ALTO WG W. Roome
Internet-Draft S. Randriamasy
Intended status: Standards Track Nokia Bell Labs
Expires: May 7, 2020 Y. Yang
Yale University
J. Zhang
Tongji University
K. Gao
Sichuan University
November 4, 2019
Unified Properties for the ALTO Protocol
draft-ietf-alto-unified-props-new-10
Abstract
This document extends the Application-Layer Traffic Optimization
(ALTO) Protocol [RFC7285] by generalizing the concept of "endpoint
properties" to generic types of entities, and by presenting those
properties as maps, similar to the network and cost maps in
[RFC7285].
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 7, 2020.
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Copyright Notice
Copyright (c) 2019 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Basic Features of the Unified Property Extension . . . . . . 6
2.1. Entity . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Entity Domain . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Entity Property . . . . . . . . . . . . . . . . . . . . . 7
2.4. New information resource and media type: ALTO Property
Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Advanced Features of the Unified Property Extension . . . . . 8
3.1. Entity Identifier and Entity Domain . . . . . . . . . . . 8
3.2. Resource-Specific Entity Domain Name . . . . . . . . . . 8
3.3. Resource-Specific Entity Property . . . . . . . . . . . . 9
3.4. Entity Hierarchy and Property Inheritance . . . . . . . . 9
3.5. Applicable Entity Domains and Properties in the Property
Map Capabilities . . . . . . . . . . . . . . . . . . . . 10
3.6. Connection between Resource-Specific Entity Domain/Entity
Property Mapping and Information Resources . . . . . . . 10
4. Protocol Specification: Basic Data Type . . . . . . . . . . . 11
4.1. Entity Domain . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1. Entity Domain Type . . . . . . . . . . . . . . . . . 11
4.1.2. Entity Domain Name . . . . . . . . . . . . . . . . . 11
4.1.3. Entity Identifier . . . . . . . . . . . . . . . . . . 12
4.1.4. Hierarchy and Inheritance . . . . . . . . . . . . . . 13
4.2. Entity Property . . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Entity Property Type . . . . . . . . . . . . . . . . 13
4.2.2. Entity Property Name . . . . . . . . . . . . . . . . 14
5. Entity Domain Types . . . . . . . . . . . . . . . . . . . . . 14
5.1. Internet Address Domain Types . . . . . . . . . . . . . . 14
5.1.1. IPv4 Domain . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. IPv6 Domain . . . . . . . . . . . . . . . . . . . . . 15
5.1.3. Hierarchy and Inheritance of Internet Address Domains 15
5.2. PID Domain . . . . . . . . . . . . . . . . . . . . . . . 17
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5.2.1. Entity Domain Type . . . . . . . . . . . . . . . . . 17
5.2.2. Domain-Specific Entity Identifiers . . . . . . . . . 17
5.2.3. Hierarchy and Inheritance . . . . . . . . . . . . . . 17
5.2.4. Relationship To Internet Addresses Domains . . . . . 17
5.3. Internet Address Properties vs. PID Properties . . . . . 17
6. Entity Domains and Property Mappings in Information Resources 18
6.1. Information Resource Export . . . . . . . . . . . . . . . 18
6.1.1. Resource-Specific Entity Domain Export . . . . . . . 18
6.1.2. Entity Property Mapping Export . . . . . . . . . . . 18
6.2. Network Map Resource . . . . . . . . . . . . . . . . . . 19
6.2.1. Resource-Specific Entity Domain . . . . . . . . . . . 19
6.2.2. Entity Property Mapping . . . . . . . . . . . . . . . 19
6.3. Endpoint Property Resource . . . . . . . . . . . . . . . 19
6.3.1. Resource-Specific Entity Domain . . . . . . . . . . . 19
6.3.2. Entity Property Mapping . . . . . . . . . . . . . . . 20
6.4. Property Map Resource . . . . . . . . . . . . . . . . . . 20
7. Property Map . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 20
7.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 20
7.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 20
7.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 20
7.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 21
8. Filtered Property Map . . . . . . . . . . . . . . . . . . . . 22
8.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 22
8.2. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 22
8.3. Accept Input Parameters . . . . . . . . . . . . . . . . . 22
8.4. Capabilities . . . . . . . . . . . . . . . . . . . . . . 23
8.5. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.6. Response . . . . . . . . . . . . . . . . . . . . . . . . 23
9. Impact on Legacy ALTO Servers and ALTO Clients . . . . . . . 25
9.1. Impact on Endpoint Property Service . . . . . . . . . . . 25
9.2. Impact on Resource-Specific Properties . . . . . . . . . 25
9.3. Impact on Other Properties . . . . . . . . . . . . . . . 26
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Network Map . . . . . . . . . . . . . . . . . . . . . . 26
10.2. Property Definitions . . . . . . . . . . . . . . . . . . 26
10.3. Information Resource Directory (IRD) . . . . . . . . . . 27
10.4. Property Map Example . . . . . . . . . . . . . . . . . . 30
10.5. Filtered Property Map Example #1 . . . . . . . . . . . . 30
10.6. Filtered Property Map Example #2 . . . . . . . . . . . . 31
10.7. Filtered Property Map Example #3 . . . . . . . . . . . . 33
10.8. Filtered Property Map Example #4 . . . . . . . . . . . . 34
11. Security Considerations . . . . . . . . . . . . . . . . . . . 35
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
12.1. application/alto-* Media Types . . . . . . . . . . . . . 36
12.2. ALTO Entity Domain Type Registry . . . . . . . . . . . . 37
12.2.1. Consistency Procedure between ALTO Address Type
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Registry and ALTO Entity Domain Type Registry . . . 38
12.2.2. ALTO Entity Domain Type Registration Process . . . . 39
12.3. ALTO Entity Property Type Registry . . . . . . . . . . . 40
12.4. ALTO Resource-Specific Entity Domain Registries . . . . 41
12.4.1. Network Map . . . . . . . . . . . . . . . . . . . . 41
12.4.2. Endpoint Property . . . . . . . . . . . . . . . . . 41
12.5. ALTO Resource Entity Property Mapping Registries . . . . 41
12.5.1. Network Map . . . . . . . . . . . . . . . . . . . . 42
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42
14. Normative References . . . . . . . . . . . . . . . . . . . . 42
Appendix A. Scope of Property Map . . . . . . . . . . . . . . . 43
A.1. Example Property Map . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction
The ALTO protocol [RFC7285] introduces the concept of "properties"
attached to "endpoint addresses", and defines the Endpoint Property
Service (EPS) to allow ALTO clients to retrieve those properties.
While useful, the EPS, as defined in [RFC7285], has at least three
limitations.
First, the EPS allows properties to be associated with only endpoints
which are identified by individual communication addresses like IPv4
and IPv6 addresses. It is reasonable to think that collections of
endpoints, as defined by CIDRs [RFC4632] or PIDs, may also have
properties. Furthermore, recent ALTO use cases show that properties
of network flows [RFC7011] and routing elements [RFC7921] are also
very useful. Since the EPS cannot be extended to those generic
entities, new services, with new request and response messages, would
have to be defined for them.
Second, the EPS only allows endpoints identified by global
communication addresses. However, an endpoint address may be a local
IP address or an anycast IP address which is also not globally
unique. Additionally, a generic entity such as a PID may have an
identifier that is not globally unique. For example, a PID
identifier may be used in several network maps, where in each network
map, this PID identifier points to a different set of addresses.
Third, the EPS is only defined as a POST-mode service. Clients must
request the properties for an explicit set of endpoint addresses. By
contrast, [RFC7285] defines a GET-mode cost map resource which
returns all available costs, so a client can get a full set of costs
once, and then processes costs lookups without querying the ALTO
server. [RFC7285] does not define a similar service for endpoint
properties. At first, a map of endpoint properties might seem
impractical, because it could require enumerating the property value
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for every possible endpoint. However, in practice, it is highly
unlikely that properties will be defined for every endpoint address.
It is much more likely that properties may be defined for only a
subset of endpoint addresses, and the specification of properties
uses an aggregation representation to allow enumeration. This is
particularly true if blocks of endpoint addresses with a common
prefix (e.g., a CIDR) have the same value for a property. Entities
in other domains may very well allow aggregated representation and
hence be enumerable as well.
