Content Delivery Network
Interconnection (CDNI) MetadataNokia3 Ely RoadMiltonCambridgeCB24 6DDUnited Kingdomben.niven-jenkins@nokia.comNokia3 Ely RoadMiltonCambridgeCB24 6DDUnited Kingdomrob.murray@nokia.comCisco Systems1414 Massachusetts AvenueBoxboroughMA01719United States of America+1-978-936-9307mcaulfie@cisco.comEricsson43 Nagog ParkActonMA01720United States of America+1 978-844-5100kevin.j.ma@ericsson.comCDNcascaded CDNcascading CDNscontent acquisitioncontent delegationrequest delegationacquisition protocoldelivery restrictiondelivery policypolicy enforcementdelivery protocolcontent expirationgeo-fencinggeofencinggeo fencinggeo-blockinggeoblockinggeo blockingfootprintcache controlThe Content Delivery Network Interconnection (CDNI) Metadata
interface enables interconnected Content Delivery Networks (CDNs) to
exchange content distribution metadata in order to enable content
acquisition and delivery. The CDNI Metadata associated with a piece of
content provides a downstream CDN with sufficient information for the
downstream CDN to service content requests on behalf of an upstream CDN.
This document describes both a base set of CDNI Metadata and the
protocol for exchanging that metadata.Content Delivery Network Interconnection (CDNI) enables a downstream Content Delivery Network (dCDN)
to service content requests on behalf of an upstream CDN (uCDN).The CDNI Metadata interface (MI) is discussed
in along with four other interfaces that
can be used to compose a CDNI solution (the CDNI Control interface,
the CDNI Request Routing Redirection interface,
the CDNI Footprint & Capabilities Advertisement interface (FCI),
and the CDNI Logging interface). describes
each interface and the relationships between them. The
requirements for the CDNI Metadata interface are specified in
.The CDNI Metadata associated with a piece of content (or with a set
of content) provides a dCDN with sufficient information for servicing
content requests on behalf of a uCDN, in accordance with the policies
defined by the uCDN.This document defines a CDNI Metadata interface that enables a
dCDN to obtain CDNI Metadata from a uCDN so that the dCDN can properly
process and respond to:Redirection requests received over the CDNI Request Routing
Redirection interface .Content requests received directly from User Agents.Specifically, this document defines:A data structure for mapping content requests and redirection
requests to CDNI Metadata objects (Sections and
).An initial set of CDNI GenericMetadata objects ().An HTTP web service for the transfer of CDNI Metadata ().This document reuses the terminology defined in .Additionally, the following terms are used throughout this document
and are defined as follows:Object - a collection of properties.Property - a key and value pair where the key is a property
name and the value is the property value or another object.This document uses the phrase "[Object] A contains [Object]
B" for simplicity when a strictly accurate phrase would be "[Object] A
contains or references (via a Link object) [Object] B".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 .Only the metadata for a small set of initial capabilities is
specified in this document. This set provides the minimum amount of
metadata for basic CDN interoperability while still meeting the
requirements set forth by .The following high-level functionality can be configured via the
CDNI Metadata objects specified in :Acquisition Source: Metadata for allowing a dCDN to fetch
content from a uCDN.Delivery Access Control: Metadata for restricting (or
permitting) access to content based on any of the following
factors:LocationTime windowDelivery protocolDelivery Authorization: Metadata for authorizing dCDN
User Agent requests.Cache Control: Metadata for controlling cache behavior of the
dCDN.The metadata encoding described by this document is extensible in
order to allow for future additions to this list.The set of metadata specified in this document covers the
initial capabilities above. It is only intended to support CDNI
for the delivery of content by a dCDN using HTTP/1.1
and for a dCDN to be able to acquire content
from a uCDN using either HTTP/1.1 or HTTP/1.1 over Transport Layer
Security (TLS) .Supporting CDNI for the delivery of content using
unencrypted HTTP/2 (as well as for a dCDN
to acquire content using unencrypted HTTP/2 or HTTP/2 over TLS)
requires the registration of these protocol names in the
"CDNI Metadata Protocol Types" registry
().Delivery of content using HTTP/1.1 over TLS or HTTP/2 over
TLS SHOULD follow the guidelines set forth in .
Offline configuration of TLS parameters between CDNs is
beyond the scope of this document.The CDNI Metadata interface was designed to achieve the following
objectives:Cacheability of CDNI Metadata objects;Deterministic mapping from redirection requests and content
requests to CDNI Metadata properties;Support for DNS redirection as well as application-specific
redirection (for example, HTTP redirection);Minimal duplication of CDNI Metadata; andLeveraging of existing protocols.Cacheability can decrease the latency of acquiring metadata while
maintaining its freshness and can therefore decrease the latency of serving
content requests and redirection requests, without sacrificing accuracy.
The CDNI Metadata interface uses HTTP and its existing caching
mechanisms to achieve CDNI Metadata cacheability.Deterministic mapping from content to metadata properties eliminates
ambiguity and ensures that policies are applied consistently by all
dCDNs.Support for both HTTP and DNS redirection ensures that the CDNI
Metadata
meets the same design principles for both HTTP-based and DNS-based
redirection schemes.Minimal duplication of CDNI Metadata improves storage efficiency
in the CDNs.Leveraging existing protocols avoids reinventing common mechanisms
such as data structure encoding (by leveraging I-JSON (Internet JSON)
) and data transport (by leveraging HTTP ).The CDNI Metadata object model describes a data structure for mapping
redirection requests and content requests to metadata properties.
Metadata properties describe how to acquire content from a uCDN,
authorize access to content, and deliver content from a dCDN. The object
model relies on the assumption that these metadata properties can be
grouped based on the hostname of the content and subsequently on the
resource path (URI) of the content. The object model associates a set of
CDNI Metadata properties with a hostname to form a default set of
metadata properties for content delivered on behalf of that hostname.
That default set of metadata properties can be overridden by properties
that apply to specific paths within a URI.Different hostnames and URI paths will be associated with different
sets of CDNI Metadata properties in order to describe the required
behavior when a dCDN Surrogate or request router is processing User
Agent requests for content at that hostname and URI path. As a result of
this structure, significant commonality could exist between the CDNI
Metadata properties specified for different hostnames, different URI
paths within a hostname, and different URI paths on different hostnames.
For example, the definition of which User Agent IP addresses should be
grouped together into a single network or geographic
location is likely to be common for a number of different hostnames;
although a uCDN is likely to have several different policies
configured to express geo-blocking rules, it is likely that a
single geo-blocking policy could be applied to multiple hostnames
delivered through the CDN.In order to enable the CDNI Metadata for a given hostname and
URI path to be decomposed into reusable sets of CDNI Metadata properties,
the CDNI Metadata interface splits the CDNI Metadata into separate
objects. Efficiency is improved by enabling a single CDNI Metadata
object (that is shared across hostnames and/or URI paths) to be retrieved
and stored by a dCDN once, even if it is referenced by the CDNI Metadata
for multiple hostnames and/or URI paths.Important Note: Any CDNI Metadata object A that contains another CDNI
Metadata object B can
include a Link object specifying a URI that can be
used to retrieve object B,
instead of embedding object B within object A.
