Network Working Group K. Ma Internet-Draft Azuki Systems, Inc. Intended status: Standards Track August 04, 2013 Expires: February 05, 2014 Content Distribution Network Interconnection (CDNI) Footprint & Capabilities Advertisement Interface draft-ma-cdni-capabilities-02 Abstract The interconnection of Content Distribution Networks (CDNs) is predicated on the ability of downstream CDNs (dCDNs) to handle end- user requests in a functionally equivalent manner to the upstream CDN (uCDN). The uCDN must be able to assess the ability of the dCDN to handle individual requests. The CDNI Footprint & Capabilities Advertisement interface (FCI) is provided for the advertisement of capabilities and the footprints to which they apply by the dCDN to the uCDN. This document describes an approach to implementing the CDNI FCI. 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 [RFC2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 05, 2014. Copyright Notice Ma Expires February 05, 2014 [Page 1] Internet-Draft CDNI Metadata August 2013 Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Capabilities . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Delivery Protocol . . . . . . . . . . . . . . . . . . . . 6 2.2. Acquisition Protocol . . . . . . . . . . . . . . . . . . 7 2.3. Redirection Mode . . . . . . . . . . . . . . . . . . . . 8 3. Capability Advertisement . . . . . . . . . . . . . . . . . . 10 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 11 Appendix A. Capability Aggregation . . . . . . . . . . . . . . . 11 A.1. Downstream CDN Aggregation . . . . . . . . . . . . . . . 11 A.2. Internal Request Router Aggregation . . . . . . . . . . . 13 A.3. Internal Capability Aggregation . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction The need for footprint and capabilities advertisement in CDNI is described in the CDNI requirements document [I-D.ietf-cdni-requirements]. Requirements FCI-1 and FCI-2 describe the need to allow dCDNs to communicate capabilities to the uCDN. Requirement FCI-3 describes how a uCDN may aggregate the footprint and capabilities information for all cascaded dCDNs and use the aggregated information in advertisements to CDNs further upstream. This concept of aggregation can apply to both organizationally different dCDNs (e.g., other CDN providers, or different business units within a larger organization) or logical entities within the same CDN (e.g., using multiple request routers for scalability reasons, to segregate surrogates based on specific protocol support, Ma Expires February 05, 2014 [Page 2] Internet-Draft CDNI Metadata August 2013 or to segregate surrogates based on software version or feature level, etc.). Appendix A contains more detailed descriptions of different footprint and capabilities management scenarios, but it is important to note that it is the ability of the dCDN to service each request in a functionally equivalent manner as the uCDN that is important, not the physical layout of resources through which it services the request. The aggregation of resource knowledge by the dCDN into a simple set of capabilities and their affective footprints, that is then advertised to the uCDN enables efficient decision making at each delegation point in the CDN interconnection hierarchy. It is assumed that an authoritative request router in each CDN will be responsible for aggregating and advertising capabilities information in a dCDN, and receiving and aggregating capabilities information in the uCDN. The CDNI Footprint & Capabilities Advertisement interface (FCI) along with the CDNI Request Routing Redirection interface (RI) make up the CDNI Request Routing Interface. As there is no other centralized CDNI controller, the authoritative request router seems the most logical place for capabilities aggregation to occur, as it is the request router that needs such information to make delegation decisions. The protocol defined herein may be implemented as part of an entity other than an authoritative request router, but for the purposes of this discussion, the authoritative request router is assumed to be the centralized capabilities aggregation point. Though there is an obvious need for the ability to exchange and update footprint and capability information in real-time, it is assumed that capabilities do not change very often. It is also assumed that the capabilities are not by themselves useful for making delegation decisions. Capability information is assumed to be input into business logic. It is the business