the RI response (to reduce the number of subsequent RI requests
      the uCDN needs to make).

   o  The scope of a cacheable response signaled in the HTTP response
      body of the RI 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.

4.2.  JSON Encoding of RI Requests and Responses

   The body of RI requests and responses is a JSON object [RFC7159] that
   contains a dictionary of key:value pairs that MUST conform to
   [RFC7493].  Senders MUST encode all (top-level object and sub-object)
   keys specified in this document in lowercase.  Receivers MUST ignore
   any keys that are unknown or invalid.






























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   The following table defines the top-level keys and indicates whether
   they are applicable to RI requests, RI responses, or both:

   +----------+------------------+-------------------------------------+
   | 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 an 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 a list  |
   |          |                  | of the CDN Provider IDs of previous |
   |          |                  | CDNs that have participated in the  |
   |          |                  | request routing for the associated  |
   |          |                  | User Agent request. On RI requests, |
   |          |                  | it contains the list of previous    |
   |          |                  | CDNs that this RI request has       |
   |          |                  | passed through. On RI responses, it |
   |          |                  | contains the list of CDNs that were |
   |          |                  | involved in obtaining the final     |
   |          |                  | redirection included in the RI      |
   |          |                  | response. See Section 4.8.          |
   |          |                  |                                     |
   | 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 coarsely constrain the      |
   |          |                  | latency of the request routing      |
   |          |                  | chain.                              |
   +----------+------------------+-------------------------------------+

             Table 1: Top-Level Keys in RI Requests/Responses





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   A single request or response MUST contain only one of the dns or http
   keys.  Requests MUST contain a cdn-path key and responses MAY contain
   a cdn-path key.  If the max-hops key is not present, then there is no
   limit on the number of CDN hops that the RI request can be propagated
   along.  If the first uCDN does not wish the RI request to be
   propagated beyond the dCDN it is making the request to, then the uCDN
   MUST set max-hops to 1.

   The cdn-path MAY be reflected back in RI responses, although doing so
   could expose information to the uCDN that a dCDN may not wish to
   expose (for example, the existence of business relationships between
   a dCDN and other CDNs).

   If the cdn-path is reflected back in the RI response, it MUST contain
   the value of cdn-path received in the associated RI request with the
   final dCDN's CDN Provider ID appended.  Transit CDNs MAY remove the
   cdn-path from RI responses but MUST NOT modify the cdn-path in other
   ways.

   The presence of an error key within a response that also contains
   either a dns or http key does not automatically indicate that the RI
   request was unsuccessful as the error key MAY be used for
   communicating additional (e.g., debugging) information.  When a
   response contains an error key as well as either a dns or http key,
   the error-code SHOULD be 1xx (e.g., 100).  See Section 4.7 for more
   details about encoding error information in RI responses.

   All implementations that support IPv4 addresses MUST support the
   encoding specified by the 'IPv4address' rule in Section 3.2.2 of
   [RFC3986].  Likewise, implementations that support IPv6 addresses
   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 MUST use a MIME media type of application/cdni as
   specified in [RFC7736], with the Payload Type (ptype) parameter set
   to 'redirection-request'.

   RI responses MUST use a MIME media type of application/cdni as
   specified in [RFC7736], with the Payload Type (ptype) parameter set
   to 'redirection-response'.








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4.4.  DNS Redirection

   The following sections provide 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 uCDN.

   o  The type of DNS query made (usually either A or AAAA).

   o  The class of DNS query made (usually IN).

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

   o  The IP address or prefix of the User Agent (if known to the uCDN).





























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   The preceding information 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.  The value of this |
   |             |         |           | field SHALL be set to either  |
   |             |         |           | 'A' or 'AAAA'.                |
   |             |         |           |                               |
   | 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 (or prefix) of |
   |             |         |           | the UA in Classless Inter-    |
   |             |         |           | Domain Routing (CIDR) format. |
   |             |         |           |                               |
   | dns-only    | Boolean | No        | If True, then dCDN MUST only  |
   |             |         |           | use DNS redirection and MUST  |
   |             |         |           | include RTs to one or more    |
   |             |         |           | surrogates in any successful  |
   |             |         |           | RI response.  CDNs MUST       |
   |             |         |           | include the dns-only property |
   |             |         |           | set to True on any cascaded   |
   |             |         |           | RI requests.  Defaults to     |
   |             |         |           | False.                        |
   +-------------+---------+-----------+-------------------------------+

                                  Table 2

   An RI request for DNS-based redirection MUST include a dns
   dictionary.  This dns dictionary MUST contain the following keys:
   resolver-ip, qtype, qclass, and qname; the value of each MUST be the
   value of the appropriate part of the User Agent's DNS query/request.
   For internationalized domain names containing non-ASCII characters,
   the value of the qname field MUST be the ASCII-compatible encoded
   (ACE) representation (A-label) of the domain name [RFC5890].






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

   POST /dcdn/ri HTTP/1.1
   Host: rr1.dcdn.example.net
   Content-Type: application/cdni; ptype=redirection-request
   Accept: application/cdni; ptype=redirection-response

   {
     "dns" : {
       "resolver-ip" : "192.0.2.1",
       "c-subnet" : "198.51.100.0/24",
       "qtype" : "A",
       "qclass" : "IN",
       "qname" : "www.example.com"
     },
     "cdn-path": ["AS64496:0"],
     "max-hops": 3
   }

4.4.2.  DNS Redirection Responses

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

   o  The IP address(es) of (or the CNAME of) RTs that are dCDN
      surrogates (if the dCDN is performing DNS-based redirection
      directly to a surrogate); or

   o  The IP address(es) of (or the CNAME of) RTs that are Request
      Routers (if the dCDN will perform request redirection itself).  A
      dCDN MUST NOT return an RT that is a Request Router if the dns-
      only key is set to True in the RI request.


















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   The preceding information 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 (see            |
   |       |           |           | [RFC6895]).                       |
   |       |           |           |                                   |
   | name  | String    | Yes       | The fully qualified domain name   |
   |       |           |           | the response relates to.          |
   |       |           |           |                                   |
   | a     | List of   | No        | Set of IPv4 Addresses of RT(s).   |
   |       | String    |           |                                   |
   |       |           |           |                                   |
   | aaaa  | List of   | No        | Set of IPv6 Addresses of RT(s).   |
   |       | String    |           |                                   |
   |       |           |           |                                   |
   | cname | List of   | No        | Set of fully qualified domain     |
   |       | String    |           | names of RT(s).                   |
   |       |           |           |                                   |
   | ttl   | Integer   | No        | TTL in seconds of DNS response.   |
   |       |           |           | Default is 0.                     |
   +-------+-----------+-----------+-----------------------------------+

                                  Table 3

   A successful RI response for DNS-based redirection MUST include a dns
   dictionary and MAY include an error dictionary (see Section 4.7).  An
   unsuccessful RI response for DNS-based redirection MUST include an
   error dictionary.  If a dns dictionary is included in the RI
   response, it MUST include the rcode and name keys and it MUST include
   at least one of the following keys: a, aaaa, or cname.  The dns
   dictionary MAY include both a and aaaa keys.  If the dns dictionary
   contains a cname key, it MUST NOT contain either an a or aaaa key.
   For internationalized domain names containing non-ASCII characters,
   the value of the cname field MUST be the ACE representation (A-label)
   of the domain name.













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   An example of a successful RI response (dCDN->uCDN) for DNS-based
   redirection with both a and aaaa keys is listed below:

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response

   {
     "dns" : {
       "rcode" : 0,
       "name" : "www.example.com",
       "a" : ["203.0.113.200", "203.0.113.201", "203.0.113.202"],
       "aaaa" : ["2001:DB8::C8", "2001:DB8::C9"],
       "ttl" : 60
     }
   }

   A further example of a successful RI response (dCDN->uCDN) for DNS-
   based redirection is listed below, in this case with a cname key
   containing the FQDN of the RT.

