Content Delivery Network Interconnection (CDNI) Request Routing: CDNI Footprint and Capabilities Advertisement using ALTO

The ability to interconnect multiple content delivery networks (CDNs) has many benefits, including increased coverage, capability, and reliability. The Content Delivery Networks Interconnection (CDNI) framework defines four interfaces to achieve the interconnection of CDNs: (1) the CDNI Request Routing Interface; (2) the CDNI Metadata Interface; (3) the CDNI Logging Interface; and (4) the CDNI Control Interface. Among the four interfaces, the CDNI Request Routing Interface provides key functions, as specified in : "The CDNI Request Routing interface enables a Request Routing function in an Upstream CDN to query a Request Routing function in a Downstream CDN to determine if the Downstream CDN is able (and willing) to accept the delegated Content Request. It also allows the Downstream CDN to control what should be returned to the User Agent in the redirection message by the upstream Request Routing function." At a high level, the scope of the CDNI Request Routing Interface, therefore, contains two main tasks: (1) determining if the dCDN (downstream CDN) is willing to accept a delegated content request, and (2) redirecting the content request coming from a uCDN (upstream CDN) to the proper entry point or entity in the dCDN. Correspondingly, the request routing interface is broadly divided into two functionalities: (1) the CDNI Footprint & Capabilities Advertisement interface (FCI) defined in , and (2) the CDNI Request Routing Redirection interface (RI) defined in . Since this document focuses on the first functionality (CDNI FCI), below is more details about it. Specifically, CDNI FCI allows both an advertisement from a dCDN to a uCDN (push) and a query from a uCDN to a dCDN (pull) so that the uCDN knows whether it can redirect a particular user request to that dCDN. A key component in defining CDNI FCI is defining objects describing the footprints and capabilities of a dCDN. Such objects are already defined in . A protocol to transport and update such objects between a uCDN and a dCDN, however, is not defined. Hence, the scope of this document is to define such a protocol by introducing a new Application-Layer Traffic Optimization (ALTO) service called "CDNI Advertisement Service". There are multiple benefits in using ALTO as a transport protocol, as discussed in . The rest of this document is organized as follows. provides non-normative background on both CDNI FCI and ALTO. introduces the most basic service, called "CDNI Advertisement Service", to realize CDNI FCI using ALTO. demonstrates a key benefit of using ALTO: the ability to integrate CDNI FCI with ALTO network maps. Such integration provides new granularity to describe footprints. introduces "Filtered CDNI Advertisement Service" to allow a uCDN to get footprints with given capabilities instead of getting the full resource, which can be large. further shows another benefit of using ALTO: the ability to query footprint properties using ALTO entity property map extension. In this way, a uCDN can effectively fetch capabilities of footprints in which it is interested. IANA and security considerations are discussed in and respectively.

The design of CDNI FCI transport using ALTO depends on the understanding of both FCI semantics and ALTO. Hence, this document starts with a non-normative review for both. The review uses the terminologies for CDNI as defined in , and ; those for ALTO as defined in and .