The remainder of this document uses the phrase
"[Object] A contains [Object] B" for simplicity when a strictly accurate
phrase would be "[Object] A contains or references (via a Link object)
[Object] B". It is generally a deployment choice for the uCDN
implementation to decide when to embed CDNI Metadata objects
and when to reference separate resources via Link objects. introduces a high-level description
of the HostIndex, HostMatch, HostMetadata, PathMatch, PatternMatch, and
PathMetadata objects, and describes the relationships between them. introduces a high-level
description of the CDNI GenericMetadata object, which represents the
level at which CDNI Metadata override occurs between HostMetadata and
PathMetadata objects. describes in detail
the specific CDNI Metadata objects and properties specified by this
document that can be contained within a CDNI GenericMetadata
object.The relationships between the HostIndex, HostMatch, HostMetadata,
PathMatch, PatternMatch, and PathMetadata objects are described in
.|HostMatch+-(1)->|HostMetadata+-------(*)------+
+---------+ +---------+ +------+-----+ |
| |
(*) |
| V
--> Contains or references V *****************
(1) One and only one +---------+ *GenericMetadata*
(*) Zero or more +--->|PathMatch| * Objects *
| +----+---++ *****************
| | | ^
(*) (1) (1) +------------+ |
| | +->|PatternMatch| |
| V +------------+ |
| +------------+ |
+--+PathMetadata+-------(*)------+
+------------+
]]>A HostIndex object (see )
contains an array
of HostMatch objects (see ) that contain
hostnames (and/or IP addresses) for which content requests might be
delegated to the dCDN. The HostIndex is the starting point for
accessing the uCDN CDNI Metadata data store. It enables the dCDN to
deterministically discover which CDNI Metadata objects it requires
in order to deliver a given piece of content.The HostIndex links hostnames (and/or IP addresses) to HostMetadata
objects (see ) via HostMatch objects. A
HostMatch object defines a hostname (or IP address) to match against a
requested host and contains a HostMetadata object.HostMetadata objects contain the default
GenericMetadata objects (see )
required to serve content for that host. When looking up CDNI
Metadata, the dCDN looks up the requested hostname (or IP address)
against the HostMatch entries in the HostIndex; from there,
it can find HostMetadata, which describes the default metadata
properties for each host as well as PathMetadata objects
(see ), via
PathMatch objects (see ). PathMatch objects
define patterns, contained inside PatternMatch objects (see ), to match against the requested URI
path. PatternMatch objects contain the pattern strings and
flags that describe the URI path to which a PathMatch applies.
PathMetadata objects contain the GenericMetadata objects
that apply to content requests matching the defined URI
path pattern. PathMetadata properties override properties
previously defined in HostMetadata or less&nbhy;specific PathMatch
paths. PathMetadata objects can contain additional PathMatch
objects to recursively define more&nbhy;specific URI paths to which
GenericMetadata properties might be applied.A GenericMetadata object contains individual CDNI Metadata objects
that define the specific policies and attributes needed to properly
deliver the associated content. For example, a GenericMetadata object
could describe the source from which a CDN can acquire a piece of
content. The GenericMetadata object is an atomic unit that can be
referenced by HostMetadata or PathMetadata objects.For example, if "example.com" is a content provider, a HostMatch
object could include an entry for "example.com" with the URI of the
associated HostMetadata object. The HostMetadata object for
"example.com" describes the metadata properties that apply to
"example.com" and could contain PathMatches for
"example.com&wj;/movies/*" and "example.com/music/*", which
in turn reference corresponding PathMetadata objects that
contain the properties for those more&nbhy;specific URI paths. The
PathMetadata object for "example.com/movies/*" describes the
properties that apply to that URI path. It could also contain a
PathMatch object for "example.com/movies/hd/*", which would
reference the corresponding PathMetadata object for the
"example.com/movies/hd/" path prefix.The relationships in are
also represented in tabular format in below.Data ObjectObjects it contains or referencesHostIndex0 or more HostMatch objects.HostMatch1 HostMetadata object.HostMetadata0 or more PathMatch objects. 0 or more GenericMetadata
objects.PathMatch1 PatternMatch object. 1 PathMetadata object.PatternMatchDoes not contain or reference any other objects.PathMetadata0 or more PathMatch objects. 0 or more GenericMetadata
objects.The HostMetadata and PathMetadata objects contain other CDNI
Metadata objects that contain properties that describe how User Agent
requests for content should be processed -- for example, where to
acquire the content from, authorization rules that should be applied,
geo&nbhy;blocking restrictions, and so on. Each such CDNI Metadata
object is a specialization of a CDNI GenericMetadata object. The
GenericMetadata object abstracts the basic information required for
metadata override and metadata distribution, from the specifics of
any given property (i.e., property semantics, enforcement options,
etc.).The GenericMetadata object defines the properties contained
within it as well as whether or not the properties are
"mandatory-to-enforce". If the dCDN does not understand or
support a mandatory-to-enforce property, the dCDN MUST NOT serve
the content. If the property is not mandatory-to-enforce, then
that GenericMetadata object can be safely ignored and the
content request can be processed in accordance with the rest of
the CDNI Metadata.Although a CDN MUST NOT serve content to a User Agent if a
mandatory&nbhy;to&nbhy;enforce property cannot be enforced, it could
still be safe to redistribute that metadata (the
"safe&nbhy;to&nbhy;redistribute" property) to another
CDN without modification. For example, in
the cascaded CDN case, a transit CDN (tCDN) could convey
mandatory&nbhy;to&nbhy;enforce metadata to a dCDN.
For metadata that does not require customization or translation (i.e.,
metadata that is safe&nbhy;to&nbhy;redistribute), the data
representation received off the wire MAY be stored and redistributed
without being understood or supported by the tCDN. However, for
metadata that requires translation, transparent redistribution of the
uCDN metadata values might not be appropriate. Certain metadata can be
safely, though perhaps not optimally, redistributed unmodified. For
example, a source acquisition address might not be optimal if
transparently redistributed, but it might still work.Redistribution safety MUST be specified for each
GenericMetadata property.
If a CDN does not understand or support a given GenericMetadata
property that is not safe-to-redistribute, the CDN MUST set the
"incomprehensible" flag to true for that GenericMetadata object
before redistributing the metadata. The
"incomprehensible" flag signals to a dCDN that the metadata was not
properly transformed by the tCDN. A CDN MUST NOT attempt to use
metadata that has been marked as "incomprehensible" by a uCDN.tCDNs MUST NOT change the value of mandatory-to-enforce
or safe&nbhy;to&nbhy;redistribute when propagating metadata to a dCDN.
Although a tCDN can set the value of "incomprehensible" to true,
a tCDN MUST NOT change the value of "incomprehensible" from
true to false. describes the action to be taken by a
tCDN for the different combinations of mandatory-to-enforce
("MtE") and safe&nbhy;to&nbhy;redistribute ("StR") properties when
the tCDN either does or does not understand the metadata in
question:MtEStRMetadata Understood by tCDNActionFalseTrueTrueCan serve and redistribute.FalseTrueFalseCan serve and redistribute.FalseFalseFalseCan serve. MUST set "incomprehensible" to true when
redistributing.FalseFalseTrueCan serve. Can redistribute after transforming the
metadata (if the CDN knows how to do so safely); otherwise, MUST set
"incomprehensible" to true when redistributing.TrueTrueTrueCan serve and redistribute.TrueTrueFalseMUST NOT serve but can redistribute.TrueFalseTrueCan serve. Can redistribute after transforming the
metadata (if the CDN knows how to do so safely); otherwise, MUST set
"incomprehensible" to true when redistributing.TrueFalseFalseMUST NOT serve. MUST set "incomprehensible" to true when
redistributing. describes the action to be taken by a
dCDN for the different combinations of mandatory-to-enforce
and "incomprehensible" (Incomp) properties, when the dCDN either does
or does not understand the metadata in question:MtEIncompMetadata Understood by dCDNActionFalseFalseTrueCan serve.FalseTrueTrueCan serve but MUST NOT interpret/apply any metadata
marked as "incomprehensible".FalseFalseFalseCan serve.FalseTrueFalseCan serve but MUST NOT interpret/apply any metadata
marked as "incomprehensible".TrueFalseTrueCan serve.TrueTrueTrueMUST NOT serve.TrueFalseFalseMUST NOT serve.TrueTrueFalseMUST NOT serve.In the metadata object model, a HostMetadata object can contain
multiple PathMetadata objects (via PathMatch objects). Each
PathMetadata object can in turn contain other PathMetadata objects.
HostMetadata and PathMetadata objects form an inheritance tree where
each node in the tree inherits or overrides the property values set by
its parent.GenericMetadata objects of a given type override all
GenericMetadata objects of the same type previously defined by any
parent object in the tree. GenericMetadata objects of a given type
previously defined by a parent object in the tree are inherited when
no object of the same type is defined by the child object. For
example, if HostMetadata for the host "example.com" contains
GenericMetadata objects of types LocationACL and TimeWindowACL
(where "ACL" means "Access Control List") while a PathMetadata object
that applies to "example.com/movies/*" defines an
alternate GenericMetadata object of type TimeWindowACL, then: The TimeWindowACL defined in the PathMetadata would override
the TimeWindowACL defined in the HostMetadata for all User Agent
requests for content under "example.com/movies/", andThe LocationACL defined in the HostMetadata would be inherited
for all User Agent requests for content under
"example.com/movies/".A single HostMetadata or PathMetadata object MUST NOT contain
multiple GenericMetadata objects of the same type. If an array of
GenericMetadata contains objects of duplicate types, the receiver MUST
ignore all but the first object of each type. provides the definitions of each
metadata object type introduced in . These
metadata objects are described as structural metadata objects, as they
provide the structure for host and URI path-based inheritance and
identify which GenericMetadata objects apply to a given User Agent
content request. provides the definitions for a base
set of core metadata objects that can be contained within a
GenericMetadata object. These metadata objects govern how User Agent
requests for content are handled. GenericMetadata objects can contain
other GenericMetadata objects as properties; these can be referred to as
sub-objects. As with all CDNI Metadata objects, the
value of the GenericMetadata sub&nbhy;objects can be either a complete
serialized representation of the sub-object or a Link object that
contains a URI that can be dereferenced to retrieve the complete
serialized representation of the property sub-object. discusses the ability to extend the
base set of GenericMetadata objects specified in this document with
additional standards-based or vendor-specific GenericMetadata objects
that might be defined in the future in separate documents.dCDNs and tCDNs MUST support the parsing of all CDNI Metadata objects
specified in this document. A dCDN does not have to implement the
underlying functionality represented by non-structural GenericMetadata
objects (though that might restrict the content that a given dCDN
will be able to serve). uCDNs as generators of CDNI Metadata only
need to support generating the CDNI Metadata that they need in order
to express the policies required by the content they are describing.
See for more details on the
specific encoding rules for CDNI Metadata objects.Note: In the following sections, the term "mandatory-to-specify" is
used to convey which properties MUST be included for a given structural
or GenericMetadata object. When mandatory-to-specify is specified as
"Yes" for an individual property, it means that if the
object containing that property is included in a metadata response, then
the mandatory-to-specify property MUST also be included (directly or by
reference) in the response. For example, a HostMatch property object
without a host to match against does not make sense; therefore, the
"host" property is mandatory-to-specify inside a HostMatch object.The subsections below describe the structural objects
introduced in .The HostIndex object is the entry point into the CDNI Metadata
hierarchy. It contains an array of HostMatch objects. An incoming
content request is checked against the hostname (or IP address)
specified by each of the listed HostMatch objects to find the
HostMatch object that applies to the request.Property: hostsDescription: Array of HostMatch objects. Hosts (HostMatch
objects) MUST be evaluated in the order they appear, and the
first HostMatch object that matches the content request
being processed MUST be used.Type: Array of HostMatch objectsMandatory-to-Specify: Yes.Example HostIndex object containing two HostMatch objects, where
the first HostMatch object is embedded and the second HostMatch
object is referenced:
},
{
"type": "MI.HostMatch",
"href": "https://metadata.ucdn.example/hostmatch1234"
}
]
}]]>The HostMatch object contains a hostname or IP address to match
against content requests. The HostMatch object also contains a
HostMetadata object to apply if a match is found.Property: hostDescription: Hostname or IP address and optional
port to match against the requested host, i.e., the
host and port as described in .
In order for a hostname or IP address in a content request
to match the hostname or IP address in the
"host" property, the value from the content request when
converted to lowercase MUST be identical to the
value of the "host" property when converted to lowercase.
All implementations MUST support IPv4 addresses
encoded as specified by the "IPv4address" rule in
Section 3.2.2 of . IPv6
addresses MUST be encoded in one of the IPv6 address
formats specified in ,
although receivers MUST support all IPv6 address
formats specified in .
Hostnames MUST conform to the Domain Name System
(DNS) syntax defined in
and . Internationalized
Domain Names (IDNs) must first be transformed to
the A-label form
as per .Type: EndpointMandatory-to-Specify: Yes.Property: host-metadataDescription: CDNI Metadata to apply when delivering
content that matches this host.Type: HostMetadataMandatory-to-Specify: Yes.Example HostMatch object with an embedded HostMetadata
object:
}
}
]]>Example HostMatch object referencing (via a Link object; see
) a HostMetadata object:A HostMetadata object contains the CDNI Metadata properties for
content served for a particular host (defined in the HostMatch
object) and possibly child PathMatch objects.Property: metadataDescription: Array of host-related metadata.Type: Array of GenericMetadata objectsMandatory-to-Specify: Yes.Property: pathsDescription: Path-specific rules. Path patterns
(PathMatch objects) MUST be evaluated in the order they
appear, and the first (and only the first)
PathMatch object that matches the content request
being processed MUST be used.Type: Array of PathMatch objectsMandatory-to-Specify: No. Default is that there
are no more&nbhy;specific paths to evaluate (i.e., an
empty list).Example HostMetadata object containing a number of embedded
GenericMetadata objects that will describe the default metadata for
the host and an embedded PathMatch object that contains a
path for which metadata exists that overrides the default metadata
for the host:
},
{
},
...
{
}
],
"paths": [
{
}
]
}]]>A PathMatch object contains a PatternMatch
object with a path to match against a resource's URI path,
as well as how to handle URI query parameters. The
PathMatch object also contains a PathMetadata object with
GenericMetadata to apply if the resource's URI matches the
pattern within the PatternMatch object.Property: path-patternDescription: Pattern to match against the requested
resource's URI.Type: PatternMatchMandatory-to-Specify: Yes.Property: path-metadataDescription: CDNI Metadata to apply when delivering
content that matches the associated PatternMatch.Type: PathMetadataMandatory-to-Specify: Yes.Example PathMatch object referencing the PathMetadata object to
use for URIs that match the case-sensitive URI path pattern
"/movies/*" (contained within an embedded PatternMatch object):A PatternMatch object contains the pattern string and flags that
describe the pattern expression.Property: patternDescription: A pattern for matching against the
URI path, i.e., against the path-absolute
. The pattern can contain
the wildcards "*" and "?", where "*" matches any
sequence of pchar or "/"
characters (including the empty string)
and "?" matches exactly one pchar character. The
three literals "$", "*", and "?" MUST be
escaped as "$$", "$*", and "$?" (where "$" is the
designated escape character). All other characters
are treated as literals.Type: StringMandatory-to-Specify: Yes.Property: case-sensitiveDescription: Flag indicating whether or not
case-sensitive matching should be used. Note:
Case insensitivity applies to ALPHA characters in
the URI path prior to percent-decoding
.Type: BooleanMandatory-to-Specify: No. Default is case-insensitive
match (i.e., a value of False).Example PatternMatch object that matches the case-sensitive URI
path pattern "/movies/*":A PathMetadata object contains the CDNI Metadata properties for
content requests that match against the associated URI path (defined
in a PathMatch object).Note that if DNS-based redirection is employed, then a dCDN will
be unable to evaluate any metadata at the PathMetadata level or
below because only the hostname of the content request is available
at Request Routing time. dCDNs SHOULD still process all
PathMetadata for the host before responding to the redirection
request to detect if any unsupported metadata is specified.
If any metadata not supported by the dCDN is marked as
mandatory-to-enforce, the dCDN SHOULD NOT accept the content
redirection request, in order to avoid receiving content requests
that it will not be able to satisfy/serve.Property: metadataDescription: Array of path-related metadata.Type: Array of GenericMetadata objectsMandatory-to-Specify: Yes.Property: pathsDescription: Path-specific rules. Path patterns
(PathMatch objects) MUST be evaluated in the order they
appear, and the first (and only the first)
PathMatch object that matches the content request
being processed MUST be used.Type: Array of PathMatch objectsMandatory-to-Specify: No. Default is that there
are no more&nbhy;specific paths to evaluate (i.e., an
empty list).Example PathMetadata object containing a number of embedded
GenericMetadata objects that describe the metadata to apply for the
URI path defined in the parent PathMatch object, as well as
a more&nbhy;specific PathMatch object.
},
{
},
...
{
}
],
"paths": [
{
}
]
}]]>A GenericMetadata object is a wrapper for managing individual
CDNI Metadata properties in an opaque manner.Property: generic-metadata-typeDescription: Case-insensitive CDNI Metadata object
type.Type: String containing the CDNI Payload Type
of the object
contained in the generic-metadata-value property
(see ).Mandatory-to-Specify: Yes.Property: generic-metadata-valueDescription: CDNI Metadata object.Type: Format/Type is defined by the value of the
generic&nbhy;metadata&nbhy;type property above.
Note: generic&nbhy;metadata&nbhy;values MUST NOT name
any properties "href" (see ).Mandatory-to-Specify: Yes.Property: mandatory-to-enforceDescription: Flag identifying whether or not the
enforcement of the property metadata is required.Type: BooleanMandatory-to-Specify: No. Default is to treat metadata as
mandatory-to-enforce (i.e., a value of True).Property: safe-to-redistributeDescription: Flag identifying whether or not the property
metadata can be safely redistributed without
modification.Type: BooleanMandatory-to-Specify: No. Default is to allow transparent
redistribution (i.e., a value of True).Property: incomprehensibleDescription: Flag identifying whether or not any CDN in
the chain of delegation has failed to understand and/or
failed to properly transform this metadata object. Note:
This flag only applies to metadata objects whose
safe-to-redistribute property has a value of False.Type: BooleanMandatory-to-Specify: No. Default is comprehensible
(i.e., a value of False).Example GenericMetadata object containing a metadata object that
applies to the applicable URI path and/or host (within a parent
PathMetadata and/or HostMetadata object, respectively):,
"generic-metadata-value":
{
}
}]]>The objects defined below are intended to be used in the
GenericMetadata object's generic-metadata-value field as defined in
, and their generic-metadata-type
property MUST be set to the appropriate CDNI Payload Type as
defined in .Source metadata provides the dCDN with information
about content acquisition, i.e., how to contact a uCDN Surrogate
or an origin server to obtain the content to be served. The
sources are not necessarily the actual origin servers operated by
the Content Service Provider (CSP) but might be a set of
Surrogates in the uCDN.Property: sourcesDescription: Sources from which the dCDN can acquire
content, listed in order of preference.Type: Array of Source objects (see )Mandatory-to-Specify: No. Default is to use
static configuration, out-of-band from the
CDNI Metadata interface.Example SourceMetadata object (which contains two Source objects)
that describes which servers the dCDN should use for acquiring
content for the applicable URI path and/or host:A Source object describes the source to be used by the dCDN for
content acquisition (e.g., a Surrogate within the uCDN or an
alternate origin server), the protocol to be used, and any
authentication method to be used when contacting that source.Endpoints within a Source object MUST be treated as
equivalent/equal. A uCDN can specify an array of sources,
ordered by preference, within a SourceMetadata object. Then,
for each Source object ranked by preference, a uCDN can
specify an array of endpoints that are equivalent (e.g., a pool of
servers that are not behind a load balancer).Property: acquisition-authDescription: Authentication method to use when
requesting content from this source.Type: Auth (see )Mandatory-to-Specify: No. Default is no authentication
required.Property: endpointsDescription: Origins from which the dCDN can acquire
content. If multiple endpoints are specified, they are
all equal, i.e., the list is not ordered by preference.Type: Array of Endpoint objects (see )Mandatory-to-Specify: Yes.Property: protocolDescription: Network retrieval protocol to use when
requesting content from this source.Type: Protocol (see )Mandatory-to-Specify: Yes.Example Source object that describes a pair of endpoints
(servers) the dCDN can use for acquiring content for the
applicable host and/or URI path:LocationACL metadata defines which locations a User Agent needs
to be in, in order to be able to receive the associated content.A LocationACL that does not include a "locations" property results
in an action of "allow all", meaning that delivery can be performed
regardless of the User Agent's location; otherwise, a CDN
MUST take the action from the first
footprint to match against the User Agent's location.
If two or more footprints overlap, the first
footprint that matches against the User Agent's location determines
the action a CDN MUST take. If the "locations" property is included
but is empty or if none of the listed footprints match the User
Agent's location, then the result is an action of "deny".Although the LocationACL, TimeWindowACL (see ), and ProtocolACL (see ) are independent GenericMetadata objects,
they can provide conflicting information to a dCDN, e.g., a content
request that is simultaneously allowed based on the LocationACL and
denied based on the TimeWindowACL. The dCDN MUST use the logical AND
of all ACLs (where "allow" is true and "deny" is false) to determine
whether or not a request should be allowed.Property: locationsDescription: ACL that allows or denies (blocks)
delivery based on the User Agent's location.Type: Array of LocationRule objects (see )Mandatory-to-Specify: No. Default is to allow all
locations.Example LocationACL object that allows the dCDN to deliver
content to any location / IP address:Example LocationACL object (which contains a LocationRule object
that in turn contains a Footprint object) that only allows the dCDN
to deliver content to User Agents in the USA:A LocationRule contains or references an array of Footprint
objects and the corresponding action.Property: footprintsDescription: Array of footprints to which the rule
applies.Type: Array of Footprint objects (see )Mandatory-to-Specify: Yes.Property: actionDescription: Defines whether the rule specifies
locations to allow or deny.Type: Enumeration [allow|deny] encoded as a lowercase
stringMandatory-to-Specify: No. Default is "deny".Example LocationRule object (which contains a Footprint object)
that allows the dCDN to deliver content to clients in the USA:A Footprint object describes the footprint to which a
LocationRule can be applied, e.g., an IPv4 address range or a
geographic location.Property: footprint-typeDescription: Registered footprint type (see
). The footprint
types specified by this document are "ipv4cidr"
(IPv4CIDR; see ), "ipv6cidr"
(IPv6CIDR; see ), "asn"
(Autonomous System Number; see ), and
"countrycode" (Country Code; see ).Type: Lowercase stringMandatory-to-Specify: Yes.Property: footprint-valueDescription: Array of footprint values conforming to the
specification associated with the registered footprint
type. Footprint values can be simple strings
(e.g., IPv4CIDR, IPv6CIDR, ASN, and Country Code);
however, other Footprint objects can be defined in the
future, along with a more complex encoding
(e.g., GPS coordinate tuples).Type: Array of footprintsMandatory-to-Specify: Yes.Example Footprint object describing a footprint covering the
USA:Example Footprint object describing a footprint covering the IP
address ranges 192.0.2.0/24 and 198.51.100.0/24:Example Footprint object describing a footprint covering the IP
address ranges 2001:db8::/32:Example Footprint object describing a footprint covering the
autonomous system 64496:TimeWindowACL metadata defines time-based restrictions.A TimeWindowACL that does not include a "times" property results
in an action of "allow all", meaning that delivery can be performed
regardless of the time of the User Agent's request;
otherwise, a CDN MUST take the action from
the first window to match against the current time.
If two or more windows overlap, the first window that
matches against the current time determines the action a CDN MUST
take. If the "times" property is included but is empty or if none of
the listed windows match the current time, then the result is an
action of "deny".Although the LocationACL (see ), TimeWindowACL, and ProtocolACL (see ) are
independent GenericMetadata objects, they can provide conflicting
information to a dCDN, e.g., a content request that is
simultaneously allowed based on the LocationACL and denied based on
the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs
(where "allow" is true and "deny" is false) to determine whether or
not a request should be allowed.Property: timesDescription: ACL that allows or denies (blocks)
delivery based on the time of a User Agent's request.Type: Array of TimeWindowRule objects (see )Mandatory-to-Specify: No. Default is to allow all time
windows.Example TimeWindowACL object (which contains a TimeWindowRule
object that in turn contains a TimeWindow object) that only allows
the dCDN to deliver content to clients between 09:00 01/01/2000
UTC and 17:00 01/01/2000 UTC:A TimeWindowRule contains or references an array of TimeWindow
objects and the corresponding action.Property: windowsDescription: Array of time windows to which the rule
applies.Type: Array of TimeWindow objects (see )Mandatory-to-Specify: Yes.Property: actionDescription: Defines whether the rule specifies time
windows to allow or deny.Type: Enumeration [allow|deny] encoded as a lowercase
stringMandatory-to-Specify: No. Default is "deny".Example TimeWindowRule object (which contains a TimeWindow
object) that only allows the dCDN to deliver content to clients
between 09:00 01/01/2000 UTC and 17:00 01/01/2000 UTC:A TimeWindow object describes a time range that can be applied
by a TimeWindowACL, e.g., start 946717200 (i.e., 09:00
01/01/2000 UTC), end: 946746000 (i.e., 17:00 01/01/2000
UTC).Property: startDescription: The start time of the window.Type: Time (see )Mandatory-to-Specify: Yes.Property: endDescription: The end time of the window.Type: Time (see )Mandatory-to-Specify: Yes.Example TimeWindow object that describes a time window from
09:00 01/01/2000 UTC to 17:00 01/01/2000 UTC:ProtocolACL metadata defines delivery protocol restrictions.A ProtocolACL that does not include a protocol-acl property
results in an action of "allow all", meaning that delivery can be
performed regardless of the protocol in the User Agent's request;
otherwise, a CDN MUST take the action from the first protocol
to match against the request protocol. If two or more request
protocols overlap, the first protocol that matches the request
protocol determines the action a CDN MUST take. If the protocol-acl
property is included but is empty or if none of the listed protocols
match the request protocol, then the result is an action of
"deny".Although the LocationACL (see ), TimeWindowACL (see ), and ProtocolACL are
independent GenericMetadata objects, they can provide conflicting
information to a dCDN, e.g., a content request that is
simultaneously allowed based on the ProtocolACL and denied based on
the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs
(where "allow" is true and "deny" is false) to determine whether or
not a request should be allowed.Property: protocol-aclDescription: ACL that allows or denies (blocks)
delivery based on delivery protocol.Type: Array of ProtocolRule objects (see )Mandatory-to-Specify: No. Default is to allow all
protocols.Example ProtocolACL object (which contains a ProtocolRule object)
that only allows the dCDN to deliver content using HTTP/1.1:A ProtocolRule contains or references an array of Protocol
objects and the corresponding action.Property: protocolsDescription: Array of protocols to which the rule
applies.Type: Array of Protocol objects (see )Mandatory-to-Specify: Yes.Property: actionDescription: Defines whether the rule specifies
protocols to allow or deny.Type: Enumeration [allow|deny] encoded as a lowercase
stringMandatory-to-Specify: No. Default is "deny".Example ProtocolRule object (which contains a Protocol object)
that allows the dCDN to deliver content using HTTP/1.1:Delivery authorization defines authorization methods for the
delivery of content to User Agents.Property: delivery-auth-methodsDescription: Options for authorizing content requests.
Delivery for a content request is authorized if any one
of the authorization methods in the list is satisfied
for that request.Type: Array of Auth objects (see )Mandatory-to-Specify: No. Default is no authorization
required.Example DeliveryAuthorization object (which contains
an Auth object):,
"auth-value":
{
}
}
]
}
}]]>A Cache object describes the cache control parameters to be
applied to the content by intermediate caches.Cache keys are generated from the URI of the content
request . In some cases, a CDN or
content provider might want certain path segments or query
parameters to be excluded from the cache key generation.
The Cache object provides guidance on what parts of the
path and query string to include.Property: exclude-path-patternDescription: A pattern for matching against the
URI path, i.e., against the path-absolute
. The pattern can contain
the wildcards "*" and "?", where "*" matches any
sequence of pchar or "/"
characters (including the empty string)
and "?" matches exactly one pchar character. The
three literals "$", "*", and "?" MUST be
escaped as "$$", "$*", and "$?" (where "$" is the
designated escape character). All other characters
are treated as literals. Cache key generation MUST
only include the portion of the path-absolute that
matches the wildcard portions of the pattern.
Note: Inconsistency between the PatternMatch pattern
() and the
exclude&nbhy;path&nbhy;pattern can result in inefficient
caching.Type: StringMandatory-to-Specify: No. Default is to use the
full URI path&nbhy;absolute to generate the cache key.Property: include-query-stringsDescription: Allows a Surrogate to specify the
URI query string parameters
to include when comparing the requested URI against
the URIs in its cache for equivalence. Matching
query parameters MUST be case insensitive. If all
query parameters should be ignored, then the list MUST be
specified and MUST be empty. If a query parameter
appears multiple times in the query string, each
instance value MUST be aggregated prior to
comparison. For consistent cache key generation,
query parameters SHOULD be evaluated in the order
specified in this array.Type: Array of stringsMandatory-to-Specify: No. Default is to consider all query
string parameters when comparing URIs.Example Cache object that instructs the dCDN to use the
full URI path and ignore all query parameters:Example Cache object that instructs the dCDN to exclude
the "CDNX" path prefix and only
include the (case-insensitive) query parameters named
"mediaid" and "providerid":Example Cache object that instructs the dCDN to exclude
the "CDNX" path prefix but includes all query parameters:An Auth object defines authentication and authorization methods
to be used during content acquisition and content delivery,
respectively.Note: This document does not define any Auth methods.
Individual Auth methods are being defined separately (e.g.,
URI Signing ).
The GenericMetadata object that contains Auth objects
is defined herein for convenience and so as not to be
specific to any particular Auth method.Property: auth-typeDescription: Auth type (The CDNI Payload Type
of the GenericMetadata
object contained in the auth-value property).Type: StringMandatory-to-Specify: Yes.Property: auth-valueDescription: An object conforming to the specification
associated with the Auth type.Type: GenericMetadata objectMandatory-to-Specify: Yes.Example Auth object:,
"auth-value":
{
}
}
}
]]>A Grouping object identifies a group of content to which a
given asset belongs.Property: ccidDescription: Content Collection IDentifier for an
application-specific purpose such as logging aggregation.Type: StringMandatory-to-Specify: No. Default is not to apply
any grouping.Example Grouping object that specifies a Content Collection
IDentifier for the content associated with
the Grouping object's parent HostMetadata and PathMetadata:This section describes the simple data types that are used for
properties of CDNI Metadata objects.A Link object can be used in place of any of the objects
described above. Link objects can be used to avoid
duplication if the same metadata information is repeated within the
metadata tree. When a Link object replaces another object, its
"href" property is set to the URI of the resource and its
"type" property is set to the CDNI Payload Type of the object
it is replacing.dCDNs can detect the presence of a Link object
by detecting the presence of a property named "href"
within the object. This means that GenericMetadata types MUST NOT
contain a property named "href" because doing so would conflict with
the ability for dCDNs to detect Link objects being used to reference
a GenericMetadata object.Property: hrefDescription: The URI of the addressable object being
referenced.Type: StringMandatory-to-Specify: Yes.Property: typeDescription: The CDNI Payload Type of the object being referenced.Type: StringMandatory-to-Specify: No. If the container
specifies the type (e.g., the HostIndex object
contains an array
of HostMatch objects, so a Link object in the list of
HostMatch objects must reference a HostMatch), then
it is not necessary to explicitly specify a type.Example Link object referencing a HostMatch object:Example Link object referencing a HostMatch object,
without an explicit type, inside a HostIndex object:
},
{
"href": "https://metadata.ucdn.example/hostmatch1234"
}
]
}
]]>When following a link, CDNI Metadata clients SHOULD
verify that the CDNI Payload Type of the object retrieved
matches the expected CDNI Payload Type, as indicated by
the Link object or containing property. For GenericMetadata objects, type
checks will prevent self-references; however, incorrect
linking can result in circular references for
structural metadata objects, specifically PathMatch and
PathMetadata objects ().
To prevent circular references, CDNI Metadata clients
SHOULD verify that no duplicate links occur for PathMatch
or PathMetadata objects.Protocol objects are used to specify protocols
(from the "CDNI Metadata Protocol Types" registry; see
) for
content acquisition or delivery.Type: StringExample:A hostname (with optional port) or an IP address
(with optional port).All implementations MUST support IPv4 addresses encoded as
specified by the "IPv4address" rule in Section 3.2.2 of . IPv6 addresses MUST be encoded in one of the
IPv6 address formats specified in ,
although receivers MUST support all IPv6 address formats
specified in . Hostnames MUST conform
to the Domain Name System (DNS) syntax defined
in and .
Internationalized Domain Names (IDNs) must first be transformed to
the A-label form
as per .Type: StringExample hostname:Example IPv4 address:Example IPv6 address (with port number):A time value expressed in seconds since the UNIX epoch
(i.e., zero hours, zero minutes, zero seconds, on January 1,
1970) Coordinated Universal Time (UTC) .Type: IntegerExample time representing 09:00:00 01/01/2000 UTC:An IPv4address Classless Inter-Domain Routing (CIDR) block
encoded as specified by the "IPv4address" rule in
Section 3.2.2 of
followed by a "/" followed by an unsigned integer representing the
leading bits of the routing prefix (i.e., IPv4 CIDR notation). Single
IP addresses can be expressed as /32.Type: StringExample IPv4CIDR:An IPv6address CIDR block encoded in one of the IPv6 address
formats specified in followed by a "/"
followed by an unsigned integer representing the leading bits of the
routing prefix (i.e., IPv6 CIDR notation). Single IP addresses can be
expressed as /128.Type: StringExample IPv6CIDR:An ASN value encoded as a string consisting of the characters "as"
(in lowercase) followed by the ASN .Type: StringExample ASN:An ISO 3166-1 alpha-2 code in
lowercase.Type: StringExample Country Code representing the USA:CDNI Metadata is used to convey information pertaining to content
delivery from the uCDN to the dCDN. For optional metadata, it can be
useful for the uCDN to know, prior to delegating any content requests
to a given dCDN, if that dCDN supports the underlying functionality
described by the metadata. If some metadata is
mandatory&nbhy;to&nbhy;enforce and the dCDN does not support it,
any delegated requests for content that requires that metadata will
fail. The uCDN will likely want to avoid delegating those requests
to that dCDN. Likewise, for any metadata that might be assigned
optional values, it could be useful for the uCDN to know, prior to
delegating any content requests to a given dCDN, which values
that dCDN supports. If the optional value assigned to a given piece
of content's metadata is not supported by the dCDN, any delegated
requests for that content can fail, so again the uCDN is likely to
want to avoid delegating those requests to that dCDN.The CDNI Footprint & Capabilities Advertisement interface (FCI)
provides a means of advertising capabilities from the dCDN to the
uCDN . Support for optional metadata types
and values can be advertised using the FCI.This section specifies an interface to enable a dCDN to retrieve CDNI
Metadata objects from a uCDN.The interface can be used by a dCDN to retrieve CDNI Metadata objects
in either of two ways:Dynamically, as required by the dCDN to process received
requests -- for example, in response to a query from a uCDN over
the CDNI Request Routing Redirection interface (RI) or in response to receiving a
request for content from a User Agent.In advance of being required -- for example, in the case of
pre&nbhy;positioned CDNI Metadata acquisition, initiated through
the "CDNI Control interface / Triggers" (CI/T) interface
.The CDNI Metadata interface is built on the principles of HTTP web
services. In particular, this means that requests and responses over the
interface are built around the transfer of representations of
hyperlinked resources. A resource in the context of the CDNI Metadata
interface is any object in the object model (as described in
Sections and ).CDNI Metadata servers (i.e., servers in the uCDN) are free to assign
whatever structure they desire to the URIs for CDNI Metadata objects,
and CDNI Metadata clients MUST NOT make any assumptions regarding the
structure of CDNI Metadata URIs or the mapping between CDNI Metadata
objects and their associated URIs. Any URIs present in the
examples in this document are purely illustrative and are not intended
to impose a definitive structure on CDNI Metadata interface
implementations.The CDNI Metadata interface uses HTTP as the underlying protocol
transport .The HTTP method in the request defines the operation the request
would like to perform. A server implementation of the CDNI Metadata
interface MUST support the HTTP GET and HEAD methods.The corresponding HTTP response returns the status of the operation
in the HTTP status code and returns the current representation of the
resource (if appropriate) in the response body. HTTP responses
that contain a response body SHOULD include an entity&nbhy;tag (ETag)
to enable validation of cached versions of returned resources.As the CDNI Metadata interface builds on top of HTTP, CDNI Metadata
server implementations MAY make use of any HTTP feature when
implementing the CDNI Metadata interface; for example, a CDNI Metadata
server MAY make use of HTTP's caching mechanisms to indicate that the
returned response/representation can be reused without
re&nbhy;contacting the CDNI Metadata server.In the general case, a CDNI Metadata server makes CDNI Metadata
objects available via unique URIs; thus, in order to retrieve
CDNI Metadata, a CDNI Metadata client (i.e., a client in
the dCDN) first makes an HTTP GET request
for the URI of the HostIndex, which provides an array of hostnames
for which the uCDN can delegate content delivery to the dCDN.In order to retrieve the CDNI Metadata for a particular request, the
CDNI Metadata client processes the received HostIndex object and finds
the corresponding HostMetadata entry (by matching the hostname in the
request against the hostnames listed in the HostMatch objects). If the
HostMetadata is linked (rather than embedded), the CDNI Metadata
client then makes an HTTP GET request for the URI specified in the
"href" property of the Link object, which points to the
HostMetadata object itself.In order to retrieve the most specific metadata for a particular
request, the CDNI Metadata client inspects the HostMetadata for
references to more&nbhy;specific PathMetadata objects (by matching
the URI path in the request against the path-pattern property items
in any PathMatch objects listed in the HostMetadata object). If
a PathMetadata object is found to match (and is linked rather than
embedded), the CDNI Metadata client makes another HTTP GET request for the
PathMetadata. Each PathMetadata object can also include references to
additional more&nbhy;specific metadata. If this is the case, the
CDNI Metadata client continues requesting PathMatch and PathMetadata
objects recursively. The CDNI Metadata client repeats this approach of
processing metadata objects and retrieving (via HTTP GETs) any linked
objects until it has all the metadata objects it requires in order to
process the redirection request from the uCDN or the content request
from a User Agent.In cases where a dCDN is not able to retrieve the entire set of
CDNI Metadata associated with a User Agent request, or it has
retrieved that metadata but it is stale according to standard
HTTP caching rules and cannot be revalidated -- for example, because
the uCDN is unreachable or returns an HTTP 4xx or 5xx status in
response to some or all of the dCDN's CDNI Metadata requests -- the
dCDN MUST NOT serve the requested content.Where a dCDN is interconnected with multiple uCDNs, the dCDN needs
to determine which uCDN's CDNI Metadata interface should be used to handle a
particular User Agent request.When HTTP redirection (e.g., HTTP 302 redirects) is
being used between CDNs, it is expected that the dCDN will be able to
determine the uCDN that redirected a particular request from
information contained in the received request (e.g., via the URI).