To address the three limitations, this document specifies a protocol
extension for defining and retrieving ALTO properties:
o The first limitation is adressed by introducing a generic concept
called ALTO Entity, which generalizes an endpoint and may
represent a PID, a network element, a cell in a cellular network,
an abstracted network element as defined in [REF path-vector], or
other physical or logical objects used by ALTO. Each entity is
included in a collection called ALTO Entity Domain. Also, each
Entity Domain includes only one type of entities. Thus, each
entity domain has a type.
o The second limitation is addressed by using resource-specific
entity domains. A resource-specific entity domain contains
entities defined and identified with respect to a given ALTO
information resource. For example, an entity domain containing
PIDs is identified w.r.t. the network map in which these PIDs are
defined. Likewise an entity domain containing local IP addresses
may be defined w.r.t. a local network.
o Finally, the third limitation is addressed by defining two new
types of ALTO information resources: Property Map, detailed in
Section 7 and Filtered Property Map, detailed in Section 8. The
former is a GET-mode resource which returns the property values
for all entities in some entity domains, and is analogous to a
network map or a cost map in [RFC7285]. The latter is a POST-mode
resource which returns the values for a set of properties and
entities requested by the client, and is analogous to a filtered
network map or a filtered cost map.
This approach is extensible, because new entity domain types can be
defined without revising the protocol specification defined in this
document. In the same way, new cost metrics and new endpoint
properties can be defined without revising the protocol specification
defined in [RFC7285].
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This document subsumes the Endpoint Property Service defined in
[RFC7285], although that service may be retained for legacy clients
(see Section 9).
2. Basic Features of the Unified Property Extension
The purpose of this extension is to convey properties on objects that
extend ALTO Endpoints and are called ALTO Entities, entities for
short. This section introduces the basic features involved in ALTO
Entity Property Maps.
2.1. Entity
The concept of ALTO Entity generalizes the concept of an ALTO
Endpoint defined in Section 2.1 of [RFC7285]. An entity is an object
that can be an endpoint and is identified by its network address, but
can also be an object that has a defined mapping to a set of one or
more network addresses or is even not related to any network address.
Examples of eligible entities are:
o a PID, defined in [RFC7285], that has a provider defined human-
readable abstract identifier defined by an ALTO network map, which
maps a PID to a set of ipv4 and ipv6 addresses;
o an autonomous system (AS), that has an AS number (ASN) as its
identifier and maps to a set of ipv4 and ipv6 addresses;
o a region representing a country, that is identified by its country
code defined by ISO 3166 and maps to a set of cellular addresses;
o a TCP/IP network flow, that has a server defined identifier
consisting of the defining TCP/IP 5-Tuple, which is an example
that all endpoints are entities while not all entities are
endpoints;
o a routing element, that is specified in [RFC7921] and includes
routing capability information;
o an abstract network element, that has a server defined identifier
and represents a network node, link or their aggregation.
2.2. Entity Domain
An entity domain defines a set of entities of same type. This type
is also called the type of the entity domain. Thus, an entity domain
type defines the type semantics and the identifier format of its
entities. An entity domain also has a name. Very often the name and
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type of an entity domain are the same. Example of such entity
domains are: "ipv4", "pid", which are defined in Section 5.1 and
Section 5.2.
Using entity domains, the ALTO property map capabilities indicate on
which entity domains an ALTO client can query properties.
2.3. Entity Property
An entity property defines a property of an entity. It is similar to
the endpoint property defined by Section 7.1 of [RFC7285]. It can be
network-aware but can also convey network-agnostic information such
as geographical location.
For example:
o an entity in the "ipv4" domain may have a property whose value is
an Autonomous System (AS) number indicating the AS that owns this
IPv4 address,
o an entity in the "pid" domain may have a property that indicates
the central geographical location of endpoints it includes.
It should be noted that some objects may be both entities and
properties. For example, a PID may be both a property of an "ipv4"
entity and an entity on which a Client may query properties such as
geographical location.
2.4. New information resource and media type: ALTO Property Map
The Unified Property extension introduces a new ALTO information
resource named Property Map. An ALTO property map provides a set of
properties on a set of entities. These entities may be of different
types. For example, an ALTO property map may define the ASN property
for both "ipv4" and "ipv6" type of entities.
The present extension also introduces a new media type.
This document uses the same definition of the information resource as
defined by [RFC7285]. Each information resource usually has a JSON
format representation following a specific schema defined by its
media type. In the present case, an ALTO property map resource is
represented by a JSON object of type InfoResourcePropertyMap and
defined by the media type "application/alto-propmap+json".
A Property Map can be queried as a GET-mode resource, thus conveying
values of all properties on all entities indicated in its
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capabilities. It can also be queried as a POST-mode resource, thus
conveying a selection of properties on a selection of entities.
3. Advanced Features of the Unified Property Extension
3.1. Entity Identifier and Entity Domain
In [RFC7285], an endpoint has an identifier explicitly associated to
the "ipv4" or "ipv6" address domain. Examples are "ipv4:192.0.2.14"
and "ipv6:2001:db8::12". In this extension, an entity domain
characterizes the type semantics and identifier format of its
entities and the identifier of an entity is explicitly associated to
its entity domain. For instance: an entity that is an endpoint with
an IPv4 address will have an identifier associated with domain
"ipv4", like "ipv4:192.0.2.14"; an entity which is a PID will have an
identifier associated with domain "pid", like "pid:mypid10".
In this document, an entity must be owned by exactly one entity
domain. And an entity identifier must point to exactly one entity.
If two entities in two different entity domains refer to the same
physical or logical object, they are treated as different entities,
as it is the case for an endpoint having an IPv4 and IPv6 address.
3.2. Resource-Specific Entity Domain Name
Some entities are defined and identified in a unique and global way.
This is the case for instance for entities that are endpoints
identified by a routable IPv4 or IPv6 address. The entity domain for
such entities can be globally defined and named "ipv4" or "ipv6".
Those entity domains are also called resource-agnostic entity domains
in this document, as they are not associated to any specific ALTO
information resources.
Some other entities and entity types are only defined relatively to a
given information resource. This is the case for entities of domain
"pid", that can only be understood with respect to the network map
where they are defined. For example: a PID named "mypid10" may be
defined by a set S1 of IP adresses, in an information resource of
type Network Map and named "netmap1". Another Network Map "netmap2"
may use the same name "mypid10" and define it with another set S2 of
IP addresses. The identifier "pid:mypid10" may thus point to
different objects because the information on the originating
information resource is lost. The reason is that "pid" denotes an
entity domain type rather than an unambiguous identifier.
To solve this ambiguity, the present extension introduces the concept
of resources-specific entity domain. This concept applies to domains
where entities are defined relatively to a given information
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resource. It can also apply to domains of entities that are defined
locally, such as local networks of objects identified with a local
IPv4 address.
In such cases, an entity domain name is explicitly associated with an
identifier of the information resource where these entities are
defined. Using a resource-specific entity domain name, an ALTO
Property Map may unambiguously indicate entity domains of the same
type, on which entity properties may be queried. Example resource-
specific entity domain names may look like: "netmap1.pid" or
"netmap2.pid". This allows to identify two distinct PID entities
such as "netmap1.pid:mypid10" or "netmap1.pid:mypid10". Resource-
specific entity domain name will be specified in Section 4.1.2.
3.3. Resource-Specific Entity Property
An entity may have properties of same type, whose values are
associated to different information resources. For instance, entity
"192.0.2.34" defined in the "ipv4" domain may have two "pid"
properties defined in two different network maps "netmap1" and
"netmap2". These properties will likely have different values in
"netmap1" and "netmap2". To distinguish between them, this document
uses the same approach proposed as in Section 10.8.1 of [RFC7285],
which is called "Resource-Specific Entity Property". When a property
value depends on a given information resource, the identifier of the
property must be explicitly associated with the information resource
that defines it.
For example, the "pid" property queried on entity "ipv4:192.0.2.34"
and defined in "netmap1" and "netmap2" respectively, may be named
"netmap1.pid" and "netmap2.pid". This allows a Client to get a
property of the same type but defined in different information
resources in a single query. Specifications are provided in
Section 4.2.
3.4. Entity Hierarchy and Property Inheritance
Enumerating all individual entities is inefficient. Some types of
entities have a hierarchy format, for example CIDRs, which stand for
sets of individual entities. A property P may not be defined for a
specific entity E, but P may be defined for a set of entities
containing E. In which case, E inherits the value of P. For entity
domains organized in a hierarchy, this can significantly reduce the
size of Property Maps and Client query payload. To reduce the size
of the property map representation, this document introduces, when
applicable, an approach called "Property Inheritance". Individual
entities can inherit property values from their upper hierarchical
levels. This will be specified in Section 4.1.4.
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3.5. Applicable Entity Domains and Properties in the Property Map
Capabilities
This section explains how the IRD capabilities of a Property Map
unambiguously expose what type of properties on what entity domains a
Client can query. A field called "mapping" enumerates the entity
domains supported by the Property Map; For each entity domain, a list
of applicable properties is provided. An example can be found in
Section 10.3. Using resource-agnostic or resource-specific entity
domains and properties allows to formulate compact an unambiguous
entity property queries relating to one or more information
resources, in particular:
o avoid a Client to query a property on entity domains on which P is
not defined,
o query for en entity E property values defined in different
information resources,
o query a property P on entities E defined in different information
resources.