(CDNI "Footprint and Capabilities Semantics") defines the semantics of CDNI FCI, provides guidance on what Footprint and Capabilities mean in a CDNI context, and specifies the requirements on the CDNI FCI transport protocol. The definitions in depend on . Below is a non-normative review of key related points of and . For detailed information and normative specification, the reader is referred to these two RFCs. Multiple types of mandatory-to-implement footprints (ipv4cidr, ipv6cidr, asn, and countrycode) are defined in . A "Set of IP-prefixes" can contain both full IP addresses (i.e., a /32 for IPv4 or a /128 for IPv6) and IP prefixes with an arbitrary prefix length. There must also be support for multiple IP address versions, i.e., IPv4 and IPv6, in such a footprint. Multiple initial types of capabilities are defined in including (1) Delivery Protocol, (2) Acquisition Protocol, (3) Redirection Mode, (4) Capabilities related to CDNI Logging, and (5) Capabilities related to CDNI Metadata. They are required in all cases and therefore considered as mandatory-to-implement capabilities for all CDNI FCI implementations. Footprint and capabilities are defined together and cannot be interpreted independently from each other. Specifically, integrates footprint and capabilities with an approach of "capabilities with footprint restrictions", by expressing capabilities on a per footprint basis. Specifically, for all mandatory-to-implement footprint types, footprints can be viewed as constraints for delegating requests to a dCDN: A dCDN footprint advertisement tells the uCDN the limitations for delegating a request to the dCDN. For IP prefixes or ASN(s), the footprint signals to the uCDN that it should consider the dCDN a candidate only if the IP address of the request routing source falls within the prefix set (or ASN, respectively). The CDNI specifications do not define how a given uCDN determines what address ranges are in a particular ASN. Similarly, for country codes, a uCDN should only consider the dCDN a candidate if it covers the country of the request routing source. The CDNI specifications do not define how a given uCDN determines the country of the request routing source. Multiple footprint constraints are additive, i.e., the advertisement of different types of footprint narrows the dCDN candidacy cumulatively. Given that a large part of Footprint and Capabilities Advertisement may actually happen in contractual agreements, the semantics of CDNI Footprint and Capabilities advertisement refers to answering the following question: what exactly still needs to be advertised by the CDNI FCI? For instance, updates about temporal failures of part of a footprint can be useful information to convey via the CDNI FCI. Such information would provide updates on information previously agreed in contracts between the participating CDNs. In other words, the CDNI FCI is a means for a dCDN (downstream CDN) to provide changes/updates regarding a footprint and/or capabilities that it has prior agreed to serve in a contract with a uCDN (upstream CDN). Hence, server push and incremental encoding will be necessary techniques.

Application-Layer Traffic Optimization (ALTO) defines an approach for conveying network layer (topology) information to "guide" the resource provider selection process in distributed applications that can choose among several candidate resources providers to retrieve a given resource. Usually, it is assumed that an ALTO server conveys information that these applications cannot measure or have difficulty measuring themselves . Originally, ALTO was motivated by optimizing cross-ISP traffic generated by P2P applications . However, ALTO can also be used for improving the request routing in CDNs. In particular, the CDNI problem statement explicitly mentions ALTO as a candidate protocol for "actual algorithms for selection of CDN or Surrogate by Request-Routing systems". The following reasons make ALTO a suitable candidate protocol for dCDN (downstream CDN) selection as part of CDNI request routing and, in particular, for an FCI protocol: Application Layer-oriented: ALTO is a protocol specifically designed to improve application layer traffic (and application layer connections among hosts on the Internet) by providing additional information to applications that these applications could not easily retrieve themselves. This matches the need of CDNI: a uCDN wants to improve application layer CDN request routing by using information (provided by a dCDN) that the uCDN could not easily obtain otherwise. Hence, ALTO can help a uCDN to select a proper dCDN by first providing dCDNs' capabilities as well as footprints (see ) and then providing costs of surrogates in a dCDN by ALTO cost maps. Security: The identification between uCDNs and dCDNs is an important requirement. ALTO maps can be signed and hence provide inherent integrity protection. Please see . RESTful Design: The ALTO protocol has undergone extensive revisions in order to provide a RESTful design regarding the client-server interaction specified by the protocol. A CDNI FCI interface based on ALTO would inherit this RESTful design. Please see . Error-handling: The ALTO protocol provides extensive error-handling in the whole request and response process (see Section 8.5 of ). A CDNI FCI interface based on ALTO would inherit this this extensive error-handling framework. Please see . Map Service: The semantics of an ALTO network map is an exact match for the needed information to convey a footprint by a dCDN, in particular, if such a footprint is being expressed by IP-prefix ranges. Please see . Filtered Map Service: The ALTO map filtering service would allow a uCDN to query only for parts of an ALTO map. For example, the ALTO filtered property map service can enable a uCDN to query properties of a part of footprints efficiently (see ). Server-initiated Notifications and Incremental Updates: When the footprint or the capabilities of a dCDN change (i.e., unexpectedly from the perspective of a uCDN), server-initiated notifications would enable a dCDN to inform a uCDN about such changes directly. Consider the case where - due to failure - part of the footprint of the dCDN is not functioning, i.e., the CDN cannot serve content to such clients with reasonable QoS. Without server-initiated notifications, the uCDN might still use a recent network and cost map from the dCDN, and therefore redirect requests to the dCDN which it cannot serve. Similarly, the possibility for incremental updates would enable efficient conveyance of the aforementioned (or similar) status changes by the dCDN to the uCDN. The newest design of ALTO supports server pushed incremental updates . Content Availability on Hosts: A dCDN might want to express CDN capabilities in terms of certain content types (e.g., codecs/ formats, or content from certain content providers). The new endpoint property for ALTO would enable a dCDN to make such information available to a uCDN. This would enable a uCDN to determine whether a dCDN actually has the capabilities for a given type of content requested. Resource Availability on Hosts or Links: The capabilities on links (e.g., maximum bandwidth) or caches (e.g., average load) might be useful information for a uCDN for optimized dCDN selection. For instance, if a uCDN receives a streaming request for content with a certain bitrate, it needs to know if it is likely that a dCDN can fulfill such stringent application-level requirements (i.e., can be expected to have enough consistent bandwidth) before it redirects the request. In general, if ALTO could convey such information via new endpoint properties, it would enable more sophisticated means for dCDN selection with ALTO. ALTO Path Vector Extension is designed to allow ALTO clients to query information such as capacity regions for a given set of flows.

The ALTO protocol is based on the ALTO Information Service Framework which consists of multiple services, where all ALTO services are "provided through a common transport protocol, messaging structure and encoding, and transaction model" . The ALTO protocol specification defines multiple initial services, e.g., the ALTO network map service and cost map service. This document defines a new ALTO service called "CDNI Advertisement Service" which conveys JSON objects of media type "application/alto-cdni+json". These JSON objects are used to transport BaseAdvertisementObject objects defined in ; this document specifies how to transport such BaseAdvertisementObject objects via the ALTO protocol with the ALTO "CDNI Advertisement Service". Similar to other ALTO services, this document defines the ALTO information resource for the "CDNI Advertisement Service" as follows.

The media type of the CDNI Advertisement resource is "application/alto-cdni+json".

A CDNI Advertisement resource is requested using the HTTP GET method.

None.

The "uses" field SHOULD NOT appear unless the CDNI Advertisement resource depends on other ALTO information resources. If the CDNI Advertisement resource has dependent resources, the resource IDs of its dependent resources MUST be included into the "uses" field. This document only defines one potential dependent resource for the CDNI Advertisement resource. See for details of when and how to use it. Future documents may extend the CDNI Advertisement resource and allow other dependent resources.

The "meta" field of a CDNI Advertisement response MUST include the "vtag" field defined in Section 10.3 of . This field provides the version of the retrieved CDNI FCI resource. If a CDNI Advertisement response depends on other ALTO information resources, it MUST include the "dependent-vtags" field, whose value is an array to indicate the version tags of the resources used, where each resource is specified in "uses" of its IRD entry. The data component of an ALTO CDNI Advertisement response is named "cdni-advertisement", which is a JSON object of type CDNIAdvertisementData:

; } CDNIAdvertisementData; ]]> Specifically, a CDNIAdvertisementData object is a JSON object that includes only one property named "capabilities-with-footprints", whose value is an array of BaseAdvertisementObject objects. The syntax and semantics of BaseAdvertisementObject are well defined in Section 5.1 of . A BaseAdvertisementObject object includes multiple properties, including capability-type, capability-value, and footprints, where footprints are defined in Section 4.2.2.2 of . To be self-contained, below is a non-normative specification of BaseAdvertisementObject. As mentioned above, the normative specification of BaseAdvertisementObject is in .

; } BaseAdvertisementObject; object { JSONString footprint-type; JSONString footprint-value<1..*>; } Footprint; ]]> For each BaseAdvertisementObject, the ALTO client MUST interpret footprints appearing multiple times as if they appeared only once. If footprints in a BaseAdvertisementObject is null or empty or not appearing, the ALTO client MUST understand that the capabilities in this BaseAdvertisementObject have the "global" coverage. Note: Further optimization of BaseAdvertisement objects to effectively provide the advertisement of capabilities with footprint restrictions is certainly possible. For example, these two examples below both describe that the dCDN can provide capabilities ["http/1.1", "https/1.1"] for the same footprints. However, the latter one is smaller in its size.

] }, { "capability-type": "FCI.DeliveryProtocol", "capability-value": { "delivery-protocols": [ "https/1.1" ] }, "footprints": [ ] } ] } } EXAMPLE 2 { "meta" : {...}, "cdni-advertisement": { "capabilities-with-footprints": [ { "capability-type": "FCI.DeliveryProtocol", "capability-value": { "delivery-protocols": [ "https/1.1", "http/1.1" ] }, "footprints": [ ] } ] } } ]]> Since such optimizations are not required for the basic interconnection of CDNs, the specifics of such mechanisms are outside the scope of this document. This document only requires the ALTO server to provide the initial FCI-specific CDNI Payload Types defined in as the mandatory-to-implement CDNI capabilities. There may be other documents extending BaseAdvertisementObject and additional CDNI capabilities. They are outside the scope of this document. To support them, future documents can extend the specification defined in this document.

Below is the information resource directory (IRD) of a simple, example ALTO server. The server provides both base ALTO information resources (e.g., network maps) and CDNI FCI related information resources (e.g., CDNI Advertisement resources), demonstrating a single, integrated environment. Specifically, the IRD announces two network maps, one CDNI Advertisement resource without dependency, one CDNI Advertisement resource depending on a network map, one filtered CDNI Advertisement resource to be defined in , one property map including "cdni-capabilities" as its entity property, one filtered property map including "cdni-capabilities" and "pid" as its entity properties, and two update stream services (one for updating CDNI Advertisement resources, and the other for updating property maps).

This basic example demonstrates a simple CDNI Advertisement resource, which does not depend on other resources. There are three BaseAdvertisementObjects in this resource and these objects' capabilities are http/1.1 delivery protocol, [http/1.1, https/1.1] delivery protocol, and https/1.1 acquisition protocol, respectively.

A benefit of using ALTO to provide CDNI Advertisement resources is that such resources can be updated using ALTO incremental updates. Below is an example that also shows the benefit of having both JSON merge patch and JSON patch to encode updates. At first, an ALTO client requests updates for "my-default-cdnifci", and the ALTO server returns the "control-uri" followed by the full CDNI Advertisement response. Then when there is a change in the delivery-protocols in that http/1.1 is removed (from [http/1.1, https/1.1] to only https/1.1) due to maintenance of the https/1.1 clusters, the ALTO server regenerates the new CDNI Advertisement resource and pushes the full replacement to the ALTO client. Later on, the ALTO server notifies the ALTO client that "192.0.2.0/24" is added into the "ipv4" footprint object for delivery-protocol https/1.1 by sending the change encoded by JSON patch to the ALTO client.

The ALTO protocol defines a concept called PID to represent a group of IPv4 or IPv6 addresses which can be applied the same management policy. The PID is an alternative to the pre-defined CDNI footprint types (i.e., ipv4cidr, ipv6cidr, asn, and countrycode). To leverage this concept, this document defines a new CDNI Footprint Type called "altopid". A CDNI Advertisement resource can depend on an ALTO network map resource and use "altopid" footprints to compress its CDNI Footprint Payload. Specifically, the "altopid" footprint type indicates that the corresponding footprint value is a list of PIDNames as defined in . These PIDNames are references of PIDs in a network map resource. Hence a CDNI Advertisement resource using "altopid" footprints depends on a network map. For such a CDNI Advertisement resource, the resource id of its dependent network map MUST be included in the "uses" field of its IRD entry, and the "dependent-vtag" field with a reference to this network map MUST be included in its response (see the example in ).

The examples below use the same IRD given in .

Below is an example network map whose resource id is "my-eu-netmap", and this map is referenced by the CDNI Advertisement example in .

This example shows a CDNI Advertisement resource that depends on a network map described in .

In this example, the ALTO client is interested in changes of "my-cdnifci-with-pid-footprints" and its dependent network map "my-eu-netmap". Considering two changes, the first one is to change footprints of the https/1.1 delivery protocol capability, and the second one is to remove "south-france" from the footprints of the https/1.1 acquisition protocol capability.

and describe CDNI Advertisement Service which can be used to enable a uCDN to get capabilities with footprint restrictions from dCDNs. However, since always getting full CDNI Advertisement resources from dCDNs is inefficient, this document introduces a new service named "Filtered CDNI Advertisement Service", to allow a client to filter a CDNI Advertisement resource using a client-given set of CDNI capabilities. For each entry of the CDNI Advertisement response, an entry will only be returned to the client if it contains at least one of the client given CDNI capabilities. The relationship between a filtered CDNI Advertisement resource and a CDNI Advertisement resource is similar to the relationship between a filtered network/cost map and a network/cost map.

A filtered CDNI Advertisement resource uses the same media type defined for the CDNI Advertisement resource in .

A filtered CDNI Advertisement resource is requested using the HTTP POST method.

The input parameters for a filtered CDNI Advertisement resource are supplied in the entity body of the POST request. This document specifies the input parameters with a data format indicated by the media type "application/alto-cdnifilter+json" which is a JSON object of type ReqFilteredCDNIAdvertisement, where:

;] } ReqFilteredCDNIAdvertisement; ]]> with fields: The same as Base Advertisement Object's capability-type defined in Section 5.1 of . The same as Base Advertisement Object's capability-value defined in Section 5.1 of . A list of CDNI capabilities defined in Section 5.1 of for which footprints are to be returned. If a list is empty or not appearing, the ALTO server MUST interpret it as a request for the full CDNI Advertisement resource. The ALTO server MUST interpret entries appearing in a list multiple times as if they appeared only once. If the ALTO server does not define any footprints for a CDNI capability, it MUST omit this capability from the response.

None.

Same to the "uses" field of the CDNI Advertisement resource (see ).

The response MUST indicate an error, using ALTO protocol error handling specified in Section 8.5 of the ALTO protocol , if the request is invalid. Specifically, a filtered CDNI Advertisement request is invalid if: the value of "capability-type" is null; the value of "capability-value" is null; the value of "capability-value" is inconsistent with "capability-type". When a request is invalid, the ALTO server MUST return an "E_INVALID_FIELD_VALUE" error defined in Section 8.5.2 of , and the "value" field of the error message SHOULD indicate this CDNI capability. The ALTO server returns a filtered CDNI Advertisement resource for a valid request. The format of a filtered CDNI Advertisement resource is the same as a full CDNI Advertisement resource (See .) The returned CDNI Advertisement resource MUST contain only BaseAdvertisementObject objects whose CDNI capability object is the superset of one of CDNI capability object in "cdni-fci-capabilities". Specifically, that a CDNI capability object A is the superset of another CDNI capability object B means that these two CDNI capability objects have the same capability type and mandatory properties in capability value of A MUST include mandatory properties in capability value of B semantically. See for a concrete example. The version tag included in the "vtag" field of the response MUST correspond to the full CDNI Advertisement resource from which the filtered CDNI Advertisement resource is provided. This ensures that a single, canonical version tag is used independently of any filtering that is requested by an ALTO client.

The examples below use the same IRD example as in .

This example filters the full CDNI Advertisement resource in by selecting only the http/1.1 delivery protocol capability. Only the second BaseAdvertisementObjects in the full resource will be returned because the second object's capability is http/1.1 and https/1.1 delivery protocols which is the superset of https/1.1 delivery protocol.

In this example, the ALTO client only cares about the updates of one advertisement object for delivery protocol capability whose value includes "https/1.1". So it adds its limitation of capabilities in "input" field of the POST request.

Besides the requirement of retrieving footprints of given capabilities, another common requirement for uCDN is to query CDNI capabilities of given footprints. Considering each footprint as an entity with properties including CDNI capabilities, a natural way to satisfy this requirement is to use the ALTO property map as defined in . This section describes how ALTO clients look up properties for individual footprints. First, it describes how to represent footprint objects as entities in the ALTO property map. Then it describes how to represent footprint capabilities as entity properties in the ALTO property map. Finally, it provides examples of the full property map and the filtered property map supporting CDNI capabilities, and their incremental updates.

A footprint object has two properties: footprint-type and footprint-value. A footprint-value is an array of footprint values conforming to the specification associated with the registered footprint type ("ipv4cidr", "ipv6cidr", "asn", "countrycode", and "altopid"). Considering each ALTO entity defined in also has two properties: entity domain type and domain-specific identifier, a straightforward approach to represent a footprint as an ALTO entity is to represent its footprint-type as an entity domain type, and its footprint value as a domain-specific identifier. Each existing footprint type can be represented as an entity domain type as follows: According to , "ipv4" and "ipv6" are two predefined entity domain types, which can be used to represent "ipv4cidr" and "ipv6cidr" footprints respectively. "pid" is also a predefined entity domain type, which can be used to represent "altopid" footprints. Note that "pid" is a resource-specific entity domain. To represent an "altopid" footprint, the specifying information resource of the corresponding "pid" entity domain MUST be the dependent network map used by the CDNI Advertisement resource providing this "altopid" footprint. However, no existing entity domain type can represent "asn" and "countrycode" footprints. To represent footprint-type "asn" and "countrycode", this document registers two new domains in in addition to the ones in . Here is an example of representing a footprint object of "ipv4cidr" type as a set of "ipv4" entities in the ALTO property map. The representation of the footprint object of "ipv6cidr" type is similar.

"ipv4:192.0.2.0/24", "ipv4:198.51.100.0/24" ]]>

The ASN domain associates property values with Autonomous Systems in the Internet.

asn

The entity identifier of an entity in an asn domain is encoded as a string consisting of the characters "as" (in lowercase) followed by the Autonomous System Number .

There is no hierarchy or inheritance for properties associated with ASN.

The COUNTRYCODE domain associates property values with countries.

countrycode

The entity identifier of an entity in a countrycode domain is encoded as an ISO 3166-1 alpha-2 code in lowercase.

There is no hierarchy or inheritance for properties associated with country codes.

This document defines a new entity property type called "cdni-capabilities". An ALTO server can provide a property map resource mapping the "cdni-capablities" entity property type for a CDNI Advertisement resource that it provides to an "ipv4", "ipv6", "asn" or "countrycode" entity domain.

The entity property type "cdni-capabilities" allows to define resource-specific entity properties. When resource-specific entity properties are defined with entity property type "cdni-capabilities", the defining information resource for a "cdni-capabilities" property MUST be a CDNI Advertisement resource provided by the ALTO server. The media type of the defining information resource for a "cdni-capabilities" property is therefore: application/alto-cdni+json

A "cdni-capabilities" property for an entity is to indicate all the CDNI capabilities that a corresponding CDNI Advertisement resource provides for the footprint represented by this entity. Thus, the value of a "cdni-capabilities" property MUST be a JSON array. Each element in a "cdni-capabilities" property MUST be an JSON object as format of CDNICapability (see ). The value of a "cdni-capabilities" property for an "ipv4", "ipv6", "asn", "countrycode" or "altopid" entity MUST include all the CDNICapability objects that are provided by the defining CDNI Advertisement resource and the represented footprint object of this entity are in their footprint restrictions.

The examples use the same IRD example given by .

This example shows a full property map in which entities are footprints and entities' property is "cdni-capabilities".

This example uses the filtered property map service to get "pid" and "cdni-capabilities" properties for two footprints "ipv4:192.0.2.0/24" and "ipv6:2001:db8::/32".

In this example, the client is interested in updates for the properties "cdni-capabilities" and "pid" of two footprints "ipv4:192.0.2.0/24" and "countrycode:fr".

This document registers two additional ALTO media types, listed in . Type Subtype Specification application alto-cdni+json application alto-cdnifilter+json application This document registers multiple subtypes, as listed in . n/a n/a Encoding considerations are identical to those specified for the "application/json" media type. See . Security considerations related to the generation and consumption of ALTO Protocol messages are discussed in Section 15 of . This document specifies formats of conforming messages and the interpretation thereof. This document is the specification for these media types; see for the section documenting each media type. ALTO servers and ALTO clients either stand alone or are embedded within other applications. n/a This document uses the mime type to refer to protocol messages and thus does not require a file extension. n/a See Authors’ Addresses section. COMMON n/a See Authors’ Addresses section. Internet Engineering Task Force (mailto:iesg@ietf.org).

As proposed in Section 7.2 of , "CDNI Metadata Footprint Types" registry is requested. A new footprint type is to be registered, listed in . Footprint Type Description Specification altopid A list of PID names of RFCthis [RFC Editor: Please replace RFCthis with the published RFC number for this document.]

As proposed in Section 11.2 of , "ALTO Entity Domain Type Registry" is requested. Two new entity domain types are to be registered, listed in . Identifier Entity Address Encoding Hierarchy & Inheritance Media Type of Defining Resource asn See of RFCthis None None countrycode See of RFCthis None None [RFC Editor: Please replace RFCthis with the published RFC number for this document.]

As proposed in Section 11.3 of , "ALTO Entity Property Type Registry" is required. A new entity property type is to be registered, listed in . Identifier Intended Semantics Media Type of Defining Resource cdni-capabilities of RFCthis application/alto-cdni+json [RFC Editor: Please replace RFCthis with the published RFC number for this document.]

As an extension of the base ALTO protocol (), this document fits into the architecture of the base protocol. And hence Security Considerations of the base protocol (Section 15 of ) fully apply when this extension is provided by an ALTO server. In the context of CDNI Advertisement, additional security considerations should be included as follows: For authenticity and integrity of ALTO information, an attacker may disguise itself as an ALTO server for a dCDN, and provide false capabilities and footprints to a uCDN using the CDNI Advertisement service. Such false information may lead a uCDN to (1) select an incorrect dCDN to serve user requests, or (2) skip uCDNs in good conditions. For potential undesirable guidance from authenticated ALTO information, a dCDN can provide a uCDN with limited capabilities and smaller footprint coverage so that the dCDN can avoid transferring traffic for a uCDN which they should have to transfer. For confidentiality and privacy of ALTO information, footprint properties integrated with ALTO property maps may expose network location identifiers (e.g., IP addresses or fine-grained PIDs). For availability of ALTO services, an attacker may conduct service degradation attacks using services defined in this document to disable ALTO services of a network. It may request potentially large, full CDNI Advertisement resources from an ALTO server in a dCDN continuously, to consume the bandwidth resources of that ALTO server. It may also query filtered property map services with many smaller individual footprints, to consume the computation resources of the ALTO server. Although protection strategies as described in Section 15 of should be applied to address aforementioned security considerations, one additional information leakage risk introduced by this document could not be addressed by these strategies. In particular, if a dCDN signs agreements with multiple uCDNs without any isolation, this dCDN may disclose extra information of one uCDN to another one. In that case, one uCDN may redirect requests which should not have to be served by this dCDN to it. To reduce the risk, a dCDN should isolate full/filtered CDNI Advertisement resources for different uCDNs. It could consider generating URIs of different full/filtered CDNI Advertisement resources by hashing its company ID, a uCDN's company ID as well as their agreements. A dCDN should avoid exposing all full/filtered CDNI Advertisement resources in one of its IRDs.

The authors thank Matt Caulfield, Danny Alex Lachos Perez, Daryl Malas and Sanjay Mishra for their timely reviews and invaluable comments. Jan Seedorf has been partially supported by the GreenICN project (GreenICN: Architecture and Applications of Green Information Centric Networking), a research project supported jointly by the European Commission under its 7th Framework Program (contract no. 608518) and the National Institute of Information and Communications Technology (NICT) in Japan (contract no. 167). The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the GreenICN project, the European Commission, or NICT. This document has also been supported by the Coordination Support Action entitled 'Supporting European Experts Presence in lnternational Standardisation Activities in ICT' ("StandlCT.eu") funded by the European Commission under the Horizon 2020 Programme with Grant Agreement no. 780439. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the European Commission.

Mr. Xiao Shawn Lin is an author of an early version of this document, with many contributions.