logic which provides the algorithms for delegation decision making. The definition of business logic occurs outside the scope of CDNI and outside the timescale of footprint and capability advertisement. It may be the case that the business logic anticipates and reacts to changes in dCDN capabilities. However, it may also be the case that business logic is tailored through offline processes as dCDN capabilities change. The FCI is agnostic to the business processes employed by any given uCDN. The footprints and capabilities that are advertised over the FCI may be used by the uCDN at its discretion to implement delegation rules. Setting proper defaults in the business logic should prevent any unwanted delegation from occurring when dCDN capabilities change, however, that is beyond the scope of this discussion. Ma Expires February 05, 2014 [Page 3] Internet-Draft CDNI Metadata August 2013 1.1. Terminology This document uses the terminology defined in section 1.1 of the CDNI Framework [I-D.ietf-cdni-framework] document. 2. Capabilities As described in Requirement FCI-2, there is a basic set of capabilities that must be supported by the FCI for the uCDN to be able to determine if the dCDN is functionally able to handle a given request. The CDNI Footprint and Capabilities Semantics [I-D.ietf-cdni-footprint-capabilities-semantics] document lists mandatory capabilities types: o Delivery Protocol o Acquisition Protocol o Redirection Mode o CDNI Logging Capabilities o CDNI Metadata Capabilities The following sections describe each of the capabilities in further detail, however, all of the capabilities can be described using the same general format. A capability object is specified as: CapabilityObject: Name: Identifier for the capability Values: List of supported options for the capability Footprint: Optional list of footprint objects The list of valid capability options for a given capability will be specific to the given capability type. Though the degenerate case may exist where the range of option values is a single value, it is anticipated that all capability types will have more than one capability option value. For consistency in the model, all capability types are implemented with lists of values. To optimize actions on the entire range of capability option values for a given capability type, the capability option value "ALL" is reserved and MUST be supported by all capability types. For completeness, the capability option value "NONE" is also reserved and MUST be supported by all capability types. If a reserved value is specified, it MUST be the only entry in the capability value list. Ma Expires February 05, 2014 [Page 4] Internet-Draft CDNI Metadata August 2013 The footprint restriction list is optional. When included, the footprint restriction list contains a list of generic footprint objects. The footprint object is specified as: FootprintObject: Type: Identifier for the capability Values: List of footprint entries Mode: Optional footprint application directive The footprint type specifies the format of the footprint value entries. The footprint object type field contains the IANA registry defined footprint type name. The CDNI Footprint and Capabilities Semantics [I-D.ietf-cdni-footprint-capabilities-semantics] document lists the mandatory footprint types as: ISO Country Code, AS number, and IP-prefix. The CDNI Footprint and Capabilities Semantics [I-D.ietf-cdni-footprint-capabilities-semantics] document defines the footprint type names for the mandatory footprint types and describes the process for defining additional optional footprint types. The footprint value "GLOBAL" is reserved and MUST be supported by all footprint types. If the reserved value "GLOBAL" is specified, it MUST be the only entry in the footprint value list. The optional footprint mode describes how the footprint should be applied. The valid footprint mode values are: "replace", "include", and "exclude". The footprint mode "replace" (represented by the integer value 0) indicates that all previous footprint information for the given footprint type (and for the capabilities to which the current footprint object applies) MUST be replaced in its entirety with the footprint information specified in the accompanying footprint value list. The footprint mode "include" (represented by the integer value 1) indicates that the any existing footprint information for the given footprint type (and for the capabilities to which the current footprint object applies) SHOULD be augmented with the footprint information specified in the accompanying footprint value list. The footprint mode "exclude" (represented by the integer value 2) indicates that the any existing footprint information for the given footprint type (and for the capabilities to which the current footprint object applies) SHOULD be reduced by the footprint information specified in the accompanying footprint value list. If no footprint mode value is specified, the default mode SHALL be understood to be "replace". Ma Expires February 05, 2014 [Page 5] Internet-Draft CDNI Metadata August 2013 The footprint restriction list MUST NOT contain multiple footprint objects of the same type. Footprint restriction information MAY be specified using multiple different footprint types. If no footprint restriction list is specified (or an empty list is specified), it SHALL be understood that all footprint types MUST be reset to "GLOBAL" coverage. Note: Further optimization of the footprint object to provide quality information for a given footprint is certainly possible, however, it is not critical to the basic interconnection of CDNs. The ability to transfer quality information in capabilities advertisements may be desirable and is noted here for completeness, however, the specifics of such mechanisms are outside the scope of this document. Multiple capability objects of the same capability type are allowed within a given FCI message as long as the capability option values do not overlap, i.e., a given capability option value MUST NOT show up in multiple capability objects within a single FCI message. If multiple capability objects for a given capability type exist, those capability objects SHOULD have different footprint restrictions; capability objects of a given capability type with identical footprint restrictions SHOULD be combined into a single capability object. 2.1. Delivery Protocol The delivery protocol refers to the protocol over which an end user (EU) has requested content. If a dCDN does not support the protocol requested by the client, then the dCDN is not a viable candidate for delegation. Though the delivery protocol is specified in the URI scheme (as defined in RFC3986 [RFC3986]) of the client request URL, protocol feature subsets or augmented protocol feature sets MAY be defined and SHOULD correspond with the protocols supported by the ProtocolACL defined in the CDNI Metadata Interface [I-D.ietf-cdni-metadata] document. The delivery protocol capability object MUST support a list of protocols for a given footprint. The delivery protocol capability SHOULD support optional footprint restriction information. The following example shows two lists of protocols with different footprints. { "capabilities": [ { "name": "delivery_protocol", "values": [ Ma Expires February 05, 2014 [Page 6] Internet-Draft CDNI Metadata August 2013 "HTTP", "RTSP", "MMS" ] }, { "name": "delivery_protocol", "values": [ "RTMP", "HTTPS" ], "footprint": [ { "type": "IPv4", "values": [ "10.1.0.0/16", "10.10.10.0/24" ] } ] } ] } In the above example, the three protocols HTTP, RTSP, and MMS are supported globally, while the protocols RTMP and HTTPS are only supported in a restricted footprint (in this case, specified by IP- prefix). A given protocol MUST NOT appear in multiple capability object value lists, within a given FCI message. 2.2. Acquisition Protocol The acquisition protocol refers to the protocol over which the dCDN may acquire content from the uCDN. If a dCDN does not support any of the protocols offered by the uCDN, then the dCDN is not a viable candidate for delegation. Though the acquisition protocol is disseminated to the dCDN in the URI scheme (as defined in RFC3986 [RFC3986]) of the URL provided by the uCDN via the CDNI Metadata Interface [I-D.ietf-cdni-metadata], protocol feature subsets or augmented protocol feature sets MAY be defined and SHOULD correspond with the protocols supported by the ProtocolACL defined in the CDNI Metadata Interface [I-D.ietf-cdni-metadata] document. The acquisition protocol capability object MUST support a list of protocols for a given footprint. The acquisition protocol capability Ma Expires February 05, 2014 [Page 7] Internet-Draft CDNI Metadata August 2013 SHOULD support optional footprint restriction information. The following example shows two lists of protocols with different footprints. { "capabilities": [ { "name": "acquisition_protocol", "values": [ "HTTP", "FTP" ] }, { "name": "acquisition_protocol", "values": [ "SFTP", "HTTPS" ], "footprint": [ { "type": "ASN", "values": [ "0", "65535" ], "mode": 2 } ] } ] } In the above example, the two protocols HTTP and FTP are supported globally, while the protocols SFTP and HTTPS are updated to only be supported in a reduced restricted footprint (in this case, specified by ASN). A given protocol MUST NOT appear in multiple capability object value lists, within a given FCI message. 2.3. Redirection Mode The redirection mode refers to the method(s) employed by request routers to perform request redirection. The CDNI framework [I-D.ietf-cdni-framework] document describes four possible request routing modes: o DNS iterative (DNS-I) Ma Expires February 05, 2014 [Page 8] Internet-Draft CDNI Metadata August 2013 o DNS recursive (DNS-R) o HTTP iterative (HTTP-I) o HTTP recursive (HTTP-R) If a dCDN supports only a specific mode or subset of modes that does not overlap with the modes supported by the uCDN, then the dCDN is not a viable candidate for delegation. The redirection mode capability object MUST support a list of redirection modes for a given footprint. The redirection mode capability SHOULD support optional footprint restriction information. The following XML-encoded example shows two lists of modes with different footprints. { "capabilities": [ { "name": "redirection_mode", "values": [ "DNS-I", "HTTP-I" ] }, { "name": "redirection_mode", "values": [ "DNS-R", "HTTP-R" ], "footprint": [ { "type": "ASN", "values": [ "9" ], "mode": 0 }, { "type": "IPv6", "values": [ "8765:4321::/36" ] } ] } ] } Ma Expires February 05, 2014 [Page 9] Internet-Draft CDNI Metadata August 2013 In the above example, iterative redirection is supported globally, while recursive redirection is only supported in a restricted footprint (in this case, specified by both ASN and IP-prefix). A given mode MUST NOT appear in multiple capability object value lists, within a given FCI message. 3. Capability Advertisement The FCI relies an HTTP-based protocol using the POST method. The dCDN request router asynchronously issues FCI messages to the uCDN request router (see Appendix A for detailed descriptions of authoritative request router capabilities aggregation scenarios). It is assumed that the dCDN request router has been configured with the uCDN request router address either through the CDNI Control interface bootstrapping function, or through some other out-of-band configuration. 4. IANA Considerations This memo includes no request to IANA. 5. Security Considerations There are a number of security concerns associated with the FCI. The FCI essentially provides configuration information which the uCDN uses to make request routing decisions. Injection of fake capability advertisement messages or the interception and discard of real capability advertisement messages may be used for denial of service (e.g., by falsely advertising or deleting capabilities or preventing capability advertisements from reaching the uCDN). dCDN capability advertisements MUST be authenticated by the uCDN to prevent unauthorized FCI message injection. uCDN FCI servers MUST be authenticated by the dCDN to prevent unauthorized interception of FCI messages. TLS with client authentication SHOULD be used for all FCI implementations. Deployments in controlled environments where physical security and IP address white-listing is employed MAY choose not to use TLS. 6. Acknowledgements The authors would like to thank Ray van Brandenburg, Gilles Bertrand, and Scott Wainner for their timely reviews and invaluable comments. 7. References 7.1. Normative References Ma Expires February 05, 2014 [Page 10] Internet-Draft CDNI Metadata August 2013 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 7.2. Informative References [I-D.ietf-cdni-footprint-capabilities-semantics] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg, R., and K. Ma, "CDNI Request Routing: Footprint and Capabilities Semantics draft-ietf-cdni-footprint- capabilities-semantics-00", July 2013. [I-D.ietf-cdni-framework] Peterson, L., Ed. and B. Davie, Ed., "Framework for CDN Interconnection draft-ietf-cdni-framework-03", February 2013. [I-D.ietf-cdni-logging] Le Faucheur, F., Bertrand, G., Oprescu, I., and R. Peterkofsky, "CDNI Logging Interface draft-ietf-cdni- logging-05", July 2013. [I-D.ietf-cdni-metadata] Niven-Jenkins, B., Murray, R., Watson, G., Caulfield, M., Leung, K., and K. Ma, "CDN Interconnect Metadata draft- ietf-cdni-metadata-02", July 2013. [I-D.ietf-cdni-requirements] Leung, K. and Y. Lee, "Content Distribution Network Interconnection (CDNI) Requirements draft-ietf-cdni- requirements-09", July 2013. Appendix A. Capability Aggregation The following sections show examples of three aggregation scenarios. In each case, CDN-U is the ultimate uCDN and CDN-P is the penultimate CDN which must perform capabilities aggregation. A.1. Downstream CDN Aggregation Figure A1 shows five organizationally different CDNs: CDN-U, CDN-P, and CDNS A, B, and C, the dCDNs of CDN-P which are being aggregated. Given the setup shown in Figure A1, we can construct a number of use cases, based on the coverage areas of each dCDN (i.e., CDNs P, A, B, and C). Note: In all cases, the reachability of the uCDN (i.e., Ma Expires February 05, 2014 [Page 11] Internet-Draft CDNI Metadata August 2013 CDN-U) is a don't care as it is assumed that the uCDN knows its own coverage area and is likely to favor itself in most situations, and if it has decided that it needs to delegate to a dCDN, then the only relevant question is if the dCDN can handle the request. ,---,---,---. ,-' `-. ( rr0.u.example.com ) `-. CDN-U ,-' `---'-+-'- --' | ,---,-+-,---. ,-' `-. ( rr0.p.example.com ) `-. CDN-P ,-' `---'-+-'---' | +---------------------+---------------------+ / | \ ,---,-+-,---. ,---,-+-,---. ,---,-+-,---. ,-' `-. ,-' `-. ,-' `-. ( rr0.a.example.com ) ( rr0.b.example.com ) ( rr0.c.example.com ) `-. CDN-A ,-' `-. CDN-B ,-' `-. CDN-C ,-' `---'---'---' `---'---'---' `---'---'---' Figure A1: CDNI dCDN Request Router Aggregation o None of the four dCDNs (CDNs P, A, B, and C) have global reachability. In this case, each CDN is likely to advertise footprint information with its capabilities, specifying its reachability. When CDN-P advertises capabilities to CDN-U, it may advertise the aggregate footprint of itself and CDNs A, B, and C. Note: CDN-P MAY exclude any dCDN, and consequently its footprint, per its own internal aggregation decision criteria. o All four dCDNs (CDNs P, A, B, and C) have global reachability. In this case, none of the CDNs is likely to advertise any footprint information as none have any footprint restrictions. When CDN-P advertises capabilities to CDN-U, the aggregate of all global reachability is global reachability. o Some of the four dCDNs (CDNs P, A, B, and C) have global reachability and some do not. In this case, even though some dCDNs do not have global reachability, the aggregate of some dCDNs having global reachability and some not should still be global reachability (for the given capability). When CDN-P advertises capabilities to CDN-U, CDN-P may advertise capabilities for which at least one dCDN has global reach as being supported with global Ma Expires February 05, 2014 [Page 12] Internet-Draft CDNI Metadata August 2013 reachability. It is up to the CDN-P request router to properly select a dCDN to process individual client requests and not choose a dCDN whose restricted footprint makes it unsuitable for delivering the requested content. A.2. Internal Request Router Aggregation Figure A2 shows CDN-U and CDN-P where CDN-P internally has four request routers: the authoritative request router rr0, and three other request routers rr1, rr2, and rr3. The use of multiple request routers may be used to distribute request routing load across resources, possibly in different geographic regions covered by CDN-P. Similar to Figure A1, the setup shown in Figure A2 requires the authoritative request router rr0 in CDN-P to aggregate capabilities information from downstream request routers rr1, rr2, and rr3. The primary difference between the scenario is that the request routers in Figure A2 are logically within the same CDN-P organization. The same reachability scenarios apply to Figure A2 as with Figure A1. ,---,---,---. ,-' `-. ( rr0.u.example.com ) `-. CDN-U ,-' `---'-+-'---' | ,---,---,---,--,-+-,--,---,---,---. ( ) ,-' +-------------------+ `-. ( | rr0.p.example.com | ) ,-' +---------+---------+ `-. ( | ) ,-' +----------+----------+ `-. ( / | \ ) ) +---------+---------+ | +---------+---------+ ( ( | rr1.p.example.com | | | rr3.p.example.com | ) `. +-------------------+ | +-------------------+ ,' ( | ) `-. +---------+---------+ ,-' ( | rr2.p.example.com | ) `-. +-------------------+ ,-' ( CDN-P ) `---'---'---'---'---'---'---'---'---' Figure A2: Local CDN Request Router Aggregation o None of the four CDN-P request routers have global reachability. In this case, each request router is likely to advertise footprint information with its capabilities, specifying its reachability. Ma Expires February 05, 2014 [Page 13] Internet-Draft CDNI Metadata August 2013 When rr0 advertises capabilities to CDN-U, it may advertise the aggregate footprint of itself and rr1, rr2, and rr3. o All four CDN-P request routers have global reachability. In this case, none of the request routers is likely to advertise any footprint information as none has any footprint restrictions. When rr0 advertises capabilities to CDN-U, the aggregate of all global reachability is global reachability. o Some of the four CDN-P request routers have global reachability and some do not. In this case, even though some request routers do not have global reachability, the aggregate of some request routers having global reachability and some not should still be global reachability (for the given capability). When rr0 advertises capabilities to CDN-U, CDN-P may advertise capabilities for which at least one request router has global reach as being supported with global reachability. It is up to the authoritative request router rr0 to properly select from the other request routers for any given request, and not choose a request router whose restricted footprint makes it unsuitable for delivering the requested content. A.3. Internal Capability Aggregation Figure A3 shows CDN-U and CDN-P where the delivery network of CDN-P is segregated by delivery protocol (e.g., RTSP, HTTP, and RTMP). Figure A3 differs from Figures A1 and A2 in that request router rr0 of CDN-P is not aggregating the capabilities advertisements of multiple other downstream request routers, but rather it is managing the disparate capabilities across resources within its own local CDN. Though not every delivery node has the same protocol capabilities, the aggregate delivery protocol capabilities advertised by CDN-A may include all delivery protocols. Note, Figure A3 should not be construed to imply anything about the coverage areas for each delivery protocol. They may all support the same delivery footprint, or they may have different delivery footprints. It is the responsibility of the request router rr0 to properly assign protocol- appropriate delivery nodes to individual content requests. If certain protocols have limited reachability, CDN-P may advertise footprint restrictions for each protocol. It should be noted that though the delivery protocol capability was selected for this example, the concept of internal capability aggregation applies to all capabilities as discussed below. ,---,---,---. ,-' `-. ( rr0.u.example.com ) Ma Expires February 05, 2014 [Page 14] Internet-Draft CDNI Metadata August 2013 `-. CDN-U ,-' `---'-+-'---' | ,---,---,---,--,-+-,--,---,---,---. ( ) ,-' +-------------------+ `-. ( | rr0.p.example.com | ) ,-' +---------+---------+ `-. ( . ) ,-' ....................... `-. ( . . . ) ) +-------------------+ . +-------------------+ ( ( |rtsp.p.example.com | . |rtmp.p.example.com | ) `. +-------------------+ . +-------------------+ ,' ( . ) `-. +-------------------+ ,-' ( |http.p.example.com | ) `-. +-------------------+ ,-' ( CDN-A ) `---'---'---'---'---'---'---'---'---' Figure A3: Local CDN Capability Segregation Another situation in which physical footprint may not matter in an aggregated view has to do with feature support (e.g., new CDNI metadata features or new redirection modes). Situations often arise when phased roll-out of software upgrades, or staging network segregation result in only certain portions of a CDN's resources supporting the new feature set. The dCDN has a few options in this case: o Enforce atomic update: The dCDN does not advertise support for the new capability until all resources have been upgraded to support the new capability. o Transparent segregation: The dCDN advertises support for the new capability, and when requests are received that require the new capability, the dCDN request router properly selects a resource which supports that capability. o Advertised segregation: The dCDN advertises support for the new capability with a footprint restriction allowing the uCDN to make delegation decisions based on the dCDN's limit support. The level of aggregation employed by the dCDN is likely to vary as business relationships dictate, however, the FCI should support all possible modes of operation. Ma Expires February 05, 2014 [Page 15] Internet-Draft CDNI Metadata August 2013 Author's Address Kevin J. Ma Azuki Systems, Inc. 43 Nagog Park Acton, MA 01720 USA Phone: +1 978-844-5100 Email: kevin.ma@azukisystems.com Ma Expires February 05, 2014 [Page 16]