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response

   {
     "dns" : {
       "rcode" : 0,
       "name" : "www.example.com",
       "cname" : ["rr1.dcdn.example"],
       "ttl" : 20
     }
   }


















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4.5.  HTTP Redirection

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

   The dictionary keys used in HTTP Redirection requests and responses
   use the following conventions for their prefixes:

   o  c- is prefixed to keys for information related to the Client (User
      Agent).

   o  cs- is prefixed to keys for information passed by the Client (User
      Agent) to the Server (uCDN).

   o  sc- is prefixed to keys for information to be passed by the Server
      (uCDN) to the Client (User Agent).

4.5.1.  HTTP Redirection Requests

   For HTTP-based redirection, the uCDN needs to pass the following
   information to the dCDN in the RI request:

   o  The IP address of the User Agent.

   o  The URI requested by the User Agent.

   o  The HTTP method requested by the User Agent.

   o  The HTTP version number requested by the User Agent.

   The uCDN may also decide to pass the presence and value of particular
   HTTP headers included in the User Agent request to the dCDN.


















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   The preceding information 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 Effective Request    |
   |                   |        |           | URI [RFC7230] requested  |
   |                   |        |           | by the UA.               |
   |                   |        |           |                          |
   | cs-method         | String | Yes       | The method part of the   |
   |                   |        |           | request-line as defined  |
   |                   |        |           | in Section 3.1.1 of      |
   |                   |        |           | [RFC7230].               |
   |                   |        |           |                          |
   | cs-version        | String | Yes       | The HTTP-version part of |
   |                   |        |           | the request-line as      |
   |                   |        |           | defined in Section 3.1.1 |
   |                   |        |           | of [RFC7230].            |
   |                   |        |           |                          |
   | cs-(<headername>) | String | No        | The field-value of the   |
   |                   |        |           | HTTP header field named  |
   |                   |        |           | <HeaderName> as a        |
   |                   |        |           | string, for example,     |
   |                   |        |           | cs-(cookie) would        |
   |                   |        |           | contain the value of the |
   |                   |        |           | HTTP Cookie header from  |
   |                   |        |           | the UA request.          |
   +-------------------+--------+-----------+--------------------------+

                                  Table 4

   An RI request for HTTP-based redirection MUST include an http
   dictionary.  This http dictionary MUST contain the following keys:
   c-ip, cs-method, cs-version, and cs-uri; the value of each MUST be
   the value of the appropriate part of the User Agent's HTTP request.

   The http dictionary of an RI request MUST contain a maximum of one
   cs-(<headername>) key for each unique header field-name (HTTP header
   field).  <headername> MUST be identical to the equivalent HTTP header
   field-name encoded in all lowercase.







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   In the case where the User Agent request includes multiple HTTP
   header fields with the same field-name, it is RECOMMENDED that the
   uCDN combine these different HTTP headers into a single value
   according to Section 3.2.2 of [RFC7230].  However, because of the
   plurality of already defined HTTP header fields and the inconsistency
   of some of these header fields concerning the combination mechanism
   defined in RFC 7230, the uCDN MAY have to deviate from using the
   combination mechanism where appropriate.  For example, it might only
   send the contents of the first occurrence of the HTTP Headers
   instead.

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

   POST /dcdn/rrri HTTP/1.1
   Host: rr1.dcdn.example.net
   Content-Type: application/cdni; ptype=redirection-request
   Accept: application/cdni; ptype=redirection-response

   {
     "http": {
       "c-ip": "198.51.100.1",
       "cs-uri": "http://www.example.com",
       "cs-version": "HTTP/1.1",
       "cs-method": "GET"
     },
     "cdn-path": ["AS64496:0"],
     "max-hops": 3
   }

4.5.2.  HTTP Redirection Responses

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

   o  A URI pointing to an RT that is the selected dCDN surrogate(s) (if
      the dCDN is performing HTTP-based redirection directly to a
      surrogate); or

   o  A URI pointing to an RT that is a Request Router (if the dCDN will
      perform request redirection itself).










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   The preceding information 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 part of |
   |                   |         |           | the status-line as      |
   |                   |         |           | defined in Section      |
   |                   |         |           | 3.1.2 of [RFC7230] to   |
   |                   |         |           | return to the UA        |
   |                   |         |           | (usually set to 302).   |
   |                   |         |           |                         |
   | sc-version        | String  | Yes       | The HTTP-version part   |
   |                   |         |           | of the status-line as   |
   |                   |         |           | defined in Section      |
   |                   |         |           | 3.1.2 of [RFC7230] to   |
   |                   |         |           | return to the UA.       |
   |                   |         |           |                         |
   | sc-reason         | String  | Yes       | The reason-phrase part  |
   |                   |         |           | of the status-line as   |
   |                   |         |           | defined in Section      |
   |                   |         |           | 3.1.2 of [RFC7230] to   |
   |                   |         |           | return to the UA.       |
   |                   |         |           |                         |
   | 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-(<headername>) | String  | No        | The field-value of the  |
   |                   |         |           | HTTP header field named |
   |                   |         |           | <HeaderName> to return  |
   |                   |         |           | to the UA. For example, |
   |                   |         |           | sc-(expires) would      |
   |                   |         |           | contain the value of    |
   |                   |         |           | the HTTP Expires        |
   |                   |         |           | header.                 |
   +-------------------+---------+-----------+-------------------------+

                                  Table 5






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   Note: The sc-(location) key in the preceding table is an example of
   sc-(<headername>) that has been called out separately as its presence
   is mandatory in RI responses.

   A successful RI response for HTTP-based redirection MUST include an
   http dictionary and MAY include an error dictionary (see
   Section 4.7).  An unsuccessful RI response for HTTP-based redirection
   MUST include an error dictionary.  If an http dictionary is included
   in the RI response, it MUST include at least the following keys:
   sc-status, sc-version, sc-reason, cs-uri, and sc-(location).

   The http dictionary of an RI response MUST contain a maximum of one
   sc-(<headername>) key for each unique header field-name (HTTP header
   field).  <headername> MUST be identical to the equivalent HTTP header
   field-name encoded in all lowercase.

   The uCDN MAY decide to not return, override, or alter any or all of
   the HTTP headers defined by sc-(<headername>) keys before sending the
   HTTP response to the UA.  It should be noted that in some cases,
   sending the HTTP Headers indicated by the dCDN transparently on to
   the UA might result in, for the uCDN, undesired behavior.  As an
   example, the dCDN might include sc-(cache-control),
   sc-(last-modified), and sc-(expires) keys in the http dictionary,
   through which the dCDN may try to influence the cacheability of the
   response by the UA.  If the uCDN would pass these HTTP headers on to
   the UA, this could mean that further requests from the uCDN would go
   directly to the dCDN, bypassing the uCDN and any logging it may
   perform on incoming requests.  Therefore, the uCDN is recommended to
   carefully consider which HTTP headers to pass on, and which to either
   override or not pass on at all.

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

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response

   {
     "http": {
       "sc-status": 302,
       "sc-version": "HTTP/1.1",
       "sc-reason": "Found",
       "cs-uri": "http://www.example.com"
       "sc-(location)":
         "http://sur1.dcdn.example/ucdn/example.com",
     }
   }



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4.6.  Cacheability and Scope of Responses

   RI responses may be cacheable.  As long as a cached RI response is
   not stale according to standard HTTP Cache-Control or other
   applicable mechanisms, it may be reused by the uCDN in response to
   User Agent requests without sending another RI request to the dCDN.

   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 (except for the c-ip field
   provided that the User Agent's c-ip is covered by the scope in the
   original RI response, as elaborated upon below).

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

                                  Table 6

   If a uCDN has multiple cached responses with overlapping scopes and a
   UA request comes in for which the User Agent's IP matches with the IP
   subnets in multiple of these cached responses, the uCDN SHOULD use
   the most recent cached response when determining the appropriate RI
   response to use.






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   The following is an example of a DNS redirection response from
   Section 4.4.2 that is cacheable by the uCDN for 30 seconds and can be
   returned to any User Agent with an IPv4 address in 198.51.100.0/24.

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response
   Cache-Control: public, max-age=30

   {
     "dns" : {
       "rcode" : 0,
       "name" : "www.example.com",
       "a" : ["203.0.113.200", "203.0.113.201"],
       "aaaa" : ["2001:DB8::C8", "2001:DB8::C9"],
       "ttl" : 60
     }
     "scope" : {
       "iprange" : ["198.51.100.0/24"]
     }
   }

   The following is an example of an 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 198.51.100.0/24.

   Note: The response to the UA is only valid for 30 seconds, whereas
   the uCDN can cache the RI response for 60 seconds.

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response
   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"
     }
     "scope" : {
       "iprange" : ["198.51.100.0/24"]
     }
   }





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4.7.  Error Responses

   From a uCDN perspective, there are two types of errors that can be
   the result of the transmission of an RI request to a dCDN:

   1.  An HTTP protocol error signaled via an HTTP status code,
       indicating a problem with the reception or parsing of the RI
       request or the generation of the RI response by the dCDN, and

   2.  An RI-level error specified in an RI response message.

   This section deals with the latter type.  The former type is outside
   the scope of this document.

   There are numerous reasons for a dCDN to be unable to return an
   affirmative RI response to a uCDN.  Reasons may include both dCDN
   internal issues such as capacity problems, as well as reasons outside
   the influence of the dCDN, such as a malformed RI request.  To aid
   with diagnosing the cause of errors, RI responses SHOULD include an
   error dictionary to provide additional information to the uCDN as to
   the reason/cause of the error.  The intention behind the error
   dictionary is to aid with either manual or automatic diagnosis of
   issues.  The resolution of such issues is outside the scope of this
   document; this document does not specify any consequent actions a
   uCDN should take upon receiving a particular error-code.

   Error information (if present) is encoded as a set of key:value pairs
   within a JSON-encoded error dictionary as follows:

   +------------+---------+-----------+--------------------------------+
   | Key        | Value   | Mandatory | Description                    |
   +------------+---------+-----------+--------------------------------+
   | error-code | Integer | Yes       | A three-digit numeric code     |
   |            |         |           | defined by the server to       |
   |            |         |           | indicate the error(s) that     |
   |            |         |           | occurred.                      |
   |            |         |           |                                |
   | reason     | String  | No        | A string providing further     |
   |            |         |           | information related to the     |
   |            |         |           | error.                         |
   +------------+---------+-----------+--------------------------------+

                                  Table 7








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   The first digit of the error-code defines the class of error.  There
   are 5 classes of errors distinguished by the first digit of the
   error-code:

      1xx: Informational (no error): The response should not be
      considered an error by the uCDN, which may proceed by redirecting
      the UA according to the values in the RI response.  The error-code
      and accompanying description may be used for informational
      purposes, e.g., for logging.

      2xx: Reserved.

      3xx: Reserved.

      4xx: uCDN error: The dCDN cannot or will not process the request
      due to something that is perceived to be a uCDN error, for
      example, the RI request could not be parsed successfully by the
      dCDN.  The last two-digits may be used to more specifically
      indicate the source of the problem.

      5xx: dCDN error: Indicates that the dCDN is aware that it has
      erred or is incapable of satisfying the RI request for some
      reason, for example, the dCDN was able to parse the RI request but
      encountered an error for some reason.  Examples include the dCDN
      not being able to retrieve the associated metadata or the dCDN
      being out of capacity.

   The following error-codes are defined and maintained by IANA (see
   Section 6).

   Error-codes with a "Reason" of "<reason>" do not have a defined value
   for their 'reason'-key.  Depending on the error-code semantics, the
   value of this field may be determined dynamically.

   +------+--------------+---------------------------------------------+
   | Code | Reason       | Description                                 |
   +------+--------------+---------------------------------------------+
   | 100  | <reason>     | Generic informational error-code meant for  |
   |      | (see         | carrying a human-readable string            |
   |      | Description) |                                             |
   |      |              |                                             |
   | 400  | <reason>     | Generic error-code for uCDN errors where    |
   |      | (see         | the dCDN cannot or will not process the     |
   |      | Description) | request due to something that is perceived  |
   |      |              | to be a uCDN error.  The reason field may   |
   |      |              | be used to provide more details about the   |
   |      |              | source of the error.                        |
   |      |              |                                             |



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   | 500  | <reason>     | Generic error-code for dCDN errors where    |
   |      | (see         | the dCDN is aware that it has erred or is   |
   |      | Description) | incapable of satisfying the RI request for  |
   |      |              | some reason.  The reason field may be used  |
   |      |              | to provide more details about the source of |
   |      |              | the error.                                  |
   |      |              |                                             |
   | 501  | Unable to    | The dCDN is unable to retrieve the metadata |
   |      | retrieve     | associated with the content requested by    |
   |      | metadata     | the UA.  This may indicate a configuration  |
   |      |              | error or that the content requested by the  |
   |      |              | UA does not exist.                          |
   |      |              |                                             |
   | 502  | Loop         | The dCDN detected a redirection loop (see   |
   |      | detected     | Section 4.8).                               |
   |      |              |                                             |
   | 503  | Maximum hops | The dCDN detected the maximum number of     |
   |      | exceeded     | redirection hops exceeding max-hops (see    |
   |      |              | Section 4.8).                               |
   |      |              |                                             |
   | 504  | Out of       | The dCDN does not currently have sufficient |
   |      | capacity     | capacity to handle the UA request.          |
   |      |              |                                             |
   | 505  | Delivery     | The dCDN does not support the (set of)      |
   |      | protocol not | delivery protocols indicated in the CDNI    |
   |      | supported    | Metadata of the content requested by the    |
   |      |              | UA.                                         |
   |      |              |                                             |
   | 506  | Redirection  | The dCDN does not support the requested     |
   |      | protocol not | redirection protocol.  This error-code is   |
   |      | supported    | also used when the RI request has the dns-  |
   |      |              | only flag set to True and the dCDN is not   |
   |      |              | supported or is not prepared to return an   |
   |      |              | RT of a surrogate directly.                 |
   +------+--------------+---------------------------------------------+

                                  Table 8














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   The following is an example of an unsuccessful RI response
   (dCDN->uCDN) for a DNS-based User Agent request:

   HTTP/1.1 500 Internal Server Error
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response
   Cache-Control: private, no-cache

   {
     "error" : {
       "error-code" : 504,
       "description" : "Out of capacity"
     }
   }

   The following is an example of a successful RI response (dCDN->uCDN)
   for an HTTP-based User Agent request containing an error dictionary
   for informational purposes:

   HTTP/1.1 200 OK
   Date: Mon, 06 Aug 2012 18:41:38 GMT
   Content-Type: application/cdni; ptype=redirection-response
   Cache-Control: private, no-cache

   {
      "http": {
       "sc-status": 302,
       "sc-version": "HTTP/1.1",
       "sc-reason": "Found",
       "cs-uri": "http://www.example.com"
       "sc-(location)":
         "http://sur1.dcdn.example/ucdn/example.com",
      },
      "error" : {
       "error-code" : 100,
       "description" :
         "This is a human-readable message meant for debugging purposes"
     }
   }












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4.8.  Loop Detection and 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 MUST
   check the cdn-path and reject any RI requests that already contain
   the dCDN's Provider ID in the cdn-path.  Transit CDNs MUST NOT
   propagate to any downstream CDNs if the number of CDN Provider IDs in
   cdn-path (before adding its 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 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,
   "AS64496:0".

   If a dCDN receives an RI request whose cdn-path already contains that
   dCDN's Provider ID, the dCDN MUST send an RI error response that
   SHOULD include an error-code of 502.

   If a dCDN receives an RI request where the number of CDN Provider IDs
   in cdn-path is greater than max-hops, the dCDN MUST send an RI error
   response that SHOULD include an error-code of 503.

   It should be noted that the loop detection and prevention mechanisms
   described above only cover preventing and detecting loops within the
   RI itself.  Besides loops within 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 continuously redirected through a loop of
   CDNs.  The specification of solutions to address data-plane request
   redirection loops between CDNs is outside of the scope of this
   document.















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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 an RI response applies more widely than the original
   request (via the scope dictionary) may significantly reduce the
   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.

5.1.  Authentication, Authorization, Confidentiality, and Integrity
      Protection

   An implementation of the CDNI Redirection interface MUST support TLS
   transport as per [RFC2818] and [RFC7230].  The use of TLS for
   transport of the CDNI Redirection interface messages allows the dCDN
   and uCDN to authenticate each other.  Once they have mutually
   authenticated each other, it allows:

   o  The dCDN and uCDN to authorize each other (to ensure they are
      transmitting/receiving CDNI Redirection messages to/from an
      authorized CDN);

   o  CDNI Redirection interface messages to be transmitted with
      confidentiality; and

   o  The integrity of the CDNI Redirection interface messages to be
      protected during the exchange.








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   In an environment where any such protection is required, mutually
   authenticated encrypted transport MUST be used to ensure
   confidentiality of the redirection information; to do so, TLS MUST be
   used (including authentication of the remote end) by the server side
   (dCDN) and the client side (uCDN) of the CDNI Redirection interface.

   When TLS is used, the general TLS usage guidance in [RFC7525] MUST be
   followed.

5.2.  Privacy

   Information passed over the RI ought to be considered personal and
   sensitive.  In particular, parts of a User Agent's original request,
   most notably the UA's IP address and requested URI, are transmitted
   over the RI to the dCDN.  The use of mutually authenticated TLS, as
   described in the previous section, prevents any other party than the
   authorized dCDN from gaining access to this information.

   Regardless of whether the uCDN and dCDN use the RI, a successful
   redirect from a uCDN to a dCDN will make that dCDN aware of the UA's
   IP address.  As such, the fact that this information is transmitted
   across the RI does not allow the dCDN to learn new information.  On
   the other hand, if a uCDN uses the RI to check with multiple
   candidate dCDNs, those candidates that do not end up getting
   redirected to do obtain information regarding end-user IP addresses
   and requested URIs that they would not have if the RI not been used.

   While it is technically possible to mask some information in the RI
   Request, such as the last bits of the UA IP address, it is important
   to note that this will reduce the effectiveness of the RI in certain
   cases.  CDN deployments need to strike a balance between end-user
   privacy and the features impacted by such masking.  This balance is
   likely to vary from one deployment to another.  As an example, when
   the UA and its DNS resolver is behind a Carrier-grade NAT, and the RI
   is used to find an appropriate delivery node behind the same NAT, the
   full IP address might be necessary.  Another potential issue when
   using IP anonymization is that it is no longer possible to correlate
   an RI Request with a subsequent UA request.













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6.  IANA Considerations

6.1.  CDNI Payload Type Parameter Registrations

   IANA has registered the following two new Payload Types in the
   "Content Delivery Network Interconnection (CDNI) Parameters" registry
   for use with the application/cdni MIME media type.

                 +----------------------+---------------+
                 | Payload Type         | Specification |
                 +----------------------+---------------+
                 | redirection-request  | RFC 7975      |
                 |                      |               |
                 | redirection-response | RFC 7975      |
                 +----------------------+---------------+

                                  Table 9

6.1.1.  CDNI RI Redirection Request Payload Type

   Purpose: The purpose of this payload type is to distinguish RI
   request messages.

   Interface: RI

   Encoding: See Section 4.4.1 and Section 4.5.1

6.1.2.  CDNI RI Redirection Response Payload Type

   Purpose: The purpose of this payload type is to distinguish RI
   response messages.

   Interface: RI

   Encoding: See Section 4.4.2 and Section 4.5.2

6.2.  RI Error Response Registry

   IANA has created a new "CDNI RI Error response code" subregistry
   within the "Content Delivery Network Interconnection (CDNI)
   Parameters" registry.  The "CDNI RI Error response code" namespace
   defines the valid values for the error-code key in RI error
   responses.  The CDNI RI Error response code MUST be a three-digit
   integer.

   Additions to the "RI Error response registry" will be made via
   "Specification Required" as defined in [RFC5226].




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   The Designated Expert will verify that new error-code registrations
   do not duplicate existing error-code definitions (in name or
   functionality), ensure that the new error-code is in accordance with
   the error classes defined in Section 4.7 of this document, prevent
   gratuitous additions to the namespace, and prevent any additions to
   the namespace that would impair the interoperability of CDNI
   implementations.

   New registrations are required to provide the following information:

      Code: A three-digit numeric error-code, in accordance with the
      error classes defined in Section 4.7 of this document.

      Reason: A string that provides further information related to the
      error that will be included in the JSON error dictionary with the
      'reason'-key.  Depending on the error-code semantics, the value of
      this field may be determined dynamically.  In that case, the
      registration should set this value to '<reason>' and define its
      semantics in the description field.

      Description: A brief description of the error-code semantics.

      Specification: Reference to the specification that defines the
      error-code in more detail.

   The entries in Table 8 are registered by this document, with the
   value of the 'Specification' field set to RFC 7975 (this document).

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <http://www.rfc-editor.org/info/rfc4291>.






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   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952,
              DOI 10.17487/RFC5952, August 2010,
              <http://www.rfc-editor.org/info/rfc5952>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC6895]  Eastlake 3rd, D., "Domain Name System (DNS) IANA
              Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
              April 2013, <http://www.rfc-editor.org/info/rfc6895>.

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

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6707]  Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", RFC 6707, DOI 10.17487/RFC6707, September
              2012, <http://www.rfc-editor.org/info/rfc6707>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <http://www.rfc-editor.org/info/rfc5890>.





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   [RTMP]     Adobe Systems Incorporated, "Real-Time Messaging Protocol
              (RTMP) specification", December 2012,
              <http://www.adobe.com/go/spec_rtmp>.

7.2.  Informative References

   [RFC7337]  Leung, K., Ed. and Y. Lee, Ed., "Content Distribution
              Network Interconnection (CDNI) Requirements", RFC 7337,
              DOI 10.17487/RFC7337, August 2014,
              <http://www.rfc-editor.org/info/rfc7337>.

   [RFC7336]  Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
              "Framework for Content Distribution Network
              Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
              August 2014, <http://www.rfc-editor.org/info/rfc7336>.

   [RFC7736]  Ma, K., "Content Delivery Network Interconnection (CDNI)
              Media Type Registration", RFC 7736, DOI 10.17487/RFC7736,
              December 2015, <http://www.rfc-editor.org/info/rfc7736>.

Acknowledgements

   The authors would like to thank Taesang Choi, Francois Le Faucheur,
   Matt Miller, Scott Wainner, and Kevin J. Ma for their valuable
   comments and input to this document.


























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Contributors

   The following persons have participated as co-authors to this
   document:

   Wang Danhua
   Huawei
   Email: wangdanhua@huawei.com

   He Xiaoyan
   Huawei
   Email: hexiaoyan@huawei.com

   Ge Chen
   China Telecom
   Email: cheng@gsta.com

   Ni Wei
   China Mobile
   Email: niwei@chinamobile.com

   Yunfei Zhang
   Email: hishigh@gmail.com

   Spencer Dawkins
   Huawei
   Email: spencer@wonderhamster.org

Authors' Addresses

   Ben Niven-Jenkins (editor)
   Nokia
   3 Ely Road
   Milton, Cambridge  CB24 6DD
   United Kingdom

   Email: ben.niven-jenkins@nokia.com


   Ray van Brandenburg (editor)
   TNO
   Anna van Buerenplein 1
   The Hague  2595DA
   The Netherlands

   Phone: +31-88-866-7000
   Email: ray.vanbrandenburg@tno.nl




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