Specifications will be provided in Section 7.4.
3.6. Connection between Resource-Specific Entity Domain/Entity Property
Mapping and Information Resources
Although the IRD capabilities of a Property Map can expose the
supported mappings in this property map, it may still not be clear to
a Client what a resource-specific entity domain is, and what an
applicable resource-specific entity property means, as those concepts
are not defined in other ALTO information resources. For example, a
Client should understand that:
o a local IPv4 entity domain "netmap1.ipv4" includes the IPv4
addresses appearing in the "ipv4" field of the endpoint address
group of each PID in the network map "netmap1";
o a "netmap1.pid" property of an IPv4 entity "ipv4:192.0.1.1"
indicates the PID defined by the network map "netmap1" and
including the IPv4 address "ipv4:192.0.1.1" in its endpoint
address group.
To help the client understanding these connections, this document
requests two new IANA registries for each information resource to
define the connection to each supported resource-specific entity
domain and entity property mapping respectively. Such a connection
is called "Information Resource Export", to explain what is an
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resource-specific entity domain or an entity property mapping
exported by an information resource. Examples of "Information
Resource Exports" of existing ALTO information resources are provided
in Section 6. Specifications are provided in Section 6.1. The
details of these new IANA registries are provided in Section 12.4 and
Section 12.5.
4. Protocol Specification: Basic Data Type
4.1. Entity Domain
4.1.1. Entity Domain Type
An entity domain has a type, which is defined by a string that MUST
be no more than 64 characters, and MUST NOT contain characters other
than US-ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A,
and U+0061-U+007A), hyphen ("-", U+002D), and low line ("_", U+005F).
For example, the strings "ipv4", "ipv6", and "pid" are valid entity
domain types.
The type EntityDomainType is used in this document to denote a JSON
string confirming to the preceding requirement.
An entity domain type defines the semantics of a type of entity
domains. Each entity domain type MUST be registered with the IANA.
The format of the entity identifiers (see Section 4.1.3) in that type
of entity domains, as well as any hierarchical or inheritance rules
(see Section 4.1.4) for those entities, MUST be specified at the same
time.
4.1.2. Entity Domain Name
Each entity domain is identified by an entity domain name, a string
of the following format:
EntityDomainName ::= [ [ ResourceID ] '.' ] EntityDomainType
This document distinguish three types of entity domains: resource-
specific entity domains, self-defined entity domain and resource-
agnostic entity domains. Their entity domain names are derived as
follows.
Each ALTO information resource MAY define a resource-specific entity
domain (which could be empty) in a given entity domain type. A
resource-specific entity domain is identified by an entity domain
name derived as follows. It MUST start with a resource ID using the
ResourceID type defined in [RFC7285], followed by the "." separator
(U+002E), followed by an EntityDomainType typed string. For example,
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if an ALTO server provides two network maps "netmap-1" and "netmap-
2", they can define two different "pid" domains identified by
"netmap-1.pid" and "netmap-2.pid" respectively. To be simplified, in
the scope of a specific information resource, the resource-specific
entity domain defined by itself can be identified by the "."
EntityDomainTyep without the ResourceID.
When the associated information resource of a resource-specific
entity domain is the current information resource itself, this
resource-specific entity domain is a self-defined entity domain, and
its ResourceID SHOULD be ignored from its entity domain name.
Given a set of ALTO information resources, there MAY be a resource-
agnostic entity domain in a given entity domain type amongst them. A
resource-agnostic entity domain is simply identified by its entity
domain type. For example, given two network maps "net-map-1" and
"net-map-2", "ipv4" and "ipv6" identify two resource-agnostic
Internet address entity domains (see Section 5.1) between them.
Note that the "." separator is not allowed in EntityDomainType and
hence there is no ambiguity on whether an entity domain name refers
to a global entity domain or a resource-specific entity domain.
4.1.3. Entity Identifier
Entities in an entity domain are identified by entity identifiers
(EntityID) of the following format:
EntityID ::= EntityDomainName ':' DomainTypeSpecificEntityID
Examples from the Internet address entity domains include individual
IP addresses such as "net1.ipv4:192.0.2.14" and
"net1.ipv6:2001:db8::12", as well as address blocks such as
"net1.ipv4:192.0.2.0/26" and "net1.ipv6:2001:db8::1/48".
The format of the second part of an entity identifier depends on the
entity domain type, and MUST be specified when registering a new
entity domain type. Identifiers MAY be hierarchical, and properties
MAY be inherited based on that hierarchy. Again, the rules defining
any hierarchy or inheritance MUST be defined when the entity domain
type is registered.
The type EntityID is used in this document to denote a JSON string
representing an entity identifier in this format.
Note that two entity identifiers with different textual
representations may refer to the same entity, for a given entity
domain. For example, the strings "net1.ipv6:2001:db8::1" and
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"net1.ipv6:2001:db8:0:0:0:0:0:1" refer to the same entity in the
"ipv6" entity domain.
4.1.4. Hierarchy and Inheritance
To make the representation efficient, some types of entity domains
MAY allow the ALTO client/server to use a hierarchical format entity
identifier to represent a block of individual entities. e.g., In an
IPv4 domain "net1.ipv4", a cidr "net1.ipv4:192.0.2.0/26" represents
64 individual IPv4 entities. In this case, the corresponding
property inheritance rule MUST be defined for the entity domain type.
The hierarchy and inheritance rule MUST have no ambiguity.
4.2. Entity Property
Each entity property has a type to indicate the encoding and the
semantics of the value of this entity property, and has a name to be
identified. One entity MAY have multiple properties in the same
type.
4.2.1. Entity Property Type
The type EntityPropertyType is used in this document to indicate a
string denoting an entity property type. The string MUST be no more
than 32 characters, and it MUST NOT contain characters other than US-
ASCII alphanumeric characters (U+0030-U+0039, U+0041-U+005A, and
U+0061-U+007A), the hyphen ("-", U+002D), the colon (":", U+003A), or
the low line ('_', U+005F).
Each entity property type MUST be registered with the IANA. The
intended semantics of the entity property type MUST be specified at
the same time.
To distinguish with the endpoint property type, the entity property
type has the following features.
o Some entity property types may be applicable to entities in only
particular types of entity domains, not all. For example, the
"pid" property is not applicable to entities in a "pid" typed
entity domain, but is applicable to entities in the "ipv4" or
"ipv6" domains.
o The intended semantics of the value of an entity property may also
depend on the entity domain type of this entity. For example,
suppose that the "geo-location" property is defined as the
coordinates of a point, encoded as (say) "latitude longitude
[altitude]." When applied to an entity that represents a specific
host computer, identified by an address in the "ipv4" or "ipv6"
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entity domain, the property defines the host's location. However,
when applied to an entity in a "pid" domain, the property would
indicate the location of the center of all hosts in this "pid"
entity.
4.2.2. Entity Property Name
Each entity property is identified by an entity property name, which
is a string of the following format:
EntityPropertyName ::= [ ResourceID ] '.' EntityPropertyType
Similar to the endpoint property type defined in Section 10.8 of
[RFC7285], each entity property may be defined by either the property
map itself (self-defined) or some other specific information resource
(resource-specific).
The entity property name of a resource-specific entity property
starts with a string of the type ResourceID defined in [RFC7285],
followed by the "." separator (U+002E) and a EntityDomainType typed
string. For example, the "pid" properties of an "ipv4" entity
defined by two different maps "net-map-1" and "net-map-2" are
identified by "net-map-1.pid" and "net-map-2.pid" respectively.
When the associated information resource of the entity property is
the current information resource itself, the ResourceID in the
property name SHOULD be ignored. For example, the ".asn" property of
an "ipv4" entity indicates the AS number of the AS which this IPv4
address is owned by.
5. Entity Domain Types
This document defines three entity domain types. The definition of
each entity domain type below includes the following: (1) entity
domain type name, (2) entity domain-specific entity identifiers, and
(3) hierarchy and inheritance semantics. Since a global entity
domain type defines a single global entity domain, we say entity
domain instead of entity domain type.
5.1. Internet Address Domain Types
The document defines two entity domain types (IPv4 and IPv6) for
Internet addresses. Both types are global entity domain types and
hence define a corresponding global entity domain as well. Since the
two domains use the same hierarchy and inheritance semantics, we
define the semantics together, instead of repeating for each.
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5.1.1. IPv4 Domain
5.1.1.1. Entity Domain Type
ipv4
5.1.1.2. Domain-Specific Entity Identifiers
Individual addresses are strings as specified by the IPv4Addresses
rule of Section 3.2.2 of [RFC3986]; blocks of addresses are prefix-
match strings as specified in Section 3.1 of [RFC4632]. To define
properties, an individual Internet address and the corresponding
full-length prefix are considered aliases for the same entity. Thus
"ipv4:192.0.2.0" and "ipv4:192.0.2.0/32" are equivalent.
