Network Working Group O. Finkelman
Internet-Draft Qwilt
Intended status: Standards Track S. Mishra
Expires: April 20, 2019 Verizon
October 17, 2018

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

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This Internet-Draft will expire on April 20, 2019.

Copyright Notice

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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 Address 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 due to scaling issues a dCDN may need to split different regions over multiple targets, or due to network problems the dCDN may have to change the target address. Due to this variable and dynamic nature of the redirect target, it may not be suitable to advertise it during bootstrap, and 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 it can be set globally for all the hosts of the uCDN.

When 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 is of one of these uCDN hosts.

A redirect target for DNS redirection is the FQDN to be used as a CNAME for the uCDN host (see [RFC1034]).

A redirect target for HTTP redirection is the hostname to be used as the first path segment in an absolute URI which is used as the Location header of the HTTP rediret response (see section 7.1.2 of [RFC7231]).

Example of Redirect Target Capability object 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": {
                 <Properties of an HttpTarget object>
         "footprints": [
           <Footprint objects>

2.1. DnsTarget

The DnsTarget object is the target address for CNAME delegation from the uCDN to the dCDN.

Example of DnsTarget object:

     "host": ""

Example of a DNS query for uCDN address "" and the corresponding CNAME redirection response:

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

2.2. HttpTarget

The HttpTarget object is the target address for http redirection from the uCDN to the dCDN.

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 should provide 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 than the original address at the uCDN 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 CNAME in case of DNS redirection mode or a host name 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 the uCDN host name from the redirect URL that may have been used to request the content from the dCDN.

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 Type 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

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

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 considerations as defined in [RFC8006] and [RFC8008] respectively.

6. Acknowledgements


7. Contributors


8. References

8.1. 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.

8.2. 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.

Authors' Addresses

Ori Finkelman Qwilt 6, Ha'harash Hod HaSharon, 4524079 Israel Phone: +972-72-2221647 EMail:
Sanjay Mishra Verizon 13100 Columbia Pike Silver Spring, MD 20904 USA EMail: