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Internet Engineering Task Force (IETF) J. Seedorf
Request for Comments: 8008 HFT Stuttgart - Univ. of Applied Sciences
Category: Standards Track J. Peterson
ISSN: 2070-1721 Neustar
S. Previdi
Cisco
R. van Brandenburg
TNO
K. Ma
Ericsson
December 2016
Content Delivery Network Interconnection (CDNI) Request Routing:
Footprint and Capabilities Semantics
Abstract
This document captures the semantics of the "Footprint and
Capabilities Advertisement" part of the Content Delivery Network
Interconnection (CDNI) Request Routing interface, i.e., the desired
meaning of "Footprint" and "Capabilities" in the CDNI context and
what the "Footprint & Capabilities Advertisement interface (FCI)"
offers within CDNI. The document also provides guidelines for the
CDNI FCI protocol. It further defines a Base Advertisement Object,
the necessary registries for capabilities and footprints, and
guidelines on how these registries can be extended in the future.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8008.
Seedorf, et al. Standards Track [Page 1]
RFC 8008 CDNI RR Footprint/Capabilities Semantics December 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Seedorf, et al. Standards Track [Page 2]
RFC 8008 CDNI RR Footprint/Capabilities Semantics December 2016
Table of Contents
1. Introduction and Scope ..........................................4
1.1. Terminology ................................................5
2. Design Decisions for Footprint and Capabilities .................6
2.1. Advertising Limited Coverage ...............................6
2.2. Capabilities and Dynamic Data ..............................7
2.3. Advertisement versus Queries ...............................8
2.4. Avoiding or Handling "Cheating" dCDNs ......................8
3. Focusing on Capabilities with Footprint Restrictions ............9
4. Footprint and Capabilities Extension ............................9
5. Capability Advertisement Object ................................11
5.1. Base Advertisement Object .................................12
5.2. Encoding ..................................................12
5.3. Delivery Protocol Capability Object .......................13
5.3.1. Delivery Protocol Capability Object Serialization ..13
5.4. Acquisition Protocol Capability Object ....................14
5.4.1. Acquisition Protocol Capability Object
Serialization ......................................14
5.5. Redirection Mode Capability Object ........................15
5.5.1. Redirection Mode Capability Object Serialization ...15
5.6. CDNI Logging Capability Object ............................16
5.6.1. CDNI Logging Capability Object Serialization .......17
5.7. CDNI Metadata Capability Object ...........................18
5.7.1. CDNI Metadata Capability Object Serialization ......19
6. IANA Considerations ............................................20
6.1. CDNI Payload Types ........................................20
6.1.1. CDNI FCI DeliveryProtocol Payload Type .............20
6.1.2. CDNI FCI AcquisitionProtocol Payload Type ..........20
6.1.3. CDNI FCI RedirectionMode Payload Type ..............20
6.1.4. CDNI FCI Logging Payload Type ......................21
6.1.5. CDNI FCI Metadata Payload Type .....................21
6.2. "CDNI Capabilities Redirection Modes" Registry ............21
7. Security Considerations ........................................22
8. References .....................................................23
8.1. Normative References ......................................23
8.2. Informative References ....................................24
Appendix A. Main Use Case to Consider .............................25
Appendix B. Semantics for Footprint Advertisement .................25
Appendix C. Semantics for Capabilities Advertisement ..............27
Acknowledgments ...................................................30
Authors' Addresses ................................................30
Seedorf, et al. Standards Track [Page 3]
RFC 8008 CDNI RR Footprint/Capabilities Semantics December 2016
1. Introduction and Scope
The CDNI working group is working on a set of protocols to enable the
interconnection of multiple CDNs. These CDNI protocols can serve
multiple purposes, as discussed in [RFC6770] -- for instance, to
extend the reach of a given CDN to areas in the network that are not
covered by that particular CDN.
The goal of this document is to achieve a clear understanding about
the semantics associated with the CDNI Request Routing Footprint &
Capabilities Advertisement interface (from now on referred to as
the FCI) [RFC7336], in particular the type of information a
downstream CDN (dCDN) "advertises" regarding its footprint and
capabilities. To narrow down undecided aspects of these semantics,
this document tries to establish a common understanding of what the
FCI needs to offer and accomplish in the context of CDNI.
Deciding on specific protocols to use for the FCI is explicitly
outside the scope of this document. However, we provide guidelines
for such FCI protocols.
We make the following general assumptions in this document:
o The CDNs participating in the CDN interconnection have already
performed a bootstrap process, i.e., they have connected to each
other, either directly or indirectly, and can exchange information
amongst each other.
o The upstream CDN (uCDN) receives footprint advertisements and/or
capability advertisements from a set of dCDNs. Footprint
advertisements and capability advertisements need not use the same
underlying protocol.
o The uCDN receives the initial Request Routing message from the
endpoint requesting the resource.
The CDNI problem statement [RFC6707] describes the Request Routing
interface as "[enabling] 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." In addition, [RFC6707] says "the CDNI
Request Routing interface is also expected to enable a Downstream CDN
to provide to the Upstream CDN (static or dynamic) information (e.g.,
resources, footprint, load) to facilitate selection of the Downstream
CDN by the Upstream CDN Request Routing system when processing
subsequent Content Requests from User Agents." It thus considers
"resources" and "load" as capabilities to be advertised by the dCDN.
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The range of different footprint definitions and possible
capabilities is very broad. Attempting to define a comprehensive
advertisement solution quickly becomes intractable. The CDNI
requirements document [RFC7337] lists the specific requirements for
the CDNI FCI in order to disambiguate footprints and capabilities
with respect to CDNI. This document defines a common understanding
of what the terms "footprint" and "capabilities" mean in the context
of CDNI and details the semantics of the footprint advertisement
mechanism and the capability advertisement mechanism.
1.1. Terminology
This document reuses the terminology defined in [RFC6707].
Additionally, the following terms are used throughout this document
and are defined as follows:
o Footprint: a description of a CDN's coverage area, i.e., the area
from which client requests may originate for content and to which
the CDN is willing to deliver content. Note: There are many ways
to describe a footprint -- for example, by address range (e.g.,
IPv4 CIDR or IPv6 CIDR (Classless Inter-Domain Routing), network
ID (e.g., Autonomous System Number (ASN)), nation boundaries
(e.g., country code), or GPS coordinates. This document does not
define or endorse the quality or suitability of any particular
footprint description method; rather, it only defines a method for
transporting known footprint descriptions in Footprint and
Capabilities Advertisement messages.
o Capability: a feature of a dCDN upon whose support a uCDN relies
when making delegation decisions. Support for a given feature can
change over time and can be restricted to a limited portion of a
dCDN's footprint. Note: There are many possible dCDN features
that could be of interest to a uCDN. This document does not
presume to define them all; rather, it describes a scheme for
defining new capabilities and how to transport them in Footprint
and Capabilities Advertisement messages.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Seedorf, et al. Standards Track [Page 5]
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2. Design Decisions for Footprint and Capabilities
A large part of the difficulty in discussing the FCI lies in
understanding what exactly is meant when trying to define a footprint
in terms of "coverage" or "reachability". While the operators of
CDNs pick strategic locations to situate Surrogates, a Surrogate with
a public IPv4 address is reachable by any endpoint on the Internet,
unless some policy enforcement precludes the use of the Surrogate.
Some CDNs aspire to cover the entire world; we refer to these as
global CDNs. The footprint advertised by such a CDN in the CDNI
environment would, from a coverage or reachability perspective,
presumably cover all prefixes. Potentially more interesting for CDNI
use cases, however, are CDNs that claim a more limited coverage area
but seek to interconnect with other CDNs in order to create a single
CDN fabric that shares resources.
Furthermore, not all capabilities need to be footprint-restricted.
Depending upon the use case, the optimal semantics of "footprints
with capability attributes" vs. "capabilities with footprint
restrictions" are not clear.
The key to understanding the semantics of footprint advertisements
and capability advertisements lies in understanding why a dCDN would
advertise a limited coverage area and how a uCDN would use such
advertisements to decide among one of several dCDNs. The following
section will discuss some of the trade-offs and design decisions that
need to be made for the CDNI FCI.
2.1. Advertising Limited Coverage
The basic use case that would motivate a dCDN to advertise limited
coverage is that the CDN was built to cover only a particular portion
of the Internet. For example, an ISP could purpose-build a CDN to
serve only their own customers by situating Surrogates in close
topological proximity to high concentrations of their subscribers.
The ISP knows the prefixes it has allocated to end users and thus can
easily construct a list of prefixes that its Surrogates were
positioned to serve.
When such a purpose-built CDN interconnects with other CDNs and
advertises its footprint to a uCDN, however, the original intended
coverage of the CDN might not represent its actual value to the
interconnection of CDNs. Consider an ISP-A and ISP-B that both field
their own CDNs, which they interconnect via CDNI. A given user E,
who is a customer of ISP-B, might happen to be topologically closer
to a Surrogate fielded by ISP-A, if E happens to live in a region
where ISP-B has few customers and ISP-A has many. In this case, is
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it ISP-A's CDN that "covers" E? If ISP-B's CDN has a failure
condition, is it up to the uCDN to understand that ISP-A's Surrogates
are potentially available as backups, and if so, how does ISP-A
advertise itself as a "standby" for E? What about the case where
CDNs advertising to the same uCDN express overlapping coverage (for
example, mixing global and limited CDNs)?
The answers to these questions greatly depend on how much information
the uCDN wants to use to select a dCDN. If a uCDN has three dCDNs to
choose from that "cover" the IP address of user E, obviously the uCDN
might be interested in knowing how optimal the coverage is from each
of the dCDNs. Coverage need not be binary (i.e., either provided or
not provided); dCDNs could advertise a coverage "score", for example,
and provided that they all reported scores fairly on the same scale,
uCDNs could use that information to make their topological optimality
decision. Alternately, dCDNs could advertise the IP addresses of
their Surrogates rather than prefix "coverage" and let the uCDN
decide for itself (based on its own topological intelligence) which
dCDN has better resources to serve a given user.
In summary, the semantics of advertising a footprint depend on
whether (1) such qualitative metrics for expressing a footprint (such
as the coverage "score" mentioned above) are included as part of the
CDNI FCI or (2) the focus is just on a "binary" footprint.
2.2. Capabilities and Dynamic Data
In cases where the apparent footprints of dCDNs overlap, uCDNs might
also want to rely on other factors to evaluate the respective merits
of dCDNs. These include facts related to the Surrogates themselves,
the network where the Surrogate is deployed, the nature of the
resource sought, and the administrative policies of the respective
networks.
In the absence of network-layer impediments to reaching Surrogates,
the choice to limit coverage is, by necessity, an administrative
policy. Much policy needs to be agreed upon before CDNs can
interconnect, including questions of membership, compensation,
volumes, and so on. A uCDN certainly will factor these sorts of
considerations into its decision to select a dCDN, but there is
probably little need for dCDNs to actually advertise them through an
interface -- they will be settled out-of-band as a precondition for
interconnection.
Other facts about the dCDN would be expressed through the interface
to the uCDN. Some capabilities of a dCDN are static, and some are
highly dynamic. Expressing the total storage built into its
Surrogates, for example, changes relatively rarely, whereas the
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amount of storage in use at any given moment is highly volatile.
Network bandwidth similarly could be expressed either as total
bandwidth available to a Surrogate or based on the current state of
the network. A Surrogate can at one moment lack a particular
resource in storage but have it the next.
The semantics of the capabilities interface will depend on how much
of the dCDN state needs to be pushed to the uCDN and, qualitatively,
how often that information needs to be updated.
2.3. Advertisement versus Queries
In a CDNI environment, each dCDN shares some of its state with the
uCDN. The uCDN uses this information to build a unified picture of
all of the dCDNs available to it. In architectures that share
detailed capability information, the uCDN could perform the entire
Request Routing operation down to selecting a particular Surrogate in
the dCDN. However, when the uCDN needs to deal with many potential
dCDNs, this approach does not scale, especially for dCDNs with
thousands or tens of thousands of Surrogates; the volume of updates
to the footprint and the capability information becomes onerous.
Were the volume of FCI updates from dCDNs to exceed the volume of
requests to the uCDN, it might make more sense for the uCDN to query
dCDNs upon receiving requests (as is the case in the recursive
redirection mode described in [RFC7336]), instead of receiving
advertisements and tracking the state of dCDNs. The advantage of
querying dCDNs would be that much of the dynamic data that dCDNs
cannot share with the uCDN would now be factored into the uCDN's
decision. dCDNs need not replicate any state to the uCDN -- uCDNs
could effectively operate in a stateless mode.
The semantics of both footprint advertisements and capability
advertisements depend on the service model here: are there cases
where a synchronous query/response model would work better for the
uCDN decision than a state replication model?
2.4. Avoiding or Handling "Cheating" dCDNs
In a situation where more than one dCDN is willing to serve a given
end user request, it might be attractive for a dCDN to "cheat" in the
sense that the dCDN provides inaccurate information to the uCDN in
order to convince the uCDN to select it over "competing" dCDNs. It
could therefore be desirable to take away the incentive for dCDNs to
cheat (in information advertised) as much as possible. One option is
to make the information the dCDN advertises somehow verifiable for
the uCDN. On the other hand, a "cheating" dCDN might be avoided or
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handled by the fact that there will be strong contractual agreements
between a uCDN and a dCDN, so that a dCDN would risk severe penalties
or legal consequences when caught cheating.
Overall, the information a dCDN advertises (in the long run) needs to
be somehow qualitatively verifiable by the uCDN, though possibly
through non-real-time out-of-band audits. It is probably an overly
strict requirement to mandate that such verification be possible
"immediately", i.e., during the Request Routing process itself. If
the uCDN can detect a cheating dCDN at a later stage, it might
suffice for the uCDN to "de-incentivize" cheating because it would
negatively affect the long-term business relationship with a
particular dCDN.
3. Focusing on Capabilities with Footprint Restrictions
Given the design considerations listed in the previous section, it
seems reasonable to assume that in most cases it is the uCDN that
makes the decision to select a certain dCDN for Request Routing based
on information the uCDN has received from this particular dCDN. It
can be assumed that cheating dCDNs will be dealt with via means
outside the scope of CDNI and that the information advertised between
CDNs is accurate. In addition, excluding the use of qualitative
information (e.g., Surrogate proximity, delivery latency, Surrogate
load) to predict the quality of delivery would further simplify the
use case, allowing it to better focus on the basic functionality of
the FCI.
Furthermore, understanding that in most cases contractual agreements
will define the basic coverage used in delegation decisions, the
primary focus of the FCI is on providing updates to the basic
capabilities and coverage by the dCDNs. As such, the FCI has chosen
the semantics of "capabilities with footprint restrictions".
4. Footprint and Capabilities Extension
Other optional "coverage/reachability" footprint types or "resource"
footprint types may be defined by future specifications. To
facilitate this, a clear process for specifying optional footprint
types in an IANA registry is specified in the "CDNI Metadata
Footprint Types" registry (defined in the CDNI Metadata interface
document [RFC8006]).
Seedorf, et al. Standards Track [Page 9]
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This document also registers CDNI Payload Types [RFC7736] for the
initial capability types (see Section 6):
o Delivery Protocol (for delivering content to the end user)
o Acquisition Protocol (for acquiring content from the uCDN or
origin server)
o Redirection Mode (e.g., DNS redirection vs. HTTP redirection as
discussed in [RFC7336])
o CDNI Logging (i.e., supported CDNI Logging fields)
o CDNI Metadata (i.e., supported GenericMetadata types)
Each Payload Type is prefaced with "FCI.". Updates to capability
objects MUST indicate the version of the capability object in a newly
registered Payload Type, e.g., by appending ".v2". Each capability
type MAY have a list of valid values. Future specifications that
define a given capability MUST define any necessary registries (and
the rules for adding new entries to the registry) for the values
advertised for a given capability type.
The "CDNI Logging record-types" registry [RFC7937] defines all known
record-types, including "mandatory-to-implement" record-types.
Advertising support for mandatory-to-implement record-types would be
redundant. CDNs SHOULD NOT advertise support for
mandatory-to-implement record-types.
The "CDNI Logging Field Names" registry [RFC7937] defines all known
CDNI Logging fields. CDNI Logging fields may be reused by different
record-types and be mandatory-to-implement in some record-types, but
they may be optional in other record-types. CDNs MUST advertise
support for optional CDNI Logging fields within the context of a
specific record-type. For a given record-type, CDNs SHOULD NOT
advertise support for mandatory-to-implement CDNI Logging fields.
The following CDNI Logging fields are defined as optional for the
"cdni_http_request_v1" record-type [RFC7937]:
o s-ccid
o s-sid
[RFC8006] requires that CDNs be able to parse all the defined
metadata objects but does not require dCDNs to support enforcement of
non-structural GenericMetadata objects. Advertising support for
"mandatory-to-enforce" GenericMetadata types MUST be provided.
Advertising support for non-mandatory-to-enforce GenericMetadata
Seedorf, et al. Standards Track [Page 10]
RFC 8008 CDNI RR Footprint/Capabilities Semantics December 2016
types SHOULD be provided. Advertisement of non-mandatory-to-enforce
GenericMetadata MAY be necessary, e.g., to signal temporary outages
and subsequent recovery. It is expected that structural metadata
will be supported at all times.
The notion of optional footprint types and capability types implies
that certain implementations might not support all kinds of
footprints and capabilities. Therefore, any FCI solution protocol
MUST define how the support for optional footprint types and
capability types will be negotiated between a uCDN and a dCDN that
use the particular FCI protocol. In particular, any FCI solution
protocol MUST specify how to handle failure cases or non-supported
footprint or capability types.
In general, a uCDN MAY ignore capabilities or footprint types it does
not understand; in this case, it only selects a suitable dCDN based
on the types of capabilities and footprints it understands.
Similarly, if a dCDN does not use an optional capability or footprint
that is, however, supported by a uCDN, this causes no problem for FCI
functionality because the uCDN decides on the remaining
capabilities/footprint information that is being conveyed by
the dCDN.
5. Capability Advertisement Object
To support extensibility, the FCI defines a generic base object
(similar to the CDNI Metadata interface GenericMetadata object)
[RFC8006] to facilitate a uniform set of mandatory parsing
requirements for all future FCI objects.
Future object definitions (e.g., regarding the CDNI Metadata or CDNI
Logging interfaces) will build off the base object defined here but
will be specified in separate documents.
Note: In the following sections, the term "mandatory-to-specify" is
used to convey which properties MUST be included when serializing a
given capability object. When mandatory-to-specify is defined as
"Yes" for an individual property, it means that if the object
containing that property is included in an FCI message, then the
mandatory-to-specify property MUST also be included.
Seedorf, et al. Standards Track [Page 11]
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5.1. Base Advertisement Object
The FCIBase object is an abstraction for managing individual CDNI
capabilities in an opaque manner.
Property: capability-type
Description: CDNI capability object type.
Type: FCI-specific CDNI Payload Type (from the "CDNI Payload
Types" registry [RFC7736])
Mandatory-to-Specify: Yes.
Property: capability-value
Description: CDNI capability object.
Type: Format/Type is defined by the value of the
capability-type property above
Mandatory-to-Specify: Yes.
Property: footprints
Description: CDNI capability footprint.
Type: List of CDNI Footprint objects (from the "CDNI Metadata
Footprint Types" registry [RFC8006])
Mandatory-to-Specify: No.
5.2. Encoding
CDNI FCI objects MUST be encoded using JSON [RFC7159] and MUST also
follow the recommendations of I-JSON (Internet JSON) [RFC7493]. FCI
objects are composed of 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
capability or the CDNI Metadata Footprint Type of the footprint).
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 capability or the CDNI Metadata
Footprint Type of the footprint).
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Dictionary keys (properties) in JSON are case sensitive. By
convention, any dictionary key (property) defined by this document
MUST be lowercase.
5.3. Delivery Protocol Capability Object
The Delivery Protocol capability object is used to indicate support
for one or more of the protocols listed in the "CDNI Metadata
Protocol Types" registry (defined in [RFC8006]).
Property: delivery-protocols
Description: List of supported CDNI delivery protocols.
Type: List of protocol types (from the "CDNI Metadata Protocol
Types" registry [RFC8006])
Mandatory-to-Specify: Yes.
5.3.1. Delivery Protocol Capability Object Serialization
The following shows an example of Delivery Protocol capability object
serialization for a CDN that supports only HTTP/1.1 without Transport
Layer Security (TLS) for content delivery.
{
"capabilities": [
{
"capability-type": "FCI.DeliveryProtocol",
"capability-value": {
"delivery-protocols": [
"http/1.1",
]
},
"footprints": [
<Footprint objects>
]
}
]
}
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5.4. Acquisition Protocol Capability Object
The Acquisition Protocol capability object is used to indicate
support for one or more of the protocols listed in the "CDNI Metadata
Protocol Types" registry (defined in [RFC8006]).
Property: acquisition-protocols
Description: List of supported CDNI acquisition protocols.
Type: List of protocol types (from the "CDNI Metadata Protocol
Types" registry [RFC8006])
Mandatory-to-Specify: Yes.
5.4.1. Acquisition Protocol Capability Object Serialization
The following shows an example of Acquisition Protocol capability
object serialization for a CDN that supports HTTP/1.1 with or without
TLS for content acquisition.
{
"capabilities": [
{
"capability-type": "FCI.AcquisitionProtocol",
"capability-value": {
"acquisition-protocols": [
"http/1.1",
"https/1.1"
]
},
"footprints": [
<Footprint objects>
]
}
]
}
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5.5. Redirection Mode Capability Object
The Redirection Mode capability object is used to indicate support
for one or more of the modes listed in the "CDNI Capabilities
Redirection Modes" registry (see Section 6.2).
Property: redirection-modes
Description: List of supported CDNI redirection modes.
Type: List of redirection modes (from the "CDNI Capabilities
Redirection Modes" registry, defined in Section 6.2)
Mandatory-to-Specify: Yes.
5.5.1. Redirection Mode Capability Object Serialization
The following shows an example of Redirection Mode capability object
serialization for a CDN that supports only iterative (i.e., not
recursive) redirection with HTTP and DNS.
{
"capabilities": [
{
"capability-type": "FCI.RedirectionMode",
"capability-value": {
"redirection-modes": [
"DNS-I",
"HTTP-I"
]
}
"footprints": [
<Footprint objects>
]
}
]
}
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5.6. CDNI Logging Capability Object
The CDNI Logging capability object is used to indicate support for
CDNI Logging record-types, as well as CDNI Logging fields that are
marked as optional for the specified record-types [RFC7937].
Property: record-type
Description: Supported CDNI Logging record-type.
Type: String corresponding to an entry from the "CDNI Logging
record-types" registry [RFC7937]
Mandatory-to-Specify: Yes.
Property: fields
Description: List of supported CDNI Logging fields that are
optional for the specified record-type.
Type: List of strings corresponding to entries from the "CDNI
Logging Field Names" registry [RFC7937]
Mandatory-to-Specify: No. Default is that all optional fields
are supported. Omission of this field MUST be interpreted as
"all optional fields are supported". An empty list MUST be
interpreted as "no optional fields are supported". Otherwise,
if a list of fields is provided, the fields in that list MUST
be interpreted as "the only optional fields that are
supported".
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5.6.1. CDNI Logging Capability Object Serialization
The following shows an example of CDNI Logging capability object
serialization for a CDN that supports the optional Content
Collection ID CDNI Logging field (but not the optional Session ID
CDNI Logging field) for the "cdni_http_request_v1" record-type.
{
"capabilities": [
{
"capability-type": "FCI.Logging",
"capability-value": {
"record-type": "cdni_http_request_v1",
"fields": ["s-ccid"]
},
"footprints": [
<Footprint objects>
]
}
]
}
The next example shows the CDNI Logging capability object
serialization for a CDN that supports all optional fields for the
"cdni_http_request_v1" record-type.
{
"capabilities": [
{
"capability-type": "FCI.Logging",
"capability-value": {
"record-type": "cdni_http_request_v1"
},
"footprints": [
<Footprint objects>
]
}
]
}
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The final example shows the CDNI Logging capability object
serialization for a CDN that supports none of the optional fields for
the "cdni_http_request_v1" record-type.
{
"capabilities": [
{
"capability-type": "FCI.Logging",
"capability-value": {
"record-type": "cdni_http_request_v1",
"fields": []
},
"footprints": [
<Footprint objects>
]
}
]
}
5.7. CDNI Metadata Capability Object
The CDNI Metadata capability object is used to indicate support for
CDNI GenericMetadata types [RFC8006].
Property: metadata
Description: List of supported CDNI GenericMetadata types.
Type: List of strings corresponding to entries from the "CDNI
Payload Types" registry [RFC7736] that correspond to CDNI
GenericMetadata objects
Mandatory-to-Specify: Yes. An empty list MUST be interpreted
as "no GenericMetadata types are supported", i.e., "only
structural metadata and simple types are supported"; otherwise,
the list must be interpreted as containing "the only
GenericMetadata types that are supported" (in addition to
structural metadata and simple types) [RFC8006].
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5.7.1. CDNI Metadata Capability Object Serialization
The following shows an example of CDNI Metadata capability object
serialization for a CDN that supports only the SourceMetadata
GenericMetadata type (i.e., it can acquire and deliver content but
cannot enforce any security policies, e.g., time, location, or
protocol Access Control Lists (ACLs)).
{
"capabilities": [
{
"capability-type": "FCI.Metadata",
"capability-value": {
"metadata": ["MI.SourceMetadata"]
},
"footprints": [
<Footprint objects>
]
}
]
}
The next example shows the CDNI Metadata capability object
serialization for a CDN that supports only structural metadata (i.e.,
it can parse metadata as a transit CDN but cannot enforce security
policies or deliver content).
{
"capabilities": [
{
"capability-type": "FCI.Metadata",
"capability-value": {
"metadata": []
},
"footprints": [
<Footprint objects>
]
}
]
}
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6. IANA Considerations
6.1. CDNI Payload Types
This document registers the following CDNI Payload Types under the
IANA "CDNI Payload Types" registry:
+-------------------------+---------------+
| Payload Type | Specification |
+-------------------------+---------------+
| FCI.DeliveryProtocol | RFC 8008 |
| FCI.AcquisitionProtocol | RFC 8008 |
| FCI.RedirectionMode | RFC 8008 |
| FCI.Logging | RFC 8008 |
| FCI.Metadata | RFC 8008 |
+-------------------------+---------------+
6.1.1. CDNI FCI DeliveryProtocol Payload Type
Purpose: The purpose of this Payload Type is to distinguish FCI
advertisement objects for supported delivery protocols
Interface: FCI
Encoding: see Section 5.3
6.1.2. CDNI FCI AcquisitionProtocol Payload Type
Purpose: The purpose of this Payload Type is to distinguish FCI
advertisement objects for supported acquisition protocols
Interface: FCI
Encoding: see Section 5.4
6.1.3. CDNI FCI RedirectionMode Payload Type
Purpose: The purpose of this Payload Type is to distinguish FCI
advertisement objects for supported redirection modes
Interface: FCI
Encoding: see Section 5.5
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6.1.4. CDNI FCI Logging Payload Type
Purpose: The purpose of this Payload Type is to distinguish FCI
advertisement objects for supported CDNI Logging record-types and
optional CDNI Logging field names
Interface: FCI
Encoding: see Section 5.6
6.1.5. CDNI FCI Metadata Payload Type
Purpose: The purpose of this Payload Type is to distinguish FCI
advertisement objects for supported CDNI GenericMetadata types
Interface: FCI
Encoding: see Section 5.7
6.2. "CDNI Capabilities Redirection Modes" Registry
IANA has created a new "CDNI Capabilities Redirection Modes" registry
in the "Content Delivery Network Interconnection (CDNI) Parameters"
registry. The "CDNI Capabilities Redirection Modes" namespace
defines the valid redirection modes that can be advertised as
supported by a CDN. Additions to the "CDNI Capabilities Redirection
Modes" namespace conform to the IETF Review policy as defined in
[RFC5226].
The following table defines the initial redirection modes:
+------------------+----------------------------------+----------+
| Redirection Mode | Description | RFC |
+------------------+----------------------------------+----------+
| DNS-I | Iterative DNS-based Redirection | RFC 8008 |
| DNS-R | Recursive DNS-based Redirection | RFC 8008 |
| HTTP-I | Iterative HTTP-based Redirection | RFC 8008 |
| HTTP-R | Recursive HTTP-based Redirection | RFC 8008 |
+------------------+----------------------------------+----------+
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7. Security Considerations
This specification describes the semantics for capabilities and
footprint advertisement objects across interconnected CDNs. It does
not, however, specify a concrete protocol for transporting those
objects. Specific security mechanisms can only be selected for
concrete protocols that instantiate these semantics. This document
does, however, place some high-level security constraints on such
protocols.
All protocols that implement these capabilities and footprint
advertisement objects are REQUIRED to provide integrity and
authentication services. Without authentication and integrity, an
attacker could trivially deny service by forging a footprint
advertisement from a dCDN that claims the network has no footprint or
capability. This would prevent the uCDN from delegating any requests
to the dCDN. Since a preexisting relationship between all dCDNs and
uCDNs is assumed by CDNI, the exchange of any necessary credentials
could be conducted before the FCI is brought online. The
authorization decision to accept advertisements would also follow
this preexisting relationship and any contractual obligations that it
stipulates.
All protocols that implement these capabilities and footprint
advertisement objects are REQUIRED to provide confidentiality
services. Some dCDNs are willing to share information about their
footprints or capabilities with a uCDN but not with other, competing
dCDNs. For example, if a dCDN incurs an outage that reduces
footprint coverage temporarily, that event could be information the
dCDN would want to share confidentially with the uCDN.
As specified in this document, the security requirements of the FCI
could be met by transport-layer security mechanisms coupled with
domain certificates as credentials (e.g., TLS transport for HTTP as
per [RFC2818] and [RFC7230], with usage guidance from [RFC7525])
between CDNs. There is no apparent need for further object-level
security in this framework, as the trust relationships it defines are
bilateral relationships between uCDNs and dCDNs rather than
transitive relationships.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159,
March 2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
"Framework for Content Distribution Network
Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
August 2014, <http://www.rfc-editor.org/info/rfc7336>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015,
<http://www.rfc-editor.org/info/rfc7493>.
[RFC7937] Le Faucheur, F., Ed., Bertrand, G., Ed., Oprescu, I., Ed.,
and R. Peterkofsky, "Content Distribution Network
Interconnection (CDNI) Logging Interface", RFC 7937,
DOI 10.17487/RFC7937, August 2016,
<http://www.rfc-editor.org/info/rfc7937>.
[RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
"Content Delivery Network Interconnection (CDNI)
Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,
<http://www.rfc-editor.org/info/rfc8006>.
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8.2. Informative References
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
[RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", RFC 6707, DOI 10.17487/RFC6707,
September 2012, <http://www.rfc-editor.org/info/rfc6707>.
[RFC6770] Bertrand, G., Ed., Stephan, E., Burbridge, T., Eardley,
P., Ma, K., and G. Watson, "Use Cases for Content Delivery
Network Interconnection", RFC 6770, DOI 10.17487/RFC6770,
November 2012, <http://www.rfc-editor.org/info/rfc6770>.
[RFC7230] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7337] Leung, K., Ed., and Y. Lee, Ed., "Content Distribution
Network Interconnection (CDNI) Requirements", RFC 7337,
DOI 10.17487/RFC7337, August 2014,
<http://www.rfc-editor.org/info/rfc7337>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525,
May 2015, <http://www.rfc-editor.org/info/rfc7525>.
[RFC7736] Ma, K., "Content Delivery Network Interconnection (CDNI)
Media Type Registration", RFC 7736, DOI 10.17487/RFC7736,
December 2015, <http://www.rfc-editor.org/info/rfc7736>.
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Appendix A. Main Use Case to Consider
Focusing on a main use case that contains a simple (yet somewhat
challenging), realistic, and generally imaginable scenario can help
narrow down the requirements for the CDNI FCI. To this end, the
following (simplified) use case can help clarify the semantics of
footprints and capabilities for CDNI. In particular, the intention
of the use case is to clarify what information needs to be exchanged
on the CDNI FCI, what types of information need to be supported in a
mandatory fashion (and which types can be considered optional), and
what types of information need to be updated with respect to a priori
established CDNI contracts.
Use case: A given uCDN has several dCDNs. It selects one dCDN for
delivery protocol A and footprint 1 and another dCDN for delivery
protocol B and footprint 1. The dCDN that serves delivery protocol B
has a further, transitive (level-2) dCDN that serves delivery
protocol B in a subset of footprint 1 where the first-level dCDN
cannot serve delivery protocol B itself. What happens if
capabilities change in the transitive level-2 dCDN that might affect
how the uCDN selects a level-1 dCDN (e.g., in case the level-2 dCDN
cannot serve delivery protocol B anymore)? How will these changes be
conveyed to the uCDN? In particular, what information does the uCDN
need to be able to select a new first-level dCDN, for either all of
footprint 1 or only the subset of footprint 1 that the transitive
level-2 dCDN served on behalf of the first-level dCDN?
Appendix B. Semantics for Footprint Advertisement
Roughly speaking, "footprint" can be defined as a dCDN's "ability and
willingness to serve". However, in addition to simple ability and
willingness to serve, the uCDN could want additional information
before deciding which dCDN to select, e.g., "how well" a given dCDN
can actually serve a given end user request. The dCDN's ability and
willingness to serve SHOULD be distinguished from the subjective
qualitative measurement of how well it can serve a given end user
request. One can imagine that such additional information is
implicitly associated with a given footprint, due to contractual
agreements, Service Level Agreements (SLAs), business relationships,
or past perceptions of dCDN quality. As an alternative, such
additional information could also be explicitly included with the
given footprint.
It is reasonable to assume that a significant part of the actual
footprint advertisement will occur out-of-band, prior to any CDNI FCI
advertisement, with footprints defined in contractual agreements
between participating CDNs. The reason for this assumption is that
any contractual agreement is likely to contain specifics about the
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dCDN coverage (footprint) to which the contractual agreement applies.
In particular, additional information to judge the delivery quality
associated with a given dCDN footprint might be defined in
contractual agreements, outside of the CDNI FCI. Further, one can
assume that dCDN contractual agreements about the delivery quality
associated with a given footprint will probably be based on
high-level aggregated statistics and will not be too detailed.
Given that a large part of the footprint advertisement will be
defined in contractual agreements, the semantics of CDNI footprint
advertisement refer 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 Request Routing interface. Such
information would provide updates on information previously agreed
upon in contracts between the participating CDNs. In other words,
the CDNI FCI is a means for a dCDN to provide changes/updates
regarding a footprint it has previously agreed to serve in a contract
with a uCDN.
Generally speaking, one can imagine two categories of footprints to
be advertised by a dCDN:
o A footprint could be defined based on coverage/reachability, where
"coverage/reachability" refers to a set of prefixes, a geographic
region, or similar boundary. The dCDN claims that it can
cover/reach "end user requests coming from this footprint".
o A footprint could be defined based on resources, where "resources"
refers to Surrogates a dCDN claims to have (e.g., the location of
Surrogates/resources). The dCDN claims that "from this footprint"
it can serve incoming end user requests.
For each of these footprint types, there are capabilities associated
with a given footprint:
o capabilities such as delivery protocol, redirection mode, and
metadata, which are supported in the coverage area for a footprint
that is defined by coverage/reachability, or
o capabilities of resources, such as delivery protocol, redirection
mode, and metadata, which apply to a footprint that is defined by
resources.
Resource footprint types are more specific than coverage/reachability
footprint types, where the actual coverage and reachability are
extrapolated from the resource location (e.g., a netmask applied to a
resource IP address to derive an IP prefix). The specific methods
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for extrapolating coverage/reachability from the resource location
are beyond the scope of this document. In the degenerate case, the
resource address could be specified as a coverage/reachability
footprint type, in which case no extrapolation is necessary.
Resource footprint types could expose the internal structure of a
CDN; this could be undesirable. As such, the resource footprint
types are not considered mandatory to support for CDNI.
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: the
advertisement of different footprint types narrows the dCDN's
candidacy cumulatively.
Independent of the exact type of a footprint, a footprint might also
include the connectivity of a given dCDN to other CDNs that are able
to serve content to users on behalf of that dCDN, to cover cases with
cascaded CDNs. Further, the dCDN needs to be able to express its
footprint to an interested uCDN in a comprehensive form, e.g., as a
data set containing the complete footprint. However, making
incremental updates to express dynamic changes in state is also
desirable.
Appendix C. Semantics for Capabilities Advertisement
In general, the dCDN needs to be able to express its general
capabilities to the uCDN. These general capabilities could indicate
if the dCDN supports a given service -- for instance, HTTP vs. HTTPS
delivery. Furthermore, the dCDN needs to be able to express
particular capabilities for service delivery in a particular
footprint area. For example, the dCDN might in general offer HTTPS
but not in some specific areas, either for maintenance reasons or
because the Surrogates covering this particular area cannot deliver
this type of service. Hence, in certain cases a footprint and
capabilities are tied together and cannot be interpreted
independently of each other. In such cases, i.e., where capabilities
need to be expressed on a per-footprint basis, it could be beneficial
to combine footprint advertisement and capabilities advertisement.
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A high-level and very rough semantic for capabilities is thus the
following: capabilities are types of information that allow a uCDN to
determine if a dCDN is able (and willing) to accept (and properly
handle) a delegated content request. In addition, capabilities are
characterized by the fact that this information can change over time
based on the state of the network or Surrogates.
At first glance, several broad categories of capabilities seem useful
to convey via an advertisement interface; however, advertising
capabilities that change highly dynamically (e.g., real-time delivery
performance metrics, CDN resource load, or other highly dynamically
changing QoS information) are beyond the scope of the CDNI FCI.
First, out of the multitude of possible metrics and capabilities, it
is hard to agree on a subset and the precise metrics to be used.
Second, it seems infeasible to specify such highly dynamically
changing capabilities and the corresponding metrics within a
reasonable time frame.
Useful capabilities refer to information that does not change highly
dynamically and that, in many cases, is absolutely necessary for
deciding on a particular dCDN for a given end user request. For
instance, if an end user request concerns the delivery of a video
file with a certain protocol, the uCDN needs to know if a given dCDN
is capable of supporting this delivery protocol.
Similar to footprint advertisement, it is reasonable to assume that a
significant part of the actual (resource) capabilities advertisement
will also occur out-of-band, prior to any CDNI FCI advertisement,
with capabilities defined in contractual agreements between
participating CDNs. The role of capability advertisement is hence
rather to enable the dCDN to update a uCDN on changes since a
contract has been set up (e.g., in case a new delivery protocol is
suddenly being added to the list of supported delivery protocols of a
given dCDN or in case a certain delivery protocol is suddenly not
being supported anymore due to failures). "Capabilities
advertisement" thus refers to conveying information to a uCDN about
changes/updates to certain capabilities with respect to a given
contract.
Given these semantics, it needs to be decided what exact capabilities
are useful and how these can be expressed. Since the details of CDNI
contracts are not known at the time of this writing (and the CDNI
interface is better off being agnostic to these contracts anyway), it
remains to be seen what capabilities will be used to define
agreements between CDNs in practice. One implication for
standardization could be to initially only specify a very limited set
of mandatory capabilities for advertisement and have, on top of that,
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a flexible data model that allows exchanging additional capabilities
when needed. Still, agreement needs to be reached regarding which
capabilities (if any) will be mandatory among CDNs.
It is not feasible to enumerate all the possible options for the
mandatory capabilities listed above (e.g., all the potential delivery
protocols or metadata options) or anticipate all the future needs for
additional capabilities. FCI object extensibility is necessary to
support future capabilities, as well as a generic protocol for
conveying any capability information (e.g., with common encoding,
error handling, and security mechanisms; further requirements for the
CDNI FCI are listed in [RFC7337]).
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Acknowledgments
Jan Seedorf is 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.
Martin Stiemerling provided initial input to this document and
valuable comments to the ongoing discussions among the authors of
this document. Thanks to Francois Le Faucheur and Scott Wainner for
providing valuable comments and suggestions for the text.
Authors' Addresses
Jan Seedorf
HFT Stuttgart - University of Applied Sciences Stuttgart
Schellingstrasse 24
Stuttgart 70174
Germany
Phone: +49-0711-8926-2801
Email: jan.seedorf@hft-stuttgart.de
Jon Peterson
NeuStar
1800 Sutter St. Suite 570
Concord, CA 94520
United States of America
Email: jon.peterson@neustar.biz
Seedorf, et al. Standards Track [Page 30]
RFC 8008 CDNI RR Footprint/Capabilities Semantics December 2016
Stefano Previdi
Cisco Systems
Via Del Serafico 200
Rome 0144
Italy
Email: sprevidi@cisco.com
Ray van Brandenburg
TNO
Anna van Buerenplein 1
The Hague 2595DA
The Netherlands
Phone: +31-88-866-7000
Email: ray.vanbrandenburg@tno.nl
Kevin J. Ma
Ericsson
43 Nagog Park
Acton, MA 01720
United States of America
Phone: +1-978-844-5100
Email: kevin.j.ma@ericsson.com
Seedorf, et al. Standards Track [Page 31]