Network Working Group O. Finkelman
Internet-Draft Qwilt
Intended status: Standards Track S. Mishra
Expires: January 30, 2020 Verizon
July 29, 2019

CDNI Request Routing Extensions


The Open Caching working group of the Streaming Video Alliance is focused on the delegation of video delivery requests from commercial CDNs to a caching layer at the ISP. In that aspect, Open Caching is a specific use case of CDNI, where the commercial CDN is the upstream CDN (uCDN) and the ISP caching layer is the downstream CDN (dCDN). The extensions specified in this document to the CDNI Metadata and FCI interfaces are derived from requirements raised by Open Caching but are applicable to CDNI use cases in general.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

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

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 January 30, 2020.

Copyright Notice

Copyright (c) 2019 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 ( 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

This document defines objects needed for Open Caching request routing. For that purpose it extends CDNI metadata [RFC8006] and CDNI Footprint and Capabilities [RFC8008]. For consistency, this document follows the CDNI notation of uCDN (the commercial CDN) and dCDN (the ISP caching layer).

This document also registers CDNI Payload Types [RFC7736] for the defined objects:

1.1. Terminology

This document reuses the terminology defined in [RFC6707], [RFC8006], [RFC8007], and [RFC8008].

Additionally, the following terms are used throughout this document and are defined as follows:

2. Redirect Target Capability Object

Iterative request redirect as defined in section 1.1 of [RFC7336] requries the provisioning of a redirect target address to be used by the uCDN in order to redirect to the dCDN. Redirect target addresses can vary between different footprints, for example, between different regions, and they may also change over time, for example as a result of network problems. Given this variable and dynamic nature of the redirect target, it may not be suitable to advertise it during bootstrap. A more dynamic and footprint oriented interface is required. Therefore, we have chosen to use the CDNI Footprint and Capabilities interface for redirect target advertisement.

Use cases

The Redirect Target capability object is used to indicate the target address the uCDN should use in order to redirect a client to the dCDN. A target may be attached to a specific uCDN host, a list of uCDN hosts, or used globally for all the hosts of the uCDN.

When a dCDN is attaching the redirect target to a specific uCDN host or a list of uCDN hosts, the dCDN MUST advertise the hosts within the Redirect Target capability object as "redirecting-hosts". In that case, the uCDN can redirect to that dCDN address, only if the request was directed to one of those uCDN hosts.

A redirect target for DNS redirection is an IP address used as an A record response or a FQDN used as an alias in a CNAME record response (see [RFC1034]) of the uCDN DNS router. Note that DNS routers make routing decisions based on either the DNS resolver's IP address or the client IP address when EDNS0 client-subnet is used (see [RFC7871]). The dCDN may choose to advertise redirect targets and footprints to cover both cases. A uCDN DNS router implemenation SHOULD prefer routing based on client IP address when it is available.

A redirect target for HTTP redirection is the URI to be used as the value for the Location header of a HTTP redirect 3xx response, typically a 302 (Found) (see section 7.1.2 of [RFC7231] and section 6.4 of [RFC7231]).

2.1. Properties of Redirect Target Capability Object

The Redirect Target capability object consists of the following properties:

The following is an example of a Redirect Target capability object serialization that advertises a dCDN target address that is attached to a specific list of uCDN "redirecting-hosts". A uCDN host that is included in that list can redirect to the advertised dCDN redirect target.

  "capabilities": [
      "capability-type": "FCI.RedirectTarget",
      "capability-value": {
          "redirecting-hosts": [
          "dns-target": {
             "host": ""
          "http-target": {
              "host": "",
              "path-prefix": "/cache/1/",
              "include-redirecting-host": true          
      "footprints": [
          <Footprint objects>

2.2. DnsTarget

The DnsTarget object gives the target address for the DNS response to delegate from the uCDN to the dCDN.

The following is an example of DnsTarget object:

    "host": ""

The following is an example of a DNS query for uCDN address "" and the corresponding CNAME redirection response:

 type A, class IN 
 type CNAME, class IN, cname

2.3. HttpTarget

The HttpTarget object gives the necessary information to construct the target Location URI for HTTP redirection.

Example of HttpTarget object with a path-prefix and include-redirecting-host:

   "host": "",
   "path-prefix": "/cache/1/",
   "include-redirecting-host": true

Example of a HTTP request for content at uCDN host "" and the corresponding HTTP response with Location header used for redirecting the client to the dCDN using the the http-target in the above example:

 GET /vod/1/movie.mp4 HTTP/1.1
 HTTP/1.1 302 Found

3. Fallback Target Address Metadata

Open Caching requires that the uCDN provide a fallback target server to the dCDN, to be used in cases where the dCDN cannot properly handle the request. To avoid redirect loops, the fallback target server's address at the uCDN MUST be differnet from the original uCDN address from which the client was redirected to the dCDN. The uCDN MUST avoid further redirection when receiving the client request at the fallback target. The fallback target is defined as a generic metadata object (see section 3.2 of [RFC8006])

Use cases

The Fallback target metadata object is used to indicate the target address the dCDN should use in order to redirect a client back to the uCDN. Fallback target is represented as endpoint objects as defined in section 4.3.3 of [RFC8006].

The uCDN fallback target address may be used as a DNS A record or CNAME record in case of DNS redirection or a hostname for HTTP redirect.

When using HTTP redirect to route a client request back to the uCDN, it is the dCDN's responsibility to use the original URL path as the client would have used for the original uCDN request, stripping, if needed, the dCDN path-prefix and/or the uCDN hostname from the redirect URL that may have been used to request the content from the dCDN.

3.1. Properties Fallback Target Address Metadata Object

The MI.FallbackTarget Metadata object consists of the following single property:

Example of a MI.FallbackTarget Metadata object that designates the host address the dCDN should use as fallback address to redirect back to the uCDN.

    "generic-metadata-type": "MI.FallbackTarget",
        "host": "fallback-a.service123.ucdn.example"

4. IANA Considerations

4.1. CDNI Payload Types

This document requests the registration of the following CDNI Payload Types under the IANA "CDNI Payload Types" registry defined in [RFC7736]:

Payload Type Specification
FCI.RedirectTarget RFCthis
MI.FallbackTarget RFCthis

[RFC Editor: Please replace RFCthis with the published RFC number for this document.]

4.1.1. CDNI FCI RedirectTarget Payload Type

Purpose: The purpose of this payload type is to distinguish RedirectTarget FCI objects

Interface: FCI

Encoding: see Section 2.1

4.1.2. CDNI MI FallbackTarget Payload Type

Purpose: The purpose of this payload type is to distinguish FallbackTarget MI objects (and any associated capability advertisement)

Interface: MI/FCI

Encoding: see Section 3.1

5. Security Considerations

This specification is in accordance with the CDNI Metadata Interface and the CDNI Request Routing: Footprint and Capabilities Semantics. As such, it is subject to the security and privacy considerations as defined in Section 8 of [RFC8006] and in Section 7 of [RFC8008] respectively.

5.1. Confidentiality and Privacy

The redirect Target FCI object potentially exposes information about the internal strcture of the dCDN network. A third party could intercept the FCI transactions and use the information to attack the dCDN. An implemenation of the FCI MUST therefore use strong authentication and encryption and strictly follow the directions for securing the interface as defined for the Metadata Interface in Section 8.3 of [RFC8006].

6. Acknowledgements

The authors thank Nir B. Sopher for reality checks against production use cases, his contribution is significant to this document. The authors also thank Ben Niven-Jenkins for his review and feedback and Kevin J. Ma for his guidance throughout the development of this document including his regular reviews.

7. References

7.1. Normative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[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.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014.
[RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M. and K. Ma, "Content Delivery Network Interconnection (CDNI) Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016.
[RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network Interconnection (CDNI) Control Interface / Triggers", RFC 8007, DOI 10.17487/RFC8007, December 2016.
[RFC8008] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg, R. and K. Ma, "Content Delivery Network Interconnection (CDNI) Request Routing: Footprint and Capabilities Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016.

7.2. Informative References

[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.
[RFC7336] Peterson, L., Davie, B. and R. van Brandenburg, "Framework for Content Distribution Network Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, August 2014.
[RFC7736] Ma, K., "Content Delivery Network Interconnection (CDNI) Media Type Registration", RFC 7736, DOI 10.17487/RFC7736, December 2015.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D. and W. Kumari, "Client Subnet in DNS Queries", RFC 7871, DOI 10.17487/RFC7871, May 2016.

Authors' Addresses

Ori Finkelman Qwilt 6, Ha'harash Hod HaSharon, 4524079 Israel EMail:
Sanjay Mishra Verizon 13100 Columbia Pike Silver Spring, MD 20904 USA EMail: