| Internet-Draft | CDNI Additional Footprint Types | December 2022 |
| Sopher & Mishra | Expires 26 June 2023 | [Page] |
Open Caching architecture is a use case of Content Delivery Networks Interconnection (CDNI) in which the commercial Content Delivery Network (CDN) is the upstream CDN (uCDN) and the ISP caching layer serves as the downstream CDN (dCDN). This document supplements the CDNI Metadata Footprint Types defined in RFC 8006. The Footprint Types defined in this document can be used for Footprint objects as part of the Metadata interface (MI) defined in RFC 8006 and for the Footprint & Capabilities Advertisement interface (FCI) defined in RFC 8008. By defining the footprint union Footprint Type, this document updates RFC 8008, allowing an additive semantic over the narrowing semantics defined in Appendix B of RFC 8008. This document also supplements RFC 9241 with relevant ALTO entity domain types. The defined Footprint Types are derived from requirements raised by Open Caching but are also applicable to CDNI use cases in general.¶
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 BCP 14 [RFC2119] [RFC8174].¶
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The Streaming Video Technology Alliance [SVTA] is a global association that works to solve streaming video challenges in an effort to improve end-user experience and adoption. The Open Caching Working Group [OCWG] of the SVTA is focused on the delegation of video delivery requests from commercial Content Delivery Networks (CDNs) to a caching layer at the ISP's network. Open Caching architecture is a specific use case of Content Delivery Networks Interconnection (CDNI) where the commercial CDN is the upstream CDN (uCDN) and the ISP caching layer is the downstream CDN (dCDN). The Open Caching Request Routing Specification [OC-RR] defines the Request Routing process and the interfaces that are required for its provisioning. This document defines and registers CDNI Footprint and Capabilities objects [RFC8008] that are required for Open Caching Request Routing.¶
For consistency with other CDNI documents this document follows the CDNI convention of uCDN (upstream CDN) and dCDN (downstream CDN) to represent the commercial CDN and ISP caching layer respectively.¶
This document registers two CDNI Metadata Footprint Types (section 7.2 of [RFC8006]) for the defined objects:¶
Section 5 of [RFC8008] describes the Footprint & Capabilities Advertisement interface (FCI) Capability Advertisement Object, which includes an array of CDNI Footprint Objects. Each such object has a footprint-type and a footprint-value, as described in section 4.2.2.2 of [RFC8006]. This document defines additional footprint types, beyond those mentioned in CDNI metadata [RFC8006].¶
Section 4.3.8 of [RFC8006] specifies the "Country Code" footprint type for listing [ISO3166-1] alpha-2 codes. Using Footprint Objects of this type, one can define an FCI Capability Advertisement Object footprint constraint that matches a specific country. Herein is defined the subdivisioncode simple data type, as well as a footprint type allowing the dCDN to define constraints matching geographic areas with better granularity, specifically using the [ISO3166-2] Country Subdivision codes.¶
The "subdivisioncode" data type specified in Section 2.1.1.1, describes a country specific subdivision using an [ISO3166-2] code. The data type is added to the list of data types described in section 4.3 of [RFC8006] that are used as properties of CDNI Metadata objects.¶
An [ISO3166-2] code in lowercase. Each code consists of two parts separated by a hyphen. The first part is the [ISO3166-1] code of the country. The second part is a string of up to three alphanumeric characters.¶
The "subdivisioncode" simple data type specified in Section 2.1.1, is added to the data types listed as footprint types in section 4.2.2.2 of [RFC8006].¶
Below is an example using a footprint object of type "subdivisioncode". The Footprint Object in this example creates a constraint matching clients in the states of New Jersey and New York, USA (ISO [ISO3166-2] codes "US-NJ" and "US-NY" respectively).¶
{
"capabilities": [
{
"capability-type": <CDNI capability object type>,
"capability-value": <CDNI capability object>,
"footprints": [
{
"footprint-type": "subdivisioncode",
"footprint-value": ["us-nj", "us-ny"]
}
]
}
]
}
¶
As described in section 5 of [RFC8008], the FCI Capability Advertisement Object includes an array of CDNI Footprint Objects. Appendix B of [RFC8008] specifies the semantics of a Footprint Objects array as a multiple, additive, footprint constraints. This implies that the advertisement of different footprint types narrows the dCDN's candidacy cumulatively.¶
Sections 4.3.5 and 4.3.6 of [RFC8006] specify the "IPv4CIDR" and "IPv6CIDR" footprint types, respectively, for listing IP unscoped address blocks. Using Footprint Objects of these types, one can define FCI Capability Advertisement Object footprint constraints that match IPv4 or IPv6 clients. However, the described "narrowing" semantic of the Footprint Objects array, as described in Appendix B of [RFC8008], prevents the usage of these objects together to create a footprint constraint that matches IPv4 clients together with IPv6 clients.¶
Below is an example for an attempt at creating an object matching IPv4 clients of subnet "192.0.2.0/24", as well as IPv6 clients of subnet "2001:db8::/32". Such a definition results in an empty list of clients, as the constraints are additives and a client address cannot be both IPv4 and IPv6.¶
{
"capabilities": [
{
"capability-type": <CDNI capability object type>,
"capability-value": <CDNI capability object>,
"footprints": [
{
"footprint-type": "ipv4cidr",
"footprint-value": ["192.0.2.0/24"]
},
{
"footprint-type": "ipv6cidr",
"footprint-value": ["2001:db8::/32"]
}
]
}
]
}
¶
To overcome the described limitation and allow a list of footprint constraints that match both IPv4 and IPv6 client subnets, this document defines the "footprintunion" footprint type. This footprint type allows the collection of multiple footprint-objects into a unified object. Therefore it resolves the above limitation and can be particularly useful to unify semantically related objects, for example, an ipv4cidr together with an ipv6cidr or a countrycode together with a subdivisoncode.¶
Note: to avoid implementation complexity, a "footprintunion" MUST not list any "footprintunion" as a value. As a union of unions is simply a union, this syntextual restrication does not result with any semantic limitation.¶
The "footprintunion" data type is based on the Footprint Object already defined in section 4.2.2.2 of [RFC8006]. The footprint-value for a "footprintunion" object is an array of Footprint objects, where the Footprint objects MUST be of any Footprint Type other than footprintunion.¶
The "footprintunion" data type specified in Section 2.2.1, is added to the data types listed as footprint types in section 4.2.2.2 of [RFC8006].¶
Below is an example using a footprint object of type "footprintunion" combining both IPv4 and IPv6 client subnets.¶
{
"capabilities": [
{
"capability-type": <CDNI capability object type>,
"capability-value": <CDNI capability object>,
"footprints": [
{
"footprint-type": "footprintunion",
"footprint-value": [
{
"footprint-type": "ipv4cidr",
"footprint-value": ["192.0.2.0/24"]
},
{
"footprint-type": "ipv6cidr",
"footprint-value": ["2001:db8::/32"]
}
]
}
]
}
]
}
¶
The footprint union also enables composing a countrycode and subdivisioncode based footprint objects. In the example below we create a constraint covering autonomous system 64496 within the US (ISO [ISO3166-1] alpha-2 code "US") and the Ontario province of Canada (ISO [ISO3166-2] code "CA-ON").¶
{
"capabilities": [
{
"capability-type": <CDNI capability object type>,
"capability-value": <CDNI capability object>,
"footprints": [
{
"footprint-type": "asn",
"footprint-value": ["as64496"]
},
{
"footprint-type": "footprintunion",
"footprint-value": [
{
"footprint-type": "countrycode",
"footprint-value": ["us"]
},
{
"footprint-type": "subdivisioncode",
"footprint-value": ["ca-on"]
}
]
}
]
}
]
}
¶
Section 6 of [RFC9241] describes how to represent footprint objects as entities in the ALTO property map. The approach is to represent the "footprint-type" as an entity domain type of the ALTO entity, and the footprint value as its domain-specific identifier. [RFC9241] further refers to the representation of footprint objects of types "asn" and "countrycode". Here we extend this definition to the "subdivisioncode" footprint-type.¶
The SUBDIVISIONCODE domain associates property values that defines codes for the names of the principal subdivisions.¶
The entity domain type of the SUBDIVISIONCODE domain is "subdivisioncode" (in lowercase).¶
The entity identifier of an entity in a SUBDIVISIONCODE is encoded as an alpha-2 [ISO3166-1] Country Code, followed by a separator and up to three alphanumeric characters.¶
There is no hierarchy or inheritance for properties associated with subdivision codes.¶
Section 7.2 of [RFC8006] creates the "CDNI Metadata Footprint Types" subregistry within the "Content Delivery Network Interconnection (CDNI) Parameters" registry.¶
This document requests the registration of the two additional Footprint Types as defined in Section 2.1 and Section 2.2 :¶
| Footprint Type | Description | Reference |
|---|---|---|
| subdivisioncode | [ISO3166-2] ISO 3166-2 country subdivision code: alpha-2 country code, followed by a hyphen-minus, and up to 3 characters from A-Z;0-9 as a code within the country. | RFCthis |
| footprintunion | A combination of other Footprint Objects | RFCthis |
[RFC Editor: Please replace RFCthis with the published RFC number for this document.]¶
Section 12.3 of [RFC9240] creates the "ALTO Entity Domain Types" registry.¶
This document requests the registration of an additional ALTO Entity Domain Types:¶
| Identifier | Entity Identifier Encoding | Hierarchy and Inheritance | Media Type of Defining Resource | Mapping to ALTO Address Type |
|---|---|---|---|---|
| subdivisioncode | See RFCthis, Section 3.1.2 | None | None | false |
[RFC Editor: Please replace RFCthis with the published RFC number for this document.]¶
This specification is in accordance with the CDNI Metadata 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. More specifically, the use of "subdivisioncode" footprint type, introduces a higher level of granularity into the published dCDN Footprint. Therefore, to meet confidentiality requirements, the use of transport-layer security mechanisms as specified in Section 7 of [RFC8008] is expected.¶
The authors would like to express their gratitude to Ori Finkelman and Kevin J. Ma for their guidance and reviews throughout the development of this document. We would also like to thank all the Area Directors for their review and feedback in improving this document.¶