5.1.2. IPv6 Domain
5.1.2.1. Entity Domain Type
ipv6
5.1.2.2. Domain-Specific Entity Identifiers
Individual addresses are strings as specified by Section 4 of
[RFC5952]; blocks of addresses are prefix-match strings as specified
in Section 7 of [RFC5952]. To define properties, an individual
Internet address and the corresponding 128-bit prefix are considered
aliases for the same entity. That is, "ipv6:2001:db8::1" and
"ipv6:2001:db8::1/128" are equivalent, and have the same set of
properties.
5.1.3. Hierarchy and Inheritance of Internet Address Domains
Both Internet address domains allow property values to be inherited.
Specifically, if a property P is not defined for a specific Internet
address I, but P is defined for some block C which prefix-matches I,
then the address I inherits the value of P defined for block C. If
more than one such block defines a value for P, I inherits the value
of P in the block with the longest prefix. It is important to notice
that this longest prefix rule will ensure no multiple inheritances,
and hence no ambiguity.
Address blocks can also inherit properties: if a property P is not
defined for a block C, but is defined for some block C' which covers
all IP addresses in C, and C' has a shorter mask than C, then block C
inherits the property from C'. If there are several such blocks C',
C inherits from the block with the longest prefix.
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As an example, suppose that a server defines a property P for the
following entities:
ipv4:192.0.2.0/26: P=v1
ipv4:192.0.2.0/28: P=v2
ipv4:192.0.2.0/30: P=v3
ipv4:192.0.2.0: P=v4
Figure 1: Defined Property Values.
Then the following entities have the indicated values:
ipv4:192.0.2.0: P=v4
ipv4:192.0.2.1: P=v3
ipv4:192.0.2.16: P=v1
ipv4:192.0.2.32: P=v1
ipv4:192.0.2.64: (not defined)
ipv4:192.0.2.0/32: P=v4
ipv4:192.0.2.0/31: P=v3
ipv4:192.0.2.0/29: P=v2
ipv4:192.0.2.0/27: P=v1
ipv4:192.0.2.0/25: (not defined)
Figure 2: Inherited Property Values.
An ALTO server MAY explicitly indicate a property as not having a
value for a particular entity. That is, a server MAY say that
property P of entity X is "defined to have no value", instead of
"undefined". To indicate "no value", a server MAY perform different
behaviours:
o If that entity would inherit a value for that property, then the
ALTO server MUST return a "null" value for that property. In this
case, the ALTO client MUST recognize a "null" value as "no value"
and "do not apply the inheritance rules for this property."
o If the entity would not inherit a value, then the ALTO server MAY
return "null" or just omit the property. In this case, the ALTO
client cannot infer the value for this property of this entity
from the Inheritance rules. So the client MUST interpret that
this property has no value.
If the ALTO server does not define any properties for an entity, then
the server MAY omit that entity from the response.
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5.2. PID Domain
The PID domain associates property values with the PIDs in a network
map. Accordingly, this entity domain always depends on a network
map.
5.2.1. Entity Domain Type
pid
5.2.2. Domain-Specific Entity Identifiers
The entity identifiers are the PID names of the associated network
map.
5.2.3. Hierarchy and Inheritance
There is no hierarchy or inheritance for properties associated with
PIDs.
5.2.4. Relationship To Internet Addresses Domains
The PID domain and the Internet address domains are completely
independent; the properties associated with a PID have no relation to
the properties associated with the prefixes or endpoint addresses in
that PID. An ALTO server MAY choose to assign some or all properties
of a PID to the prefixes in that PID.
For example, suppose "PID1" consists of the prefix
"ipv4:192.0.2.0/24", and has the property "P" with value "v1". The
Internet address entities "ipv4:192.0.2.0" and "ipv4:192.0.2.0/24",
in the IPv4 domain MAY have a value for the property "P", and if they
do, it is not necessarily "v1".
5.3. Internet Address Properties vs. PID Properties
Because the Internet address and PID domains are completely separate,
the question may arise as to which entity domain is the best for a
property. In general, the Internet address domains are RECOMMENDED
for properties that are closely related to the Internet address, or
are associated with, and inherited through, blocks of addresses.
The PID domain is RECOMMENDED for properties that arise from the
definition of the PID, rather than from the Internet address prefixes
in that PID.
For example, because Internet addresses are allocated to service
providers by blocks of prefixes, an "ISP" property would be best
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associated with the Internet address domain. On the other hand, a
property that explains why a PID was formed, or how it relates a
provider's network, would best be associated with the PID domain.
6. Entity Domains and Property Mappings in Information Resources
6.1. Information Resource Export
Each information resource MAY export a set of entity domains and
entity property mappings.
6.1.1. Resource-Specific Entity Domain Export
Each type of information resource MAY export several types of entity
domains. For example, a network map resource defines a "pid" domain,
a "ipv4" domain and a "ipv6" domain (which may be empty).
When a new ALTO information resource type is registered, if this type
of information resource can export an existing type of entity domain,
the corresponding document MUST define how to export such type of
entity domain from such type of information resource.
When a new entity domain type is defined, if an existing type of
information resource can export an entity domain in this entity
domain type, the corresponding document MUST define how to export
such type of entity domain from such type of information resource.
6.1.2. Entity Property Mapping Export
For each entity domain which could be exported by an information
resource, this information resource MAY also export some mapping from
this entity domain to some entity property. For example, a network
map resource can map an "ipv4" entity to its "pid" property.
When a new ALTO information resource type is registered, if this type
of information resource can export an entity domain in an existing
entity domain type, and map entities in this entity domain to an
existing type of entity property, the corresponding document MUST
define how to export such type of an entity property.
When a new ALTO entity domain type or a new entity property type is
defined, if an existing type of resource can export an entity domain
in this entity domain type, and map entities in this entity domain to
this type of entity property, the corresponding document MUST define
how to export such type of an entity property.
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6.2. Network Map Resource
The ALTO network map resource defined by the media type "application/
alto-networkmap+json" exports the following types of entity domains
and entity property mappings.
6.2.1. Resource-Specific Entity Domain
An ALTO network map resource defines a "pid" domain, an "ipv4" domain
and an "ipv6" domain by follows:
o The defined "pid" domain includes all PIDs in keys of the
"network-map" object.
o The defined "ipv4" domain includes all IPv4 addresses appearing in
the "ipv4" field of the endpoint address group of each PID.
o The defined "ipv6" domain includes all IPv6 addresses appearing in
the "ipv6" field of the endpoint address group of each PID.
6.2.2. Entity Property Mapping
For each of the preceding entity domains, an ALTO network map
resource provides the properties mapping as follows:
ipv4 -> pid: An "networkmap" typed resource can map an "ipv4" entity
to a "pid" property whose value is a PID defined by this
"networkmap" resource and including the IPv4 address of this
entity.
ipv6 -> pid: An "networkmap" typed resource can map an "ipv6" entity
to a "pid" property whose value is a PID defined by this
"networkmap" resource and including the IPv6 address of this
entity.
6.3. Endpoint Property Resource
The ALTO endpoint property resource defined by the media type
"application/alto-endpointprop+json" exports the following types of
entity domains and entity property mappings.
6.3.1. Resource-Specific Entity Domain
An ALTO endpoint property resource defined an "ipv4" domain and an
"ipv6" domain by follows:
o The defined "ipv4" domain includes all IPv4 addresses appearing in
keys of the "endpoint-properties" object.
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o The defined "ipv6" domain includes all IPv6 addresses appearing in
keys of the "endpoint-properties" object.
6.3.2. Entity Property Mapping
For each of the preceding entity domains, an ALTO endpoint property
resource exports the properties mapping from it to each supported
global endpoint property. The property value is the corresponding
global endpoint property value in the "endpiont-properties" object.
6.4. Property Map Resource
To avoid the nested reference and its potential complexity, this
document does not specify the export rule of resource-specific entity
domain and entity property mapping for the ALTO property map resource
defined by the media type "application/alto-propmap+json" (see
Section 7.1).
7. Property Map
A property map returns the properties defined for all entities in one
or more domains, e.g., the "location" property of entities in "pid"
domain, and the "ASN" property of entities in "ipv4" and "ipv6"
domains.
Section 10.4 gives an example of a property map request and its
response.
7.1. Media Type
The media type of a property map is "application/alto-propmap+json".
7.2. HTTP Method
The property map is requested using the HTTP GET method.
7.3. Accept Input Parameters
None.
7.4. Capabilities
The capabilities are defined by an object of type
PropertyMapCapabilities:
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object {
EntityPropertyMapping mappings;
} PropertyMapCapabilities;
object-map {
EntityDomainName -> EntityPropertyName<1..*>;
} EntityPropertyMapping
with fields:
mappings: A JSON object whose keys are names of entity domains and
values are the supported entity properties of the corresponding
entity domains.
7.5. Uses
The "uses" field of a property map resource in an IRD entry specifies
dependent resources of this property map. It is an array of the
resource ID(s) of the resource(s).
7.6. Response
If the entity domains in this property map depend on other resources,
the "dependent-vtags" field in the "meta" field of the response MUST
be an array that includes the version tags of those resources, and
the order MUST be consistent with the "uses" field of this property
map resource. The data component of a property map response is named
"property-map", which is a JSON object of type PropertyMapData,
where:
object {
PropertyMapData property-map;
} InfoResourceProperties : ResponseEntityBase;
object-map {
EntityID -> EntityProps;
} PropertyMapData;
object {
EntityPropertyName -> JSONValue;
} EntityProps;
The ResponseEntityBase type is defined in Section 8.4 of [RFC7285].
Specifically, a PropertyMapData object has one member for each entity
in the property map. The entity's properties are encoded in the
corresponding EntityProps object. EntityProps encodes one name/value
pair for each property, where the property names are encoded as
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strings of type PropertyName. A protocol implementation SHOULD
assume that the property value is either a JSONString or a JSON
"null" value, and fail to parse if it is not, unless the
implementation is using an extension to this document that indicates
when and how property values of other data types are signaled.
For each entity in the property map:
o If the entity is in a resource-specific entity domain, the ALTO
server SHOULD only return self-defined properties and resource-
specific properties which depend on the same resource as the
entity does. The ALTO client SHOULD ignore the resource-specific
property in this entity if their mapping is not registered in the
ALTO Resource Entity Property Transfer Registry of the type of the
corresponding resource.
o If the entity is in a shared entity domain, the ALTO server SHOULD
return self-defined properties and all resource-specific
properties defined for all resource-specific entities which have
the same domain-specific entity identifier as this entity does.
For efficiency, the ALTO server SHOULD omit property values that are
inherited rather than explicitly defined; if a client needs inherited
values, the client SHOULD use the entity domain's inheritance rules
to deduce those values.
8. Filtered Property Map
A filtered property map returns the values of a set of properties for
a set of entities selected by the client.
Section 10.5, Section 10.6, Section 10.7 and Section 10.8 give
examples of filtered property map requests and responses.
8.1. Media Type
The media type of a property map resource is "application/alto-
propmap+json".
8.2. HTTP Method
The filtered property map is requested using the HTTP POST method.
8.3. Accept Input Parameters
The input parameters for a filtered property map request are supplied
in the entity body of the POST request. This document specifies the
input parameters with a data format indicated by the media type
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"application/alto-propmapparams+json", which is a JSON object of type
ReqFilteredPropertyMap:
object {
EntityID entities<1..*>;
EntityPropertyName properties<1..*>;
} ReqFilteredPropertyMap;
with fields:
entities: List of entity identifiers for which the specified
properties are to be returned. The ALTO server MUST interpret
entries appearing multiple times as if they appeared only once.
The domain of each entity MUST be included in the list of entity
domains in this resource's "capabilities" field (see Section 8.4).
properties: List of properties to be returned for each entity. Each
specified property MUST be included in the list of properties in
this resource's "capabilities" field (see Section 8.4). The ALTO
server MUST interpret entries appearing multiple times as if they
appeared only once.
Note that the "entities" and "properties" fields MUST have at
least one entry each.
8.4. Capabilities
The capabilities are defined by an object of type
PropertyMapCapabilities, as defined in Section 7.4.
8.5. Uses
Same to the "uses" field of the Property Map resource (see
Section 7.5).
8.6. Response
The response MUST indicate an error, using ALTO protocol error
handling, as defined in Section 8.5 of [RFC7285], if the request is
invalid.
Specifically, a filtered property map request can be invalid as
follows:
o An entity identifier in "entities" in the request is invalid if:
* The domain of this entity is not defined in the "entity-
domains" capability of this resource in the IRD;
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* The entity identifier is an invalid identifier in the entity
domain.
A valid entity identifier is never an error, even if this filtered
property map resource does not define any properties for it.
If an entity identifier in "entities" in the request is invalid,
the ALTO server MUST return an "E_INVALID_FIELD_VALUE" error
defined in Section 8.5.2 of [RFC7285], and the "value" field of
the error message SHOULD indicate this entity identifier.
o A property name in "properties" in the request is invalid if this
property name is not defined in the "properties" capability of
this resource in the IRD.
It is not an error that a filtered property map resource does not
define a requested property's value for a particular entity. In
this case, the ALTO server MUST omit that property from the
response for that endpoint.
If a property name in "properties" in the request is invalid, the
ALTO server MUST return an "E_INVALID_FIELD_VALUE" error defined
in Section 8.5.2 of [RFC7285]. The "value" field of the error
message SHOULD indicate the property name.
The response to a valid request is the same as for the Property Map
(see Section 7.6), except that:
o If the requested entities include entities in the shared entity
domain, the "dependent-vtags" field in its "meta" field MUST
include version tags of all dependent resources appearing in the
"uses" field.
o If the requested entities only include entities in resource-
specific entity domains, the "dependent-vtags" field in its "meta"
field MUST include version tags of resources which requested
resource-specific entity domains and requested resource-specific
properties are dependent on.
o The response only includes the entities and properties requested
by the client. If an entity in the request is identified by a
hierarchical identifier (e.g., an "ipv4" or "ipv6" address block),
the response MUST cover properties for all identifiers in this
hierarchical identifier.
It is important that the filtered property map response MUST include
all inherited property values for the requested entities and all the
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entities which are able to inherit property values from them. To
achieve this goal, the ALTO server MAY follow three rules:
o If a property for a requested entity is inherited from another
entity not included in the request, the response SHOULD include
this property for the requested entity. For example, A full
property map may skip a property P for an entity A (e.g.,
ipv4:192.0.2.0/31) if P can be derived using inheritance from
another entity B (e.g., ipv4:192.0.2.0/30). A filtered property
map request may include only A but not B. In such a case, the
property P SHOULD be included in the response for A.
o If there are entities covered by a requested entity but having
different values for the requested properties, the response SHOULD
include all those entities and the different property values for
them. For example, considering a request for property P of entity
A (e.g., ipv4:192.0.2.0/31), if P has value v1 for
A1=ipv4:192.0.2.0/32 and v2 for A2=ipv4:192.0.2.1/32, then, the
response SHOULD include A1 and A2.
o If an entity in the response is already covered by some other
entities in the same response, it SHOULD be removed from the
response for compactness. For example, in the previous example,
the entity A=ipv4:192.0.2.0/31 SHOULD be removed because A1 and A2
cover all the addresses in A.
An ALTO client should be aware that the entities in the response MAY
be different from the entities in its request.
9. Impact on Legacy ALTO Servers and ALTO Clients
9.1. Impact on Endpoint Property Service
Since the property map and the filtered property map defined in this
document provide the functionality of the Endpoint Property Service
(EPS) defined in Section 11.4 of [RFC7285], it is RECOMMENDED that
the EPS be deprecated in favor of Property Map and Filtered Property
Map. However, ALTO servers MAY provide an EPS for the benefit of
legacy clients.
9.2. Impact on Resource-Specific Properties
Section 10.8 of [RFC7285] defines two categories of endpoint
properties: "resource-specific" and "global". Resource-specific
property names are prefixed with the ID of the resource they depend
upon, while global property names have no such prefix. The property
map and the filtered property map defined in this document defines
the similar categories for entity properties. The difference is that
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there is no "global" entity properties but the "self-defined" entity
properties as the special case of the "resource-specific" entity
properties instead.
9.3. Impact on Other Properties
In general, there should be little or no impact on other previously
defined properties. The only consideration is that properties can
now be defined on blocks of entity identifiers, rather than just
individual entity identifiers, which might change the semantics of a
property.
10. Examples
10.1. Network Map
The examples in this section use a very simple default network map:
defaultpid: ipv4:0.0.0.0/0 ipv6:::0/0
pid1: ipv4:192.0.2.0/25
pid2: ipv4:192.0.2.0/28 ipv4:192.0.2.16/28
pid3: ipv4:192.0.3.0/28
pid4: ipv4:192.0.3.16/28
Figure 3: Example Default Network Map
And another simple alternative network map:
defaultpid: ipv4:0.0.0.0/0 ipv6:::0/0
pid1: ipv4:192.0.2.0/28 ipv4:192.0.2.16/28
pid2: ipv4:192.0.3.0/28 ipv4:192.0.3.16/28
Figure 4: Example Alternative Network Map
10.2. Property Definitions
Beyond "pid", the examples in this section use four additional
properties for Internet address domains, "ISP", "ASN", "country" and
"state", with the following values:
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ISP ASN country state
ipv4:192.0.2.0/23: BitsRus - us -
ipv4:192.0.2.0/28: - 12345 - NJ
ipv4:192.0.2.16/28: - 12345 - CT
ipv4:192.0.2.1: - - - PA
ipv4:192.0.3.0/28: - 12346 - TX
ipv4:192.0.3.16/28: - 12346 - MN
Figure 5: Example Property Values for Internet Address Domains
And the examples in this section use the property "region" for the
PID domain of the default network map with the following values:
region
pid:defaultpid: -
pid:pid1: us-west
pid:pid2: us-east
pid:pid3: us-south
pid:pid4: us-north
Figure 6: Example Property Values for Default Network Map's PID
Domain
Note that "-" means the value of the property for the entity is
"undefined". So the entity would inherit a value for this property
by the inheritance rule if possible. For example, the value of the
"ISP" property for "ipv4:192.0.2.1" is "BitsRus" because of
"ipv4:192.0.2.0/24". But the "region" property for "pid:defaultpid"
has no value because no entity from which it can inherit.
Similar to the PID domain of the default network map, the examples in
this section use the property "ASN" for the PID domain of the
alternative network map with the following values:
ASN
pid:defaultpid: -
pid:pid1: 12345
pid:pid2: 12346
Figure 7: Example Property Values for Alternative Network Map's PID
Domain
10.3. Information Resource Directory (IRD)
The following IRD defines the relevant resources of the ALTO server.
It provides two property maps, one for the "ISP" and "ASN"
properties, and another for the "country" and "state" properties.
The server could have provided a single property map for all four
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properties, but did not, presumably because the organization that
runs the ALTO server believes any given client is not interested in
all four properties.
The server provides two filtered property maps. The first returns
all four properties, and the second just returns the "pid" property
for the default network map.
The filtered property maps for the "ISP", "ASN", "country" and
"state" properties do not depend on the default network map (it does
not have a "uses" capability), because the definitions of those
properties do not depend on the default network map. The Filtered
Property Map for the "pid" property does have a "uses" capability for
the default network map, because that defines the values of the "pid"
property.
Note that for legacy clients, the ALTO server provides an Endpoint
Property Service for the "pid" property for the default network map.
"meta" : {
...
"default-alto-network-map" : "default-network-map"
},
"resources" : {
"default-network-map" : {
"uri" : "http://alto.example.com/networkmap/default",
"media-type" : "application/alto-networkmap+json"
},
"alt-network-map" : {
"uri" : "http://alto.example.com/networkmap/alt",
"media-type" : "application/alto-networkmap+json"
},
.... property map resources ....
"ia-property-map" : {
"uri" : "http://alto.example.com/propmap/full/inet-ia",
"media-type" : "application/alto-propmap+json",
"uses": [ "default-network-map", "alt-network-map" ],
"capabilities" : {
"mappings": {
"ipv4": [ ".ISP", ".ASN" ],
"ipv6": [ ".ISP", ".ASN" ]
}
}
},
"iacs-property-map" : {
"uri" : "http://alto.example.com/propmap/full/inet-iacs",
"media-type" : "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
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"uses": [ "default-network-map", "alt-network-map" ],
"capabilities" : {
"mappings": {
"ipv4": [ ".ISP", ".ASN", ".country", ".state" ],
"ipv6": [ ".ISP", ".ASN", ".country", ".state" ]
}
}
},
"region-property-map": {
"uri": "http://alto.exmaple.com/propmap/region",
"media-type": "application/alto-propmap+json",
"accepts": "application/alto-propmapparams+json",
"uses" : [ "default-network-map", "alt-network-map" ],
"capabilities": {
"mappings": {
"default-network-map.pid": [ ".region" ],
"alt-network-map.pid": [ ".ASN" ],
}
}
},
"ip-pid-property-map" : {
"uri" : "http://alto.example.com/propmap/lookup/pid",
"media-type" : "application/alto-propmap+json",
"accepts" : "application/alto-propmapparams+json",
"uses" : [ "default-network-map", "alt-network-map" ],
"capabilities" : {
"mappings": {
"ipv4": [ "default-network-map.pid",
"alt-network-map.pid" ],
"ipv6": [ "default-network-map.pid",
"alt-network-map.pid" ]
}
}
},
"legacy-endpoint-property" : {
"uri" : "http://alto.example.com/legacy/eps-pid",
"media-type" : "application/alto-endpointprop+json",
"accepts" : "application/alto-endpointpropparams+json",
"capabilities" : {
"properties" : [ "default-network-map.pid",
"alt-network-map.pid" ]
}
}
}
Figure 8: Example IRD
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10.4. Property Map Example
The following example uses the properties and IRD defined above to
retrieve a Property Map for entities with the "ISP" and "ASN"
properties.
Note that, to be compact, the response does not include the entity
"ipv4:192.0.2.0", because values of all those properties for this
entity are inherited from other entities.
Also note that the entities "ipv4:192.0.2.0/28" and
"ipv4:192.0.2.16/28" are merged into "ipv4:192.0.2.0/27", because
they have the same value of the "ASN" property. The same rule
applies to the entities "ipv4:192.0.3.0/28" and "ipv4:192.0.3.0/28".
Both of "ipv4:192.0.2.0/27" and "ipv4:192.0.3.0/27" omit the value
for the "ISP" property, because it is inherited from
"ipv4:192.0.2.0/23".
GET /propmap/full/inet-ia HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,application/alto-error+json
HTTP/1.1 200 OK
Content-Length: ###
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{"resource-id": "default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
{"resource-id": "alt-network-map",
"tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
]
},
"property-map": {
"ipv4:192.0.2.0/23": {".ISP": "BitsRus"},
"ipv4:192.0.2.0/27": {".ASN": "12345"},
"ipv4:192.0.3.0/27": {".ASN": "12346"}
}
}
10.5. Filtered Property Map Example #1
The following example uses the filtered property map resource to
request the "ISP", "ASN" and "state" properties for several IPv4
addresses.
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Note that the value of "state" for "ipv4:192.0.2.0" is the only
explicitly defined property; the other values are all derived by the
inheritance rules for Internet address entities.
POST /propmap/lookup/inet-iacs HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,application/alto-error+json
Content-Length: ###
Content-Type: application/alto-propmapparams+json
{
"entities" : [ "ipv4:192.0.2.0",
"ipv4:192.0.2.1",
"ipv4:192.0.2.17" ],
"properties" : [ ".ISP", ".ASN", ".state" ]
}
HTTP/1.1 200 OK
Content-Length: ###
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{"resource-id": "default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
{"resource-id": "alt-network-map",
"tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
]
},
"property-map": {
"ipv4:192.0.2.0":
{".ISP": "BitsRus", ".ASN": "12345", ".state": "PA"},
"ipv4:192.0.2.1":
{".ISP": "BitsRus", ".ASN": "12345", ".state": "NJ"},
"ipv4:192.0.2.17":
{".ISP": "BitsRus", ".ASN": "12345", ".state": "CT"}
}
}
10.6. Filtered Property Map Example #2
The following example uses the filtered property map resource to
request the "ASN", "country" and "state" properties for several IPv4
prefixes.
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Note that the property values for both entities "ipv4:192.0.2.0/26"
and "ipv4:192.0.3.0/26" are not explicitly defined. They are
inherited from the entity "ipv4:192.0.2.0/23".
Also note that some entities like "ipv4:192.0.2.0/28" and
"ipv4:192.0.2.16/28" in the response are not listed in the request
explicitly. The response includes them because they are refinements
of the requested entities and have different values for the requested
properties.
The entity "ipv4:192.0.4.0/26" is not included in the response,
because there are neither entities which it is inherited from, nor
entities inherited from it.
POST /propmap/lookup/inet-iacs HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,application/alto-error+json
Content-Length: ###
Content-Type: application/alto-propmapparams+json
{
"entities" : [ "ipv4:192.0.2.0/26",
"ipv4:192.0.3.0/26",
"ipv4:192.0.4.0/26" ],
"properties" : [ ".ASN", ".country", ".state" ]
}
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HTTP/1.1 200 OK
Content-Length: ###
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{"resource-id": "default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
{"resource-id": "alt-network-map",
"tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
]
},
"property-map": {
"ipv4:192.0.2.0/26": {".country": "us"},
"ipv4:192.0.2.0/28": {".ASN": "12345",
".state": "NJ"},
"ipv4:192.0.2.16/28": {".ASN": "12345",
".state": "CT"},
"ipv4:192.0.2.0": {".state": "PA"},
"ipv4:192.0.3.0/26": {".country": "us"},
"ipv4:192.0.3.0/28": {".ASN": "12345",
".state": "TX"},
"ipv4:192.0.3.16/28": {".ASN": "12345",
".state": "MN"}
}
}
10.7. Filtered Property Map Example #3
The following example uses the filtered property map resource to
request the "pid" property for several IPv4 addresses and prefixes.
Note that the entity "ipv4:192.0.3.0/27" is redundant in the
response. Although it can inherit a value of "defaultpid" for the
"pid" property from the entity "ipv4:0.0.0.0/0", none of addresses in
it is in "defaultpid". Because blocks "ipv4:192.0.3.0/28" and
"ipv4:192.0.3.16/28" have already covered all addresses in that
block. So an ALTO server who wants a compact response can omit this
entity.
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POST /propmap/lookup/pid HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,application/alto-error+json
Content-Length: ###
Content-Type: application/alto-propmapparams+json
{
"entities" : [
"ipv4:192.0.2.128",
"ipv4:192.0.3.0/27" ],
"properties" : [ "default-network-map.pid" ]
}
HTTP/1.1 200 OK
Content-Length: ###
Content-Type: application/alto-propmap+json
{
"meta": {
"dependent-vtags": [
{"resource-id": "default-network-map",
"tag": "3ee2cb7e8d63d9fab71b9b34cbf764436315542e"},
{"resource-id": "alt-network-map",
"tag": "c0ce023b8678a7b9ec00324673b98e54656d1f6d"}
]
},
"property-map": {
"ipv4:192.0.2.128": {"default-network-map.pid": "defaultpid"},
"ipv4:192.0.2.0/27": {"default-network-map.pid": "defaultpid"},
"ipv4:192.0.3.0/28": {"default-network-map.pid": "pid3"},
"ipv4:192.0.3.16/28": {"default-network-map.pid": "pid4"}
}
}
10.8. Filtered Property Map Example #4
The following example uses the filtered property map resource to
request the "region" property for several PIDs defined in "default-
network-map". The value of the "region" property for each PID is not
defined by "default-network-map", but the reason why the PID is
defined by the network operator.
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POST /propmap/lookup/region HTTP/1.1
Host: alto.example.com
Accept: application/alto-propmap+json,application/alto-error+json
Content-Length: ###
Content-Type: application/alto-propmapparams+json
{
"entities" : ["default-network-map.pid:pid1",
"default-network-map.pid:pid2"],
"properties" : [ ".region" ]
}
HTTP/1.1 200 OK
Content-Length: ###
Content-Type: application/alto-propmap+json
{
"meta" : {
"dependent-vtags" : [
{"resource-id": "default-network-map",
"tag": "7915dc0290c2705481c491a2b4ffbec482b3cf62"}
]
},
"property-map": {
"default-network-map.pid:pid1": {
".region": "us-west"
},
"default-network-map.pid:pid2": {
".region": "us-east"
}
}
}
11. Security Considerations
Both Property Map and Filtered Property Map defined in this document
fit into the architecture of the ALTO base protocol, and hence the
Security Considerations (Section 15 of [RFC7285]) of the base
protocol fully apply: authenticity and integrity of ALTO information
(i.e., authenticity and integrity of Property Maps), potential
undesirable guidance from authenticated ALTO information (e.g.,
potentially imprecise or even wrong value of a property such as geo-
location), confidentiality of ALTO information (e.g., exposure of a
potentially sensitive entity property such as geo-location), privacy
for ALTO users, and availability of ALTO services should all be
considered.
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A particular fundamental security consideration when an ALTO server
provides a Property Map is to define precisely the policies on who
can access what properties for which entities. Security mechanisms
such as authentication and confidentiality mechanisms then should be
applied to enforce the policy. For example, a policy can be that a
property P can be accessed only by its owner (e.g., the customer who
is allocated a given IP address). Then, the ALTO server will need to
deploy corresponding mechanisms to realize the policy. The policy
may allow non-owners to access a coarse-grained value of the property
P. In such a case, the ALTO server may provide a different URI to
provide the information.
12. IANA Considerations
This document defines additional application/alto-* media types, and
extends the ALTO endpoint property registry.
12.1. application/alto-* Media Types
This document registers two additional ALTO media types, listed in
Table 1.
+--------------+--------------------------+-----------------------+
| Type | Subtype | Specification |
+--------------+--------------------------+-----------------------+
| application | alto-propmap+json | Section 7.1 |
| application | alto-propmapparams+json | Section 8.3 |
+--------------+--------------------------+-----------------------+
Table 1: Additional ALTO Media Types.
Type name: application
Subtype name: This document registers multiple subtypes, as listed
in Table 1.
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: Encoding considerations are identical to
those specified for the "application/json" media type. See
[RFC7159].
Security considerations: Security considerations related to the
generation and consumption of ALTO Protocol messages are discussed
in Section 15 of [RFC7285].
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Interoperability considerations: This document specifies formats of
conforming messages and the interpretation thereof.
Published specification: This document is the specification for
these media types; see Table 1 for the section documenting each
media type.
Applications that use this media type: ALTO servers and ALTO clients
either stand alone or are embedded within other applications.
Additional information:
Magic number(s): n/a
File extension(s): This document uses the mime type to refer to
protocol messages and thus does not require a file extension.
Macintosh file type code(s): n/a
Person & email address to contact for further information: See
Authors' Addresses section.
Intended usage: COMMON
Restrictions on usage: n/a
Author: See Authors' Addresses section.
Change controller: Internet Engineering Task Force
(mailto:iesg@ietf.org).
12.2. ALTO Entity Domain Type Registry
This document requests IANA to create and maintain the "ALTO Entity
Domain Type Registry", listed in Table 2.
+-------------+---------------------------+-------------------------+
| Identifier | Entity Identifier | Hierarchy & Inheritance |
| | Encoding | |
+-------------+---------------------------+-------------------------+
| ipv4 | See Section 5.1.1 | See Section 5.1.3 |
| ipv6 | See Section 5.1.2 | See Section 5.1.3 |
| pid | See Section 5.2 | None |
+-------------+---------------------------+-------------------------+
Table 2: ALTO Entity Domains.
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This registry serves two purposes. First, it ensures uniqueness of
identifiers referring to ALTO entity domains. Second, it states the
requirements for allocated entity domains.
12.2.1. Consistency Procedure between ALTO Address Type Registry and
ALTO Entity Domain Type Registry
One potential issue of introducing the "ALTO Entity Domain Type
Registry" is its relationship with the "ALTO Address Types Registry"
already defined in Section 14.4 of [RFC7285]. In particular, the
entity identifier of a type of an entity domain registered in the
"ALTO Entity Domain Type Registry" MAY match an address type defined
in "ALTO Address Type Registry". It is necessary to precisely define
and guarantee the consistency between "ALTO Address Type Registry"
and "ALTO Entity Domain Registry".
We define that the ALTO Entity Domain Type Registry is consistent
with ALTO Address Type Registry if two conditions are satisfied:
o When an address type is already or able to be registered in the
ALTO Address Type Registry [RFC7285], the same identifier MUST be
used when a corresponding entity domain type is registered in the
ALTO Entity Domain Type Registry.
o If an ALTO entity domain type has the same identifier as an ALTO
address type, their addresses encoding MUST be compatible.
To achieve this consistency, the following items MUST be checked
before registering a new ALTO entity domain type in a future
document:
o Whether the ALTO Address Type Registry contains an address type
that can be used as an entity identifier for the candidate domain
identifier. This has been done for the identifiers "ipv4" and
"ipv6" in Table 2.
o Whether the candidate entity identifier of the type of the entity
domain is able to be an endpoint address, as defined in Sections
2.1 and 2.2 of [RFC7285].
When a new ALTO entity domain type is registered, the consistency
with the ALTO Address Type Registry MUST be ensured by the following
procedure:
o Test: Do corresponding entity identifiers match a known "network"
address type?
* If yes (e.g., cell, MAC or socket addresses):
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+ Test: Is such an address type present in the ALTO Address
Type Registry?
- If yes: Set the new ALTO entity domain type identifier to
be the found ALTO address type identifier.
- If no: Define a new ALTO entity domain type identifier
and use it to register a new address type in the ALTO
Address Type Registry following Section 14.4 of
[RFC7285].
+ Use the new ALTO entity domain type identifier to register a
new ALTO entity domain type in the ALTO Entity Domain Type
Registry following Section 12.2.2 of this document.
* If no (e.g., pid name, ane name or country code): Proceed with
the ALTO Entity Domain Type registration as described in
Section 12.2.2.
12.2.2. ALTO Entity Domain Type Registration Process
New ALTO entity domain types are assigned after IETF Review [RFC5226]
to ensure that proper documentation regarding the new ALTO entity
domain types and their security considerations has been provided.
RFCs defining new entity domain types SHOULD indicate how an entity
in a registered type of domain is encoded as an EntityID, and, if
applicable, the rules defining the entity hierarchy and property
inheritance. Updates and deletions of ALTO entity domains follow the
same procedure.