With knowledge of which uCDN routed the request, the dCDN can choose
the correct uCDN from which to obtain the HostIndex. Note that the
HostIndexes served by each uCDN can be unique.In the case of DNS redirection, there is not always sufficient
information carried in the DNS request from User Agents to determine
the uCDN that redirected a particular request (e.g., when content from
a given host is redirected to a given dCDN by more than one uCDN);
therefore, dCDNs will have to apply local policy when deciding which
uCDN's CDNI Metadata interface to use.The URI for the HostIndex object of a given uCDN needs to be
configured in the dCDN. All other objects/resources
are then discoverable from the HostIndex object by following any links
in the HostIndex object, and through the referenced HostMetadata and
PathMetadata objects and their GenericMetadata sub-objects.Manual configuration of the URI for the HostIndex object is
outside the scope of this document.CDNI Metadata objects MUST be encoded as I-JSON objects containing a dictionary of (key,value) pairs where
the keys are the property names and the values are the associated
property values.The keys of the dictionary are the names of the properties
associated with the object and are therefore dependent on the specific
object being encoded (i.e., dependent on the CDNI Payload Type of the
returned resource). Likewise, the values associated with each property
(dictionary key) are dependent on the specific object being encoded
(i.e., dependent on the CDNI Payload Type of the returned resource).Dictionary keys (properties) in I-JSON are case sensitive. By
convention, any dictionary key (property) defined by this document (for
example, the names of CDNI Metadata object properties) MUST be
lowercase.The set of GenericMetadata objects can be extended with additional
(standards-based or vendor-specific) metadata objects through the
specification of new GenericMetadata objects. The GenericMetadata
object defined in specifies a
type field and a type-specific value field that allow any
metadata to be included in either the HostMetadata or
PathMetadata arrays.As with the initial GenericMetadata types defined in , future GenericMetadata types MUST specify
the information necessary for constructing and decoding the
GenericMetadata object.Any document that defines a new GenericMetadata type MUST:Register the CDNI Payload Type
used to identify the new GenericMetadata
type being specified.Define the set of properties associated with the new
GenericMetadata object. GenericMetadata
MUST NOT contain a property named "href" because doing so would
conflict with the ability to detect Link objects
(see ).For each property, define a name, description, type, and
whether or not the property is mandatory-to-specify.Describe the semantics of the new type, including its purpose,
and provide a use case to which it applies, including an example
encoded in I-JSON.Describe the security and privacy consequences, for
both the User Agent and the CDNs, of the new
GenericMetadata object.Describe any relation to, conflict with, or obsolescence of
other existing CDNI Metadata objects.Note: In the case of vendor-specific extensions,
vendor-identifying CDNI Payload Type names will decrease the
possibility of GenericMetadata type collisions.
It is RECOMMENDED that any vendor&nbhy;specific extensions use
vendor&nbhy;identifying CDNI Payload Type names.At any given time, the set of GenericMetadata types supported by
the uCDN might not match the set of GenericMetadata types supported by
the dCDN.In cases where a uCDN sends metadata containing a
GenericMetadata type that a dCDN does not support, the dCDN MUST
enforce the semantics of the mandatory-to-enforce property. If
a dCDN does not understand or is unable to perform the functions
associated with any mandatory-to-enforce metadata, the dCDN
MUST NOT service any requests for the corresponding content.Note: Ideally, uCDNs would not delegate content requests to a dCDN
that does not support the mandatory-to-enforce metadata associated
with the content being requested. However, even if the uCDN has
a priori knowledge of the metadata supported by the dCDN
(e.g., via the FCI or through out-of-band negotiation between
CDN operators), metadata support can fluctuate or be inconsistent
(e.g., due to miscommunication, misconfiguration, or temporary
outage). Thus, the dCDN MUST always evaluate all metadata associated
with redirection and content requests and reject any requests
where mandatory&nbhy;to&nbhy;enforce metadata associated with
the content cannot be enforced.It is possible that new metadata definitions will obsolete or
conflict with existing GenericMetadata (e.g., a future revision of the
CDNI Metadata interface could redefine the Auth GenericMetadata object
or a custom vendor extension could implement an alternate Auth metadata
option). If multiple metadata (e.g., MI.Auth.v2, vendor1.Auth, and
vendor2.Auth) all conflict with an existing GenericMetadata object
(i.e., MI.Auth) and all are marked as mandatory-to-enforce, it could
be ambiguous as to which metadata should be applied, especially in the
case of overlapping functionality.As described in , metadata
override only applies to metadata objects of the same exact type
found in HostMetadata and nested PathMetadata structures. The CDNI
Metadata interface does not support enforcement of dependencies
between different GenericMetadata types. It is the responsibility of the CSP
and the CDN operators to ensure that metadata assigned to a given
piece of content do not conflict.Note: Because metadata is inherently ordered in HostMetadata and
PathMetadata arrays, as well as in the PathMatch hierarchy,
multiple conflicting metadata types MAY be used; however, metadata
hierarchies SHOULD ensure that independent PathMatch root objects are
used to prevent ambiguous or conflicting metadata definitions.The version of CDNI Metadata objects is conveyed inside the
CDNI Payload Type that is included in either (1) the HTTP
Content-Type header (for example, "Content-Type: application/cdni;
ptype=MI.HostIndex" when retrieved via a link) or (2) in the
link type (), generic-metadata-type
(), or auth&nbhy;type
() properties in the JSON payload.
The CDNI Payload Type uniquely identifies the
specification defining that object, including any relation to,
conflicts with, or obsolescence of other metadata. There is
no explicit version mapping requirement; however, for ease of
understanding, metadata creators SHOULD make new versions of
metadata easily visible via the CDNI Payload Type, e.g., by
appending a version string. Note: A version string is
optional on the first version (e.g., MI.HostIndex) but could
be added for subsequent versions (MI.HostIndex.v2,
MI.HostIndex.v3, etc.).Except when referenced by a Link object, nested metadata
objects (i.e., structural metadata below the HostIndex;
and Source, LocationRule, TimeWindowRule, ProtocolRule, Footprint,
and TimeWindow objects) can be serialized into a
JSON payload without explicit CDNI Payload Type information.
The type is inferred from the outer structural metadata,
GenericMetadata, or Auth object CDNI Payload Type. To avoid
ambiguity when revising nestable metadata objects, any
outer metadata object(s) MUST be reversioned and allocated new
CDNI Payload Type(s) at the same time. For example, the
MI.HostIndex object defined in this document contains an array
of MI.HostMatch objects, each of which in turn contains a
MI.HostMetadata object. If a new MI.HostMetadata.v2 object
were required, the outer MI.HostIndex and MI.HostMatch
objects would need to be revised, e.g., to MI.HostIndex.v2 and
MI.HostMatch.v2, respectively. Similarly, if a new
MI.TimeWindowRule.v2 object were required, the outer
MI.TimeWindowACL object would need to be revised, e.g., to
MI.TimeWindowACL.v2; however, the MI.TimeWindowRule.v2 object could
still contain MI.TimeWindow objects, if so specified.HTTP requests sent to a metadata server SHOULD include
an Accept header with the CDNI Payload Type of the expected object.
Metadata clients can specify multiple CDNI Payload Types
in the Accept header; for example, if a metadata client is capable of
processing two different versions of the same type of object (defined
by different CDNI Payload Types), it might decide to include both
in the Accept header.All CDNI Metadata objects use the media type
"application/cdni". The CDNI Payload Type for each object then
contains the object name of that object as defined by this document,
prefixed with "MI.".
lists the CDNI Payload Types for the metadata objects (resources)
specified in this document.Data ObjectCDNI Payload TypeHostIndexMI.HostIndexHostMatchMI.HostMatchHostMetadataMI.HostMetadataPathMatchMI.PathMatchPatternMatchMI.PatternMatchPathMetadataMI.PathMetadataSourceMetadataMI.SourceMetadataSourceMI.SourceLocationACLMI.LocationACLLocationRuleMI.LocationRuleFootprintMI.FootprintTimeWindowACLMI.TimeWindowACLTimeWindowRuleMI.TimeWindowRuleTimeWindowMI.TimeWindowProtocolACLMI.ProtocolACLProtocolRuleMI.ProtocolRuleDeliveryAuthorizationMI.DeliveryAuthorizationCacheMI.CacheAuthMI.AuthGroupingMI.GroupingA dCDN requests the HostIndex and receives the following object
with a CDNI Payload Type of "MI.HostIndex":If the incoming request has a Host header with "video.example.com",
then the dCDN would fetch the HostMetadata object from
"https://metadata.ucdn.example/host1234" expecting a
CDNI Payload Type of "MI.HostMetadata":Suppose that the path of the requested resource matches the
"/videos&wj;/movies/*" pattern; the next metadata requested
would be for "https://metadata.ucdn.example/host1234/pathDEF" with an
expected CDNI Payload Type of "MI.PathMetadata":Finally, if the path of the requested resource also matches the
"/videos/movies/hd/*" pattern, the dCDN would also fetch the following
object from "https://metadata.ucdn.example/host1234/pathDEF/path123"
with a CDNI Payload Type of "MI.PathMetadata":The final set of metadata that applies to the requested
resource includes a SourceMetadata, a LocationACL, a ProtocolACL,
and a TimeWindowACL.This document requests the registration of the following
entries under the "CDNI Payload Types" registry hosted by IANA:Payload TypeSpecificationMI.HostIndexRFC 8006MI.HostMatchRFC 8006MI.HostMetadataRFC 8006MI.PathMatchRFC 8006MI.PatternMatchRFC 8006MI.PathMetadataRFC 8006MI.SourceMetadataRFC 8006MI.SourceRFC 8006MI.LocationACLRFC 8006MI.LocationRuleRFC 8006MI.FootprintRFC 8006MI.TimeWindowACLRFC 8006MI.TimeWindowRuleRFC 8006MI.TimeWindowRFC 8006MI.ProtocolACLRFC 8006MI.ProtocolRuleRFC 8006MI.DeliveryAuthorizationRFC 8006MI.CacheRFC 8006MI.AuthRFC 8006MI.GroupingRFC 8006Purpose: The purpose of this Payload Type is to
distinguish HostIndex MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish HostMatch MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish HostMetadata MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish PathMatch MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish PatternMatch MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish PathMetadata MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish SourceMetadata MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish Source MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish LocationACL MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish LocationRule MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish Footprint MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish TimeWindowACL MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish TimeWindowRule MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish TimeWindow MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish ProtocolACL MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish ProtocolRule MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish DeliveryAuthorization MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish Cache MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish Auth MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see Purpose: The purpose of this Payload Type is to
distinguish Grouping MI objects (and any associated capability
advertisement)Interface: MI/FCIEncoding: see IANA has created a new "CDNI Metadata Footprint
Types" subregistry in the "Content Delivery Network
Interconnection (CDNI) Parameters" registry. The "CDNI
Metadata Footprint Types" namespace defines the valid
Footprint object type values used by the Footprint object described
in . Additions to the
"CDNI Metadata Footprint Types" namespace
conform to the Specification Required policy as defined in . The Designated Expert will verify that new type
definitions do not duplicate existing type definitions and prevent
gratuitous additions to the namespace. New registrations are
required to provide a clear description of how to interpret
new footprint types.The following table defines the initial values for the
"CDNI Metadata Footprint Types" registry:Footprint TypeDescriptionSpecificationipv4cidrIPv4 CIDR address blockRFC 8006ipv6cidrIPv6 CIDR address blockRFC 8006asnAutonomous System Number (ASN)RFC 8006countrycodeISO 3166-1 alpha-2 codeRFC 8006IANA has created a new "CDNI Metadata Protocol
Types" subregistry in the "Content Delivery Network
Interconnection (CDNI) Parameters" registry. The "CDNI
Metadata Protocol Types" namespace defines the valid Protocol
object values () used by the
SourceMetadata and ProtocolACL objects. Additions to the Protocol
namespace conform to the Specification Required policy as
defined in , where the specification
defines the Protocol Type and the protocol to which it is
associated. The Designated Expert will
verify that new protocol definitions do not duplicate
existing protocol definitions and prevent gratuitous additions
to the namespace.The following table defines the initial Protocol values
corresponding to the HTTP and HTTPS protocols:Protocol TypeDescriptionType SpecificationProtocol Specificationshttp/1.1Hypertext Transfer Protocol -- HTTP/1.1RFC 8006RFC 7230https/1.1HTTP/1.1 over TLSRFC 8006RFC 7230, RFC 2818A malicious metadata server, proxy server, or attacker
impersonating an authentic uCDN CDNI Metadata interface without
being detected could provide false metadata to a dCDN
that either:Denies service for one or more pieces of content to one or more
User Agents; Directs dCDNs to contact malicious origin servers instead of
the actual origin servers, so that malware or slanderous
alternate content may be substituted for legitimate content; orRemoves delivery restrictions (e.g., LocationACL,
TimeWindowACL, ProtocolACL, or Auth metadata), allowing
access to content that would otherwise be denied and thus
possibly violating license restrictions and incurring
unwarranted delivery costs.Unauthorized access to metadata could also enable a malicious
metadata client to continuously issue metadata requests in order
to overload a uCDN's metadata server or servers.Unauthorized access to metadata could further result in
leakage of private information. A malicious metadata client
could request metadata in order to gain access to origin
servers, as well as information pertaining to content restrictions.An implementation of the CDNI Metadata interface MUST use mutual
authentication and message authentication codes to prevent
unauthorized access to, and undetected modification of, metadata (see
).Unauthorized viewing of metadata could result in leakage of private
information. Content provider origin and policy information is
conveyed through the CDNI Metadata interface. A third party
could intercept metadata transactions in order to gain access
to origin servers, as well as information pertaining to
content restrictions and usage patterns.Note: The distribution of metadata by a uCDN to dCDNs could
introduce privacy concerns for some content providers, e.g.,
dCDNs accepting content requests for a content provider's
content might be able to obtain additional information and
usage patterns relating to the users of a content provider's
services. Content providers with concerns about divulging
information to dCDNs can instruct their uCDN partners not to
use CDNI when delivering their content.An implementation of the CDNI Metadata interface MUST use strong
encryption to prevent unauthorized interception or monitoring
of metadata (see ).An implementation of the CDNI Metadata interface MUST support TLS
transport as per and .TLS MUST be used by the server side (uCDN) and the
client side (dCDN) of the CDNI Metadata interface, including
authentication of the remote end, unless alternate methods are
used for ensuring the security of the information in the CDNI
Metadata interface requests and responses (such as setting up
an IPsec tunnel between the two CDNs or using a physically
secured internal network between two CDNs that are owned by
the same corporate entity).The use of TLS for transport of the CDNI Metadata interface
messages allows the dCDN and uCDN to authenticate each other.Once the dCDN and uCDN have mutually authenticated each other,
TLS allows:The dCDN and uCDN to authorize each other (to ensure that
they are transmitting/receiving CDNI Metadata requests and
responses from an authorized CDN);CDNI Metadata interface requests and responses to be
transmitted with confidentiality; andThe integrity of the CDNI Metadata interface requests and
responses to be protected during the exchange.When TLS is used, the general TLS usage guidance in MUST be followed.Codes for the representation of names of countries and their subdivisions -- Part 1: Country codesThe International Organization for StandardizationInformation Technology Portable Operating System Interface (POSIX) Part 1: System Application Program Interface (API) [C Language]Institute of Electrical and Electronics EngineersContent Delivery Network Interconnection (CDNI) Control Interface / TriggersContent Delivery Network Interconnection (CDNI) Request Routing:
Footprint and Capabilities SemanticsURI Signing for CDN Interconnection (CDNI)The authors would like to thank David Ferguson, Francois Le Faucheur,
Jan Seedorf, and Matt Miller for their valuable comments and input to
this document.The authors would also like to thank Grant Watson and
Kent Leung for their contributions to this document.