Registered ALTO entity domain type identifiers MUST conform to the
syntactical requirements specified in Section 4.1.2. Identifiers are
to be recorded and displayed as strings.
Requests to the IANA to add a new value to the registry MUST include
the following information:
o Identifier: The name of the desired ALTO entity domain type.
o Entity Identifier Encoding: The procedure for encoding the
identifier of an entity of the registered type as an EntityID (see
Section 4.1.3). If corresponding entity identifiers of an entity
domain match a known "network" address type, the Entity Identifier
Encoding of this domain identifier MUST include both Address
Encoding and Prefix Encoding of the same identifier registered in
the ALTO Address Type Registry [RFC7285]. For the purpose of
defining properties, an individual entity identifier and the
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corresponding full-length prefix MUST be considered aliases for
the same entity.
o Hierarchy: If the entities form a hierarchy, the procedure for
determining that hierarchy.
o Inheritance: If entities can inherit property values from other
entities, the procedure for determining that inheritance.
o Mapping to ALTO Address Type: A boolean value to indicate if the
entity domain type can be mapped to the ALTO address type with the
same identifier.
o Security Considerations: In some usage scenarios, entity
identifiers carried in ALTO Protocol messages may reveal
information about an ALTO client or an ALTO service provider.
Applications and ALTO service providers using addresses of the
registered type should be made aware of how (or if) the addressing
scheme relates to private information and network proximity.
This specification requests registration of the identifiers "ipv4",
"ipv6" and "pid", as shown in Table 2.
12.3. ALTO Entity Property Type Registry
This document requests IANA to create and maintain the "ALTO Entity
Property Type Registry", listed in Table 3.
To distinguish with the "ALTO Endpoint Property Type Registry", each
entry in this registry is an ALTO entity property type defined in
Section 4.2.1. Thus, registered ALTO entity property type identifier
MUST conform to the syntactical requirements specified in that
section.
The initial registered ALTO entity property types are listed in
Table 3.
+-------------+---------------------------------+
| Identifier | Intended Semantics |
+-------------+---------------------------------+
| pid | See Section 7.1.1 of [RFC7285] |
+-------------+---------------------------------+
Table 3: ALTO Entity Property Types.
Requests to the IANA to add a new value to the registry MUST include
the following information:
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o Identifier: The unique id for the desired ALTO entity property
type. The format MUST be as defined in Section 4.2.1 of this
document. It includes the information of the applied ALTO entity
domain and the property name.
o Intended Semantics: ALTO entity properties carry with them
semantics to guide their usage by ALTO clients. Hence, a document
defining a new type SHOULD provide guidance to both ALTO service
providers and applications utilizing ALTO clients as to how values
of the registered ALTO entity property should be interpreted.
This document requests registration of the identifier "pid", as shown
in Table 3.
12.4. ALTO Resource-Specific Entity Domain Registries
12.4.1. Network Map
Media-type: application/alto-networkmap+json
+---------------------+---------------------+
| Entity Domain Type | Intended Semantics |
+---------------------+---------------------+
| ipv4 | See Section 6.2.1 |
| ipv6 | See Section 6.2.1 |
| pid | See Section 6.2.1 |
+---------------------+---------------------+
Table 4: ALTO Network Map Resource-Specific Entity Domain.
12.4.2. Endpoint Property
Media-type: application/alto-endpointprop+json
+---------------------+---------------------+
| Entity Domain Type | Intended Semantics |
+---------------------+---------------------+
| ipv4 | See Section 6.3.1 |
| ipv6 | See Section 6.3.1 |
+---------------------+---------------------+
Table 5: ALTO Endpoint Property Resource-Specific Entity Domain.
12.5. ALTO Resource Entity Property Mapping Registries
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12.5.1. Network Map
Media-type: application/alto-networkmap+json
+-----------------+-----------------+-------------+-----------------+
| Mapping | Entity Domain | Property | Intended |
| Descriptor | Type | Type | Semantics |
+-----------------+-----------------+-------------+-----------------+
| ipv4 -> pid | ipv4 | pid | See Section |
| | | | 6.2.2 |
| ipv6 -> pid | ipv6 | pid | See Section |
| | | | 6.2.2 |
+-----------------+-----------------+-------------+-----------------+
Table 6: ALTO Network Map Entity Property Mapping.
13. Acknowledgments
The authors would like to thank discussions with Kai Gao, Qiao Xiang,
Shawn Lin, Xin Wang, Danny Perez, and Vijay Gurbani. The authors
thank Dawn Chen (Tongji University), and Shenshen Chen (Tongji/Yale
University) for their contributions to earlier drafts.
14. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
2006, <https://www.rfc-editor.org/info/rfc4632>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
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[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC7921] Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
Nadeau, "An Architecture for the Interface to the Routing
System", RFC 7921, DOI 10.17487/RFC7921, June 2016,
<https://www.rfc-editor.org/info/rfc7921>.
Appendix A. Scope of Property Map
Using entity domains to organize entities, an ALTO property map
resource can be regarded as given sets of properties for given entity
domains. If we ignore the resource-agnostic entity domains, we can
regard an ALTO property map resource as a set of (ri, di) => (ro, po)
mappings, where (ri, di) means a resource-specific entity domain of
type di defined by the information resource ri, and (ro, po) means a
resource-specific entity property po defined by the information
resource ro.
For each (ri, di) => (ro, po) mapping, the scope of an ALTO property
map resource must be one of the cases in the following diagram:
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domain.resource domain.resource
(ri) = r (ri) = this
+-----------------|-----------------+
prop.resource | Export | Non-exist |
(ro) = r | | |
+-----------------|-----------------+
prop.resource | Extend | Define |
(ro) = this | | |
+-----------------|-----------------+
where "this" represents the resulting property map resource, and "r"
represents an existing ALTO information resource other the resulting
property map resource.
o ri = ro = r ("export" mode): the property map resource just
transforms the property mapping di => po defined by r into the
unified representation format and exports it. For example: r =
"netmap1", di = "ipv4", po = "pid". The property map resource
exports the "ipv4 => pid" mapping defined by "netmap1".
o ri = r, ro = this ("extend" mode): the property map extends
properties of entities in the entity domain (r, di) and defines a
new property po on them. For example: the property map resource
("this") defines a "geolocation" property on domain "netmap1.pid".
o ri = ro = this ("define" mode): the property map defines a new
intrinsic entity domain and defines property po for each entity in
this domain. For example: the property map resource ("this")
defines a new entity domain "asn" and defines a property
"ipprefixes" on this domain.
o ri = this, ro = r: in the scope of a property map resource, it
does not make sense that another existing ALTO information
resource defines a property for this property map resource.
A.1. Example Property Map
The following figure shows an example property map called Property
Map 1, which depends on two network maps and provides three sets of
mappings by
o exporting a mapping from ipv4 entities to PIDs defined by two
different network maps,
o extending geo-location properties to ipv4 entities defined by
Network Map 1,
o and defining a new mapping from ASNs to traffic load properties.
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(Define)
+----------+ +-------------+
->| Property |<-----------------------------|--------| asn | load |
/ | Map 1 | | |-------------|
/ +----------+ | | 1234 | 95% |
| ^ | | 5678 | 70% |
| | \ +-------------+
| | (Export) \ (Extend)
| +---------+ +------------------------+ \ +--------------+
| | Network |----| ipv4 | pid | -----| geo-location |
| | Map 1 | |------------------------| +--------------+
| +---------+ | 192.168.0.0/24 | pid1 | - - - -> | New York |
| | 192.168.1.0/24 | pid2 | - - - -> | Shanghai |
| +------------------------+ +--------------+
| (Export)
\ +---------+ +------------------------+
---| Network |----| ipv4 | pid |
| Map 2 | |------------------------|
+---------+ | 192.168.0.0/24 | Paris |
| ... | ... |
+------------------------+
More detailed examples are shown in Section 10.
Authors' Addresses
Wendy Roome
Nokia Bell Labs (Retired)
124 Burlington Rd
Murray Hill, NJ 07974
USA
Phone: +1-908-464-6975
Email: wendy@wdroome.com
Sabine Randriamasy
Nokia Bell Labs
Route de Villejust
NOZAY 91460
FRANCE
Email: Sabine.Randriamasy@nokia-bell-labs.com
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Y. Richard Yang
Yale University
51 Prospect Street
New Haven, CT 06511
USA
Phone: +1-203-432-6400
Email: yry@cs.yale.edu
Jingxuan Jensen Zhang
Tongji University
4800 Caoan Road
Shanghai 201804
China
Email: jingxuan.n.zhang@gmail.com
Kai Gao
Sichuan University
Chengdu 610000
China
Email: kaigao@scu.edu.cn
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